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What is RELAP-7?

RELAP-7 is a next generation nuclear systems safety analysis code being developed at the Idaho National Laboratory (INL).  The most important development goals of RELAP-7 are to take advantage of the previous thirty years of advancements in computer architecture, software design, numerical methods, and physical models in order to provide capabilities needed for the Risk Informed Safety Margin Characterization (RISMC) methodology and to support nuclear power plant (NPP) safety analysis. The end result will be a reactor systems analysis capability that retains and improves upon RELAP5-3D's knowledge and extends the analysis capability and improves accuracy for all reactor systems simulation scenarios. The code is being developed based on INL's modern scientific software development framework – MOOSE (Multi-Physics Object-Oriented Simulation Environment).

RELAP-7 will retain and improve the basic analysis capability of RELAP5 and will represent a significant increase in capability over RELAP5. The four major improvements are 1) A well-posed seven-equation two-phase flow model (liquid, gas, and interface pressures); 2) Improved numerical approximations resulting in second-order accuracy in both space and time versus the first order approximations; 3) Implicit tightly coupled time integration for long duration transients, such as providing plant behavior for full life fuel cycle evaluations; 4) the ability to tightly couple to higher fidelity physics, such as the BISON nuclear fuels performance application; and 5) the ability to easily couple to multi-dimensional core simulators being developed in other programs (NEAMS TREAT simulator and CASL's). The INL is working very closely with EPRI to define industry and regulatory requirements for RELAP-7.