基于分立元器件固态逻辑的核电厂汽动辅给水泵超速保护系统建模与可靠性分析

Modeling and Reliability Analysis of Overspeed Protection System for Auxiliary Feedwater Pump in Nuclear Power Plant Based on Discrete Component Solid-State Logic

摘要:

针对压水堆核电厂汽动辅助给水泵机械超速保护系统存在调节死区大、非线性增益显著及响应滞后等问题，提出了一种基于“磁场感知+分立元件硬逻辑”的开环保护方案。建立了差压调速系统动力学模型，揭示了低流量工况下转速失稳的机理；为规避软件共模故障风险，设计了基于高精度磁敏传感器与符合GJB 548B标准分立芯片的“三取二”硬件表决架构；建立了马尔可夫状态转移模型以量化评估系统安全完整性，并进行了测量不确定度评定。实验结果表明，系统合成标准不确定度为0.64 rpm，三通道同步偏差小于0.02%，脱扣响应时间约20 ms。经马尔可夫模型验证，系统满足SIL3安全完整性等级要求，并通过了核安全级1E级环境鉴定。工程应用表明，该方案已在核电厂机组大修技改中成功实施，超速试验一次合格率达100%，大修关键路径缩短约 8 h。该方案将连续非线性闭环调节转变为离散开环保护，有效提升了设备的运行稳定性与安全性。

Abstract:

Aiming at the problems of large dead zone, significant nonlinear gain, and response lag in the mechanical overspeed protection system of the turbine-driven auxiliary feedwater pump(TDAFWP)in pressurized water reactor(PWR)nuclear power plants, an open-loop protection scheme based on"magnetic field perception+discrete component hard logic"is proposed. A dynamic model of the differential pressure speed regulation system is established to reveal the mechanism of speed instability under low-flow conditions. A"two-out-of-three"(2oo3)hardware voting architecture based on high-precision magnetic sensors and discrete chips conforming to the GJB 548B standard is designed to eliminate the risk of software common cause failures. A Markov state transition model is established to quantitatively evaluate the safety integrity of the system, and the measurement uncertainty is assessed. Experimental results show that the combined standard uncertainty of the system is 0.64 rpm, the synchronous deviation among the three channels is less than 0.02%, and the trip response time is approximately 20 ms. The system is verified to meet the SIL3 safety integrity level through the Markov model and has passed the nuclear safety class 1E environmental qualification. Engineering application shows that the proposed scheme has been successfully implemented in a nuclear power plant outage, achieving a 100% first-pass rate in overspeed trip tests and reducing the outage critical path by approximately 8 h. The proposed scheme transforms continuous nonlinear closed-loop regulation into discrete open-loop protection, effectively improving the operational stability and safety of the equipment.