BACKGROUND OF THE INVENTION
TECHNICAL FIELD
[0001] The present invention relates to a heat exchanger for heat-exchanging primary cooling
water at an atomic power plant and also relates to a decontamination method and a
decontamination apparatus for decontaminating a heat transfer tube of the heat exchanger.
BACKGROUND ART
[0002] In nuclear power generating facilities as an atomic power plant, a steam generator
(a heat exchanger) for obtaining steam to drive a turbine connected to a power generator
is employed. In the steam generator, a plurality of vertically-mounted and reversed-U-shaped
heat transfer tubes are arranged in a cylindrical body unit. In nuclear power generating
facilities, a heat exchanger tube of the steam generator is provided with a circulating
system for making primary cooling water heated by a reactor pass through the heat
transfer tube of the steam generator and for again returning the primary cooling water
to the reactor. An inlet of secondary cooling water is provided in an intermediate
portion of the body unit of the steam generator. While the primary cooling water passes
through the heat transfer tube, the primary cooling water is heat-exchanged with secondary
cooling water. Steam generated by this heat exchange is discharged from the uppermost
portion of the body unit through a steam-water separator and a moisture separator
arranged in the body unit, and is sent to the turbine. In the nuclear power plant
facility, to reduce impurities included in the primary cooling water that circulates
through the circulating system, a demineralizer is provided. A demineralizing system
of primary cooling water supplies primary cooling water taken out from the circulating
system to the demineralizer through the regenerative heat exchanger and nonregenerative
heat exchanger. The primary cooling water demineralized by the demineralizer is again
returned to the circulating system through the regenerative heat exchanger. In this
demineralizing system also, the primary cooling water is heat exchanged by the regenerative
heat exchanger and the nonregenerative heat exchanger.
[0003] In the steam generator, the heat exchanger such as the regenerative heat exchanger
and the nonregenerative heat exchanger in the atomic power plant, because primary
cooling water passes through the heat transfer tube that performs the heat exchange,
an inner surface of the heat transfer tube is contaminated by radiation. When the
heat exchanger is replaced by new one due to aged deterioration or the like, to reduce
the exposure to radiation of an operator when the used heat exchanger is dismantled,
it is necessary to decontaminate inside of the heat transfer tube.
[0004] As a conventional cleaning method of a tube through which radioactive fluid used
in a nuclear power plant or a nuclear fuel reprocessing plant flows, there has been
known a technique of sending particles, in which particle materials are mixed, into
the tube (see, for example, Japanese Patent Application Laid-open No.
S60-678895).
[0005] However, because the heat transfer tube of the steam generator as the heat exchanger
is formed into U-shape as described above, particle materials that reach a curved
portion (a bent portion) from a straight portion collide against an outer side inner
wall surface of the curved portion, and the inner wall surface is excessively ground
as compared with other portion. If the excessive grinding is continued, the curved
portion is perforated, and radioactive secondary waste can leak outside of the heat
transfer tube.
[0006] The present invention has been achieved in view of the above circumstances, and an
object of the present invention is to provide a decontamination method of a heat exchanger
and a decontamination apparatus capable of preventing a heat transfer tube from being
perforated by partial excessive grinding.
DISCLOSURE OF INVENTION
[0007] According to an aspect of the present invention, a decontamination method of a heat
exchanger for decontaminating inside of a heat transfer tube in a heat exchanger includes:
a step of flowing air into the heat transfer tube, and setting a flow rate of abrasive
particles to be mixed into air based on a pressure loss between an inlet side and
an outlet side of the heat transfer tube; a step of calculating a permissible grinding
time required until a curved portion of the heat transfer tube reaches a permissible
grinding thickness based on the flow rate of the abrasive particles; and a step of
flowing air being mixed with the abrasive particles into the heat transfer tube within
the permissible grinding time, and backwardly flowing air mixed with the abrasive
particles into the heat transfer tube.
[0008] Advantageously, in the decontamination method of a heat exchanger, at the step of
flowing air being mixed with the abrasive particles into the heat transfer tube, the
air with the abrasive particles is caused to flow into the heat transfer tube for
a time that is a half of the permissible grinding time and then the air with the abrasive
particles is caused to backwardly flow into the heat transfer tube for a time that
is a half of the permissible grinding time.
[0009] According to another aspect of the present invention, a decontamination method of
a heat exchanger for decontaminating inside of a heat transfer tube in a heat exchanger
includes: a step of flowing air into the heat transfer tube, and setting a flow rate
of abrasive particles to be mixed into air based on a pressure loss between an inlet
side and an outlet side of the heat transfer tube; a step of calculating a permissible
grinding time required until a curved portion of the heat transfer tube reaches a
permissible grinding thickness based on the flow rate of the abrasive particles, and
calculating a decontamination grinding time required until the entire heat transfer
tube reaches a decontamination-accomplishment grinding amount; and a step of flowing
air being mixed with the abrasive particles into the heat transfer tube and backwardly
flowing the air with the abrasive particles into the heat transfer tube within the
decontamination grinding time when the permissible grinding time is longer than the
decontamination grinding time, and flowing the air with the abrasive particles into
the heat transfer tube and backwardly flowing the air with the abrasive particles
into the heat transfer tube within the permissible grinding time when the permissible
grinding time is shorter than the decontamination grinding time.
[0010] Advantageously, in the decontamination method of a heat exchanger, at the step of
flowing air being mixed with the abrasive particles into the heat transfer tube, the
air with the abrasive particles is caused to flow into the heat transfer tube for
a time that is a half of the decontamination grinding time and then the air with the
abrasive particles is caused to backwardly flow into the heat transfer tube for a
time that is a half of the decontamination grinding time when the permissible grinding
time is longer than the decontamination grinding time, and the air with the abrasive
particles is caused to flow into the heat transfer tube for a time that is a half
of the permissible grinding time and then the air with the abrasive particles is caused
to backwardly flow into the heat transfer tube for a time that is a half of the permissible
grinding time when the permissible grinding time is shorter than the decontamination
grinding time.
[0011] According to still another aspect of the present invention, a decontamination apparatus
of a heat exchanger for decontaminating inside of a heat transfer tube in a heat exchanger
includes: a forward inflow circuit that causes air to reach a second port from a first
port of the heat transfer tube and to flow into the heat transfer tube; a backward
inflow circuit that causes air to reach the first port from the second port of the
heat transfer tube (304) and to flow into the heat transfer tube; a switching unit
that selectively switches between the forward inflow circuit and the backward inflow
circuit; an abrasive supplying unit that measures an amount of abrasive particles
and mixes the abrasive particles into air that flows into the heat transfer tube;
and a control unit that controls the switching unit and the abrasive supplying unit.
The control unit causes the switching unit to switch between the forward inflow circuit
and the backward inflow circuit, flows air into the heat transfer tube, sets a flow
rate of abrasive particles to be mixed into the air based on a pressure loss between
an inlet side and an outlet side of the heat transfer tube, calculates a permissible
grinding time required until a curved portion of the heat transfer tube reaches a
permissible grinding thickness based on the flow rate of the abrasive particles, mixes
the abrasive particles into the air by the abrasive supplying unit, and causes the
switching unit to switch between the forward inflow circuit and the backward inflow
circuit within the permissible grinding time.
[0012] Advantageously, in the decontamination apparatus of a heat exchanger, the control
unit calculates the permissible grinding time, and when a time that is a half of the
permissible grinding time is elapsed after the switching unit switches the circuit
to the forward inflow circuit while mixing the abrasive particles into air by the
abrasive supplying unit, the switching unit switches the circuit to the backward inflow
circuit.
[0013] According to still another aspect of the present invention, a decontamination apparatus
of a heat exchanger for decontaminating inside of a heat transfer tube in a heat exchanger
includes: a forward inflow circuit that causes air to reach a second port from a first
port of the heat transfer tube and to flow into the heat transfer tube; a backward
inflow circuit that causes air to reach the first port from the second port of the
heat transfer tube and to flow into the heat transfer tube; a switching unit that
selectively switches between the forward inflow circuit and the backward inflow circuit;
an abrasive supplying unit that measures an amount of abrasive particles and mixes
the abrasive particles into air that flows into the heat transfer tube; and a control
unit that controls the switching unit and the abrasive supplying unit. The control
unit causes the switching unit to switch between the forward inflow circuit and the
backward inflow circuit, flows air into the heat transfer tube, sets a flow rate of
abrasive particles to be mixed into the air based on a pressure loss between an inlet
side and an outlet side of the heat transfer tube, calculates a permissible grinding
time required until a curved portion of the heat transfer tube reaches a permissible
grinding thickness based on the flow rate of the abrasive particles, calculates a
decontamination grinding time that is required unit the entire heat transfer tube
reaches the decontamination-accomplishment grinding amount, the switching unit switches
between the forward inflow circuit and the backward inflow circuit within the decontamination
grinding time while mixing the abrasive particles into the air by the abrasive supplying
unit when the permissible grinding time is longer than the decontamination grinding
time, and the switching unit switches between the forward inflow circuit and the backward
inflow circuit within the permissible grinding time while mixing the abrasive particles
into the air by the abrasive supplying unit when the permissible grinding time is
shorter than the decontamination grinding time.
