Storage pool racks have been replaced at unit 4 of Russia’s Balakovo NPP, after many years of work, the plant announced on 27 January.

The personnel of Balakovoatomenergoremont completed 56 tasks to modernise the unit during the scheduled repair outage that ended on 20, Atomenergoremont said in a statement. In particular, work was completed to replace the storage pool racks with racks for dense used fuel storage and structures of the fuel assembly storage compartments were also replaced.

"That work began in 2012, and it took 25 days to complete upgrading of the first compartment of the fuel pool. As experience was gained in performing such operations, more technological tools and devices were introduced and the work time was reduced to 20 days," said Anatoly Burlakov, director of Balakovoatomenergoremont.

This whole operation took nine years, but it has increased the period between outages for the units to 18 months from one year. Replacement of drainage concrete and floor cladding increased the reliability of structural elements of the compartments and the safety of nuclear power plant equipment.

During the latest outage of Balakovo 4, the main and auxiliary equipment of the reactor and turbine sections, electrical equipment and instrumentation were repaired. Among the other modernisation measures were upgrading of the high-pressure steam regeneration system. This involved replacing the steam pipelines of the third extraction, and drainage pipelines of the first, second, third extraction of the turbine. Their total weight was more than 16 tons. During modernisation of the high pressure heater pipe systems, more than 2000 coils were replaced.

A large amount of work was also undertaken to replace the ventilation equipment. The main difficulty was that replacement of ventilation equipment took place in inaccessible places where there was no possibility of using mechanical tools. In this regard, the specialists used non-standard technical solutions, with strict adherence to the safety requirements of the work.

The workshop for the repair of electrical equipment to support the extension of the service life of unit 4 carried out preventive maintenance measures. These included replacement of control cabinets for relay protection and automation (URZA) with microprocessor panels PMS-80, and replacement of control and power cables with a total length of more than 120 km. Some 108 cabinets of complete transformer substations were installed and adjusted, software and hardware complexes of the PTC SAR were replaced on three security systems, and more than 5000 measuring channels were tested.

During the repair, for the first time, ultrasonic testing of welded joints of pipelines and equipment was carried out on 1,849 components, radiographic testing of welded joints on 937 pipelines and equipment, and ultrasonic measurement of the thickness of the base metal of pipelines and equipment on more than 1200 items.

All work on the repair and modernisation of the equipment was carried out jointly with specialists from the Balakovo NPP and colleagues from the Volgodonsk, Kalinin, Kursk, Novovoronezh, Smolensk, Ural branches of Atomenergoremont in full compliance with anti-epidemiological measures.

The Balavoko nuclear plant comprises four VVER-1000 V-320 units, commissioned in 1985, 1987,1988 and 1993. In 2016, Balakovo 1 underwent life extension upgrades and is now licensed to operate until 2045. Two additional VVER-1000 units (Balakovo 5 and Balakovo 6) were started in 1987 and 1988 but the construction was suspended in 1992.