Validation of NUIT for Nuclides Composition Calculation With PWR Spent Fuel Isotropic Measurement

Abstract

Abstract The NUIT (Nuclide Inventory Tool) is a reactor core nuclide inventory calculation code, which has been developed by Institute of Nuclear and New Energy Technology (INET), Tsinghua University. NUIT is able to compute instantaneous and integral values of various physical parameters including isotope composition, decay heat, particle spectrum, and radioactivity in fuel burnup, material activation, and decay calculations. The validation of the NUIT is an important process to ensure the correctness and applicability of the newly developed code. Presently, there is a lack of validation of the nuclide density calculation function of NUIT. Hence, this work is to validate this function of the NUIT code based on the PWR spent fuel isotopic compositions benchmark issued by the Oak Ridge National Laboratory in the SCALE program. In this work, the 103 spent fuel samples from 9 PWR plants are used to validate the nuclide composition calculation function of the NUIT, in which the initial enrichment of U-235 ranges from 2.453% to 4.657%, and the burnup ranges from 7.8 GWd/MTU to 60.7 GWd/MTU. The results show that NUIT’s nuclide density calculation results are in good agreement with the experimental values in general and the average error is about 10% for all nuclide density calculation cases. The typical nuclides, such as U-235, U-238, and Pu-239, etc., have an average calculation error of less than 5%, and most of the average errors of other actinide nuclides and fission products, such as Am, Cm, and Pu, etc., are within 10%∼40%, which meets the requirements of the radioactive source term analysis for the reactor core. Meanwhile, the comparison results show that the calculation accuracy of NUIT is comparable to other radioactive source term programs such as SCALE and OpenMC. The validation results further demonstrate NUIT’s capabilities in nuclide composition calculations.