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Up to four reactors at Sosnovy Bor nuclear plant could be shut down
Oldest reactor already closed over graphite problems
Problems caused by ageing threaten to force the premature closure of four reactors at the Russian Sosnovy Bor nuclear power plant on the southern shore of the Gulf of Finland.
The Russian nuclear power company Rosenergoatom has told the Finnish Radiation and Nuclear Safety Authority (STUK) that one of the plant’s four reactors has been shut down, and will remain out of commission for the foreseeable future. The closure of the oldest unit was reported on Thursday by the Swedish-language newspaper Hufvudstadsbladet.
During a shutdown for maintenance in May it came out that the graphite rods used to slow the nuclear reaction had swollen and had cracks in them. The swelling alters the shape of the reactor core, which increases the risk of a nuclear accident.
The safety of Sosnovy Bor is an important question on the northern side of the Gulf of Finland as well; the plant lies just 100 kilometres from Finland’s south coast.
The expansion of the graphite in the reactor core is a sign of ageing, says Heikki Reponen of STUK.
The expansion is dangerous, because it could twist tubing inside the graphite. The tubes should remain straight, because the control rods that are used in controlling the reactor need to move freely inside them.
The first reactor, which came on line in 1973, is the oldest of the units, but the second unit is only two years younger. Reponen says that it appears that the problems are not limited to the first reactor.
Reponen says that there is no indication that the swelling of the graphite would have affected the use of the control rods yet.
He also praises what he sees as a responsible decision by Russia to shut down the reactor, even though the four new reactors that are to replace the old ones will not be ready for a few years.
The graphite-controlled reactors at Sosnovy Bor are the same type as those at Chernobyl. Similar ageing reactors are in use in other parts of Russia, including those at Kursk in the southwest of Russia.
The reactors of the Kola nuclear power plant, located near the Finnish border, use the same kind of pressurised water technology as the reactors at the Loviisa plant on Finland's south coast.
No official decision on shutting down the number-one reactor at Sosnovy Bor has been made public in Russia yet. A permanent decision on the fate of the plant is expected soon.