Issues in the calculation of the tritium production of the fluoride-salt-cooled high-temperature reactors using SCALE

Background: The Fluoride-salt-cooled high-temperature reactor (FHR) is a thermal reactor using molten salt (2LiF-BeF₂, FLiBe) as coolant and TRISO (Tri-structural Isotropic) as fuel and graphite as moderator. Isotopes, such as ⁶Li, ⁷Li, ⁹Be and ¹⁹F in the FLiBe coolant, generate tritium under the neutron irradiation. Tritium can easily permeate through metal at high temperature and may be a radiation source to the workers and public. Tritium can also react with F and create TF, which is highly corrosive and may cause damage to the structural materials. Purpose: We used different versions of SCALE to calculate the tritium production of a typical FHR and analyzed the difference among the computational results. Methods: We have created 3D models using the same FHR design parameters in SCALE. Results: The results show that in the calculation of tritium production from lithium, the TRITON (Transport Rigor Implemented with Time-dependent Operation for Neutronic depletion) module of SCALE6 handles the lithium element incorrectly and introduces significant differences compared with the previous versions of SCALE. When we calculate the tritium production from ⁹Be and ¹⁹F, different versions of SCALE give different results because the reactions are defined differently. Conclusion: Our analyses show that when SCALE is used to calculate the tritium production of the FHR, SCALE6 is the preferred version. However, the temporary file, ft33f001, created by TRITON as the cross section library, and ORIGEN-S can be used to calculate the tritium production in order to correct the mishandling of lithium element in SCALE6. (authors)