Rosenergoatom's Novovoronezh 3, the oldest VVER-440 in operation, has begun a new lease of life, defying previous western assessments that first-generation Soviet-design reactors should be decommissioned rapidly because they couldn't be upgraded to international safety levels.
In what officials of the Russian utility said is a model for life extension of the other VVER-440s at Novovoronezh, Novovoronezh 3 received a licence for another five years of operation from safety authority Gosatomnadzor (GAN). Previously, it had been operating on annual licences, pending completion of a major upgrading project.
Russian nuclear officials said western-style safety assessments show that the early VVER-440s have many inherent safety features that are absent on western reactors, and after upgrading, can more than compete on safety terms with reactors of their vintage, or younger, in the West.
The modernisation of Novovoronezh 3, which began in the 1980s, but drew the largest investment over the last three years, lowered the estimated core damage frequency (CDF) from 1.8-4.5x10-3 (assessed in 1993) to 3.44x10-5 (assessed last year). This recent CDF figure is better than many PWRs in the West, and well below the 10-4 probability level accepted by the IAEA's International Nuclear Safety Advisory Group (Insag) for operating reactors.
Nikolai Sorokin, operations director for Rosenergoatom, said that the utility plans to upgrade the other first-generation VVERs and eight RBMK-1000s over the next eight years, using the same principles and under the same rules. Rosenergoatom plans to submit an application this year for long-term operation of Kursk 1, an early RBMK currently temporarily shut down for modernisation. Further units at Kursk and Leningrad would be upgraded for longer-term operation after that, with the last modernisation project scheduled to be completed at Kursk 2 in 2009.
The new safety system added to Novovoronezh 3 ensures containment integrity even in the event of a guillotine break of a 500mm diameter primary pipe. The principle of the system is similar to one installed at the first generation VVER-440s, Bohunice V1 units 1 and 2, in Slovakia. In case of a main coolant pipe break, the system combats confinement breach by directing primary steam into a powerful condenser that filters radioactive products before releasing the air to the atmosphere.
Russian officials said their system, which complements the VVER-440 design's original large safety margins, is twice as effective in reducing radioactivity releases as the Bohunice system.