Multi-Physics Modeling of the OECD/NEA MPCMIV Benchmark Transient Scenario

Abstract

The Organization for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) is conducting the Multi-physics Pellet Cladding Mechanical Interaction Validation (MPCMIV) benchmark aiming at providing guidelines for multi-physics transient validation. In the benchmark, two cold ramp tests performed in boiling water reactor (BWR) conditions are modeled using neutronics, thermal-hydraulic, and fuel performance in single-physics and multi-physics models. Both cold ramp tests consist of a short irradiation (less than one minute) at fixed R2 power where the rodlet is inserted in the core for a certain amount of time before the reactor is shutdown. In this work, the first cold ramp test is investigated using a multi-physics coupling with MOOSE based codes: GRIFFIN for reactor physics, THM for thermal-hydraulics, and BISON for fuel performance. For THM, the 1-D model consists of the entire in-pile loop system, while BISON models only the fuel rodlet in 2D-RZ and GRIFFIN models part of the in-pile at the location of the reactor core using 3D (only the local domain around the rodlet is modelled by the codes). The first step is to perform verification and validation activities consisting of mesh and time-step convergence studies and comparison to measurements for each single physics model. Due to the amplitude of the incoming neutron current on the in-pile loop being unknown, a calibration is performed to reproduce the coolant temperature measurements. Finally, the coupling temporal cladding axial elongation evolution prediction is compared against measurements, showing good agreement.