Rosatom launches annealing technology for VVER-1000 units

27 November 2018

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Rosatom announced yesterday it has extended the service life of unit 1 of its Balakovo nuclear power plant in the Saratov region of Russia by using thermal annealing on the VVER-1000's reactor pressure vessel. The Russian state nuclear corporation said it was a global first for the industry to anneal a large-capacity RPV and that the technology could extend the service lives of VVER-1000 units around the world by up to 30 years.

Annealing of the RPV of Balakovo unit 1 (Image: Rosatom)

The technology used for the procedure, which was designed by scientists from the Kurchatov Institute, uses heat treatment to restore the original physical properties of the metal in an RPV.

"Today, there are about 37 VVER-1000 around the world. Annealing [of a reactor vessel] is a new and, currently, only technology in the world that enables the extension of the service life of a reactor. This technology will be available for export," Rosatom Director General Alexey Likhachov said.

Annealing could extend the service life of VVER-1000s by between 15 and 30 years, thus helping to avoid global emissions of up to 7.8 billion tonnes of CO2, as well as boost the safety and economic performance of nuclear power plants, Rosatom said. For the extended operational service period, the levelised cost of energy could decrease to as little as USD29 per MWt-hour, which is less than the marginal cost of coal-fired power generation, it added.

Mikhail Kovalchuk, president of the Kurchatov Institute, noted that the long-term operation of VVER-type reactors under neutron irradiation leads to the degradation of the metal properties in RPVs, which limits the service life of the given nuclear power plant. The patented VVER-1000 RPV recovery annealing technology can be adapted for water-moderated nuclear power units of any design and capacity, he said.

The pilot recovery annealing of the RPV of unit 1 of the Balakovo plant was carried out this month and led to the recovery of the structure and mechanical properties of the RPV’s metal to its original state, he said, adding that the procedure had extended the unit's service life by 15 years.

Previously, similar technology was tried and tested at smaller reactors of medium capacity - VVER-440s - at the following nuclear power plants: Novovoronezh and Kola in Russia, Rovno in Ukraine, Metsamor in Armenia, Greifswald in Germany and Kozloduy in Bulgaria. Annealing enabled an extension to the service lives of these of between 45 and 60 years, Rosatom said.

The VVER-1000 RPV is larger in diameter and has thicker steel structures than the VVER-440 RPV, thus requiring development of a new technology for the annealing of large-capacity RPVs, it said. The metal in the RPV was slowly heated to a temperature of +565 degrees Celsius, after which began the “stationary annealing” process, which lasted 100 hours. The metal was then slowly cooled.

All the technical data gathered during the procedure will be compiled into a report that will be submitted to the national regulator, Rostekhnadzor, "for approval to conduct further reactor operations", it added.

Researched and written by World Nuclear News

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