[0014] Advantageously, in the decontamination apparatus of a heat exchanger, the control
unit calculates the permissible grinding time and the decontamination grinding time,
the switching unit switches the circuit to the backward inflow circuit when the permissible
grinding time is longer than the decontamination grinding time and when a time that
is a half of the decontamination grinding time is elapsed after the switching unit
switches the circuit to the forward inflow circuit while mixing the abrasive particles
into the air by the abrasive supplying unit, and the switching unit switches the circuit
to the backward inflow circuit when the permissible grinding time is shorter than
the decontamination grinding time and when a time that is a half of the permissible
grinding time is elapsed after the switching unit switches the circuit to the forward
inflow circuit while mixing the abrasive particles into the air by the abrasive supplying
unit.
[0015] With regard to the above statements, the other purposes, features, advantages, technical
and industrial meanings of the present invention, it would be more understandable
by reading the best mode(s) for carrying out the invention below, referencing attached
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016]
Fig. 1 is a schematic diagram of an atomic power plant to which a decontamination
method of a heat exchanger and a decontamination apparatus according to a first embodiment
of the present invention are applied.
Fig. 2 is a schematic diagram of a steam generator (a heat exchanger) according to
the first embodiment of the present invention.
Fig. 3 is a schematic perspective view of the decontamination apparatus of a heat
exchanger according to the first embodiment of the present invention.
Fig. 4 is a schematic diagram of the decontamination apparatus of a heat exchanger
according to the first embodiment of the present invention.
Fig. 5 is a schematic diagram of the decontamination apparatus of a heat exchanger
according to the first embodiment of the present invention.
Fig. 6 is a schematic diagram of a point A of a curved portion of a heat transfer
tube.
Fig. 7 is a flowchart of a decontaminating operation in the first embodiment of the
present invention.
Fig. 8 is a flowchart of an operation (a decontamination method) of the decontamination
apparatus according to the first embodiment of the present invention.
Figs. 9 depict a relationship between a grinding amount and a grinding time, for a
comparison between a general example and the present invention.
Fig. 10 is a schematic diagram of measuring points in an experiment of a heat transfer
tube.
Fig. 11 is a flowchart of an operation (a decontamination method) of a decontamination
apparatus according to a second embodiment of the present invention.
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0017] Exemplary embodiments of a decontamination method of a heat exchanger and a decontamination
apparatus according to the present invention will be explained below in detail with
reference to the accompanying drawings. The present invention is not limited to the
embodiments. In addition, constituent elements in the embodiments include those that
can be easily assumed by those skilled in the art or that are substantially equivalent.
[First Embodiment]
[0018] Fig. 1 depicts an atomic power plant to which a decontamination method of a heat
exchanger and a decontamination apparatus according to a first embodiment of the present
invention are applied. In the present embodiment, an atomic power plant 1 is a nuclear
power plant facility, and a reactor 2 is a PWR (Pressurized Water Reactor).
[0019] In the atomic power plant 1, the reactor 2, a steam generator 3, a pressurizer 4,
a primary cooling-water pump 5, and a regenerative heat exchanger 11 are arranged
in a containment vessel 1W. A turbine 8, a steam condenser 9, and a power generator
10 are arranged outside of the containment vessel 1W. A nuclear fuel 2C is arranged
in a pressure vessel of the reactor 2. The pressure vessel is filled with primary
cooling water (for example, light water) C1. The primary cooling-water pump 5 and
the reactor 2 are connected to each other through a primary cooling-water first supply-passage
6A. The reactor 2 and the steam generator 3 are connected to each other through a
primary cooling-water second supply-passage 6B. The steam generator 3 and the primary
cooling-water pump 5 are connected to each other through a primary cooling-water recovery
passage 6C.
[0020] According to this configuration, the primary cooling water C1 discharged from the
primary cooling-water pump 5 is supplied into the pressure vessel of the reactor 2
through the primary cooling-water first supply-passage 6A. The primary cooling water
C1 is heated by thermal energy generated by atomic fission reaction of nuclear fuel
2C arranged in the pressure vessel. The heated primary cooling water C1 is supplied
to the steam generator 3 through the primary cooling-water second supply-passage 6B.
The primary cooling water C1 passes through heat transfer tubes 304 of the steam generator
3 and then the primary cooling water C1 flows out from the steam generator 3, returns
to the primary cooling-water pump 5 through the primary cooling-water recovery passage
6C, and is again discharged into the pressure vessel of the reactor 2 from the primary
cooling-water first supply-passage 6A.
[0021] The steam generator 3 includes the heat transfer tubes 304 in plural, secondary cooling
water C2 outside of the heat transfer tubes 304 is heated and boiled by the primary
cooling water C1 flowing in the heat transfer tubes 304, and high temperature and
high pressure steam of the secondary cooling water C2 is produced. The steam generator
3 and the turbine 8 are connected to each other through a steam supply passage 7S.
The steam condenser 9 and the steam generator 3 are connected to each other through
a secondary cooling-water recovery passage 7R. According to this configuration, the
high temperature and high pressure steam of the secondary cooling water C2 produced
by the steam generator 3 is supplied to the turbine 8 through the steam supply passage
7S and the steam drives the turbine 8. Electricity is generated by the power generator
10 connected to a drive shaft of the turbine 8. The secondary cooling water C2 after
it drove the turbine 8 becomes liquid in the steam condenser 9, and it is again sent
to the steam generator 3 through the secondary cooling-water recovery passage 7R.
[0022] The reactor 2 is a pressurized water reactor, and the pressurizer 4 is connected
to the primary cooling-water second supply-passage 6B. The pressurizer 4 applies a
pressure to the primary cooling water C1 in the primary cooling-water second supply-passage
6B. According to the structure, the primary cooling water C1 is not boiled even if
it is heated by the thermal energy generated by the atomic fission reaction of the
nuclear fuel 2C, and the primary cooling water C1 circulates through the reactor 2
and its cooling system in its liquid phase state. The cooling system of the reactor
2 includes the primary cooling-water pump 5, the primary cooling-water first supply-passage
6A, the primary cooling-water second supply-passage 6B, the steam generator 3, and
the primary cooling-water recovery passage 6C. The primary cooling water C1 flows
through the cooling system of the reactor 2.
[0023] The atomic power plant 1 includes a demineralizer 16 to reduce impurities included
in the primary cooling water C1. The demineralizer 16 includes a first demineralizer
16A and a second demineralizer 16B. The demineralizer 16 is arranged outside of the
containment vessel 1W. The first demineralizer 16A is a cooling-water hotbed demineralizer,
and the second demineralizer 16B is a cooling-water cation demineralizer. The primary
cooling water C1 taken out from an inlet side (an upstream side) of the primary cooling-water
pump 5 is supplied from the cooling system of the reactor 2 to the demineralizer 16,
and the primary cooling water C1 is subjected to the demineralizing processing, and
the demineralized primary cooling water C1 is returned to an outlet side (a downstream
side) of the primary cooling-water pump 5.
[0024] A demineralizing processing system of the primary cooling water C1 includes a primary
cooling-water taking-out passage 13A, a regenerative heat exchanger 11, a primary
cooling-water passage 13B, a nonregenerative heat exchanger 12, a primary cooling-water
passage 13C, the demineralizer 16, a primary cooling-water passage 13D, a volume control
tank 14, and primary cooling-water returning passages 13E and 13F. The regenerative
heat exchanger 11 and the primary cooling-water recovery passage 6C constituting the
cooling system of the reactor 2 are connected to each other through the primary cooling-water
taking-out passage 13A. The regenerative heat exchanger 11 and the nonregenerative
heat exchanger 12 are connected to each other through the primary cooling-water passage
13B. The nonregenerative heat exchanger 12 and the demineralizer 16 are connected
to each other through the primary cooling-water passage 13C. The demineralizer 16
and the volume control tank 14 are connected to each other through the primary cooling-water
passage 13D. The volume control tank 14 and the regenerative heat exchanger 11 are
connected to each other through the primary cooling-water returning passage 13E. The
regenerative heat exchanger 11 and the primary cooling-water first supply-passage
6A are connected to each other through the primary cooling-water returning passage
13F. The primary cooling-water returning passage 13E includes a charging pump 15.
