Les cahiers de l'ASN #04 - DECOMMISSIONING CHALLENGES

And elsewhere? With regard to the decommissioning of nuclear installations following their final shutdown, the international consensus, as expressed in the IAEA safety standards, recognizes two strategies: • deferred dismantling: the parts of the installation containing radioactive substances are kept in or brought to a safe state for several decades before the decommissioning operations begin; • immediate dismantling: decommissioning is initiated as soon as the facility is shut down, without a waiting period, although the dismantling operations can take a long time. United Kingdom The United Kingdom has about thirty definitively shut down power reactors, the vast majority of which are gas-cooled, but there are also a few reactors using other technologies (advanced gas-cooled reactors, heavy water reactors, fast neutron reactors), as well as half-a-dozen definitively shut down research reactors. Although immediate dismantling is legally possible, the strategy currently most widely used in the United Kingdom for power reactors is deferred dismantling. The main reasons put forward are the high level of activation of certain materials (such as graphite), which require decay times of several decades before handling, and the lack of disposal routes for radioactive waste in general. Canada In Canada, the NPP delicensing* plans cover a 50-year period. The licensee wishing to obtain an operating license for an NPP is required to present a delicensing* plan which specifies how they intend to manage the decommissioning and decontamination of their installation. As soon as the delicensing* permit is obtained, implementation of the plan can begin. The activities in this phase include the decontamination and dismantling of the installation. At present, 6 pressurised heavy water nuclear reactors (PHWRs) are undergoing decommissioning. Decommissioning strategies can vary from one country to another. However, most of them refer to the standards set out by the International Atomic Energy Agency (IAEA). United States In the United States, the licensees of nuclear installations (civil or military) can choose from among three decommissioning strategies: immediate dismantling, deferred dismantling, or isolation of the installation by encapsulation (entombment) until radiological levels compatible with delicensing* are attained. To date, about ten nuclear installations have been decommissioned and twenty are undergoing decommissioning. Twelve reactors, including 6 PWRs and 4 boiling water reactors (BWR) are undergoing deferred dismantling and 10 others immediate dismantling, including 4 PWRs and 5 BWRs. * See glossary page 30 24 • Les cahiers de l’ASN • June 2022 BNIs BEING DECOMMISSIONED

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