Analysis on Water Ingress Accident of a Gas Cooled Reactor
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摘要: 气冷堆受工作环境或运行状态影响，可能发生其所特有且造成严重事故后果的进水事故。针对美国气冷堆S4堆设计方案，模拟分析在正常运行工况下冷凝器部分传热管破裂导致的进水事故，研究事故造成的正反应性引入、回路超压等事故后果。利用反应堆蒙特卡洛程序RMC计算进水过程中谱移吸收体材料Ir对反应性引入的影响，并利用自主研发的气冷堆系统分析程序HXRTRAN计算进水过程中的温度及布雷顿循环回路压强数据。结果表明，进水事故发生时，0.5 kg进水量将导致布雷顿循环回路的压强超过10 MPa，可能会造成更大面积的冷凝器管路破损并导致水二次灌入；同时进水将导致大量正反应性引入，若堆内燃料表面添加了谱移吸收体材料Ir，堆芯可在进水事故下自发降功率，当水蒸气量超过5 kg后，堆芯功率快速下降至额定功率的2.2%左右，并逐渐接近停堆。可见谱移吸收体材料Ir对于堆芯进水导致的正反应性引入具有显著的抑制效果。Abstract: The gas cooled reactor is featured with high inherent safety, small size, and a simple start-up process. However, the water ingress accident might occur due to the influence of the working environment or operating status. Based on the design scheme of the Submersion-Subcritical Safe Space(S4) reactor, this work simulated and analyzed the water ingress accident caused by the rupture of the heat transfer tube of the condenser under normal operating conditions, and studied the accident consequences such as the introduction of positive reactivity, the overpressure of the Brayton cycle. This work calculated the influence of spectral shift materials on reactivity introduction during the water ingress process with the Reactor Monte Carlo code RMC. And the temperature and Brayton cycle pressure were calculated during the water ingress process with the gas cooled reactor transient analysis code, HXRTRAN. The results show that when a water ingress accident occurs, 0.5 kg water ingress causes the pressure of the Brayton cycle to exceed 10 MPa, which may lead to larger damage to the condenser pipeline and secondary seawater injection. Meanwhile, water ingress may lead to a large amount of positive reactivity introduction. If spectral shift absorbers, Ir, are added to the fuel surface in the reactor, the core may reduce power or even subcritical shutdown spontaneously in the water ingress accident. When the amount of water vapor exceeds 5 kg, the core power quickly decreases to about 2.2% FP and gradually approaches shutdown. Therefore, the spectral shift materials, Ir, have a significant inhibition effect on the introduction of positive reactivity caused by water ingress of the core.
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图 3 S4堆的闭式布雷顿循环系统示意图
Figure 3. Schematic Diagram of Closed Brayton Cycle System for S4 Reactor
图 4 闭式布雷顿循环系统温熵图
S—熵；T—温度
Figure 4. Temperature-entropy Diagram for the Close Brayton Cycle System
图 6 有/无谱移吸收体材料Ir时不同进水量下堆芯功率变化
Figure 6. Core Power Changes at Different Water Ingress Mass with or without Spectral shift absorber Materials Ir
图 7 有/无谱移吸收体材料Ir时不同进水量下布雷顿循环系统电功率及热电转换效率变化
Figure 7. Changes in Electrical Power and Thermoelectric Conversion Efficiency of the Brayton System at Different Water Ingress Mass with or without Spectral Shift Absorber Materials Ir
图 8 有/无谱移吸收体材料Ir时不同进水量下堆芯进出口气体温度变化
Figure 8. Temperature Changes of Core Inlet and Outlet Gas at Different Water Ingress Mass with or without Spectral Shift Absorber Materials Ir
表 1 稳态计算结果对比表
Table 1. Comparison of Steady-state Calculation Results
参数 文献值 计算值 误差/% 反应堆总功率/W 471000 470945 0 堆芯进口温度/K 981.4 977.7 0.4 堆芯出口温度/K 1149.0 1151.0 0.2 单个布雷顿流量/(kg·s−1) 1.834 1.750 4.6 压气机进口温度/K 400.0 401.1 0.3 压气机出口温度/K 483.5 491.7 1.7 压气机压比 1.50 1.56 4.0 压气机转速/( r·s−1) 750 775 3.3 透平出口温度/K 1007.6 1009.2 0.2 回热器出口温度/K 517.8 522.8 1.0 回热器回热度 0.95 0.94 1.1 布雷顿循环热效率 0.285 0.296 3.9 负载-系统总效率 0.278 0.281 1.3 循环温度比 2.8725 2.8696 0.1 
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表 2 引入不同质量水蒸气的反应性变化
Table 2. Reactivity Changes with Different Water Vapor Ingress Mass
水蒸气质量/kg 有谱移吸收体材料Ir 无谱移吸收体材料Ir keff 反应性
引入量/pcmkeff 反应性
引入量/pcm0 1.027225 0 1.036790 0 0.5 1.027214 −1 1.037493 65 1.0 1.027426 19 1.038474 156 2.0 1.027330 10 1.039739 273 5.0 1.024698 −240 1.041566 442 10.0 1.019874 −701 1.042135 494 15.0 1.015947 −1080 1.043830 650 20.0 1.014226 −1247 1.047885 1021 23.5 1.014404 −1230 1.052886 1474 keff—有效增殖系数；1pcm—10−5
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表 3 有谱移吸收体材料Ir时不同进水量下的堆芯功率、燃料和基体温度
Table 3. Core Power, Temperature of Fuel and Monolith at Different Water Ingress Masses with Spectral Shift Absorbers Ir
水蒸气
质量/kg反应性引
入量/pcm功率份
额/%FP全堆燃
料均温/K全堆基
体均温/K燃料峰
值温度/K基体峰
值温度/K0 0 100 1190 1158 1313 1261 0.5 −1 99.4 1190 1157 1311 1259 1.0 19 110.9 1215 1178 1349 1293 2.0 9 105.6 1203 1169 1332 1278 5.0 −240 3.1 976 975 980 978 10.0 −701 2.2 973 972 976 975 15.0 −1080 2.2 973 972 976 975 20.0 −1247 2.2 973 972 976 975 23.5 −1230 2.2 973 972 976 975 FP—满功率
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表 4 无谱移吸收体材料Ir时不同进水量下的堆芯功率、燃料和基体温度
Table 4. Core Power, Temperature of Fuel and Monolith at Different Water Ingress Mass without Spectral Shift Absorbers Ir
水蒸气
质量/kg反应性引
入量/pcm功率份
额/%FP全堆燃
料均温/K全堆基
体均温/K燃料峰
值温度/K基体峰
值温度/K0 0 100 1190 1158 1313 1261 0.5 65 79.1 1145 1119 1242 1200 1.0 156 59.7 1103 1082 1176 1144 2.0 273 57.3 1097 1077 1168 1137
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