Research on Calculation of Coolant Radiolysis Products in Operating Conditions during the Shutdown of PWRs
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摘要: 压水堆大修时活化腐蚀产物源项控制是降低集体剂量最有力的手段，冷却剂辐解的影响必须予以考虑。本文基于水辐解反应动力学原理，构建了冷却剂辐解动力学模型，根据该模型计算得到了主要辐解产物H2O2、O2和H2在各工况的生成情况，并讨论了微观反应机理。结果表明：①在停堆下行过程中，冷却剂温度从310℃逐步下降到60℃，溶解氢浓度逐步降为0，一回路从还原性转为氧化性，H2O2和O2的生成显著上升；②温度、B/Li浓度、溶解氢浓度、H2O2和O2初始浓度等多种因素均会影响辐解产物的浓度；③H2O2和O2是相互促进生成的关系，H2可以显著抑制H2O2和O2的生成，但高浓度的H2O2会保护H2免遭·OH的消耗。本文研究结果将为压水堆大修下行工况参数的选择以及活化腐蚀产物源项控制提供参考和指导。Abstract: The control of radioactive source of the activated corrosion products during the shutdown of PWRs is one of the most effective means to reduce the CRE. The effect of coolant radiolysis should be taken into account. In this paper, a coolant radiolysis kinetic model was developed based on water radiolysis reaction kinetics. The main radiolysis products such as H2O2, O2 and H2 under different conditions were obtained through the kinetic calculations. The reaction mechanism was also discussed. The results showed that: ① during the shutdown, as the temperature of coolant decreases from 310℃ to 60℃, and the concentration of dissolved H2 decreased to 0, the coolant changes from reductive to oxidative. The radiolysis generation of H2O2 and O2 is significantly promoted;② the generation of radiolysis products is affected by the chemical parameters, such as concentrations of B/Li, dissolved H2, dissolved O2 and H2O2; ③ the generation of H2O2 and O2 are mutually promoted by each other. The presence of H2 can inhibit the generation of H2O2 and O2 to some extent. The presence of high concentration of H2O2 will protect H2 from the consumption of ·OH. The results in this paper may provide important references and guidances for the selection of operating parameters under different conditions during the shutdown of PWRs and the control of activated corrosion products.
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Key words:
- PWR /
- Shutdown /
- Coolant /
- Radiolysis products
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图 1 310℃时不同条件下辐解产物随时间的变化（CB=100 mg/kg，CLi=0.6 mg/kg）
Figure 1. Variation of Radiolysis Products with Time under Different Conditions at 310℃ (CB=100 mg/kg, CLi=0.6 mg/kg)
图 2 291℃时不同条件下辐解产物随时间的变化（CB=1200 mg/kg，
$ {C_{{{\text{O}}_2}}} $ =5 μg/kg）Figure 2. Variation of Radiolysis Products with Time under Different Conditions at 291℃(CB=1200 mg/kg,
$ {C_{{{\text{O}}_2}}} $ =5 μg/kg)
图 3 177℃时不同条件下辐解产物随时间的变化
Figure 3. Variation of Radiolysis Products with Time under Different Conditions at 177℃
图 4 130℃时不同条件下辐解产物随时间的变化
Figure 4. Variation of Radiolysis Products with Time under Different Conditions at 130℃
图 5 不同H2O2初始浓度下辐解产物随时间的变化（CB=2350 mg/kg，CLi=0.05 mg/kg，T=70℃，
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg）Figure 5. Variation of Radiolysis Products with Time under Different Initial Concentrations of H2O2 (CB=2350 mg/kg, CLi=0.05 mg/kg, T=70℃,
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg)
图 6 不同温度下辐解产物随时间的变化（CB=2350 mg/kg，CLi=0.05 mg/kg，
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg，$ {C_{{{\text{H}}_{\text{2}}}{{\text{O}}_2}}} $ =10 mg/kg）Figure 6. Variation of Radiolysis Products with Time at Different Temperatures (CB=2350 mg/kg, CLi=0.05 mg/kg,
