Study on the Application of Spectral Shift Absorber in Special Criticality Safety
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摘要: 特殊临界安全是空间反应堆(尤其是快中子堆)设计中需要重点考虑的问题,快中子空间反应堆一旦发生发射掉落事故掉入水、干沙或湿沙中,中子慢化能力增强,反应性上升,可能会导致反应堆发生临界安全事故,设计时需确保反应堆在各类掉落事故工况下始终保持次临界。谱移吸收材料(SSA)是一种共振能区中子比快中子能区中子吸收截面大得多的材料,将其应用于快中子空间反应堆中可以显著提升反应堆的临界安全性。以液态金属回路冷却快中子空间反应堆为研究对象,采用蒙特卡罗方法的MCNP程序建模计算,对梳理出来的5种SSA材料性能及湿沙含水量对于事故反应性的影响进行分类量化研究,以指导反应堆的特殊临界安全设计。研究结果表明,SSA材料的堆内使用及合理布置解决了反应堆的特殊临界安全问题。本研究成果可为后续相关堆型的临界安全设计提供有益参考。
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关键词:
- 快中子空间反应堆 /
- 发射掉落事故 /
- 谱移吸收材料(SSA) /
- 特殊临界安全
Abstract: Special criticality safety is a key issue in the design of space reactors, especially fast reactors. Once a fast neutron space reactor falls into water, dry sand or wet sand due to launch drop accident, the neutron moderating ability and reactivity will increase, which may lead to a criticality safety accident of the reactor. During the design, it is necessary to ensure that the reactor remains subcritical under all drop accidents. Spectral shift absorber (SSA) is a kind of material with much larger neutron absorption cross section in resonance energy region than in fast neutron energy region. Its application in fast neutron space reactor can significantly improve the criticality safety performance of fast neutron space reactor. Taking the fast neutron space reactor cooled by the liquid metal circuit as the research object, the MCNP program of Monte Carlo method is used for modeling and calculation, and the effects of the properties of five SSAs and the moisture content of wet sand on the accident reactivity is classified and quantified to guide the special criticality safety design of the reactor. The results show that the special criticality safety problem of the reactor is solved by the in-reactor use and reasonable arrangement of spectral SSA. The results of this study can provide a useful reference for the criticality safety design of related reactor types. -
表 1 堆芯筒体外侧涂0.01 mm的SSA材料时的价值比
Table 1. Value Ratio When 0.01 mm SSA Is Coated on the Outside of the Core Barrel
材料 工况Ⅰ 工况Ⅱ 工况Ⅲ 工况Ⅳ Eu2O3 −0.54 2.19 −0.35 2.67 Gd2O3 0.76 4.52 1.37 4.96 BC4 0.92 5.50 1.74 6.38 Ir 0.47 −0.18 −0.17 0.25 Mo-14Re 0.21 0.46 −0.59 −0.30 表 2 SSA材料用作堆中心安全棒时的价值比
Table 2. Value Ratio of SSA Used as Reactor Center Safety Rod
材料 工况Ⅰ 工况Ⅱ 工况Ⅲ 工况Ⅳ Eu2O3 0.52 3.53 0.96 3.74 Gd2O3 1.42 4.17 1.85 4.40 BC4 −0.51 0.16 −0.81 0.78 Ir 0.36 1. 50 0.41 2.47 Mo-14Re 0.49 1.34 0.15 1.08 表 3 SSA材料用作燃料元件包壳时的价值比
Table 3. Value Ratio of SSA Used as Fuel Element Cladding
材料 工况Ⅰ 工况Ⅱ 工况Ⅲ 工况Ⅳ Ir 0.20 1.84 0.35 1.92 Mo-14Re 0.33 1.73 0.43 1.56 表 4 事故工况汇总
Table 4. Summary of Accident Conditions
工况编号 堆外掩埋物 反应堆 堆芯进水 1 水 完整 否 2 水 完整 是 3 湿沙 完整 否 4 湿沙 完整 是 5 干沙 完整 否 6 干沙 完整 是 7 水 裸堆 否 8 水 裸堆 是 9 湿沙 裸堆 否 10 湿沙 裸堆 是 11 干沙 裸堆 否 12 干沙 裸堆 是 13 水 密实 否 14 湿沙 密实 否 15 干沙 密实 否 表 5 湿沙密度随含水量的变化
Table 5. Wet Sand Density Changes with Water Content
材料 编号 SiO2体积分数 水体积分数 密度/(g·cm−3) 干沙 1 0.8621 0 2.000 湿沙 2 0.8621 0.05 2.050 3 0.8621 0.1 2.100 4 0.8621 0.1379 2.1379 5 0.85 0.15 2.122 6 0.8 0.2 2.056 7 0.7 0.3 1.924 8 0.6 0.4 1.792 9 0.5 0.5 1.660 10 0.4 0.6 1.528 11 0.3 0.7 1.396 12 0.2 0.8 1.264 13 0.1 0.9 1.132 水 14 0 1 1.000 表 6 湿沙包覆工况下的keff
Table 6. keff under the Condition of Wet Sand Coating
湿沙含水量/% 密度/(g·cm−3) 工况4的keff 工况10的keff 100 1.00 0.92167 0.93012 40 1.79 0.93214 0.94943 30 1.92 0.93566 0.95344 20 2.06 0.93942 0.95737 13.79 2.14 0.94683 0.96687 10 2.10 0.94147 0.96234 5 2.05 0.93856 0.95790 0 2.00 0.93661 0.95448 表 7 临界计算结果
Table 7. Criticality Calculation Results
项目 keff 反应性/% 正常运行 1.02569 2.51 冷态停堆 0.89285 −12.0 事故工况4 0.94683 −5.62 事故工况6 0.93661 −6.77 事故工况10 0.96687 −3.43 事故工况12 0.95448 −4.77 事故工况14 0.94137 −6.23 事故工况15 0.93549 −6.90 -
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