3 Nov (NucNet): The technology used to solve problems with reactor graphite swelling at the Leningrad-1 nuclear reactor unit in Russia will now be used to carry out similar work at other large RBMK units, state nuclear corporation Rosatom has said.
In the corporation’s annual report, director-general Sergei Kiriyenko said the successful repairs to the 925-megawatt Leningrad-1 RBMK light-water graphite reactor were “the most important outcome” for the country’s nuclear industry in 2013.
He said the repairs were carried out using technology that could now be used to carry out similar work at the remaining three Leningrad units, and the Kursk and Smolensk nuclear stations, where similar reactors are in operation.
Alexander Lokshin, Rosatom’s first deputy chief executive officer for operations management, said the Leningrad repairs were of “unprecedented complexity” and the technology and tooling had to be developed from scratch. He said the repairs had helped operator Rosenergoatom to avoid “huge losses” at the station.
With the work proving successful, Rosatom said all large RBMK reactors in Russia are likely undergo similar repairs. In 2012, Rosatom said the work would involve the replacement of up to 350 process channels.
In July 2012, problems caused by reactor graphite swelling lead Rosenergoatom to consider the possibility of shutting down Leningrad-1 earlier than scheduled. At one point, the company considered withdrawing the unit from commercial operation and using it only as a test facility to study graphite degradation and RBMK ageing management.
The RBMK has individual fuel channels surrounded by the graphite blocks that form the reactor’s moderator. Each channel is individually cooled by water which is allowed to boil in the fuel tube. The design had serious shortcomings, which contributed to the 1986 Chernobyl accident.
The only remaining large RBMKs still in commercial operation are at Leningrad, Smolensk and Kursk – a total of 11 units. There are four small RBMK units of 11 megawatts each in commercial operation at the Bilibino station, but these are not affected.
Rosenergoatom said the problem with the unit was swelling and cracking of the graphite stack, one of the key components in RBMK reactors.
Channel-type graphite RBMKs are one of the three reactor types used in Russia for commercial nuclear power stations. The other two are the VVER pressurised water reactor, which like all PWRs uses water as a moderator, not graphite, and the BN fast neutron reactor with liquid metal cooling and no moderator.
Development of RBMK technology stopped after the Chernobyl accident in 1986 and the last power generation unit of this type commissioned was the 925-megawatt Smolensk-3 in 1990. All reactors commissioned in Russia since then have been PWRs.
The last RBMK reactors operating outside Russia were at Lithuania’s two-unit Ignalina nuclear station. Ignalina-1 was shut down in 2004 and Ignalina-2 in 2009. Both units were closed in accordance with the conditions of the country’s entry into the EU.
Rosenergoatom had known for some time that the swelling and cracking of the graphite stack could be a potential problem. The company said early in 2012 that graphite degradation in RBMK reactors was likely to begin after 40 to 45 years of operation.
But at Leningrad-1, which according to the International Atomic Energy Agency began commercial operation in November 1974, problems with graphite swelling began earlier than expected. Rosenergoatom said the problem was a concern “primarily” at Leningrad and not at other RBMK units.
But the company also told NucNet that operational plans needed to be established for all 11 RBMK units in Russia.
Phase two of the Leningrad nuclear power station (Leningrad II), which consists of two VVER V-491 1,085-megawatt PWRs, is under construction on a nearby site.