[0025] The primary cooling water C1 is taken out from the primary cooling-water taking-out
passage 13A, that is, from the inlet side (the upstream side) of the primary cooling-water
pump 5. The primary cooling water C1 taken out from the cooling system of the reactor
2 is introduced into the regenerative heat exchanger 11 and then it is introduced
into the demineralizer 16 through the primary cooling-water passage 13B, the nonregenerative
heat exchanger 12, and the primary cooling-water passage 13C, and the primary cooling
water C1 is subjected to the demineralizing processing.
The demineralized primary cooling water C1 is temporarily stored in the volume control
tank 14 through the primary cooling-water passage 13D. Thereafter, the primary cooling
water C1 is sent to the regenerative heat exchanger 11 by the charging pump 15 provided
in the primary cooling-water returning passage 13E. The primary cooling water C1 that
passed through the regenerative heat exchanger 11 is returned to the primary cooling-water
first supply-passage 6A, that is, the outlet side (the downstream side) of the primary
cooling-water pump 5 through the primary cooling-water returning passage 13F.
[0026] In the present embodiment, the heat exchanger to which the decontamination method
and the decontamination apparatus are applied is the steam generator 3, the regenerative
heat exchanger 11, and the nonregenerative heat exchanger 12 through which the primary
cooling water C1 filled in the pressure vessel of the reactor 2 passes. In the present
embodiment, the steam generator 3 is described as a main subject. Fig. 2 depicts the
steam generator (the heat exchanger) according to the present embodiment.
[0027] As shown in Fig. 2, the steam generator 3 extends in a vertical direction, and is
of a tightly closed hollow cylindrical shape. The steam generator 3 includes a body
unit 301 having an upper half and a lower half, and a diameter of the lower half is
slightly smaller than that of the upper half. A cylindrical tube-group outer cylinder
302 is provided in the lower half of the body unit 301 at a predetermined distance
between the tube-group outer cylinder 302 and an inner wall surface of the body unit
301. The tube-group outer cylinder 302 extends to a tube plate 303. A lower end of
the tube-group outer cylinder 302 is arranged at a lower portion in the lower half
of the body unit 301. A heat transfer tube group 304A including the plurality of reversed-U-shaped
heat transfer tubes 304 is provided in the tube-group outer cylinder 302. Each of
the heat transfer tubes 304 is arranged such that the U-shaped curved portion thereof
is oriented upward, and an end of the heat transfer tube 304 oriented downward is
supported by the tube plate 303, and an intermediate portion of the heat transfer
tube 304 is supported by a plurality of tube support plates 305. A large number of
through holes (not shown) are formed in the tube support plates 305, and the heat
transfer tubes 304 pass through the through holes in a non-contact state.
[0028] A water chamber 306 is provided in a lower end of the body unit 301. The water chamber
306 is divided into an inlet chamber 306A and an outlet chamber 306B by a division
wall 307. A first port 304a of each of the heat transfer tubes 304 is in communication
with the inlet chamber 306A, and a second port 304b of each of the heat transfer tubes
304 is in communication with the outlet chamber 306B. An inlet nozzle 306AA that is
in communication with outside of the body unit 301 is formed in the inlet chamber
306A, and an outlet nozzle 306BB that is in communication with outside of the body
unit 301 is formed in the outlet chamber 306B. The primary cooling-water second supply-passage
6B to which the primary cooling water C1 is sent from the reactor 2 is connected to
the inlet nozzle 306AA. The primary cooling-water recovery passage 6C through which
the primary cooling water C1 after it has been exchanged is sent to the reactor 2
is connected to the outlet nozzle 306BB.
[0029] A steam-water separator 308 that separates fed water into steam and hot water, and
a moisture separator 309 that reduces moisture of the separated steam and brings the
steam into a state close to dry steam are provided in the upper half of the body unit
301. A feedwater tube 310 for feeding the secondary cooling water C2 into the body
unit 301 from outside is inserted between the steam-water separator 308 and the heat
transfer tube group 304A. A steam discharge port 311 is formed in an upper end of
the body unit 301. A feedwater passage 312 is provided in the lower half of the body
unit 301. The feedwater passage 312 downwardly flows the secondary cooling water C2
fed into the body unit 301 from the feedwater tube 310 between the body unit 301 and
the tube-group outer cylinder 302, and returns the secondary cooling water C2 at the
tube plate 303, and flows the secondary cooling water C2 upward along the heat transfer
tube group 304A. The steam supply passage 7S for sending steam to the turbine 8 is
connected to the steam discharge port 311. The secondary cooling-water recovery passage
7R for supplying secondary cooling water C2 obtained by cooling steam used in the
turbine 8 by the steam condenser 9 is connected to the feedwater tube 310.
[0030] According to the steam generator 3, the primary cooling water C1 heated by the reactor
2 is sent to the inlet chamber 306A, the primary cooling water C1 circulates through
the large number of heat transfer tubes 304, and reaches the outlet chamber 306B.
The secondary cooling water C2 cooled by the steam condenser 9 is sent to the feedwater
tube 310, the secondary cooling water C2 passes through the feedwater passage 312
in the body unit 301 and rises along the heat transfer tube group 304A. At that time,
heat exchange is performed between the high pressure and high temperature primary
cooling water C1 and the secondary cooling water C2. The cooled primary cooling water
C1 is returned to the reactor 2 from the outlet chamber 306B. The secondary cooling
water C2 heat exchanged with the high pressure and high temperature primary cooling
water C1 rises in the body unit 301, and is separated into steam and hot water by
the steam-water separator 308. The moisture of the separated steam is reduced by the
moisture separator 309 and then sent to the turbine 8.
[0031] In the steam generator 3, the upper end of the heat transfer tube group 304A including
the plurality of heat transfer tubes 304 is formed into a hemispherical shape by the
reversed-U-shaped curved portion of the heat transfer tube 304. Specifically, one
of the heat transfer tubes 304 with the curved portion having the smallest curvature
is arranged at a center portion of the heat transfer tube group 304A, and heat transfer
tubes 304 with larger curved portions having greater curvatures are arranged toward
outside of the hemispherical shape in sequence. By superposing the arranged tubes
and reducing the outer heat transfer tubes 304 in sequence, the upper end of the heat
transfer tube group 304A is formed into the hemispherical shape.
[0032] As described above, in the steam generator 3, because the primary cooling water C1
passes through the heat transfer tube 304 that performs the heat exchange, the inner
surface of the heat transfer tube 304 is contaminated by radiation. When the steam
generator 3 is replaced by new one due to aged deterioration or the like, to reduce
the exposure to radiation of an operator when the used steam generator 3 is dismantled,
it is necessary to decontaminate inside of the heat transfer tube 304.
[0033] The decontamination apparatus according to the present embodiment is described below.
Figs. 3 to 5 depict the decontamination apparatus of the heat exchanger according
to the present embodiment. A decontamination apparatus 100 includes a forward inflow
circuit 101, a backward inflow circuit 102, an abrasive circulating unit 103, circuit
connecting units 104, and a control unit 105.
[0034] As indicated by solid arrows in Figs. 4 and 5, the forward inflow circuit 101 flows
air mixed with abrasive particles from the first port 304a of the heat transfer tube
304 to the second port 304b, and then flows it into the heat transfer tube 304. As
shown in Fig. 3, the forward inflow circuit 101 includes a compressor 106, a supply
passage 107, an abrasive supplying unit 108, a switching unit 109, a first supply/recovery
passage 110, a second supply/recovery passage 111, a recovery passage 112, and a recovering
and separating unit 113.
[0035] The compressor 106 compresses air to high pressure. Air compressed by the compressor
106 is sent out as jet stream through the supply passage 107 connected to the compressor
106. The abrasive supplying unit 108 is interposed in an intermediate portion of the
supply passage 107. The abrasive supplying unit 108 is formed as a hopper for example,
a predetermined amount of abrasive particles is supplied to the supply passage 107
and is mixed into the jet stream of air. In the present embodiment, particles of alumina
(aluminum oxide) are mainly used as the abrasive particles, and an average particle
diameter thereof is 0.5 millimeter. Other examples of the abrasive particles are ceramic
particles and metal (such as stainless or iron) particles. The supply passage 107
is connected to the first supply/recovery passage 110 through the switching unit 109.
The switching unit 109 is described later. The first supply/recovery passage 110 is
connected to the first port 304a of the heat transfer tube 304, and includes a pressure
gage 110A. The second supply/recovery passage 111 is connected to the second port
304b of the heat transfer tube 304 and the second supply/recovery passage 111 includes
a pressure gage 111A. The second supply/recovery passage 111 is connected to the recovery
passage 112 through the switching unit 109. The recovery passage 112 is connected
to the recovering and separating unit 113. Air that passed through the heat transfer
tube 304 passes through the recovery passage 112. The recovering and separating unit
113 recovers abrasive particles mixed into air that passes through the recovery passage
112, and recovers secondary waste that has been ground by the abrasive particles,
and separates the abrasive particles and the secondary waste from each other. The
separated secondary waste is stored in the recovering and separating unit 113, and
the separated abrasive particles are returned to the abrasive supplying unit 108.
