Some aspects of the re-extension of the reactor plant life with VVER-440 on the example of Novovoronezh NPP UNIT 4
The re-modernization of power Unit No. 4 of Novovoronezh NPP with the purpose of its further safe operation proved the possibility of a new approach to the extension of the resource characteristics and significantly increases the possibility of operation of reactor plants VVER-440. In the present article, the authors analyze the existing problems of the power unit with VVER-440 (B-179), show possible ways to solve the identified shortcomings, as well as the final state of the updated power unit, in particular, a significant expansion of the range of design accidents to the maximum possible associated with the rupture of the main circulation pipelines (GTP) (DN = 500 mm). In addition, a unique experience in the use of safety systems of Unit No. 3, decommissioned, to improve the reliability and additional redundancy of security systems of Unit No. 4. In particular, the activities within the modernization framework had allowed to expand significantly the spectrum of the design basis accidents with the primary coolant leak with a nominal diameter of 100 mm to the maximum possible, associated with the break of the Main Circulation Pipeline (MCP) (DN 500 mm). In addition, a unique experience was gained in applying the safety systems of power Unit No. 3, which was finally shutdown to be prepared for decommissioning, to increase reliability and to provide additional redundancy for safety systems of the Unit No. 4.
The results of the activities performed have demonstrated the correctness of the adopted concept of re-extending the service life of Unit No.4 and ensured the Unit compliance with up-to-date safety requirements in nuclear power engineering including, from the point of view of safety impact by the first-level probabilistic safety analysis model (PSA-1) for internal initiating events.
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