Analysis of influence of canceling secondary neutron sources ontritium source terms in pressurized water reactors
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摘要: 在压水堆正常运行期间，氚贡献了压水堆液相流出物总活度的95%以上，是反应堆设计和运行中的关键放射性核素之一。通过对美国在运的8台堆芯设计非常相似的机组2000至2019年期间氚排放数据进行较为深度的数据清洗和分析研究，得出采用不锈钢包壳的Sb-Be次级中子源的氚释放是压水堆机组氚源项的重要来源之一，统计机组中次级中子源产氚贡献平均为7.5 TBq·a−1，结合理论计算，符合当前包壳材料发展和运行管理水平下的渗透比例10%～20%。取消次级中子源约可以降低20%的因氚排放造成的公众剂量，还可以降低氚源项对厂址规划机组数量的制约。此外，研究还发现，氚排放量的显著波动受到液态集中排放的显著影响，特别是在美国压水堆大修之前或期间，这将有助于优化未来机组放射性排放管理。Abstract: During the normal operation of pressurized water reactors, tritium contributes more than 95% of the total activity of liquid phase effluent from pressurized water reactors, and it is one of the key radionuclides in reactor design and operation. Through in-depth data cleaning and analysis of tritium emission data from eight units operating in the United States with very similar core designs from 2000 to 2019, it is concluded that tritium emission from Sb-Be secondary neutron sources using stainless steel cladding is one of the important sources of tritium source terms for pressurized water reactor units. According to statistics, the average contribution of tritium production from secondary neutron sources in the units is 7.5 TBq·a−1, combined with theoretical calculations, The penetration ratio in line with the current cladding material development and operation management level is 10%−20%. The elimination of secondary neutron sources can reduce the public dose caused by tritium emissions by about 20%, and can also reduce the constraints of tritium source terms on the number of units planned for the plant site. In addition, it also found that significant fluctuations in tritium emissions are significantly affected by concentrated liquid emissions, especially before or during the overhaul of pressurized water reactors in the United States, which will help optimize the management of radioactive emissions from future units.
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Key words:
- tritium /
- secondary neutron source /
- stainless steel cladding /
- pressurized water reactor
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表 1 压水堆中氚生产的核反应
Table 1. Nuclear reaction of tritium production in PWR
region nuclear reactions fuel $ {\text{U/Pu + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{}}{\text{FP1 + FP2 + }}{}_{\text{1}}^{\text{3}}{\text{H}} $ antimony-beryllium
(in secondary source)${}_{\text{4}}^{\text{9}}{\text{Be + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{2}}^{\text{6}}{\text{He}}$⇨${}_{\text{2}}^{\text{6}}{\text{He}}\xrightarrow{{\text{β }}}{}_{\text{3}}^{\text{6}}{\text{Li}}$⇨${}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{1}}^{\text{3}}{\text{H}}$
${}_{\text{4}}^{\text{9}}{\text{Be + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{{\text{(n,T)}}}}{}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{1}}^{\text{3}}{\text{H}}$⇨${}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n,n}}\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{0}}^{\text{1}}{\text{n + }}{}_{\text{1}}^{\text{3}}{\text{H}}$boric acid
(in the primary coolant and control rod)${}_{\text{5}}^{{\text{10}}}{\text{B + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},2\alpha )}}{\text{2}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{1}}^{\text{3}}{\text{H}}$
${}_{\text{5}}^{{\text{10}}}{\text{B + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n,n}}\alpha )}}{}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n + }}{}_{\text{2}}^{\text{4}}{\text{He}}$⇨${}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{1}}^{\text{3}}{\text{H}}$
${}_{\text{5}}^{{\text{10}}}{\text{B + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{2}}^{\text{4}}{\text{He}}$⇨${}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n,n}}\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{0}}^{\text{1}}{\text{n + }}{}_{\text{1}}^{\text{3}}{\text{H}}$${}_{\text{5}}^{{\text{11}}}{\text{B + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{{\text{(n,T)}}}}{}_{\text{4}}^{\text{9}}{\text{Be + }}{}_{\text{1}}^{\text{3}}{\text{H}}$⇨${}_{\text{4}}^{\text{9}}{\text{Be + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{2}}^{\text{6}}{\text{He}}$
${}_{\text{2}}^{\text{6}}{\text{He}}\xrightarrow{{\text{β }}}{}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{{{ - 1}}}^{\text{0}}{\text{e}}$⇨${}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{1}}^{\text{3}}{\text{H}}$
${}_{\text{4}}^{\text{9}}{\text{Be + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{{\text{(n,T)}}}}{}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{1}}^{\text{3}}{\text{H}}$⇨${}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n,n}}\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{0}}^{\text{1}}{\text{n + }}{}_{\text{1}}^{\text{3}}{\text{H}}$lithium hydroxide
(in the primary coolant)${}_{\text{3}}^{\text{6}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{1}}^{\text{3}}{\text{H}}$
${}_{\text{3}}^{\text{7}}{\text{Li + }}{}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n,n}}\alpha )}}{}_{\text{2}}^{\text{4}}{\text{He + }}{}_{\text{0}}^{\text{1}}{\text{n + }}{}_{\text{1}}^{\text{3}}{\text{H}}$deuterium
(in the primary coolant)${}_{\text{1}}^{\text{2}}{\text{H + }}_{\text{0}}^{\text{1}}{\text{n}}\xrightarrow{{({\text{n}},\gamma )}}{}_{\text{1}}^{\text{3}}{\text{H}}$ 
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表 2 机组信息
Table 2. Information of the reactors
reactor thermal capacity/MW number of assemblies active height/cm fuel configuration secondary neutron source (SNS) period of discharge group 1 A 3411 193 12 17×17 N 2000—2019 B 3411 193 12 17×17 N 2001—2019 C 3438 193 12 17×17 N 2001—2011 D 3438 193 12 17×17 N 2001—2011 group 2 E 3459 193 12 17×17 Y 2001—2019 F 3468 193 12 17×17 Y 2000—2019 G 3455 193 12 17×17 Y 2001—2019 H 3455 193 12 17×17 Y 2001—2019
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表 3 氚排放量统计结果
Table 3. Statistical results of tritium emissions
unit average tritium emission/(TBq·a−1) maximum tritium emission/(TBq·a−1) gaseous liquid total gaseous liquid total group 1 A 3.8 18.2 22.0 4.8 32.4 37.1 B 3.0 22.2 25.2 4.8 33.5 38.3 C 2.1 21.5 23.6 2.6 33.8 36.4 D 2.2 22.6 24.8 2.5 34.3 36.8 All 2.8±0.7 21.1±1.7 23.9±1.2 4.8±1.1 34.3±1.6 38.3±1.2 group 2 E 3.9 26.9 30.8 5.4 36.5 44.0 F 3.9 29.3 33.2 4.6 37.7 41.9 G 2.6 28.8 31.4 3.6 39.1 41.9 H 2.5 27.6 30.1 3.2 37.1 38.8 All 3.2±0.7 28.1±0.9 31.4±1.1 5.4±0.8 39.1±1.0 44.0±1.8
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