Jet stream air after the abrasive particles and the secondary waste are recovered
therefrom is discharged from the recovering and separating unit 113 through a blower
(not shown).
[0036] That is, the forward inflow circuit 101 sends the jet stream air compressed by the
compressor 106 to the supply passage 107, the switching unit 109, the first supply/recovery
passage 110, the heat transfer tube 304, the second supply/recovery passage 111, the
switching unit 109, the recovery passage 112, and the recovering and separating unit
113 in this order, thereby flowing air in which the abrasive particles are mixed by
the abrasive supplying unit 108 to the second port 304b from the first port 304a of
the heat transfer tube 304, and flowing the air into the heat transfer tube 304.
[0037] As shown with dashed lines in Figs. 4 and 5, the backward inflow circuit 102 flows
air mixed with the abrasive particles to the first port 304a from the second port
304b of the heat transfer tube 304, and flows the air into the heat transfer tube
304. Like the forward inflow circuit 101, the backward inflow circuit 102 includes
the compressor 106, the supply passage 107, the abrasive supplying unit 108, the switching
unit 109, the first supply/recovery passage 110, the second supply/recovery passage
111, the recovery passage 112, and the recovering and separating unit 113.
[0038] The switching unit 109 selectively switches such that the switching unit 109 connects
the supply passage 107 to the first supply/recovery passage 110, connects the recovery
passage 112 to the second supply/recovery passage 111, connects the supply passage
107 to the second supply/recovery passage 111, and connects the recovery passage 112
to the first supply/recovery passage 110. A circuit in which the supply passage 107
is connected to the first supply/recovery passage 110 and the recovery passage 112
is connected to the second supply/recovery passage 111 by the switching unit 109 is
the forward inflow circuit 101. A circuit in which the supply passage 107 is connected
to the second supply/recovery passage 111 and the recovery passage 112 is connected
to the first supply/recovery passage 110 by the switching unit 109 is the backward
inflow circuit 102.
[0039] That is, the backward inflow circuit 102 sends the jet stream air compressed by the
compressor 106 to the supply passage 107, the switching unit 109, the second supply/recovery
passage 111, the heat transfer tube 304, the first supply/recovery passage 110, the
switching unit 109, the recovery passage 112, and the recovering and separating unit
113 in this order, thereby flowing air in which the abrasive particles are mixed by
the abrasive supplying unit 108 to the first port 304a from the second port 304b of
the heat transfer tube 304 and flowing the air into the heat transfer tube 304.
[0040] The abrasive circulating unit 103 includes the abrasive supplying unit 108 and the
recovering and separating unit 113. The abrasive supplying unit 108 supplies a predetermined
amount of abrasive particles to the supply passage 107 and mixes the abrasive particles
into the jet stream air. The recovering and separating unit 113 recovers the abrasive
particles and the secondary waste mixed in the air that passes through the recovery
passage 112, separates the abrasive particles and the secondary waste from each other,
stores the secondary waste, and returns the abrasive particles to the abrasive supplying
unit 108. That is, the abrasive circulating unit 103 is commonly provided in the forward
inflow circuit 101 and the backward inflow circuit 102. The abrasive circulating unit
103 recovers abrasive particles coming from the downstream side of the jet stream
air, returns the recovered abrasive particles to the upstream side of the jet stream
air, and circulates and uses the abrasive particles.
[0041] The abrasive circulating unit 103 does not need to be provided. In this case, as
shown in Fig. 5, a recovering unit 120 that recovers and stores abrasive particles
and secondary waste mixed in the air that passes through the recovery passage 112
is provided in the recovery passage 112 instead of the recovering and separating unit
113.
[0042] As shown in Fig. 3, the circuit connecting units 104 are provided on the inlet chamber
306A and the outlet chamber 306B of the steam generator 3, and the circuit connecting
units 104 connect the first supply/recovery passage 110 and the second supply/recovery
passage 111 of the circuits 101 and 102 to a port of any of the plurality of heat
transfer tubes 304. The circuit connecting units 104 include a connection nozzle 114.
[0043] The connection nozzle 114 forms a connecting portion that connects the first supply/recovery
passage 110 and the second supply/recovery passage 111 to the ports of the heat transfer
tubes 304. It is preferable that the connection nozzle 114 connects the first supply/recovery
passage 110 and the second supply/recovery passage 111 to one of the heat transfer
tubes 304 in a one-to-one relationship. The connection nozzle 114 is provided on supporting
members (not shown) arranged on the inlet chamber 306A and the outlet chamber 306B,
and the connection nozzle 114 is connected to and separated from the port of the heat
transfer tube 304 by an actuator (not shown).
[0044] The control unit 105 is constituted by a microcomputer. The control unit 105 includes
a storage unit 105a, a computing unit 105b, and a time register 105c. The compressor
106, the abrasive supplying unit 108, the switching unit 109, the pressure gages 110A
and 111A, and the circuit connecting unit 104 are connected to the control unit 105.
The compressor 106, the abrasive supplying unit 108, the switching unit 109, and the
circuit connecting unit 104 are subject to centralized control by the control unit
105 according to programs and data stored in the storage unit 105a in advance, a grinding
time calculated by the computing unit 105b, and a time measured by the time register
105c.
[0045] The storage unit 105a is constituted by a RAM or a ROM, and programs and data are
stored therein. The programs and data stored in the storage unit 105a are for driving
the compressor 106, the abrasive supplying unit 108, the switching unit 109, and the
circuit connecting unit 104. Particularly, data used by the computing unit 105b that
calculates the grinding time suitable for each of the heat transfer tubes 304 is stored
in the storage unit 105a.
[0046] The computing unit 105b calculates a permissible grinding time (tA) required until
the curved portion (a point A: see Fig. 6) of the heat transfer tube 304 reaches its
permissible grinding thickness (thinnest grinding thickness within a range such that
a hole is not generated) in forward inflow and backward inflow based on the data stored
in the storage unit 105a, and based on pressures obtained by the pressure gages 110A
and 111A by flowing air into the forward inflow circuit 101 or the backward inflow
circuit 102. The forward inflow is to flow air mixed with the abrasive particles into
the forward inflow circuit 101, and the backward inflow is to flow the air mixed with
the abrasive particles into the backward inflow circuit 102.
[0047] Specifically, the computing unit 105b measures pressure losses in the inflow circuits
101 and 102 by an inlet-side pressure and an outlet-side pressure of the inflow circuits
101 and 102 obtained from the pressure gages 110A and 111A. The computing unit 105b
calculates the flow velocity (V) of air from the measured pressure losses. When calculating
the flow velocity (V) of air, an inner diameter of the heat transfer tube 304 is set
constant, a length of the heat transfer tube 304 is preset for each of the heat transfer
tubes 304 corresponding to a position to which the connection nozzle 114 is connected
by the circuit connecting unit 104, and the data is stored in the storage unit 105a.
The computing unit 105b sets a mixture ratio [mass of abrasive particles/mass of air]
(C) suitable for grinding in accordance with the flow velocity (V). The mixture ratio
(C) is obtained by an experiment carried out in advance, and is stored in the storage
unit 105a. The mass of abrasive particles and diameters of the abrasive particles
are set constant, and are stored in the storage unit 105a. The computing unit 105b
sets a flow rate (Qp) of the abrasive particles based on the flow velocity (V) of
air, the mass of the abrasive particles, and the diameters of the abrasive particles.
The computing unit 105b calculates a permissible grinding time (tA[min]) required
until the curved portion (the point A: see Fig. 6) of the heat transfer tube 304 reaches
its permissible grinding thickness (thinnest grinding thickness within a range such
that a hole is not generated) in forward inflow and backward inflow based on the following
equation 1.

[0048] In the equation 1, WA represents a grinding amount [mm], b represents a constant
obtained by an experiment carried out in advance and stored in the storage unit 105a,
α represents a collision angle of the abrasive particles, and this is an angle formed
between an inflow direction of the abrasive particles and a tangent of the inner wall
surface at the point A where the abrasive particles that flow into the heat transfer
tube 304 in a direction of the arrow in Fig. 6 collide against the curved portion
and the curved portion is most excessively ground. The angle (α) is preset for each
of the heat transfer tubes 304 corresponding to a position to which the connection
nozzle 114 is connected by the circuit connecting unit 104, and the angle is stored
in the storage unit 105a. That is, the permissible grinding time (tA) required until
the curved portion (the point A) of the heat transfer tube 304 is ground by a grinding
amount (WA) corresponding to the permissible grinding thickness in forward inflow
and backward inflow is calculated by the equation 1.
