压水堆停堆过程活化腐蚀产物源项计算研究

Study on Source Term Calculation of Activated Corrosion Products during the Shutdown Process of Pressurized Water Reactors

摘要: 压水堆停堆期间，一回路热工水力与水化学条件的剧烈变化会导致堆芯及回路表面沉积的活化腐蚀产物(ACPs)大量释放，使冷却剂放射性活度浓度显著升高，进而增加大修人员受照剂量并可能延误大修进度。本文研究了典型压水堆停堆氧化运行过程，建立了用于停堆氧化工况ACPs源项计算的数学模型，并在CATE3.0程序基础上开发了相应功能模块，实现了CATE程序对于压水堆稳态运行与瞬态停堆工况的全寿期模拟能力。随后采用改进的CATE程序计算了典型压水堆一回路算例，系统分析了代表性ACPs核素⁵⁸Co和⁶⁰Co的活度浓度随反应堆运行时间和参数的变化。结果表明：在稳态运行阶段，⁵⁸Co活度浓度先增加后达到平衡，而⁶⁰Co活度浓度则持续增加；进入停堆氧化运行阶段，⁵⁸Co和⁶⁰Co的变化趋势类似，即在注入30% H₂O₂后活度浓度迅速上升1至2个数量级，峰值的计算值与核电厂测量值较为接近；在净化阶段，⁵⁸Co和⁶⁰Co峰值降低约90%，显著抑制再沉积。本研究为压水堆停堆工况活化腐蚀产物源项计算提供了可用的仿真工具，其分析结果可为核电厂的源项控制和辐射防护优化提供参考。

Abstract: During pressurized water reactor shutdowns, drastic changes in primary loop thermal-hydraulic and hydrochemical conditions trigger massive release of activated corrosion products (ACPs) deposited on core and loop surfaces. This significantly elevates coolant radioactivity concentrations, thereby increasing radiation exposure for maintenance personnel and potentially delaying overhaul schedules. This study investigates the oxidation process during typical shutdowns of pressurized water reactor. A mathematical model for calculating ACP source terms under shutdown oxidation conditions was established. A corresponding functional module was developed based on the CATE3.0 program, enabling the CATE program to perform full-lifetime simulations for both steady-state operation and transient shutdown conditions of pressurized water reactors. Subsequently, the enhanced CATE program was employed to calculate a typical pressurized water reactor primary loop case study. A systematic analysis was conducted on the activity concentration variations of representative ACPs nuclides ⁵⁸Co and ⁶⁰Co with respect to reactor operating time and parameters. Results indicate: during steady-state operation, the activity concentration of ⁵⁸Co initially increases before reaching equilibrium, while that of ⁶⁰Co continues to rise; During the oxidation operation phase after shutdown, both ⁵⁸Co and ⁶⁰Co exhibit similar trends: activity concentrations rapidly increase by one to two orders of magnitude after 30% H₂O₂ injection, with calculated peak values closely matching measured values from nuclear power plants. During the purification phase, peak concentrations of both ⁵⁸Co and ⁶⁰Co decrease by approximately 90%, significantly suppressing redeposition. This study provides a viable simulation tool for calculating the source terms of activated corrosion products under shutdown conditions of the pressurized water reactor. Its analytical results offer valuable reference for source term control and radiation protection optimization at nuclear power plants.