Fidelity Enhancement of Nuclear Power Plant Simulators Utilizing High Fidelity Simulation Predictions

Accurate simulation of nuclear power plant behavior is necessary for both engineering and training applications. An engineering grade simulator, used for design, safety analysis and operations, is characterized by high fidelity, computational power, lack of real-time capability, and user non-interactive environment. By contrast, a training grade simulator, used for operator training and education, is characterized by lower fidelity, less computational power, realtime capability, and user interactive environment (e.g. freeze, interrupt, snap, reset, retrace, redirect and visual display capabilities). This project’s objective is to take the most overall desirable characteristics of both nuclear power plant engineering and training grade simulators, while increasing their respective fidelities, to create a simulator with a more productive environment for engineering applications and facilitate commonality across engineering and training grade simulators. This will result in increased engineering productivity, economic improvements via enhanced designs and operations via margin utilization, and more realistic training and education. In Phase 1, with the limited budget, the focus of the work was on improving fidelity of the neutronics portion of currently deployed core simulators which run in real time, using the VERA-CS high-fidelity core simulator to “inform” a currently deployed simulator, NESTLE. It was demonstrated that using VERA-CS to “inform” NESTLE, resulted in tremendous enhancement to its fidelity. In this manner, the nuclear industries’ current usage of PC based computer resources and real time simulation capability could be retained, while only requiring a limited usage of HPC resources that are associated with executing VERA-CS. VERA-CS not only has high fidelity in neutronics simulation, via usage of the MPACT code, based upon transport theory, many energy group, fine mesh, and hundreds of isotopes tracked, but also has high fidelity regarding core T-H. This is achieved by utilizing core T-H simulator, CTF that treats two-fluids-three fields, along with mass, momentum and energy exchanges between subchannels, an important phenomenon for certain accident scenarios. However, to minimize computer resources, Phase II will develop and employ a coarse control volume version of CTF, which will require adjustment of closure relations to improve agreement with finer subchannel CTF models. Phase II will also incorporate the core simulator into the overall nuclear power plant simulator utilizing an enhanced RELAP5-3D system T-H code and refine the interactive environment characteristic of training grade simulators to better support engineering applications. In Phase II, and based on results from Phase I, WSC plans to develop and commercialize two products: 1. Engineering Simulators that uses a fully integrated NESTLE-RELAP5-CTF model, building upon Phase I advances. In this case, NESTLE and CTF will model the core neutronics and T-H, while RELAP5 will model the entire nuclear steam supply system (NSSS) plus control and protection logic. This will call for Phase II to extend the Phase I work, by introducing dependence on burnup and enabling transient simulation capability for NESTLE; developing a coarse control volume CTF model used to predict core T-H feedback, developed by adjusting closure relationships to improve agreement with standard subchannel CTF predictions; integrating the RELAP5-3D NSSS T-H simulation with an enhanced reactor vessel model to better treat core subchannel mixing and lower/upper plenum fluid flow; and, finally, enhancing the human-machine interface associated with training simulators to meet the needs of an engineering simulator. 2. Real-time Training Simulators that uses a fully integrated RELAP5-NESTLE model that is currently in use by WSC, but now utilizing the results of Phase I along with further enhancements of NESTLE neutronics data input and some of the RELAP5-3D features noted above. In this case, NESTLE will model the neutronics inside the core, while RELAP5 will model the total NSSS T-H providing the core T-H feedback.