Comparison of VVER1000 plant respond during MSLB scenario using TRACE and RELAP computer codes

This paper presents a comparison of the results from simulation of „Main steam line break (MSLB) “accident using RELAP5/mod3.3 and TRACE50p5 computer codes. The work is based on the VVER-1000 MSLB OECD benchmark. The main purpose of this work was to demonstrate the capability of the TRACE computer code for modelling of 3D thermal hydraulic reactor vessel at the integral VVER 1000 model and to predict correctly the plant respond and spatial disturbance in the reactor vessel. In addition, this investigation was focused on validation of the correct predictability of the important integral parameters in VVER1000 TRACE 50p5 models. The other objectives were to provide the elements for the safety, to validate the safety analysis tools and to improve codes and methods for VVER comprehensive safety assessment. The investigated scenario is a “Main steam line break (MSLB) with inside diameter (ID) 580 mm” in a VVER1000 between the steam generator (SG) and the steam isolation valve (SIV), outside of the containment. This event is characterized with significant spatial effects in the core caused by asymmetric cooling and assumed stuck-out of control rods after SCRAM. One of the major concerns for this case is the possible return of power and criticality after SCRAM, as a result of the reactor core overcooling. The reactor state is at the beginning of 1 st fuel campaign. For the purpose of the investigation, the simulation of MSLB accident with RELAP5/MOD3.3 and TRACE50p5 computer codes with modelling of reactor physics using point kinetics has been performed initially. Additionally, the 3D thermal hydraulic reactor vessel model with a point kinetic physics has been developed at the integral VVER1000 TRACE 50p5 model. The newly developed integral model of VVER1000 with 3D reactor vessel of TRACE50p5 has been validated with simulation of MSLB accident by code to code comparison with already validated VVER1000 models of RELAP5/MOD3.3 and 1D TRACE50p5 codes. The comparison between the results predicted by the codes demonstrates good agreement, except some of the parameters. The newly developed integral VVER1000 with 3D vessel model of TRACE50p5 predicts reasonable results. The predicted results by used computer codes demonstrate the stability of the reactor system during the accident progression of “Main steam line break”.