Analysis of the connection of an idle MCP with three operating without a preliminary reduction in the power of the VVER-1000 reactor

Abstract

The paper analyzes the transient process caused by connecting an idle loop (turning on an idle main circulation pump (MCP)) without preliminary reduction in the power of a VVER-1000 reactor plant (RP) operating at a rated power corresponding to three MCPs. The process under consideration is included in the “Reactive accidents” section of materials for justifying the safety of VVER-1000. Modeling is carried out on the example of the 3rd power unit of the Kalinin NPP [1]. For the calculations, we used the improved evaluation code ATHLET [2], which is included in the AC2 software package, officially obtained by the National Research Nuclear University MEPhI on the basis of a license agreement with Gesellschaft fur Anlagen-und Reaktorsicherheit (GRS) gGmbH, Germany [3]. The ATHLET code has been certified in Russia for calculating stationary and transient conditions in water cooled reactors [4]. For the conservatism of the calculation, the study did not take into account the work of the PRL, APR, WP-1, WP-2 and AWP, the functioning of which is aimed at limiting the increase in the reactor power during the transient process. Blocking the signal to turn off the MCP on the fact of a decrease in the level in the SG and of the three ECCS systems, the operation of only one system is taken into account. For a number of reasons, this calculation was carried out for the end of the campaign. Implementation of design safety criteria for the adopted transition scenario is demonstrated.