压水堆核电厂一次屏蔽深穿透计算研究

Study on Primary Shielding Calculation Based on PWR Power Plant

摘要: 基于三维全堆芯PIN-BY-PIN功率分布的反应堆一次屏蔽计算是核电厂辐射屏蔽设计的重点和难点，是典型的大型复杂源项和几何深穿透屏蔽问题。针对AP1000核电厂，采用蒙特卡罗程序及离散纵标程序DORT，对一次屏蔽混凝土墙进行详细的计算分析。通过开发蒙特卡罗程序面源续算技术，有效地解决了蒙特卡罗程序深穿透难收敛问题，获得可信的统计结果。结果表明，所开发的蒙特卡罗程序面源续算技术有效地解决了大规模深穿透难收敛问题；一次屏蔽计算中，蒙特卡罗程序与DORT计算得到的快中子、中能中子及光子注量率结果吻合良好；热中子计算结果随着径向距离增加，误差逐渐累积，尤其是在一次屏蔽墙混凝土中DORT计算结果偏小。经研究分析两种方法计算结果相对偏差主要是由反应截面数据库不同导致。所采用的处理蒙特卡罗程序深穿透问题的面源续算方法以及AP1000一次屏蔽的研究结论对实际核电工程设计具有参考价值。

Abstract: The primary shielding calculation based on 3D PIN-BY-PIN power distribution of the whole reactor core is one of the most important and difficult problems for the radiation shielding design of a nuclear power plant, and it is a typical deep penetration problem with complex source and geo-metry. Using the three-dimensional Monte Carlo code and two-dimensional Discrete Ordinate code DORT, this paper performs a detailed comparison of the primary shielding design results of AP1000. To solve the deep penetration problem of the Monte Carlo code, and to obtain reliable results, the surface source bootstrapping calculation function of the Monte Carlo code is studied. Numerical results demonstrate that the surface source bootstrapping calculation function of the Monte Carlo code is a very effective method to solve the deep penetration problem. And the comparison results indicate that distributions of fast neutron, middle-range energy neutron and gamma ray agree well. But the result of thermal neutron calculated by DORT is smaller than that of the Monte Carlo code, especially in primary concrete shield wall. The difference between the results of the above two methods mainly comes from the difference of the cross-section libraries. The surface source bootstrapping calculation method of the Monte Carlo code and the conclusion of AP1000 primary shielding are valuable for the practical nuclear power project.