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(11) | EP 2 821 999 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Containers for radioactive waste |
| (57) A container (10) for radioactive waste comprises a ductile cast iron body (12) having
an opening (14) through which an item containing radioactive waste or radioactive
waste material itself may be placed into the container (10). The opening (14) is closed
by a transport lid (16), which is bolted onto the body (12) of the container (10)
to cover the opening (14). The rim of the opening (14) has a corrosion resistant lining
(22) and the first or transport lid (16) is also of a corrosion resistant material
having a high nuclear radiation shielding capability. A first seal (24) is inset beneath
the lid (16) and compressed against a lip (26).
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Technical Field
[0001] This invention relates to containers for radioactive materials and to the storage and disposal of radioactive waste.
[0002] Radioactive waste has four categories:
- HLW [high level waste] which has high radiation output requiring significant shielding: heat emissions require specially designed containers having incident resistant containment and certification for storage and transport of these materials;
- ILW [Intermediate Level Waste] which has high radiation output requiring significant radiation shielding, but with a lower level of heat output: ILW still requires specially designed containers having incident resistant containment and certification for storage and transport;
- LLW [Low Level Waste] which requires low radiation shielding and minimal provision for heat output but requiring specialist design containers having a degree of incident resistant containment;
- VLLW [Very Low Level Waste] requiring no special capabilities for containment or shielding for handling or for storage facilities.
Background Art
[0004] At present in the United Kingdom and in many other countries there is a problem with the storage of radioactive waste material as no long term disposal facility has been approved. The main options being considered involve disposal underground, but such facilities, even when approved, are many years away from construction.
[0005] As a result, storage of radioactive waste pending ultimate disposal takes place above ground in specially constructed buildings, in water-filled ponds or in pits below ground. For above ground storage the waste is first placed into a container and then the container with its contents is placed in the storage facility.
[0006] However this solution has problems. One existing container comprises stainless steel outer skin having a concrete interior into which the waste is placed and immobilised with concrete grout. A more recent solution has involved the use of a ductile cast iron container, the cast iron being up to about 160 mm thick.
[0007] It has been found that existing stainless steel and concrete containers present problems because stainless steel and concrete containers deteriorate over time and become corroded from the inside. Such a ductile cast iron container has a cast iron lid bolted on to the container with a seal. The cast iron surface is not corrosion resistant and may not maintain a seal giving rise to a risk when stored for a long time. Furthermore degradation of the waste inside such a container releases gases causing pressure to build within the container with the risk of ultimate failure of the lid bolts, particularly if dropped. All such containers have to undergo a drop test for safety purposes: there is evidence that the seals of such ductile cast iron containers will fail the test after a period of time well before the anticipated availability of underground disposal facilities in the United Kingdom, around 40 years in the future.
[0008] Whilst the existing containers are adequate for short term storage in specialist facilities having specialist remote handling facilities, the identified problems indicate the stainless steel containers should not be used for storage outside specialist facilities and the existing ductile cast iron containers can only for short term storage outdoors (say 1 year). A further problem arises when consideration is given to moving such containers as deterioration may prevent their transport away from their current location without repackaging in specialist facilities using specialist remote handing equipment.
Summary of invention
[0010] According to the present invention a container for radioactive waste comprises a ductile cast iron body having an opening through which an item containing radioactive waste or radioactive waste material itself may be placed into the container, the opening being closable by a first or transport lid, the first or transport lid being boltable onto the body of the container to cover the opening, characterised in that that around the opening is a lip having a corrosion resistant lining, the first or transport lid is of a corrosion resistant material having a high nuclear radiation shielding capability, and a first seal is provided beneath the first or transport lid and compressed against the lip when the first or transport lid is bolted to the body of the container.
[0013] In one arrangement the first seal is inset into the surface of the lid facing the lip and is compressed against the lip when the lid is bolted to the container. It is possible for the first seal to be recessed into a groove in the lip, and to be compressed against the lid, although this arrangement is less convenient.
[0015] Ideally the bolts bolting the first lid to the container are high elongation stainless steel bolts of a material compatible with the ductile cast iron.
[0016] In one embodiment the container itself receives radioactive waste, in such an embodiment the container is provided with a second or inner lid which is mounted by bolts on a seat extending into the opening, the inner lid being of ductile cast iron, the depth of the lid being substantially the same as the thickness of the container.