[0049] The time register 105c measures the decontaminating time (the grinding time) in the
decontamination apparatus 100.
[0050] The decontamination method that is an operation of the decontamination apparatus
100 is described with reference to flowcharts in Figs. 7 and 8.
[0051] In the present embodiment, when the heat exchanger is replaced by new one due to
aged deterioration or the like, to prevent an operator from being irradiated with
radiation when the used heat exchanger is dismantled, the inside of the heat transfer
tube is decontaminated, and the decontamination apparatus and the decontamination
method are applied.
[0052] When a decontaminating operation is performed, a greenhouse 118 (see Fig. 3) is first
installed to cover the side of the water chamber 306 of the used steam generator 3
(Step S1). According to this configuration, a periphery of the water chamber 306 is
isolated to prevent the radiation from being scattered.
[0053] Next, the decontamination apparatus 100 outside of the steam generator 3 is prepared
(Step S2). That is, the decontamination apparatus 100 is installed outside of the
greenhouse 118. Specifically, the supply passage 107 is connected to the compressor
106, the abrasive supplying unit 108 is connected to the supply passage 107, and the
supply passage 107 is connected to the switching unit 109. The recovery passage 112
is connected to the recovering and separating unit 113, and the recovery passage 112
is connected to the switching unit 109. The first supply/recovery passage 110 and
the second supply/recovery passage 111 are connected to the switching unit 109.
[0054] Next, a manhole of the water chamber 306 of the steam generator 3 is opened, and
the inlet nozzle 306AA of the inlet chamber 306A and the outlet nozzle 306BB of the
outlet chamber 306B are opened (Step S3).
[0055] Next, the decontamination apparatus 100 inside of the steam generator 3 is prepared
(Step S4). That is, the circuit connecting units 104 are installed for the inlet chamber
306A and the outlet chamber 306B. At that time, an operator wears radiation protective
clothing to prevent the operator from being exposed to radiation.
[0056] Next, the decontamination is performed (Step S5). At Step S5, the decontamination
apparatus 100 according to the present embodiment is operated, and the decontamination
method is applied.
[0057] Finally, when the decontamination is completed, the decontamination apparatus 100
is dismounted (Step S6). Because the inside of the heat transfer tube 304 is decontaminated
after Step S6, the steam generator 3 can be dismantled.
[0058] The operation (the decontamination method) of the decontamination apparatus 100 at
Step S5 is shown in the flowchart of the operation (the decontamination method) of
the decontamination apparatus in Fig. 8. First, the control unit 105 connects the
first supply/recovery passage 110 to the first port 304a of desired one of the heat
transfer tubes 304, and connects the second supply/recovery passage 111 to the second
port 304b of desired one of the heat transfer tubes 304 by the circuit connecting
unit 104 (Step S11). At the same time, the control unit 105 causes the switching unit
109 to switch the circuit to the forward inflow circuit 101 (Step S12).
[0059] Next, the control unit 105 operates the compressor 106 to draw air, measures pressures
on the side of the inlet (on the side of the first port 304a) and on the side of the
outlet (on the side of the second port 304b) of the heat transfer tube 304, and sets
the flow rate (Qp) of the abrasive particles based on a pressure loss between the
inlet side and the outlet side of the heat transfer tube 304 (Step S13).
[0060] Next, the control unit 105 calculates the permissible grinding time (tA) required
until the curved portion (the point A) of the heat transfer tube 304 reaches its permissible
grinding thickness in forward inflow and backward inflow (Step 14).
[0061] Next, the control unit 105 equalizes the forward inflow time (tA forward), the backward
inflow time (tA backward), and the permissible grinding time (tA/2), mixes the abrasive
particles into air, switches the switching unit 109, and performs a grinding operation
in forward inflow and backward inflow (Step S15).
[0062] That is, in the forward inflow circuit 101, air mixed with the abrasive particles
is caused to reach the second port 304b from the first port 304a of the heat transfer
tube 304 and to flow into the heat transfer tube 304, and the inside of the heat transfer
tube 304 is decontaminated. When the forward inflow time (tA forward) that is the
permissible grinding time (tA/2) is elapsed, the control unit 105 causes the switching
unit 109 to switch the circuit to the backward inflow circuit 102. According to this
configuration, in the backward inflow circuit 102, the air mixed with the abrasive
particles is caused to reach the first port 304a from the second port 304b of the
heat transfer tube 304 and to flow into the heat transfer tube 304, and the inside
of the heat transfer tube 304 is continuously decontaminated. When the backward inflow
time (tA backward) that is the remaining permissible grinding time (tA/2) is elapsed,
the control unit 105 stops the inflow of air, and the decontaminating operation is
completed.
[0063] Steps S11 to S15 are repeatedly performed until the decontaminating operation of
all of the heat transfer tubes 304 of the steam generator 3 is completed in a state
where the circuit connecting unit 104 connects the first supply/recovery passage 110
and the second supply/recovery passage 111 to the next heat transfer tube 304.
[0064] At Step S12, the switching unit 109 can switch the circuit to the backward inflow
circuit 102. In this case, at Step S15, in the backward inflow circuit 102, air mixed
with the abrasive particles is caused to reach the first port 304a from the second
port 304b of the heat transfer tube 304 and to flow into the heat transfer tube 304,
and when the backward inflow time (tA backward) that is the permissible grinding time
(tA/2) is elapsed, the switching unit 109 switches the circuit to the forward inflow
circuit 101, and in the forward inflow circuit 101, air mixed with the abrasive particles
is caused to reach the second port 304b from the first port 304a of the heat transfer
tube 304 and the air is caused to flow into the heat transfer tube 304, and when the
forward inflow time (tA forward) that is the remaining permissible grinding time (tA/2)
is elapsed, the inflow of air is stopped, and the decontaminating operation is completed.
[0065] In this manner, the decontamination method of the first embodiment includes a step
of flowing air into the heat transfer tube 304 and setting a flow rate of the abrasive
particles that are mixed into the air based on a pressure loss between the inlet side
and the outlet side of the heat transfer tube 304, a step of calculating the permissible
grinding time (tA) required until the curved portion (the point A) of the heat transfer
tube 304 reaches its permissible grinding thickness, and a step of flowing, into the
heat transfer tube 304, the air mixed with the abrasive particles for a time that
is a half of the permissible grinding time (tA) and then backwardly flowing the air
mixed with the abrasive particles into the heat transfer tube 304 for a time that
is a half of the permissible grinding time (tA).
[0066] According to this decontamination method, the permissible grinding time (tA) required
until the curved portion (the point A) reaches its permissible grinding thickness
is calculated, and the inside of the heat transfer tube 304 is ground by the forward
inflow and the backward inflow for a time that is a half of the permissible grinding
time (tA) each. As a result, because a case that the curved portion is excessively
ground is avoided, it is possible to prevent the heat transfer tube 304 from being
perforated by partial excessive grinding.
[0067] The permissible grinding thickness of the curved portion (the point A) is the thinnest
thickness within a range such that the curved portion is not perforated, and when
the curved portion is ground to this grinding thickness, other inside portions of
the heat transfer tube 304 are ground to such an extent that the other inside portions
are appropriately decontaminated.
[0068] According to the decontamination method of the first embodiment, the forward inflow
circuit 101 and the backward inflow circuit 102 are switched by the switching unit
109, and the second port 304b of the heat transfer tube 304 is switched from downstream
to upstream of the jet stream air. As shown in Fig. 9(a) for example, in all of grinding
steps of a general example, when air mixed with the abrasive particles is caused to
reach the second port 304b from the first port 304a of the heat transfer tube 304
and to flow into the heat transfer tube 304, and when the decontamination is performed
until the upstream side (on the side of the first port 304a of the heat transfer tube
304) is caused to reach the target grinding amount, the downstream side (on the side
of the second port 304b of the heat transfer tube 304) is excessively ground and a
large amount of secondary waste is generated. On the other hand, in all of the grinding
steps of the first embodiment shown in Fig. 9(b), a switching operation is performed
such that air mixed with the abrasive particles in mid-course is caused to reach the
first port 304a from the second port 304b of the heat transfer tube 304 and to flow
into the heat transfer tube 304. According to this configuration, the decontamination
effect can be equalized over the entire length of the heat transfer tube 304 without
excessively grinding the heat transfer tube 304, and the decontamination time can
be shortened.
[0069] The decontamination method according to the first embodiment includes a step of recovering
the abrasive particles coming from the downstream side of the jet stream air when
the air mixed with the abrasive particles is caused to flow into the heat transfer
tube 304, and a step of returning the recovered abrasive particles to the upstream
side of the jet stream air. According to this decontamination method, it is possible
to further suppress the amount of secondary waste generated, by using the abrasive
particles coming from the downstream side of the jet stream air again for the decontamination.
