Considering the world energy demand increase in order to fulfill an environmental and economic sustainability, the energy policy of each country has to diversify the sources of energy and use stable, safe energy production option able of producing electricity in a clean way contributing in cutting the CO2 emission. In the framework of the sustainable development, today the use of advanced nuclear power plant, have an important role in the environmental and economic sustainability of country energy strategy. In the last 20 years, in fact, the international community, taking into account the operational experience of the nuclear reactors, starts the development of new advanced reactor designs considering also the use of natural circulation for the cooling of the core in normal and transient conditions. In this framework, Oregon State University (OSU) has constructed, under a U.S. Department of Energy grant, a system level test facility to examine natural circulation phenomena characterizing the Multi-Application Small Light Water Reactor (MASLWR) design, a small modular integral pressurized light water reactor relying on natural circulation during both steady state and transient operation. It includes an integrated helical coil steam generator as well. Starting from an experimental campaign in support of the MASLWR concept design verification, the planned work, will be not only to specifically investigate the concept design further but also advance the broad understanding of integral natural circulation reactor plants and accompanying passive safety features as well. An IAEA International Collaborative Standard Problem (ICSP) on “Integral PWR Design Natural Circulation Flow Stability and Thermo-hydraulic Coupling of Containment and Primary System During Accidents” is hosting at OSU and the experimental data will be developed at the OSU-MASLWR facility. The purpose of this IAEA ICSP is to provide experimental data on single/two-phase flow instability phenomena under natural circulation conditions and coupled containment/reactor vessel behavior in integral-type light water reactors. These data can be used to assess thermal hydraulic codes for reactor system design and analysis as well. The first planned test investigates a stepwise reduction in the primary mass inventory of the facility while operating at reduced power (decay power). The second planned test, investigates a loss of feed water transient with subsequent primary blowdown due to automatic depressurization system actuation and long term cooling phase. The target of this paper is to contribute to the thermal hydraulic analysis of the expected phenomena of these transients on the basis of the TRACE V5 Patch 01 calculated data developed during the double-blind phase of the ICSP.

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