ABSTRACT

Critical analysis of 120 light-water moderation lattices composed of 2.6 wt% UO₂ fuel rods or 3.0 wt%-PuO₂ uranium-plutonium mixed oxide (MOX) fuel rods was performed using a continuous-energy Monte Carlo calculation code to validate the JENDL-4.0 nuclear data library. As a result, the average neutron multiplication factor (k_eff) of the 35 UO₂ lattices (hydrogen-to-heavy-metal atomic ratio (H/HM): 4.3–8.7) was 0.99930 with the uncertainty of 0.00005 (1 σ), and that of the 85 MOX lattices (H/HM: 12.0–27.6) was 0.99856 with the uncertainty of 0.00006 (1 σ). The k_eff values of the UO₂ lattices partly showed a decreasing trend with H/HM, while those of the MOX lattices an increasing trend. The k_eff values of the MOX lattices presented an increasing trend with the measurement dates. Assuming that the trend was relating to the uncertainties in the neutron capture cross-section of ²⁴¹Am, a simulation to modify the cross-section was performed by increasing the atomic number densities of ²⁴¹Am in the MOX fuel. It indicated that the neutron-flux-average capture cross-sections of ²⁴¹Am for the MOX lattices should be increased by 10% to 20% from those calculated by the cross-section in JENDL-4.0.

摘要

使用连续能量蒙特卡罗计算代码对由 2.6 wt% UO ₂燃料棒或 3.0 wt%-PuO ₂铀-钚混合氧化物 (MOX) 燃料棒组成的 120 个轻水慢化晶格进行临界分析，以验证 JENDL -4.0 核数据库。因此，35 个 UO ₂晶格（氢与重金属原子比 (H/HM)：4.3–8.7）的平均中子倍增因子 ( k _eff ) 为 0.99930，不确定度为 0.00005 (1 σ) , 85 个 MOX 晶格 (H/HM: 12.0–27.6) 的值为 0.99856，不确定性为 0.00006 (1 σ)。UO ₂的k _eff值晶格部分随 H/HM 呈下降趋势，而 MOX 晶格则呈上升趋势。MOX晶格的k _eff值随着测量日期的增加呈增加趋势。假设该趋势与²⁴¹ Am中子捕获截面的不确定性有关，通过增加MOX 燃料中²⁴¹ Am的原子序数密度来进行修改截面的模拟。这表明MOX 晶格的²⁴¹ Am中子通量平均俘获截面应比 JENDL-4.0 中的截面计算增加 10% 至 20%。