b'Reactor Core Isolation CoolingMechanistic component models improve boiling water reactor risk assessments.System Model DevelopmentT he reactor core isolation cooling (RCIC) system is an emergency safety and Implementation in thesystem used in over 20 U.S. boiling water reactors. The coupled system can cool the core with little to no outside power and is composed of a Reactor Excursion and LeakTerry steam turbine, a pump, and the containment wetwell. The 2011 accident at Analysis Program Fukushima Daiichi highlighted the importance of the RCIC system, which provided core cooling to Unit 2 for 70 hours during an extended station blackout. Current systems-level codes model the RCIC system with generic models that do not consider RCIC-specific phenomenon and therefore have limited ability to correctly simulate event progression during RCIC system operation. The goal of this project was to develop physics-based models of an integral RCIC system and incorporate the TOTAL APPROVED AMOUNT:models into the Reactor Excursion and Leak Analysis Program (RELAP)-7 code.$60,000 over 1 year This project resulted in new RELAP-7 component models that can easily and PROJECT NUMBER:accurately simulate long-term operation of a complete RCIC system. An original 21A1057-006 wetwell model was implemented in RELAP-7. This model captures buoyancy-induced thermal stratification effects due to injection of the Terry turbine exhaust PRINCIPAL INVESTIGATOR:steam. This phenomenon is not accounted for in current systems-level analysis Jack Cavaluzzi codes, yet the pressure suppression capacity of the wetwell is largely influenced CO-INVESTIGATOR: by the energy redistribution due to RCIC turbine steam exhaust. Original one- and David Andrs, INL two-phase turbine models were developed and implemented in RELAP-7. The new wetwell, one-phase turbine, and existing one-phase pump components were coupled to simulate a complete RCIC system at normal operating conditions. The two-phase turbine component was designed to have performance degradation as a function of incoming liquid water content. The two-phase turbine was coupled to the one-phase pump to demonstrate the self-regulating mode that was observed at Fukushima Daiichi Unit 2. These new component additions enhance modeling capability and are valid for a wider range of RCIC operation space than current systems-level analysis codes. The mechanistic component models allow simulation of long-term RCIC performance, which can improve boiling water reactor plant guidelines and risk assessments. The improved turbomachinery components can also be used for general turbine and pump modeling.TALENT PIPELINE:Jack Cavaluzzi, studentat Texas A&M UniversityPUBLICATION:Cavaluzzi, J., D. Andrs, and K. V. Kirkland, Two-zone stratified wetwell model development and implementation for RELAP-7, Annals of Nuclear Energy 164 (2021) 108592.(a) Two-zone RCIC schematic. (b) Stratified wetwell simulation results compared to experimental data from Texas A&M Nuclear Heat Transfer Systems Laboratory.51'