[0070] In the decontamination method according to the first embodiment, at the step of flowing
the air mixed with the abrasive particles into the heat transfer tube 304, air mixed
with the abrasive particles can be made to flow into the heat transfer tube 304 within
the permissible grinding time (tA), and air mixed with the abrasive particles can
be made to flow into the heat transfer tube 304 backwardly. That is, the decontamination
is not limited to a case that a time (tA/2) that is a half of the permissible grinding
time (tA) is spent for each of the forward inflow time (tA forward) and the backward
inflow time (tA backward), the forward inflow time (tA forward) and the backward inflow
time (tA backward) can slightly be different from each other, and effects described
above can be obtained.
[0071] The decontamination apparatus 100 according to the first embodiment includes the
forward inflow circuit 101 that causes air to reach the second port 304b from the
first port 304a of the heat transfer tube 304 and to flow into the heat transfer tube
304, the backward inflow circuit 102 that causes air to reach the first port 304a
from the second port 304b of the heat transfer tube 304 and to flow into the heat
transfer tube 304, the switching unit 109 switches between the forward inflow circuit
101 and the backward inflow circuit 102, the abrasive supplying unit 108 that measures
the abrasive particles and mixes the abrasive particles into air flowing into the
heat transfer tube 304 while measuring the amount of the abrasive particles, and the
control unit 105 for controlling the switching unit 109 and the abrasive supplying
unit 108.
The control unit 105 causes the switching unit 109 to switch between the forward inflow
circuit and the backward inflow circuit, flows air into the heat transfer tube 304,
sets the flow rate of the abrasive particles to be mixed into air based on the pressure
loss between the inlet side and the outlet side of the heat transfer tube 304, calculates
the permissible grinding time (tA) required until the curved portion (the point A)
of the heat transfer tube 304 reaches the permissible grinding thickness based on
the flow rate of the abrasive particles, mixes the abrasive particles into air by
the abrasive supplying unit 108, and when a time that is a half of the permissible
grinding time (tA) is elapsed after the switching unit 109 switches the circuit to
the forward inflow circuit 101, the switching unit 109 switches the circuit to the
backward inflow circuit 102.
[0072] According to the decontamination apparatus 100, the decontamination method described
above can be performed, a case that the curved portion is excessively ground is avoided,
and it is possible to prevent the heat transfer tube 304 from being perforated by
partial excessive grinding. Further, the decontamination effect can be equalized over
the entire length of the heat transfer tube 304, and the decontamination time can
be shortened.
[0073] The decontamination apparatus 100 according to the first embodiment includes the
abrasive circulating unit 103 that recovers abrasive particles coming from the downstream
side of the jet stream air and that returns the recovered abrasive particles to the
upstream side of the jet stream air. According to the decontamination apparatus 100,
it is possible to further suppress the amount of secondary waste generated, by using
the abrasive particles coming from the downstream side of the jet stream air again
for the decontamination.
[0074] According to the decontamination apparatus 100 of the first embodiment, the control
unit 105 can calculate the permissible grinding time (tA), mix the abrasive particles
into air by the abrasive supplying unit 108, and causes the switching unit 109 to
switch between the forward inflow circuit 101 and the backward inflow circuit 102
within the permissible grinding time (tA). That is, the present invention is not limited
to the case that time (tA/2) that is a half of the permissible grinding time (tA)
is spent for each of the forward inflow time (tA forward) and the backward inflow
time (tA backward), the forward inflow time (tA forward) and the backward inflow time
(tA backward) can be slightly different from each other, and effects described above
can be obtained.
[Second Embodiment]
[0075] In a second embodiment, a decontamination method that is an operation of the decontamination
apparatus 100 is different from that of the first embodiment. Therefore, in the second
embodiment described below, only the control unit 105 that is a configuration concerning
the operation of the decontamination apparatus 100 is described, and like constituent
elements of the first embodiment are denoted by like reference numerals and explanations
thereof will be omitted.
[0076] The control unit 105 is constituted by a microcomputer.
[0077] The control unit 105 includes the storage unit 105a, the computing unit 105b, and
the time register 105c. The compressor 106, the abrasive supplying unit 108, the switching
unit 109, the pressure gages 110A and 111A, and the circuit connecting unit 104 are
connected to the control unit 105. The compressor 106, the abrasive supplying unit
108, the switching unit 109, and the circuit connecting unit 104 are subject to centralized
control by the control unit 105 according to programs and data stored in the storage
unit 105a in advance, a grinding time calculated by the computing unit 105b, and a
time measured by the time register 105c.
[0078] The storage unit 105a is constituted by a RAM or a ROM, and programs and data are
stored therein. The programs and data stored in the storage unit 105a are for driving
the compressor 106, the abrasive supplying unit 108, the switching unit 109, and the
circuit connecting unit 104. Particularly, data used by the computing unit 105b that
calculates the grinding time suitable for each of the heat transfer tubes 304 is stored
in the storage unit 105a.
[0079] The computing unit 105b calculates a permissible grinding time (tA) required until
the curved portion (the point A: see Fig. 6) of the heat transfer tube 304 reaches
its permissible grinding thickness (thinnest grinding thickness within a range such
that a hole is not generated) in forward inflow and backward inflow based on the data
stored in the storage unit 105a, and based on pressures obtained by the pressure gages
110A and 111A by flowing air into the forward inflow circuit 101 or the backward inflow
circuit 102. The forward inflow is to flow air mixed with abrasive particles into
the forward inflow circuit 101, and the backward inflow is to flow the air mixed with
abrasive particles into the backward inflow circuit 102.
[0080] Specifically, the computing unit 105b measures pressure losses in the inflow circuits
101 and 102 by an inlet-side pressure and an outlet-side pressure of the inflow circuits
101 and 102 obtained from the pressure gages 110A and 111A. The computing unit 105b
calculates the flow velocity (V) of air from the measured pressure losses. When calculating
the flow velocity (V) of air, an inner diameter of the heat transfer tube 304 is set
constant, a length of the heat transfer tube 304 is preset for each of the heat transfer
tubes 304 corresponding to a position to which the connection nozzle 114 is connected
by the circuit connecting unit 104, and the data is stored in the storage unit 105a.
The computing unit 105b sets a mixture ratio [mass of abrasive particles/mass of air]
(C) suitable for grinding in accordance with the flow velocity (V). The mixture ratio
(C) is obtained by an experiment carried out in advance, and is stored in the storage
unit 105a. The mass of abrasive particles and diameters of the abrasive particles
are set constant, and are stored in the storage unit 105a. The computing unit 105b
sets a flow rate (Qp) of the abrasive particles based on the flow velocity (V) of
air, the mass of the abrasive particles, and the diameters of the abrasive particles.
The computing unit 105b calculates a permissible grinding time (tA[min]) required
until the curved portion (the point A: see Fig. 6) of the heat transfer tube 304 reaches
its permissible grinding thickness (thinnest grinding thickness within a range such
that a hole is not generated) in forward inflow and backward inflow based on the following
equation 1.

[0081] In the equation 1, WA represents a grinding amount [mm], b represents a constant
obtained by an experiment carried out in advance, and stored in the storage unit 105a,
α represents a collision angle of the abrasive particles, and this is an angle formed
between the inflow direction of the abrasive particles and a tangent of the inner
wall surface at the point A where the abrasive particles that flow into the heat transfer
tube 304 in the direction of the arrow in Fig. 6 collide against the curved portion
and the curved portion is most excessively ground. The angle (α) is preset for each
of the heat transfer tubes 304 corresponding to a position to which the connection
nozzle 114 is connected by the circuit connecting unit 104, and the angle is stored
in the storage unit 105a. That is, the permissible grinding time (tA) required until
the curved portion (the point A) of the heat transfer tube 304 is ground by a grinding
amount (WA) corresponding to the permissible grinding thickness in forward inflow
and backward inflow is calculated by the equation 1.
[0082] Further, the computing unit 105b calculates a decontamination grinding time (2t)
required until the entire heat transfer tube 304 reaches the decontamination-accomplishment
grinding amount (W) at which the decontamination of the entire heat transfer tube
304 is achieved in the forward inflow and backward inflow based on the data stored
in the storage unit 105a, and based on pressures obtained by the pressure gages 110A
and 111A by flowing air into the forward inflow circuit 101 or the backward inflow
circuit 102.
[0083] Specifically, the computing unit 105b measures a pressure loss in the inflow circuits
101 and 102 from inlet side pressure and outlet side pressure of the inflow circuits
101 and 102 obtained from the pressure gages 110A and 111A. The computing unit 105b
calculates the flow rate (V) of air from the measured pressure loss. When calculating
the flow rate (V) of air, an inner diameter of the heat transfer tube 304 is set constant,
the length of the heat transfer tube 304 is present for each of the heat transfer
tubes 304 corresponding to a position to which the connection nozzle 114 is connected
by the circuit connecting unit 104, and the data is stored in the storage unit 105a.
