Analysis of tritium source term in an integrated small reactor
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摘要: 基于一体化小堆堆芯设计特点,分析了氚的产生途径,建立了主回路冷却剂中氚源项计算模型。计算结果表明,单台一体化小堆堆芯氚年产量为1.81 TBq,其主要贡献来源是二次中子源材料Sb-Be和控制棒吸收体材料B4C受中子活化产生,占比分别达到46%和51%。通过对沸水堆(BWR)运行电厂氚的排放数据进行统计,证明了理论分析结果的包络性。基于该分析结果,提出了减小一体化小堆运行期间氚产生量的途径,为一体化小堆优化设计提供指引。分析表明,取消二次中子源或中子源棒采用双层包壳结构,以及控制棒吸收体材料进行更换(如更换为Ag-In-Cd或者铪),将会显著减小一体化小堆的氚产生量。Abstract:
Background Tritium production pathways are well-established for large pressurized water reactors (PWRs). Integrated small reactors (ISRs), however, operate without soluble boron reactivity control and use no chemical additives (e.g., lithium hydroxide) for pH adjustment, necessitating dedicated analysis of their tritium sources.Purpose This study aims to identify tritium production pathways in ISRs, establish a computational model for quantifying tritium source terms, and propose design optimizations to minimize tritium generation.Methods A theoretical model was established by solving differential equations for tritium production and removal based on identified neutron activation reaction mechanisms. Key parameters included neutron flux and nuclear cross-sections derived from Monte Carlo simulations of the ISR core. Validation was performed against normalized operational tritium release data from boiling water reactors (BWRs) with analogous B4C control rods and Sb-Be neutron sources, considering thermal power and load factors.Results The annual tritium production in ISR primary coolant is 1.81 TBq. The primary contributors are neutron-activated products from Sb-Be and B4C material, accounting for 46% and 51% of the total production, respectively. Analysis of tritium discharge data from operational BWRs validates the conservatism of the theoretical results.Conclusions Optimizing secondary neutron sources (canceling Sb-Be or using double-encapsulated cladding) and replacing B4C control rods with non-tritium-producing absorbers (e.g., Ag-In-Cd or hafnium) could reduce ISR tritium production significantly. These measures are technically feasible based on PWRs operational experience and are recommended for ISR design enhancements. Future work will refine release fractions of control rods using plant-specific operational data. -
表 1 一体化小堆产氚反应机理
Table 1. Nuclear reactions of tritium production in integrated small reactors
production region nuclear reactions direct source primary coolant $ {}_{1}^{2}\mathrm{H}+{}_{0}^{1}{\rm{n}}\xrightarrow{({\rm{n}},{\text{γ}} )}{}_{1}^{3}\mathrm{H} $ indirect source fuel rod $ \mathrm{U}/\mathrm{P}\mathrm{u}+{}_{0}^{1}{\rm{n}}\to \mathrm{F}\mathrm{P}1+\mathrm{F}\mathrm{P}2+{}_{1}^{3}\mathrm{H} $ secondary source rod $ {}_{4}^{9}\mathrm{B}\mathrm{e}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{2}^{6}\mathrm{H}\mathrm{e}\underset{}{\Rightarrow }{}_{2}^{6}\mathrm{H}\mathrm{e}\xrightarrow{\beta }{}_{3}^{6}\mathrm{L}\mathrm{i}\underset{}{\Rightarrow }{}_{3}^{6}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{1}^{3}\mathrm{H} $
$ {}_{4}^{9}\mathrm{B}\mathrm{e}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},\mathrm{T})}{}_{1}^{3}\mathrm{H}+{}_{3}^{7}\mathrm{L}\mathrm{i}\underset{}{\Rightarrow }{}_{3}^{7}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},\mathrm{n}{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{0}^{1}{\rm{n}}+{}_{1}^{3}\mathrm{H} $control rod $ {}_{5}^{10}\mathrm{B}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},2{\text{α}})}2{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{1}^{3}\mathrm{H} $
$ {}_{5}^{10}\mathrm{B}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{3}^{7}\mathrm{L}\mathrm{i}\underset{}{\Rightarrow }{}_{3}^{7}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},\mathrm{n}{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{0}^{1}{\rm{n}}+{}_{1}^{3}\mathrm{H} $
$ {}_{5}^{10}\mathrm{B}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},\mathrm{n}{\text{α}})}{}_{3}^{6}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}+{}_{2}^{4}\mathrm{H}\mathrm{e}\underset{}{\Rightarrow }{}_{3}^{6}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{1}^{3}\mathrm{H} $
$ {}_{5}^{11}\mathrm{B}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},\mathrm{T})}{}_{4}^{9}\mathrm{B}\mathrm{e}+{}_{1}^{3}\mathrm{H}\underset{}{\Rightarrow }{}_{4}^{9}\mathrm{B}\mathrm{e}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{2}^{6}\mathrm{H}\mathrm{e}\underset{}{\Rightarrow }{}_{2}^{6}\mathrm{H}\mathrm{e}\xrightarrow{\beta }{}_{3}^{6}\mathrm{L}\mathrm{i}\underset{}{\Rightarrow }{}_{3}^{6}\mathrm{L}\mathrm{i}+{}_{0}^{1}{\rm{n}}\xrightarrow{(\mathrm{n},{\text{α}})}{}_{2}^{4}\mathrm{H}\mathrm{e}+{}_{1}^{3}\mathrm{H} $表 2 冷却剂中氚的年产生量
Table 2. Annual tritium production in coolant
production source annual tritium production/(TBq·a−1) contribution share/% primary coolant 0.02 1 fuel rod 0.03 2 secondary source rod 0.83 46 control rod 0.93 51 total 1.81 / -
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