基于NECP-Bamboo程序的商用压水堆乏燃料组件核素成分分析

Nuclide Composition Evaluation for Commercial PWR Nuclear Spent Fuel Assembly Based on NECP-Bamboo

乏燃料组件核素成分的精确计算是乏燃料临界安全分析等工作的输入条件,放射性源项计算是乏燃料组件核素成分分析的典型应用。国内现有程序由于存在数据库中核素种类不全、辐照过程无法完全模拟等弊端,限制了乏燃料后处理安全分析的可靠性和经济性。本文基于完全自主化的压水堆堆芯分析软件NECP-Bamboo,研发了商用压水堆乏燃料组件核素成分计算程序Bamboo-SFuel,利用辐照后实验(PIE)实测数据对核素成分进行了定量验证与分析,通过与Scale程序包计算结果进行对比验证了程序源项计算的精度,还探究了不同燃耗数据库对核素成分和源项计算结果的影响。数值结果表明,Bamboo-SFuel能精确分析不同辐照条件下商用压水堆乏燃料组件的核素成分和放射性源项,使用NECP-Bamboo程序中不同核素数目的燃耗数据库对重要核素成分计算结果影响不大,但对总的放射性源项计算结果影响较大;基于内置的包含1547种核素的燃耗数据库,该程序可同时给出可靠的乏燃料临界安全分析和辐射安全分析关注的重要核素成分。

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 of247Cm is the largest(-31.059%),while the relative deviation of125Sb 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 1547 to 233 nuclides,many nuclides with large photon source terms are also deleted,such as231Th,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 1547 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 is238Pu with-29.443%,while 0.69%in source term calculation for radiation safety analysis.