A Multi-Physics Adaptive Time Step Coupling Algorithm for Light-Water Reactor Core Transient and Accident Simulation

Alexey Cherezov,Deokjung Lee,Jinsu Park,Hanjoo Kim,Jiwon Choe

doi:10.3390/en13236374

Abstract

A new reactor core multi-physics system addresses the pellet-to-cladding heat transfer modeling to improve full-core operational transient and accident simulation used for assessment of reactor core nuclear safety. The rigorous modeling of the heat transfer phenomena involves strong interaction between neutron kinetics, thermal-hydraulics and nuclear fuel performance, as well as consideration of the pellet-to-cladding mechanical contact leading to dramatic increase in the gap thermal conductance coefficient. In contrast to core depletion where parameters smoothly depend on fuel burn-up, the core transient is driven by stiff equation associated with rapid variation in the solution and vulnerable to numerical instability for large time step sizes. Therefore, the coupling algorithm dedicated for multi-physics transient must implement adaptive time step and restart capability to achieve prescribed tolerance and to maintain stability of numerical simulation. This requirement is met in the MPCORE (Multi-Physics Core) multi-physics system employing external loose coupling approach to facilitate the coupling procedure due to little modification of constituent modules and due to high transparency of coupling interfaces. The paper investigates the coupling algorithm performance and evaluates the pellet-to-cladding heat transfer effect for the rod ejection accident of a light water reactor core benchmark.

Highlights

Multiphysics analysis attracts a lot of attention of nuclear engineers worldwide as it helps to produce more realistic results in terms of reactor core safety margins
MPCORE has been applied for a full-core Pressurized Water Reactor (PWR) Benchmark for Evaluation
Zero Power (HZP) for the BEAVRS reactor core is subjected to MPCORE calculation in order to evaluate the impact of dynamic pellet-to-cladding heat transfer on design and safety of LWR

Summary

Introduction

Multiphysics analysis attracts a lot of attention of nuclear engineers worldwide as it helps to produce more realistic results in terms of reactor core safety margins. The Computational Reactor Physics and Experiment Laboratory of Ulsan National Institute of Science and Technology (UNIST CORE lab) has developed MPCORE (Multi-Physics CORE) code [8] capable for both depletion and transient analysis of a light-water reactor core with the dynamic pellet-to-cladding heat transfer coefficient taking into account fuel rod irradiation, thermal-mechanics and corrosion phenomena. The new multiphysics system implements the external loose coupling of pin-by-pin neutronics, thermal-hydraulics and fuel performance using the external adaptive time step selection algorithm to achieve the reactor core high-fidelity simulation with prescribed. This work is devoted to the application of the adaptive time step integration algorithm, analysis of the code computational performance and evaluation of the pellet-to-cladding heat transfer effect on the safety parameters using for reactor core rod ejection accident (REA) transient [10,11,12]

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Results

Conclusion