Russian state nuclear corporation Rosatom revealed it has extended the service life of unit 1 of the Balakovo NPP for 15 years by applying thermal annealing to the VVER-1000's reactor pressure vessel (RPV). This is the world’s first annealing of a large-capacity RPV.
Previously Russia has successfully annealed the smaller VVER-440 reactor RPVs, and Rosatom says that the technology can now be used to extend the service lives of VVER-1000 units around the world by 15 to 30 years.
The annealing technology was developed by researchers at the Kurchatov Institute, which first announced the success of the new technology on 15 November. It uses heat to restore the original physical properties of the metal in an RPV. The pilot annealing at Balakovo was carried out jointly by nuclear utility Rosenergoatom, design bureau OKBM Gidropress and the Kurchatov Institute.
"Today, there are about 37 VVER-1000 around the world. Annealing is new and, currently, the only technology in the world that enables the extension of the service life of a reactor," said Rosatom Director General Alexey Likhachov. “This technology will be available for export."
The extended operational service period of a reactor achieved using annealing could reduce the levelised cost of energy to as little as $29/MWt-hour, which is less than the marginal cost of coal-fired power generation, Rosatom noted.
Kurchatov Institute president Mikhail Kovalchuk explained that the long-term neutron irradiation experienced by VVER-type reactors results in degradation of the metal properties in RPVs, which limits the life of the plant. He added that the VVER-1000 RPV recovery annealing technology can be adapted for water-moderated nuclear power units of any design and capacity.
Annealing has been used to extend the lives of VVER 440 units to 45-60 years at the Novovoronezh and Kola nuclear stations in Russia, Rovno in Ukraine, Metsamor in Armenia, Greifswald Germany and Kozloduy in Bulgaria. However, the thicker steel structures of the larger VVER-1000 RPV made it necessary to develop a new annealing technology, Rosatom said.
The metal in the Balakovo 1 RPV was slowly heated to a temperature of more than 565 degrees Celsius, after which a “stationary annealing” process began, which lasted 100 hours. The metal was then slowly cooled. All the technical data relating to the procedure will be compiled into a report for submission to the Russian nuclear regulator, Rostekhnadzor, "for approval to conduct further reactor operations".