Analysis of the Multi-Application Small Light-Water Reactor (MASLWR) Design Natural Circulation Phenomena

Today the use of advanced nuclear power plant, have an important role in the environment and economic sustainability of country energy strategy considering the capacity of a nuclear reactor of producing energy in safe and stable way contributing in cutting the CO2 emissions. In the last 20 years, in fact, the international community, taking into account the excellent operational experience of the nuclear reactors, starts the development of new advanced reactor designs, by including also the use of the natural circulation for the cooling of the core in normal and transient conditions. In this international framework, Oregon State University has constructed, under a U.S. Department of Energy grant, a system level test facility to examine natural circulation phenomena of importance to Multi-Application Small Light-Water Reactor (MASLWR) design. The MASLWR is a small modular integral pressurized water reactor relying on natural circulation during both steady state and transient operation, including an integrated helical coil steam generator. Starting from an experimental campaign in support of the MASLWR concept design verification, the planned work, related to the OSU-MASLWR test facility, will be not only to specifically investigate the MASLWR concept design further but also advance the broad understanding of integral natural circulation reactor plants and accompanying passive safety features as well. Four tests have been performed at this facility in order to assess the thermal hydraulic behavior of the MASLWR design in normal and transient operation and to assess the passive safety system under transient condition. This paper illustrates a preliminary analyses, performed by TRACE code, aiming at the evaluation of the code capability in predicting natural circulation, heat exchange from primary to secondary side by helical steam generator in superheated condition and primary/containment coupling phenomena typical of the MASLWR design. The tests take into account for this analysis are the OSU-MASLWR-001, an inadvertent actuation of 1 submerged ADS valve and the OSU-MASLWR-002, a natural circulation test investigating primary system flow rates and secondary side steam superheat for a variety of core power levels and feed water flow rate. The analyses of the calculated data show that the TRACE code predicts the phenomena of interest of the selected tests.