[0018] The second or inner lid ideally has a step around its perimeter, which sits on the seat, with the lower, narrower cross sectioned portion of the second or inner lip extending down further into the opening below the step.
[0019] In the arrangement described in the previous paragraph, ideally a further seal seals between the inner perimeter edge of the step and the outer edge of the step.
[0020] Ideally the bolts bolting the second or inner lid to the lid support are high elongation stainless steel bolts.
[0021] The second or inner lid normally has removable plug, which is vented through a high integrity filter to allow the escape of gas. The plug serves two purposes; it can be used to pour grout into the container to render the contents immobile, but also can be removed to allow inspection of the contents. This plug is not absolutely essential however.
[0022] The first or transport lid may also have one or more removable plugs, which may also be vented to allow the escape of gas, and which can be removed to allow inspection below the first lid or transport lid and/or to provide a test point.
[0023] In one arrangement the first seal comprises, in section, circular or ovoid shaped lobes linked to each other by the seal material. In this arrangement a plug providing a test point as described in the preceding paragraph plugs a passage between the top of the first or transport lid and a volume between the two circular or ovoid sections of such a double circle or ovoid first seal.
[0024] In one embodiment such a container is adapted to receive an item in the form of a sealed container of conventional form said sealed container containing radioactive waste. Such a conventional container may for example be a skip used to store radioactive waste in a pond. It could also be one of the known containers which is failing.
Brief description of drawings
[0025] Examples of the invention will now be described with reference to the accompanying drawings, in which;
Figure 1 illustrates in exploded form schematic form the main components of a cylindrical container according to the invention;
Figure 2 illustrates in exploded form schematic form the main components of a box shaped container according to the invention;
Figure 3 is a top view of the container of figure 2;
Figure 4 is a perspective view of the closed container of figure 3;
Figure 5 is a section on the line Z-Z of figure 3;
Figure 6 is shows detail of the area A of figure 5;
Figures 7 and 8 shows the seal of containers of figures 2 to 4 in greater detail, figure 8 being a section on the line L-L of figure 7;
Figure 9 is a section on the line Y-Y of figure 3;
Figure 10 is a partial section on the line X-X of figure 3;
Figure 11 shows a different embodiment of the invention with a container designed to receive a skip containing radioactive waste;
Figure 12A shows the container of figure 11 being lifted;
Figure 12B shows the partially cut away container of figure 11 with the first or transport lid closed; and
Figure 13 illustrates flexibility of the invention showing, without limitation, a number of exterior shapes and forms into which containers according to the invention have been made.
Description of embodiments
[0026] In figure 1 a container 10 for radioactive waste comprises a cylindrical ductile cast iron body 12 with an opening 14 at one end through which waste material may be placed into the container. The opening may be closed by a first or transport lid 16. The first or transport lid 16, which is of stainless steel, is bolted onto the container to cover the opening 14 using high elongation stainless steel bolts 18. The rim of the opening 14 forms a lip 20 onto which the first or transport lid 16 can be mounted and has a stainless steel lining 22. An impervious seal 24 (not visible in figure 1) is inset in a recess beneath the lid 16 and compressed against the lip 20.
[0027] A second or inner lid 30 of ductile cast iron is mounted using high elongation stainless steel bolts 32 on a seat 34 extending into the opening; the depth of the lid is substantially the same as the thickness of the container.
[0028] The first or transport lid 16 and the second or inner lid 30 both have filtered vents 26 and 36 respectively. The vent in the outer or transport lid 16 has a cover 28 which be bolted over the vent 26 for transport purposes. Both vents 26 and 36 are bolted in place but the bolts can be removed to facilitate inspection below the relevant lids. In figure 1 the vent 36 in the second or inner lid is of greater diameter than that in the first or transport lid allowing the vent 36 also to be used for process purposes, such as pouring grout into the container to surround the contents of the container.
[0030] In figures 2 to 10, the container for radioactive waste 40 is box shaped having at its upper and lower corners standard ISO Twistlock pockets 42 (seen in figure 4) to enable the container to be lifted.
