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RELAP-7 (Reactor Excursion and Leak Analysis Program-7) is the nuclear reactor system safety analysis code currently under development at the Idaho National Laboratory (INL) for the Risk Informed Safety Margin Characterization (RISMC) Pathway as part of the Light Water Reactor Sustainability Program.  It is an evolution in the RELAP-series reactor systems safety analysis applications. The RELAP-7 code development is taking advantage of the progresses made in the past three decades to achieve simultaneous advancement of physical models, numerical methods, coupling of software, multi-parallel computation, and software design. 

RELAP-7 uses the INL’s open source MOOSE (Multi-Physics Object-Oriented Simulation Environment) framework for efficiently and effectively solving computational engineering problems. Unlike the traditional system codes, all the physics in RELAP-7 can be solved simultaneously (i.e., fully coupled), resolving important dependencies, and significantly reducing spatial and temporal errors relative to traditional approaches. This allows RELAP-7 development to focus strictly on systems analysis-type physical modeling and gives priority to the retention and extension of RELAP5’s system safety analysis capabilities.  In addition to the mechanistic calculations that are performed in RELAP-7 to represent plant physics, it has been designed to be integrated into probabilistic evaluation using the RISMC methodology.  The RISMC methodology can optimize plant safety and performance by incorporating plant impacts, physical aging, and degradation processes into the safety analysis.