The computing unit 105b sets a mixture ratio [mass of abrasive particles/mass of air]
(C) suitable for grinding in accordance with the flow velocity (V). The mixture ratio
(C) is obtained by an experiment carried out in advance, and is stored in the storage
unit 105a. The mass of abrasive particles and diameters of the abrasive particles
are set constant, and are stored in the storage unit 105a. The computing unit 105b
calculates a decontamination grinding time (2t[min]) required until the entire heat
transfer tube 304 reaches the decontamination-accomplishment grinding amount (W) at
which the decontamination of the entire heat transfer tube 304 is achieved.

[0084] In the equation 2, W represents a grinding amount [µm]. Further, a, n1, and n2 represent
regression constants, and they are based on the grinding amount obtained by measuring
a pressure in an experiment carried out in advance at measuring points P1 to P9 in
the heat transfer tube 304 as shown in Fig. 10, and the regression constants are stored
in the storage unit 105a. That is, the decontamination grinding time (2t) required
until the entire heat transfer tube 304 reaches the decontamination-accomplishment
grinding amount (W) at which the decontamination of the entire heat transfer tube
304 is achieved is calculated by the equation 2.
[0085] The time register 105c measures the decontaminating time (the grinding time) in the
decontamination apparatus 100.
[0086] The decontamination method that is the operation of the decontamination apparatus
100 is described with reference to a flowchart in Fig. 11.
[0087] In the present embodiment, when the heat exchanger is replaced by new one due to
aged deterioration or the like, to prevent an operator from being irradiated with
radiation when the used heat exchanger is dismantled, the inside of the heat transfer
tube is decontaminated, and the decontamination apparatus and the decontamination
method are applied.
[0088] The decontaminating operation is shown in the flowchart of the decontaminating operation
of Fig. 7 described in the first embodiment. The operation (the decontamination method)
of the decontamination apparatus 100 at Step S5 in Fig. 7 is shown in the flowchart
of the operation (the decontamination method) of the decontamination apparatus in
Fig. 11. The control unit 105 connects the first supply/recovery passage 110 to a
first port 304a of desired one of the heat transfer tubes 304, and connects the second
supply/recovery passage 111 to the second port 304b of desired one of the heat transfer
tubes 304 by the circuit connecting unit 104 (Step S21). At the same time, the control
unit 105 causes the switching unit 109 to switch the circuit to the forward inflow
circuit 101 (Step S22).
[0089] Next, the control unit 105 operates the compressor 106 to flow air in, measures pressures
on the inlet side (on the side of the first port 304a) and on the outlet side (on
the side of the second port 304b) of the heat transfer tube 304, and sets the flow
rate (Qp) of the abrasive particles based on a pressure loss between the inlet side
and the outlet side of the heat transfer tube 304 (Step S23).
[0090] Next, the control unit 105 calculates a permissible grinding time (tA) required until
the curved portion (the point A) of the heat transfer tube 304 reaches the permissible
grinding thickness in the forward inflow and the backward inflow (Step S24).
[0091] Next, the control unit 105 calculates the decontamination grinding time (2t) required
until the entire heat transfer tube 304 reaches the decontamination-accomplishment
grinding amount (W) in the forward inflow and the backward inflow (Step S25).
[0092] Next, the permissible grinding time (tA) and the decontamination grinding time (2t)
are compared with each other, and when the permissible grinding time (tA) is longer
than the decontamination grinding time (2t) (YES at Step S26), the control unit 105
equalizes the forward inflow time (t forward) and backward inflow time (t backward),
and the decontamination grinding time (2t/2), and mixes abrasive particles into air,
switches the switching unit 109, and performs a grinding operation by forward inflow
and backward inflow (Step S27).
[0093] That is, in the forward inflow circuit 101, air mixed with the abrasive particles
is caused to reach the second port 304b from the first port 304a of the heat transfer
tube 304 and to flow into the heat transfer tube 304, and the inside of the heat transfer
tube 304 is decontaminated. When the forward inflow time (t forward) that is the decontamination
grinding time (2t/2) is elapsed, the control unit 105 causes the switching unit 109
to switch the circuit to the backward inflow circuit 102. According to this configuration,
in the backward inflow circuit 102, air mixed with the abrasive particles is caused
to reach the first port 304a from the second port 304b of the heat transfer tube 304
and to flow into the heat transfer tube 304, and the inside of the heat transfer tube
304 is continuously decontaminated. When the backward inflow time (t backward) that
is the remaining decontamination grinding time (2t/2) is elapsed, the control unit
105 stops the inflow of air, and completes the decontaminating operation.
[0094] Meanwhile, at Step S26, when the permissible grinding time (tA) is shorter than the
decontamination grinding time (2t) (NO at Step S26), the control unit 105 equalizes
the forward inflow time (tA forward), the backward inflow time (tA backward), and
the permissible grinding time (tA/2), mixes the abrasive particles into air, switches
the switching unit 109, and performs the grinding operation by forward inflow and
backward inflow (Step S28).
[0095] That is, in the forward inflow circuit 101, air mixed with the abrasive particles
is caused to reach the second port 304b from the first port 304a of the heat transfer
tube 304 and to flow into the heat transfer tube 304, and the inside of the heat transfer
tube 304 is decontaminated. When the forward inflow time (tA forward) that is the
permissible grinding time (tA/2) is elapsed, the control unit 105 causes the switching
unit 109 to switch the circuit to the backward inflow circuit 102. With this configuration,
in the backward inflow circuit 102, air mixed with the abrasive particles is caused
to reach the first port 304a from the second port 304b of the heat transfer tube 304
and to flow into the heat transfer tube 304, and the inside of the heat transfer tube
304 is continuously decontaminated. When the backward inflow time (tA backward) that
is the remaining permissible grinding time (tA/2) is elapsed, the control unit 105
stops the inflow of air, and completes the decontaminating operation.
[0096] Steps S21 to S28 are repeatedly performed until the decontaminating operation of
all of the heat transfer tubes 304 of the steam generator 3 is completed while connecting
the first supply/recovery passage 110 and the second supply/recovery passage 111 to
the next heat transfer tube 304 by the circuit connecting unit 104.
[0097] At Step S22, the switching unit 109 can switch the circuit to the backward inflow
circuit 102. In this case, at Step S27, in the backward inflow circuit 102, air mixed
with the abrasive particles is caused to reach the first port 304a from the second
port 304b of the heat transfer tube 304 and to flow into the heat transfer tube 304,
and when the backward inflow time (t backward) that is the decontamination grinding
time (2t/2) is elapsed, the switching unit 109 switches the circuit to the forward
inflow circuit 101, and in the forward inflow circuit 101, air mixed with the abrasive
particles is caused to reach the second port 304b from the first port 304a of the
heat transfer tube 304 and to flow into the heat transfer tube 304, and when the forward
inflow time (t forward) that is the remaining decontamination grinding time (2t/2)
is elapsed, the inflow of air is stopped, and the decontaminating operation is completed.
At Step S28, in the backward inflow circuit 102, air mixed with the abrasive particles
is caused to reach the first port 304a from the second port 304b of the heat transfer
tube 304 and to flow into the heat transfer tube 304, and when the backward inflow
time (tA backward) that is the permissible grinding time (tA/2) is elapsed, the switching
unit 109 switches the circuit to the forward inflow circuit 101, and in the forward
inflow circuit 101, air mixed with the abrasive particles is caused to reach the second
port 304b from the first port 304a of the heat transfer tube 304 and to flow into
the heat transfer tube 304, and when the forward inflow time (t forward) that is the
remaining permissible grinding time (tA/2) is elapsed, the inflow of air is stopped,
and the decontaminating operation is completed.
[0098] The decontamination method according to the second embodiment includes a step of
flowing air into the heat transfer tube 304, and setting a flow rate of abrasive particles
to be mixed into the air based on a pressure loss between the inlet side and the outlet
side of the heat transfer tube 304, a step of calculating the permissible grinding
time (tA) required until the curved portion (the point A) of the heat transfer tube
304 reaches the permissible grinding thickness, and calculating the decontamination
grinding time (2t) required until the entire heat transfer tube 304 reaches the decontamination-accomplishment
grinding amount (W), and a step of flowing air mixed with the abrasive particles into
the heat transfer tube 304 for a time that is a half of the decontamination grinding
time (2t) and then backwardly flowing air mixed with the abrasive particles into the
heat transfer tube 304 for a time that is a half of the decontamination grinding time
(2t) when the permissible grinding time (tA) is longer than the decontamination grinding
time (2t), and flowing air mixed with the abrasive particles into the heat transfer
tube 304 for a time that is a half of the permissible grinding time (tA) and then
backwardly flowing air mixed with the abrasive particles into the heat transfer tube
304 backwardly for a time that is a half of the permissible grinding time (tA) when
the permissible grinding time (tA) is shorter than the decontamination grinding time
(2t).
