SAFETY OF LONG-TERM INTERIM DRY STORAGE OF USED NUCLEAR FUEL

Interim storage of used nuclear fuel is a reliable solution. It provides an intermediate solution while waiting for a decision concerning disposal sites or recycling. Intermediate storage is safe as shown by important industrial feedback and the operational records. Nevertheless, this safety and reliability are well established within a domain of constraints: the respect of regulatory requirements for storage systems and a limited time, 40 years, sometimes extended. For 25 years, interim storage systems have provided an excellent level of safety. Safety studies cover very severe accidents and natural disasters or extreme conditions: aircraft crash, fire, earthquake, cask burial, cask tip-over, fuel cladding breach. Aircraft crash testing has been achieved successfully on cask specimens. Storage time may now have to be extended. Whatever the choice be for the management of used fuel, it will have to be transported from the storage facility to somewhere else for centralized storage, for recycling or for disposal. In the debate, two different questions are raised: the technical investigations and the safety principles. For the assessment of long-term storage, several investigations are presently being carried out concerning the following issues: degradation process of fuel cladding, degradation of neutron poison material, degradation process of canister material, stress corrosion cracking, concrete degradation, seal degradation. It is important for sustainability to maintain two safety principles: ? First, that there should be an end point to the interim storage period, and that radioactive waste shall be managed in such a way that it will not impose undue burden on future generations, ? Secondly, retrievability for safe management of used fuel There is no guarantee that the fuel characteristics can be maintained in perpetuity. The objective of the R&D is to set a limit for which the cladding integrity is maintained. This is the first line of defence for handling, transportability and especially for safety criticality evaluations. In the long term, R&D investigations must progress taking into account the principle that storage shall remain an intermediate step as well as the principle of retrievability of used fuel