[0031] The container 40 comprises a ductile cuboidal cast iron body 44 with an opening 46 in the top 48 of the cube through which waste material may be placed into the container. The opening may be closed by a first or transport stainless steel lid 50. The rim 52 of the opening 46 has a lip 54 stepped down below the general level of the top 48 of the container. The lip 54 has a stainless steel lining 56. A seal 58 (seen in figures 5 to 10) is inset into a channel 60 (seen in figure 5, 6, 9 and 10 beneath the lid 50 and compressed against the lip 54. The lid 50 is bolted in place on lip 54 using high elongation stainless steel bolts 64.
[0032] A second or inner lid 66 of ductile cast iron is mounted using high elongation stainless steel bolts 72 on a lid seat 68 extending into the opening 46, the depth of the inner or second lid 66 is substantially the same as the thickness of the container 40. The perimeter of the second or inner lid 66 has a step 70 so that the lower part of the lid 66 can locate within the seat 68. The second or inner lid 66 has a vent 74 performing similar functions to vent 36 in figure 1. An inspection port and simple vent 51 is fitted to the first or transport lid 50. A testing port 55 is provided near the rim of lid 50; this port 55 extends down from the top of the lid to a channel 60 as seen in figure 9, in which seal 58 is seated.
[0034] The first or transport lid 50 has lid lifting points 53 (shown in figures 3 and 4) to assist with lifting the lid (but not the container).
[0035] In figures 5 and 6 detail of the vent 74 can be seen. The vent 74 has comprises a plug 78 with a vertical channel 80 partially penetrating into the plug from the top. A standard HEPA filter 82 is located in channel 80, which becomes narrower below the filter before terminating at a side channel 84 leading laterally out from the plug. Excess gas in the container can pass around the wall of the plug 78 into the channel 84 and from there through filter 82 into the space 86 between the second or inner lid 66 and the first or transport lid 50.
[0036] Also shown in figure 6 is a combined inspection port and vent 51 with an HEPA filter plug screwed into a hole 96 in the first or transport lid 50. A circular seal 99 prevents leakage around the HEPA filter 98. If required a cover for transport purposes can be provided as described for item 28 of figure 1.
[0037] In figures 7 to 10 detail of the seal 58 beneath the first or transport lid 50 can be seen The seal 58 comprises two circular sectioned lobes 88 joined by a flat link 90. In plan, as in figure 7, the seal itself forms a closed circle. The circular lobes 88 have opposed circular sectioned cut outs 92; one inner one aligned towards the centre of the plan circle of the seal 58 the other outwards. The seal 58 is located in a cut out 60 close to the edge of the underside of lid 50. When lid 50 is bolted in place on lip 54, the circular lobes 88 become squeezed into ovoid cross section as seen in figure 5; the cut outs 92 aiding the compression. The seal 58 is clamped in place by a series of screws passing through the flat link 90 into the first or transport lid 50.
[0038] In figure 9 detail of seals around the second or inner lid 66 can be seen. The inner upper edge of seat has a seal 100 around its periphery which is squeezed by the inner corner of step 70. The second or inner lid is located in place by recess 102 in lid 66, onto step 68.
[0039] Figure 10 shows detail of the testing port 55. Port 55 extends down from the top of the lid 50 to a channel 60 in which seal 58 is seated. The port has a step 107 with a stem 106 of a sealing plug 108 extending down into the port 55. External screw treads of the cap of the plug engage with internal screw threads above the step 107, and urge a seal 110 against the step 107 so sealing the testing port. Removal of the plug 108 enables testing of the space 122 between the lobes 88 of the seal 58 for leakage past the seal 58.
[0040] Moving on to figures 11, 12A and 12B an example of an alternative embodiment of the invention is shown. A box shaped container 200 according to the invention has at its upper and lower corners standard ISO Twistlock pockets 202 to enable the container to be lifted.
[0041] The container 200 comprises a ductile cuboidal cast iron body 204 with an opening 206 in the top 208 of the cube through which a skip 210 containing radioactive waste material may pass; typically the skip would have previously contained the radioactive waste in a pond. The opening 206 may be closed by a transport lid 212 of ductile cast iron. The rim of the opening is formed in a lip 214 stepped down below the general level of the top 208 of the container. The lip 214 has a nickel lining 216. A seal is inset into a channel beneath the lid 212, in a similar way to the seal 58 described with reference to figures 2 to 10, and compressed against the nickel lining 216. The lid 212 is bolted in place on lip 214 using high elongation stainless steel bolts 218.The lid 212 has a step 213, allowing the lower part of lid 212 to locate within the lip 214.