[0099] According to this decontamination method, the permissible grinding time (tA) and
the decontamination grinding time (2t) are calculated, and when the permissible grinding
time (tA) is longer than the decontamination grinding time (2t) and the entire heat
transfer tube 304 reaches the decontamination-accomplishment grinding amount (W) before
the curved portion (the point A) reaches the permissible grinding thickness, a higher
priority is given to the decontamination grinding time (2t), and the inside of the
heat transfer tube 304 is ground by the forward inflow and backward inflow for the
time that is a half of the decontamination grinding time (2t) each. When the permissible
grinding time (tA) is shorter than the decontamination grinding time (2t), a higher
priority is given to the permissible grinding time (tA), and the inside of the heat
transfer tube 304 is ground by the forward inflow and backward inflow for the time
that is a half of the permissible grinding time (tA) each. As a result, a case that
the curved portion is excessively ground can be avoided, and it is possible to prevent
the heat transfer tube 304 from being perforated by partial excessive grinding. Further,
the decontamination can be performed within the shortest decontaminating time.
[0100] The grinding thickness permitted for the curved portion (the point A) is the thinnest
grinding thickness within a range such that the curved portion is not perforated,
and when the curved portion is ground into this grinding thickness, other inside portions
of the heat transfer tube 304 are ground to such an extent that the other inside portions
are appropriately decontaminated. Therefore, even if a higher priority is given to
the permissible grinding time (tA) when the permissible grinding time (tA) is shorter
than the decontamination grinding time (2t), the entire heat transfer tube 304 can
appropriately be decontaminated.
[0101] According to the decontamination method of the second embodiment, the forward inflow
circuit 101 and the backward inflow circuit 102 are switched by the switching unit
109, and the second port 304b of the heat transfer tube 304 is switched from the downstream
to the upstream of the jet stream air. As shown in Fig. 9(a) for example, in all of
the grinding steps of the general example, when air mixed with the abrasive particles
is caused to reach the second port 304b from the first port 304a of the heat transfer
tube 304 and to flow into the heat transfer tube 304, and when the decontamination
is performed until the upstream side (on the side of the first port 304a of the heat
transfer tube 304) is caused to reach the target grinding amount, the downstream side
(on the side of the second port 304b of the heat transfer tube 304) is excessively
ground and a large amount of secondary waste is generated. On the other hand, in all
of the grinding steps of the first embodiment shown in Fig. 9(b), a switching operation
is performed such that air mixed with the abrasive particles in mid-course is caused
to reach the first port 304a from the second port 304b of the heat transfer tube 304
and to flow into the heat transfer tube 304. According to this configuration, the
decontamination effect can be equalized over the entire length of the heat transfer
tube 304 without excessively grinding the heat transfer tube 304, and the decontamination
time can be shortened.
[0102] The decontamination method according to the second embodiment includes a step of
recovering the abrasive particles coming from the downstream side of the jet stream
air when the air mixed with the abrasive particles is caused to flow into the heat
transfer tube 304, and a step of returning the recovered abrasive particles to the
upstream side of the jet stream air. According to this decontamination method, it
is possible to further suppress the amount of secondary waste generated, by using
the abrasive particles coming from the downstream side of the jet stream air again
for the decontamination.
[0103] In the decontamination method according to the second embodiment, the step of flowing
air mixed with the abrasive particles into the heat transfer tube 304 can be a step
of flowing air mixed with the abrasive particles into the heat transfer tube 304 and
backwardly flowing air mixed with the abrasive particles into the heat transfer tube
304 within the decontamination grinding time (2t) when the permissible grinding time
(tA) is longer than the decontamination grinding time (2t), and flowing air mixed
with the abrasive particles into the heat transfer tube 304 and backwardly flowing
air mixed with the abrasive particles into the heat transfer tube 304 within the permissible
grinding time (tA) when the permissible grinding time (tA) is shorter than the decontamination
grinding time (2t). That is, the present invention is not limited to a case that the
decontaminating operation is performed while using a time that is a half (tA/2) of
the permissible grinding time (tA) as the forward inflow time (tA forward) and the
backward inflow time (tA backward), or not limited to a case that the decontaminating
operation is performed while using a time that is a half (2t/2) of the decontamination
grinding time (2t) as the forward inflow time (tA forward) and the backward inflow
time (tA backward). The forward inflow time (tA forward, t forward) and the backward
inflow time (tA backward, t backward) can slightly be different from each other, and
effects described above can be obtained.
[0104] The decontamination apparatus 100 according to the second embodiment described above
includes the forward inflow circuit 101 that causes air to reach the second port 304b
from the first port 304a of the heat transfer tube 304 and to flow into the heat transfer
tube 304, the backward inflow circuit 102 that causes air to reach the first port
304a from the second port 304b of the heat transfer tube 304 and to flow into the
heat transfer tube 304, the switching unit 109 that selectively switches between the
forward inflow circuit 101 and the backward inflow circuit 102, the abrasive supplying
unit 108 that mixes abrasive particles into air flowing into the heat transfer tube
304 while measuring the amount of abrasive particles, and the control unit 105 that
controls the switching unit 109 and the abrasive supplying unit 108. The control unit
105 causes the switching unit 109 to switch between the forward inflow circuit and
the backward inflow circuit, flows air into the heat transfer tube 304, sets the flow
rate of the abrasive particles that are mixed into air based on the pressure loss
between the inlet side and the outlet side of the heat transfer tube 304, calculates
the permissible grinding time (tA) required until the curved portion (the point A)
of the heat transfer tube 304 reaches the permissible grinding thickness based on
the flow rate of the abrasive particles, and calculates the decontamination grinding
time (2t) required until the entire heat transfer tube 304 reaches the decontamination-accomplishment
grinding amount (W). When the permissible grinding time (tA) is longer than the decontamination
grinding time (2t), and when a time that is a half of the decontamination grinding
time (2t) is elapsed after the switching unit 109 switches the circuit to the forward
inflow circuit 101 while mixing the abrasive particles into air by the abrasive supplying
unit 108, the switching unit 109 switches the circuit to the backward inflow circuit
102. When the permissible grinding time (tA) is shorter than the decontamination grinding
time (2t), and when a time that is a half of the permissible grinding time (tA) is
elapsed after the switching unit 109 switches the circuit to the forward inflow circuit
101 while missing the abrasive particles into the air by the abrasive supplying unit
108, the switching unit 109 switches the circuit to the backward inflow circuit 102.
[0105] According to the decontamination apparatus 100, the decontamination method can be
performed, a case that the curved portion is excessively ground is avoided, and it
is possible to prevent the heat transfer tube 304 from being perforated by partial
excessive grinding. Further, the decontamination can be performed within the shortest
decontamination time. Further, the decontamination effect can be equalized over the
entire length of the heat transfer tube 304, and the decontamination time can be shortened.
[0106] The decontamination apparatus 100 according to the second embodiment includes the
abrasive circulating unit 103 that recovers abrasive particles coming from the downstream
side of the jet stream air and returns the recovered abrasive particles to the upstream
side of the jet stream air. According to the decontamination apparatus 100, it is
possible to further suppress the amount of secondary waste generated, by using the
abrasive particles coming from the downstream side of the jet stream air again for
the decontamination.
[0107] According to the decontamination apparatus 100 of the second embodiment, when the
permissible grinding time (tA) is longer than the decontamination grinding time (2t),
the control unit 105 can cause the switching unit 109 to switch between the forward
inflow circuit 101 and the backward inflow circuit 102 within the decontamination
grinding time (tA) while mixing the abrasive particles into air by the abrasive supplying
unit 108. When the permissible grinding time (tA) is shorter than the decontamination
grinding time (2t), the control unit 105 can cause the switching unit 109 to switch
between the forward inflow circuit 101 and the backward inflow circuit 102 within
the permissible grinding thickness (2t) while mixing the abrasive particles into air
by the abrasive supplying unit 108. That is, the present invention is not limited
to the case that the decontaminating operation is performed while using a time that
is a half (tA/2) of the permissible grinding time (tA) as the forward inflow time
(tA forward) and the backward inflow time (tA backward), or not limited to a case
that the decontaminating operation is performed while using a time that is a half
(2t/2) of the decontamination grinding time (2t) as the forward inflow time (tA forward)
and the backward inflow time (tA backward). The forward inflow time (tA forward, t
forward) and the backward inflow time (tA backward, t backward) can slightly be different
from each other, and effects described above can be obtained.
[0108] As described above, the decontamination method of a heat exchanger and the decontamination
apparatus according to the present invention are suitable to prevent a heat transfer
tube from being perforated by partial excessive grinding.