GB2198682A

GB2198682A - Flask for receiving radioactive material

Info

Publication number: GB2198682A
Application number: GB08630424A
Authority: GB
Inventors: David Minshall; Peter Charles Guilfoyle; Gary Mark Buckley
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1986-12-19
Filing date: 1986-12-19
Publication date: 1988-06-22
Anticipated expiration: 2006-12-19
Also published as: GB2198682B; GB8630424D0

Abstract

A flask for receiving radioactive material, such as waste generated in the reprocessing of spent nuclear fuel, comprises a container 12 having a plurality of elongate fins 16 which are provided with a cover 18. A neutron absorbing material 24 is disposed in the spaces defined between the container, cover and adjacent fins such that an air gap 26 is present between the cover and neutron absorbing material to allow for differential expansion. Suitable neutron absorbing materials include materials comprising a boron compound and a silicone polymer. <IMAGE>

Description

Flask for receiving radioactive material This invention relates to a flask for receiving radioactive material, and is particularly but not exclusively concerned with a flask for use in transporting radioactive material.

Even after spent nuclear fuel has been removed from a nuclear reactor it continues to emit heat and radioactivity due to decay of fission products present in the spent fuel. For this reason, the spent fuel is usually stored under water in a cooling pond located close to the reactor for a short period to allow nuclei with short half-lives to decay and the level of heat and radioactivity emitted to fall. Following this storage period close to the nuclear reactor, the spent fuel is usually transported to another site for reprocessing or further storage. During reprocessing of the spent fuel, radioactive waste is generated which, as it contains the fission products, emits both heat and radioactivity. The waste is transferred to engineered stores where it is stored to allow the radioactivity to die away.To facilitate handling. and storage of the waste it may be converted into a stable glass-like solid termed vitrified waste.

It is desirable that any containers used to transport radioactive material be able to attenuate the radioactivity ad heat emitted from the material.

According to the present invention there is provided a flask for receiving radioactive material, said flask comprising a container having a plurality of elongate fins, the fins being provided with a cover which is disposed so as to define a space between the container, cover and adjacent fins, said space containing a material capable of absorbing neutrons and a gap, the gap being provided to allow for expansion of the material and the fins.

Preferably the cover locates on the ends of the fins. The cover may comprise a plurality of plates which are fastened to the fins, by for example screws. A filler having a high thermal conductivity may be disposed between and around the joints between the cover and the fins to increase the area of contact between the cover and fins, and thereby facilitate the dissipation of heat from the radioactive material within the container to the environment via the fins and cover.

The material capable of absorbing neutrons may comprise a silicone polymer and a boron containing compound.

The fins may be tapered.

The invention will now be further described, by way of example only, with reference to the Figure in the accompanying drawing which is a diagrammatic sectional view of a flask for use in transporting vitrified radioactive waste within a nuclear estalishment.

The Figure shows a flask 10 comprising a thick as taking part in the heat dissipation mechanism, the cover plates 18 also act as a protective cover for the flask 10. The filler 22 increases the area of contact and improves the thermal contact between the cover plates 18 and the fins 16, and therefore improves the rate of transfer of heat into the environment. The thermal contact between the cover plates 18 and the fins 16 is also increased by the use of screws to fasten the plates 18 to the fins 16. Provision of the air gap 26 allows for expansion of the neutron absorbing material 24 and the fins 16.

Gamma rays emitted by the radioactive waste are attenuated by the container 12 which is typically thickwalled for this purpose, whilst neutrons are attenuated by the neutron absorbing material 24. The width of the fins 16 is typically small compared with the distance between adjacent fins 16 so that the discontinuities in the absorbing material 24 is kept to a minimum.

It should be understood that the flask may have other uses apart from the transportation of radioactive waste within nuclear establishments, such as the storage of radioactive materials, for example, spent nuclear fuel, and in the transportation of radioactive material from one site to another.

walled cylindrical container 12 having a base 14 and elongate tapered fins 16 which are substantially parallel to the longitudinal axis of the container 12. For simplicity only eight fins 16 are shown but there are typically about twenty four such fins 16. The container 12 and fins 16 are formed from a metal such as spheriodal graphite iron and are cast as one unit. Cover plates 18, typically formed from mild steel, locate on shoulders 20 provided on the fins 16 and are fastened to the fins 16 by screws (not shown). A filler 22 having a high thermal conductivity such as that marketed under the name of DEVCON (registered trade mark) is disposed at and around the joints between the cover plates 18 and fins 16, and between adjacent cover plates 18. A layer of neutron absorbing material, 24 containing a silicone polymer and a boron containing compound, is disposed between the fins 16 and adjacent to the outer wall of the container 12 so that there is an air gap 26 between the absorbing material 24 and cover plates 18. Typically, the air gap 26 has a thickness equal to about 6% of the thickness of the absorbing material 24.

In use, radioactive waste such as vitrified radioactive waste (not shown) is placed inside the container 12 and a lid (not shown) secured to the container 12. Heat generated by the radioactive waste passes through'the container 12, fins 16 and into the cover plates 18, and then into the environment. As well

Claims

Claims 1. A flask for receiving radioactive material, said flask comprising a container having a plurality of elongate fins, the fins being provided with a cover which is disposed so as to define a space between the container, cover and adjacent fins, said space containing a material capable of absorbing neutrons and a gap, the gap being provided to allow for expansion of the neutron absorbing material and the fins.
2. A flask as claimed in Claim 1 in which the cover locates on the ends of the fins.
3. A flask as claimed in Claim 1 or 2 in which a filler having a high thermal conductivity is disposed between and around the joints between the cover and the fins to increase the area of contact between the cover and fins, and thereby facilitate the dissipation of heat from the radioactive material within the container to the environment via the fins and cover.
4. A flask as claimed in Claim 1, 2 or 3 in which the neutron absorbing material comprises a silicone polymer and a boron-containing compound.
5. A flask as claimed in any one of the preceding claims in which the fins are tapered.
6. A flask for receiving radioactive material substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.