French regulator issues fresh notice for reactor pit measures at Bugey
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"In particular, it prescribes the implementation of technical devices to keep the reactor pit dry, to spread the corium on the bottom of the reactor pit and the adjacent room and passive flooding of the corium by water, aimed at preventing the foundation slab from being breached in the event of core meltdown," ASN's new information note says, adding that the measures are specific to the reactors at Bugey.
The deadlines for the work at EDF’s Bugey nuclear power plant in France were April 2021, December 2021 and June 2022 for reactors 2, 4 and 5, respectively.
However, during the shutdown of Bugey reactor 2 in February 2022, after an operating cycle with the device for keeping the reactor pit dry in place, "EDF identified damage to this device" and in April, when reactor 4 was shut down it identified "similar damage to the seal fitted to reactor 4".
ASN said: "EDF sent ASN technical information aimed at assessing the impact of the presence of water in the bottom of the reactor pit, resulting from the damage observed on the seals of reactors 2 and 4, on the spreading of the corium and on its passive reflooding, and more generally on the objective of preventing basemat breakthrough in the event of core meltdown. The studies transmitted by EDF show that the objective of preventing the breakthrough of the foundation raft has not been called into question, which has led ASN to consider that dealing with the deviation within two years is appropriate."
It adds that reactor 3 at Bugey is to undergo its fourth 10-year inspection in the second half of 2023 "and the improved device will be installed on this occasion".
The four pressurised water reactors at Bugey - units 2-5 - were built and connected to the grid in the 1970s. Bugey 1 was a gas-cooled reactor which was built from 1965 with its first grid connection in 1972. It was shut down permanently in 1994.
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