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg,$ {C_{{{\text{H}}_{\text{2}}}{{\text{O}}_2}}} $ =10 mg/kg)
图 7 不同CLi下辐解产物随时间的变化（CB=2350 mg/kg，T=70℃，
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg，$ {C_{{{\text{H}}_{\text{2}}}{{\text{O}}_2}}} $ =10 mg/kg）Figure 7. Variation of Radiolysis Products with Time under Different Concentrations of Li (CB=2350 mg/kg, T=70℃,
$ {C_{{{\text{O}}_2}}} $ =8 mg/kg,$ {C_{{{\text{H}}_{\text{2}}}{{\text{O}}_2}}} $ =10 mg/kg)
图 8 压水堆大修下行各工况下辐解产物H2O2、O2和H2的平衡浓度
Figure 8. Equilibrium Concentration of Radiolysis Products (H2O2, O2, H2) under Different Operating Conditions during the Shutdown of a PWR
表 1 某压水堆大修下行工况参数表
Table 1. Table of Parameters under Different Operating Conditions during the Shutdown of a PWR
序号 工况描述 温度（T）/
℃压力/
MPa硼浓度（CB）/
(mg·kg−1)锂浓度（CLi）/
(mg·kg−1)溶解氢浓度（${C}_{ {\text{H} }_{\tiny {2} } }'$）①/
(cm3·kg−1)氧气浓度（${C}_{ {\text{O} }_{\tiny{2} } }$）/
( μg·kg−1)②1 降功率前48~24 h 310 15.71 通常在100左右 0.60 10~35 5 2 降功率前24 h 10 5 3 热停平台 291 15.71 1200 0.20 10 5 0.60 3.30 4 中停平台-1
碱性还原方案177 2.74 2000~2400 <0.05 5 5 0.50 1 2.07~2.70 5 中停平台-2 130 2.74 2200~2400 <0.05 5 5 0.50 1.65 6 氧化运行 60~80 2.74 2350 0.05~1.30 0 0~104（添加0~20 mg/kg H2O2） 注：①${C}_{{\text{H}}_{\text{2}}}' $指的是冷却剂中注氢后达到的溶解氢浓度；②1 μg/kg=0.03125 mol/L 
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表 2 H3BO3、LiOH和 H2O解离反应与解离平衡常数
Table 2. Dissociation Reaction and Equilibrium Constants of H3BO3, LiOH and H2O
序号 反应式 平衡常数（K） 1 B(OH)3 + OH− $\rightleftharpoons $ B(OH)4− K1 = −1573.21/T − 28.8397 − 0.011748×T + 13.2258×lgT 2 2B(OH)3 + OH− $\rightleftharpoons $ B2(OH)7− K2 = −2756.10/T + 18.9660 − 5.835×lgT 3 3B(OH)3 + OH− $\rightleftharpoons $ B3(OH)10− K3 = −3339.50/T + 8.08400 − 1.497×lgT 4 4B(OH)3 + 2OH− $\rightleftharpoons $ B4(OH)142− K4 = −12820.0/T + 134.560 − 42.105×lgT 5 5B(OH)3 + 3OH− $\rightleftharpoons $ B5(OH)183− K5= −14099.0/T + 118.115 − 36.237×lgT 6 LiOH $\rightleftharpoons $ Li+ + OH− K6 = −1.655×10−9×T 3 +4.24×10−7×T 2+1.62×10−3×T+0.1631 7 Li+ + B(OH)4− $\rightleftharpoons $ LiB(OH)4 K7 = 2.12 8 H2O $\rightleftharpoons $ H+ + OH− K8 = −[−4.098 − 3245/T + 2.23×105/T 2 − 3.998×107/T 3 + (13.95 − 1262.3/T + 8.56×105/T 2) ×lgρ] ρ—密度
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表 3 停堆1 d时堆芯的剩余剂量率
Table 3. Calculated Reactor Core Residual Dose Rate 1 Day after Shutdown
类别 中子 次级γ γ 剂量率/（Gy·h−1） 2.02×10−2 2.91×10−3 1.20×105
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表 4 压水堆大修下行工况冷却剂pH值计算结果
Table 4. Calculation Results of Coolant pH Value under Different Operating Conditions during the Shutdown of a PWR
T/℃ 纯水pH值 CB/ (mg·kg−1) CLi/ (mg·kg−1) pH值 310 5.75 100 0.60 7.24 291 5.67 1200 0.20 0.60 3.30 5.83 6.28 7.01 177 5.71 2000 0.05 0.50 1 2.07 2.70 4.84 5.39 5.67 5.98 6.09 5.71 2400 0.05 0.50 1 2.07 2.70 4.77 5.27 5.55 5.85 5.97 130 5.92 2200 0.05 0.50 1.65 4.73 5.22 5.71 5.92 2400 0.05 0.50 1.65 4.70 5.16 5.64 80 6.31 2350 0.05 1.30 4.64 5.44 70 6.41 2350 0.05 1.30 4.63 5.42 60 6.52 2350 0.05 1.30 4.62 5.40
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