压水堆主冷却剂中氚源项计算分析

压水堆主回路冷却剂流经堆芯时，水中固有及特加核素受中子辐照后会产生氚，氚几乎全部以气体和液体的形式排入环境，造成氚污染。因此，氚是压水堆辐射环境影响评价的主要关注内容之一。本文以AP1000为例，根据压水堆主回路冷却剂中氚的产生途径及其随时间的变化情况建立详细的计算模型，计算压水堆主回路冷却剂中的氚活度并分析各产氚途径对氚产生量的贡献。计算结果表明：主回路冷却剂中的氚主要来源于可溶性硼的中子活化和铀裂变，对氚产生量的贡献达80%以上；在⁷Li纯度为99.9%时，AP1000主回路中的年产氚量为5.23×10¹³ Bq，锂产氚量占总量的14.01%，随⁷Li纯度的增加，锂产氚量的贡献呈线性减小，在⁷Li纯度为99.99%时，锂产氚量占总量的3.18%。其他途径对氚的产生量贡献很小，可忽略。根据以上结果，可通过控制主回路冷却剂中添加的初始硼浓度、提高燃料包壳质量、增加LiOH中⁷Li的纯度等多种途径来降低主冷却剂中氚的产生量，从而减少氚对环境的放射性污染。

Calculation Analysis of Tritium Source Term in PWR

During AP1000 operation, the water itself in the primary loop and special nuclides added in the water will be activated by neutrons. Tritium is main activation product and it is drawing more and more attention as they are almost discharged into environment in form of gas or liquid. Therefore, it’s essential to study tritium generation in the primary coolant. In this paper, the tritium generation and consumption mechanism of the primary coolant in AP1000 nuclear power plant was studied and the tritium calculation model was established. Based on the tritium calculation model, the tritium activity in the coolant loop of AP1000 was calculated and the contribution of various ways to generate tritium was analyzed. The results show that the quantity of tritium is mainly from the activation reaction of soluble boron by absorbing neutron and fission of uranium, which contributes more than 80%. The tritium production in AP1000 primary coolant is 5.23×10¹³ Bq/a at the purity of ⁷Li is 99.9%, which accounts for 14.01% of total tritium production. With the increase of ⁷Li purity, the contribution of lithium decreases linearly. When the purity of ⁷Li is 99.99%, the tritium produced from lithium accounts for 3.18%. Based on the above results, the generation of tritium in coolant can be reduced by controlling the initial boron concentration added in coolant, improving the quality of the fuel cladding, and increasing the purity of ⁷Li in LiOH.