Status of the Independent Validation of TRACE Code for SMR Safety Analyses

Small modular reactors (SMRs) are considered one of the most promising technologies for the near term development of nuclear power generation. In particular, the integral pressurized water reactors (iPWR) appear to be the closest to market deployment among SMR technologies because they start from the well-established operating large light water reactor (LWR) technology and include evolutionary designs aiming to enhance the plant safety. The lower SMR core power, compared to large reactors, allows to exploit several passive safety features. Deterministic safety analyses conducted by best estimate thermohydraulic system codes demonstrate a fundamental role in designing mitigation strategies and evaluating plant safety. SMRs are generally characterized by some common features of the operating reactors and by other unique features, e.g. containment interactions with the RCS, low pressure phenomena, and phenomena specific to new system components or reactor configurations. Therefore, it is needed to qualify these computational tools for the phenomena characterizing SMR operation and transient conditions. Among the available best estimate thermohydraulic system codes, TRACE (TRAC/RELAP Advanced Computational Engine) is being developed by USNRC to simulate the thermohydraulic behaviour of operating reactors and advanced designs like SMR. In the past few years an independent validation of a SMR design, led by ENEA, has been carried out in the USNRC CAMP (Code Application and Maintenance Program) framework following the TRACE code development in related areas. The experimental data developed in the OSU-MASLWR facility was used for these validation activities. More recently a numerical scaling analysis was conducted to give insights about the TRACE scaling-up capability against single-phase natural circulation in integral type reactors. The paper summarizes the TRACE independent validation activities of OSU-MASLWR tests against the natural circulation phenomena inside the integral RPV, RPV/containment coupling phenomena taking place in the mitigation of SBLOCA scenario, and the status of the current code capabilities.