Yuanzineng kexue jishu (Mar 2023)
Nuclide Composition Evaluation for Commercial PWR Nuclear Spent Fuel Assembly Based on NECP-Bamboo
Abstract
Accurate nuclide composition of nuclear spent fuel (NSF) assemblies is the most important condition for both criticality safety analysis and radiation safety analysis of NSF. The calculation of radioactive source terms is a typical application of nuclide composition calculation for NSF. There are drawbacks in the existing programs, such as the insufficient nuclides in the database and the inability to fully simulate the irradiation process, which limit the reliability and economy of NSF reprocessing safety analysis. Based on the completely autonomous PWR-core analysis software NECP-Bamboo, a nuclide composition calculation program named Bamboo-SFuel was independently developed for commercial PWR NSF, and the measured data of post-irradiation experiment (PIE) in SFCOMP database developed by NEA (Nuclear Energy Agency) were used to quantitatively verify and analyze the program. The experiments employed cover a variety of fuel types, component types and operating conditions including power level, boron concentration, fuel temperature and moderator temprature. In addition, a VERA benchmark problem was computed by using both Bamboo-SFuel and SCALE to verify the calculation accuracy of the source term including radioactivity, decay heat, photon source and neutron source. The influence of different depletion data libraries including 3838, 1547 and 233 nuclides respectively on the calculated nuclide composition and source term was also investigated. Encouraging conclusions are demonstrated by the numerical results. Bamboo-SFuel can accurately calculate both the nuclide composition and the radioactive source term of commercial PWR NSF under different irradiation conditions. Among the actinide nuclides, the average relative deviation of 247Cm is the largest (-31.059%), while the relative deviation of 125Sb in fission products is the largest, which is 27.35%. About the source term, the maximum relative deviation of photon source term is 0.69%, the maximum relative deviation of spontaneous fission neutron source term is 0.17%, and the maximum relative deviation of (α,n) neutron source term is 0.43%. The influence of different depletion databases in NECP-Bamboo code system on the calculation results of important nuclide components is very small. But the influence on the calculation results of the total radioactive source items like photon source term is as large as 99.99%, because the conservation of photon source terms is not taken into account when the depletion database is compressed from 1 547 to 233 nuclides, many nuclides with large photon source terms are also deleted, such as 231Th, and the photon yield of these nuclides at some energy points is large, resulting in a large deviation in the calculation of corresponding energy groups at these energy points. By using the depletion data library with 1 547 nuclides contained in the NECP-Bamboo code system, all the important nuclides concerning in both criticality safety analysis and radiation safety analysis of NSF can be accurately evaluated. The maximum relative deviation in nuclide composition for criticality safety analysis is 238Pu with -29.443%, while 0.69% in source term calculation for radiation safety analysis.
