Systematic approach for the analytical validation of Kozloduy NPP, VVER-1000/V320 symptom based emergency operating procedures

Abstract

This paper presents the development and application of methodology used in analytical validation of emergency operating procedures (EOPs) for Kozloduy Nuclear Power Plant (KNPP), VVER-1000/V320 units. EOPs provide generic guidance to a reactor plant operator in maneuvering the plant to a safe, stable condition in the event of an unexpected plant transient or emergency. These procedures have been analytically validated in order to provide technical justification that the prescribed operator actions are reasonable, effective and prudent. This evaluation is accomplished by systematically evaluating the procedures using specialized thermal-hydraulic computer codes designed for nuclear reactor plant simulation. Thermal-hydraulic computer code calculations have been performed to simulate the symptoms presented to the operator to diagnose challenges to the critical safety functions (CSFs). The accomplished emergency operating procedures' (EOPs') analyses are designed to provide the response of monitored plant parameters to identify symptoms available to the operators, timing of the loss of critical safety functions and timing of operator actions to avoid the loss of critical safety functions or core damage. The principal acceptance criteria for EOPs are averting the onset of core damage. The RELAP5/MOD3.2 computer code has been used in performing the analyses in a VVER-1000 Nuclear Power Plant (NPP) model. EOPs' analysis methodology assumes realistic boundary conditions in validating operator actions. A model of VVER-1000 based on Unit 6 of KNPP has been developed for the system's thermal-hydraulic code RELAP5/MOD3.2 at the Institute for Nuclear Research and Nuclear Energy of Bulgarian Academy of Sciences (INRNE-BAS), Sofia, and was used for simulating the bounding scenarios. The work was possible through participation of leading specialist from KNPP and with the assistance of Pacific Northwest National Laboratory (PNNL), under the International Nuclear Safety Program (INSP) of the United States Department of Energy.