Chromium Carbide Coatings for Inner-Side Fuel Cladding Protection: A Reactor Physics–Based Performance Analysis

Chromium carbide (CrC) coatings were proposed as an accident-tolerant fuel complementary concept to provide enhanced protection for the inner side of nuclear fuel claddings, with preliminary results showing promising performance. To evaluate the neutronics performance of CrC coatings, a reactor physics–based analysis was performed. A single VVER-1200 fuel assembly was used as a model, and the Monte Carlo code MCNPX was used to perform the calculations. Results were compared to previous work on metallic chromium performance as inner-side coating material. Results showed that CrC coatings generally have less negative impacts on neutronics performance compared to chromium coatings. Neutron flux spectra showed slight reductions in the thermal energy region that reached up to −0.6% in a 40-µm CrC internally coated fuel assembly at an energy of 0.025 eV. The analysis of CrC internally coated fuel assembly nuclide inventories showed a relative increase in the isotopic concentration of some nuclides such as ²³⁹Pu and ²⁴¹Pu, which was less than 1% for the cases considered. Comparing the calculated negative neutronics impacts, such as thermal neutron flux and fuel assembly operating time reductions, caused by CrC and Cr coating materials, the study revealed that the difference between these induced negative neutronics impacts is proportional to coating thickness. Therefore, CrC coatings will be most effective in terms of mitigating negative neutronics impacts when the specified coating thickness is large.