Validation of NUIT for Decay Heat Predictions of PWR Spent Fuel Assemblies

Abstract

Abstract Decay heat prediction is essential for nuclear reactor safety, waste management and spent fuel disposal. The NUIT code is dedicated for nuclide inventory calculations, which was developed by Institute of Nuclear and New Energy Technology (INET), Tsinghua University. NUIT is able to compute isotope density, radioactivity, decay heat, photon spectrum and other source term quantities. The problem-specific neutron spectrum and tabular effective one-group cross-section library produced by neutron transport codes were utilized by NUIT. Therefore, the NUIT code could be applied to many types of fission reactors, such as HTGR, PWR, BWR, etc. In this paper, validation of the NUIT’s capabilities in predicting decay heat for spent fuel assemblies was conducted with measured decay heat data from PWRs. The test cases for validation include measurements of 52 fuel assemblies (14 × 14, 15 × 15 and 17 × 17 fuel designs) that were irradiated in 5 PWR plants, with burnup values ranging from 19.7 to 51 GWd/tU. The cooling periods for the measured samples vary from 2.4 to 26.7 years, which are times of interest to spent fuel transportation and storage applications. The multi-group neutron spectrum provided by Monte Carlo code OpenMC was utilized to collapse into one-group cross sections. The decay heats for different fuel assemblies were obtained and compared with measurement data. The validation results show satisfactory agreement between NUIT results and reported measurement data. This work helps to obtain uncertainty margins in decay heat predictions with NUIT code.