The Leningrad NPP-2: the process of filling the reactor building envelope channels has begun

The second-to-last stage of installing the internal reactor building envelope preload system has begun at the second VVER-1200 power block of the Leningrad NPP-2: the team has started to inject special cement grout into the channels located within the envelope that contain steel super-tough prestressing strands.

All in all, the specialists will have to fill 76 horizontal and 50 vertical channels. This process will prevent rope deflection and increase their tension evenness in all directions.

‘Injection is a complex and critical process. Its proper completion will influence the durability and stability of the containment, which is one of the barriers preventing radionuclides from spreading around if there is a hypothetical accident. The designed life span on the preload system is at least 60 years, which is 10 years longer than the designed life span of the power block itself. Later on, the ropes may be replaced and repaired, which is why the preload system’s life span may be extended for several decades’, Andrey Korpachev, the I tier engineer of the construction control department at the Leningrad NPP-2 Capital Construction Unit, said.

The cement grout in use contains special additions that make it strong, non-shrinking, and formable. When this solution fills the channels and gets consolidated, the pre-stressing activities for the internal envelope will be initiated at the second power block: the ropes will be tightened one by one with special screws to enwrap the reactor building as a network, thus making the whole construction even more durable. Special sensors will be installed in the envelope to control the stretching force throughout the whole operation period of the power block.

The whole set of works related to launching the internal reactor building envelope preload system at the second VVER-1200 power block will last until Q4 this year and will serve as a starting point for the most critical part of the pre-commissioning activities – the containment tightness and strength tests.

The Leningrad NPP is the country’s first plant with RBMK-1000 reactors (uranium-graphite circuit-type reactor running on thermal neutrons). The decision that marked its construction was taken in September 1966 by a resolution of the Central Committee of the Communist Party of the USSR and the Council of Ministers No. 800-252. According to that document, the Leningrad NPP was supposed to become a core in a network of nuclear power plants with RBMK-1000 reactors that were supposed to produce a substantial share of electric power. The construction of the Leningrad NPP was going well, and by 1973 the first power block was fully erected. On December 23, 1973, following stable 72-hours’ operation at the capacity of 150 megawatt, the State Commission signed the acceptance certificate stating that the first power block of the Leningrad nuclear power plant is commissioned for pilot production. 

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