Serpent/SCF pin-level multiphysics solutions for the VERA Fuel Assembly benchmark

Continuous improvement in nuclear industry safety standards and reactor designers’ and operators’ commercial goals represent a push for the development of highly accurate methodologies in reactor physics. Those methodologies are usually oriented to improve the prediction capabilities of specific reactors’ parameters under steady state and transient scenarios by the use of coupled state-of-the-art calculation codes. As a result, an important effort to develop highly accurate multiphysics approaches for nuclear reactor analysis is being held by diverse organizations and stakeholders around the world. Under this framework, the European Research and Innovation project McSAFE is a coordinated effort started in September 2017 with the objective of moving Monte Carlo (MC) stand-alone and coupled solution methodologies to become valuable tools for industry like applications for LWRs of generations II and III. As part of this project several developments in coupling strategies for transient and steady-state calculations are being developed, implemented and tested. Such capabilities assessment, together with the imperative verification and validation process are carried out inside McSAFE in a graded approach by the detailed comparison with high-quality benchmarks. As part of this approach, this work presents the main results obtained for the Fuel Assembly (FA) coupled Neutronic-Thermalhydraulic VERA Benchmark (namely VERA problem #6) proposed by the CASL consortium. For this purpose a pin-by-pin coupling scheme using the Serpent 2 MC code (developed by VTT, Finland) and the subchannel code SUBCHANFLOW (developed by KIT, Germany) was developed. Results are obtained and compared with diverse available published data from several similar high-fidelity calculation projects, both in terms of integral parameters and detailed axial profiles inside the FA at pin or coolant subchannel level. In addition, main additional key aspects of the problem are also presented and discussed. The results obtained and presented with the proposed approach show a very good agreement with available results from several similar high-fidelity projects, which encourages to continue to more complex problems and provides relevant insights for further developments and implementations.