[0042] A large lug 220 is fitted to the top of lid 212 to enable to lid to be lifted and other shaped lugs 222 (figure 12B) fitted to the sides of the container enable manoeuvring by mechanical handling equipment.
[0043] As can be seen in figure 12A the Twistlock pockets 202 provide for easy lifting by normal cranes.
[0045] The thickness of the ductile cast iron of the containers may vary according to the specific application but typically they are 30mm thick for the smallest containers up to 300mm or more for big containers handling particularly energetic materials. The appropriate thickness is determined using normal design criteria for ductile cast iron radioactive product interactions.
1. A container for radioactive waste comprises a ductile cast iron body (12, 44, 204)
having an opening (14, 46, 206) through which an item containing radioactive waste
or radioactive waste material itself may be placed into the container, the opening
being closable by a first or transport lid (16, 50, 212), the first or transport lid
(16, 50, 212) being boltable onto the body of the container (10, 40, 200) to cover
the opening, characterised in that that around the opening is a lip (20, 54, 214) having a corrosion resistant lining
(22, 56, 216), the first or transport lid (16, 50, 212) is of a corrosion resistant
material having a high nuclear radiation shielding capability, and a first seal (24,
58) is provided beneath the first or transport lid and compressed against the lip
(20, 54, 214) when the first or transport lid is bolted (16, 50, 212) to the body
of the container (10, 40, 200).
2. A container for radioactive waste according to claim 1 characterised in that the first or transport lid (16, 50, 212) comprises stainless steel.
3. A container for radioactive waste according to claim 1 or 2 in which the lining (22,
56, 216) is nickel or stainless steel.
4. A container for radioactive waste according to claim 1, 2, or 3 characterised in that the first seal (24, 58) is inset into the surface of the first or transport lid (16,
50, 212) facing the lip (20, 54, 214) and is compressed against the lip when the lid
is bolted to the container.
5. A container for radioactive waste according to any preceding claim characterised in that the lip (54, 214) is stepped down below the top surface (48, 208) of the container.
6. A container for radioactive waste according to any one of claims 1 to 5 characterised in containing a further container (210) containing radioactive waste.
7. A container for radioactive waste according to any one of claims 1 to 5 characterised in that the container (10, 40) itself receives radioactive waste, said container having a
second or inner lid (30, 66) which is mounted by bolts (32, 72) on a seat (34, 68)
extending into the opening, the second or inner lid being of ductile cast iron, the
depth of the second or inner lid (30, 66) or inner being substantially the same as
the thickness of the container.
8. A container for radioactive waste according to claim 7 characterised in that the upper surface of the second lid (32, 72) and the lip (20, 54) are in the same
plane.
9. A container for radioactive waste according to claim 7 or 8 characterised in that the second or inner seal has a circumferential step (70) and a seal (100) seals between
the circumferential step and the seat (34, 68).
10. A container for radioactive waste according to any one of claims 7 to 9 characterised in that the second or inner lid (32, 72) has at least one removable plug (74), which is vented
through a high integrity filter to allow the escape of gas.
11. A container for radioactive waste according to any preceding claim characterised in that the first or transport lid (16, 50) has at least one removable plug (26, 51) which
can be removed to allow inspection below the first lid or transport lid and/or to
provide a test point.
12. A container for radioactive waste according to any preceding claim characterised in additionally comprising high elongation stainless steel bolts (18, 32, 64, 74, 218).
13. A container for radioactive waste according to any preceding claim characterised in comprising a vent (26, 51) in the first or transport lid (16, 40) to allow the escape
of gas.
14. A container for radioactive waste according to any preceding claim characterised in that the first seal (58) comprises, in section, circular or ovoid shaped lobes (88) linked
to each other by the seal material (90).
15. A container for radioactive waste according to claim 14, characterised in that the first or transport lid (50) has at least one vented and removable plug (108)
is which can be removed to allow to provide a test point (55) said plug being inserted
in a passage (112) between the top of the first or transport lid (50) and a volume
between the two circular or ovoid sections (88) of such a double circle or ovoid first
seal (58).