基于三维输运方法的压水堆主冷却剂^(16)N源项计算分析

Analysis of16N Source Term in PWRs Primary Coolant System Based on Three-dimensional Transport Method

在反应堆功率运行期间,一回路冷却剂水中的^(16)O受高能中子照射,活化生成^(16)N。^(16)N衰变会释放出高能γ射线,是反应堆内冷却剂系统放射性的主要来源。对一回路冷却剂中^(16)N源项进行计算可为反应堆屏蔽设计提供依据。^(16)N活度浓度及其在一回路中的分布是安全审评中的关键参数。为了精确计算^(16)N源项,本文首先使用JSNT程序计算了堆芯及其相邻区域的高能快中子注量率分布,然后考虑冷却剂在反应堆压力容器内的流动和照射情况,以及其在一回路中的流动和衰变情况,编制了^(16)N源项计算程序,在计算过程中考虑了快中子注量率的三维分布。以某三代压水堆核电厂为例计算了^(16)N源项在一回路中的分布。计算结果表明,使用三维中子注量率分布可以得到更精细的^(16)N源项分布;上下腔室内中子注量率对一回路中^(16)N源项分布影响很小,可以不予考虑。

16O in the primary coolant of PWRs is irradiated by high energy neutron,and transformed into16N. High energy γ is released w hile16N decays. It＇ s the main radiation source in the primary coolant system. Calculation of16Nsource term in the primary system is needed to perform reactor shielding design.The concentration and distribution of16Nin the primary coolant system is key parameters in nuclear safety regulation. In order to get precise16N source term,JSNT is used to obtain high energy neutron distribution in both reactor core and adjacent regions. An16N source term calculation code is developed considering increase of16N in the coolant by irradiation and decrease by decay out of the reactor press vessel. In the calculation,three-dimensional neutron flux distribution is used.16N source term is obtained using this code for a typical Gen-III PWR. The results show that detailed16N source term distribution can be obtained using three-dimensional neutron flux distribution and neutron in the upper and low er plenum has little effect on the16N source term distribution and can be neglected in the calculation.