Thermal-Hydraulic System Code Assessment for Transient Analyses Involving Accident Management Procedures in VVER-1000 Reactors

There are still ongoing analyses of the experimental programs in the accident area within the framework of nuclear reactor safety. The objective of this paper is to demonstrate and improve the predictive capabilities of thermal-hydraulic system codes in the evaluation of transient and accident scenarios. This document presents the activities aimed at the assessment of the thermalhydraulic system codes performed within the Project TACIS R2.03/97 Contract 3.03.03 Part A (EC founded). The basis for the code assessment is the experimental program of the Accident Management Test Matrix, developed in the framework of the Project. The reference facility is the PSB-VVER, a simulator of VVER-1000 (V-320 design) nuclear power plant, operated at Electrogorsk Research and Engineering Center. This matrix includes 12 experiments dealing with Loss Of Coolant Accident, Loss Of Feed Water, Station Black-Out, Primary to Secondary side leak, and Natural Circulation scenarios. Four codes (CATHARE2, RELAP5, ATHLET and KORSAR) are applied with a different extent and with a different purposes by various Institutions in the post test phase. All the experiments are simulated with CATHARE2/V1.5b and RELAP5/Mod3.3 codes by University of Pisa. The other codes are used to perform the post test analysis of some specific tests, allowing a general view of the code capabilities and highlighting the strongest and the weakest points of the models implemented in the codes.