Some aspects of the VVER-440 reactor plant life re-extension: a case study of the Novovoronezh NPP Unit 4

Abstract

The re-modernization of Unit 4 at the Novovoronezh NPP (Novovoronezh-4) made it possible to take a new approach to the problem of extending the VVER-440 reactor plant life and operation. The authors analyze the existing problems of the VVER-440/179 power unit, showing possible solutions to the identified shortcomings and the final state of the updated power unit. Modernization works significantly expanded the range of design-basis accidents from the primary coolant leak from an opening (DN = 100 mm) to the maximum possible, associated with a rupture of the main circulation pipelines (MCP) (DN = 500 mm). A unique experience was gained in using the safety systems of Unit 3, which was finally shutdown for decommissioning, to increase reliability and provide additional redundancy for the safety systems of Unit 4. The results of the performed works showed the correctness of the adopted concept of re-extending the service life of Unit 4 and ensured its compliance with the modern safety requirements in nuclear power engineering, including as it relates to the safety impact of the first-level probabilistic safety analysis model (PSA-1) for internal initiating events.

Analysis of accidents of the WWER-1000 reactor in which emergency cooling heat exchangers operate

“…Proceeding from the fact that ECCS system is an important system for NPP safety and takes a key role in the localization of NI accidents, a lot of research has been devoted to the analysis of this system, which is part of not only the WWER-1000 NI, but also other reactors. An example of such research is works [6][7][8], which consider the operation of ECCS system as part of WWER-440, WWER-1000 and CANDU reactors. Currently, work is being actively carried out to lifetime extension of Ukrainian NPPs units, and therefore there is an urgent task in justifying the safe operation of NPP equipment, and ECHE heat exchangers in particular.…”