Over 1000 Tonnes of Nuclear Waste To Be Stored At Sizewell B

Over 1000[1] Tonnes of Nuclear Waste To Be Stored At Sizewell B
Despite over 60 years of producing highly radioactive waste we still have no way of disposing of it. The waste from nuclear plants such as Sizewell B was originally intended to be sent to Sellafield for reprocessing or processing for long term disposal. Since this has not happened the ponds used to store the spent fuel at the plant are now reaching capacity. It is now proposed that the fuel is transferred to ‘dry storage casks’ on the site.

Spent Fuel

Nuclear fission reactors work by splitting uranium atoms to produce two smaller atoms and large amounts of energy. The atoms that are produced are often not stable and undergo radioactive decay producing radiation and further heat (called decay heat). Some of these atoms also act as ‘poisons’ to the nuclear fission process and so the fuel has to discarded before fuel is fully utilised. Modern reactors get about 4% of the energy theoretically available from the fuel.
Spent fuel is therefore highly radioactive (deadly in minutes) and continues to produce heat which must be removed to avoid the fuel rods overheating and burning. They are therefore put into ponds of water which provides cooling and stops most of the radiation.
However, fuel ponds must be continuously monitored and maintained and are susceptible to leaks and possible terrorist attacks.

Dry Storage

The amount of ‘decay heat’ from the fuel decreases with time and after a period of about 5 years (for current reactors) it is possible to take the fuel out of the ponds and store it in ‘dry storage’. The fuel rods are transferred to a large metal canister in the cooling ponds and then removed and dried. The canister is then welded shut to stop radioactive material from escaping. However the can does not stop much of the intense radiation so the canister is placed inside a larger concrete storage cask. Air flow between the metal canister and the concrete storage cask provides cooling, however, the metal canister can still reach temperatures of 400°C.

Safety

Dry storage of spent nuclear fuel is undoubtedly safer than storage in cooling ponds. However, the task of moving the fuel from the ponds to the casks is not straight forward. The whole process must be done within a strict time limit to stop the fuel from overheating and there must be adequate protection against the intense radiation at all times.
In the USA there have been several occasions when hydrogen gas has ignited while the canister was being welded. There is also a problem if the welds are defective since it is not easy to transfer a canister at 400°C back into the cooling pond. A defective canister at Palisades nuclear power plant is still there after 17 years.

Dumping Democracy

Sizewell B is being allowed to store the waste there since it is already licensed to store nuclear material. However, when the plans for the power plant were being discussed in the 1990s it was never intended that the spent fuel would remain on the site for such a long period.

Eventual Disposal

Although the Committee on Radioactive Waste Management (CoRWM) has recommended that the UK’s nuclear waste be disposed of underground this is still only a recommendation and there are many technical obstacles to overcome before this happens. No suitable site has yet been established and there are still many issues around how the waste should be stored in such a site. Although time deadlines have been set for setting up such a facility these will cannot be met if these obstacles cannot be overcome.
Even if a long term waste disposal facility is established the waste from Sizewell B may not be moved until the end of this century.
Even after this time the amount of waste will contain thousands of times more radioactivity than what was released at Chernobyl.

Waste Disposal – The US Experience

There are no long term nuclear waste disposal facilities anywhere in the world. The US planned to use Yucca Mountain to dispose of waste. Although it was meant to start accepting waste in 1998 the plan was recently dropped due to unfavourable geology after $9billion (£5.7billion) had already been spent developing the site. The US government may also face liabilities of up to $11billion (£7billion) for failing to meet their contractual obligation with nuclear power companies.[2]

New Build – “If your in a hole stop digging!”

New reactors are also proposed at Sizewell. Not only would this add to the amount of spent fuel at the new plants would produce waste that is substantially different to that currently being created.
In an attempt to make new nuclear economic EdF and other nuclear power companies are proposing to burn a larger percentage of the fuel (from 4% to 6%). Although this sounds better since less fuel is used to produce the same amount of electricity it creates new technical challenges to both short term and long term storage of waste.
The waste from the new plants would be more radioactive and therefore would produce much more heat when removed from the reactor. This would increase the time that it would be necessary to store the spent fuel under water.
The radiation emitted by the fuel is also very different with many more neutrons being emitted[3] Not only does this affect the type of radiation shielding that is required it is not known what the long term affect of the neutrons would have on storage canisters.
1 See Spent Fuel At Sizewell

2 http://www.powermag.com/nuclear/The-U-S-Spent-Nuclear-Fuel-Policy-Road-to-Nowhere_2651.html

3 Nuclide Importance to Criticality Safety, Decay Heating, and Source Terms Related to Transport and Interim Storage of High-Burnup LWR Fuel.NUREG/CR-6700 ORNL/TM-2000/284

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