水压试验在承压设备安全评价中的作用与利弊分析

Analysis of Role and Pros and Cons of Hydraulic Test in Pressure Equipment Safety Assessment

依据RSE-M标准实施在役检查的机组,投运后反应堆冷却剂系统约10年应进行1次系统水压试验,试验压力为反应堆压力容器设计压力的1.2倍。本文采用断裂力学方法分析了1.2倍设计压力水压试验能检出的极限缺陷尺寸。分析结果表明,1.2倍设计压力定期水压试验对缺陷的高检验能力与设备载荷维持设计安全系数不可兼得。基于长期运行经验,在实施恰当无损检查前提下,RSE-M标准1.2倍设计压力定期水压试验在核安全一级设备承压能力定期评价中的作用极其有限,却降低了压力容器的运行安全系数,增加了设备疲劳损伤和裂纹扩展的风险。综合考虑定期水压试验实施的利弊,建议取消10年周期的1.2倍设计压力定期水压试验,以试验周期更短的密封试验取代。

Some nuclear power plants are instructed according to French RCC-M standard materials and design methods in China,and in-service inspections are carried out according to the“Rules for In-service Inspection of Mechanical Equipment in the Nuclear Island of Nuclear Power Plants(RSE-M)”,which requires in-service hydraulic test for the reactor coolant system every 10 years after the plant is put into operation.The test pressure is 1.2 times the design pressure of the reactor pressure vessel.ASMEⅪ,“Rules for In-service Inspection of Nuclear Power Plant Components”eliminates the requirement for in-service hydraulic tests based on fracture mechanics analysis to determine the defect detection capability of hydraulic tests,concluding that hydraulic tests at no more than 1.1 times the operating pressure can detect defects that non-destructive inspection is unlikely to miss.Compared with the in-service hydraulic test required by ASMEⅪ,test pressure of periodic hydraulic required RSE-M is higher and the test temperature is lower.Also there are differences in the calculation methods of stress intensity factor in fracture mechanics between the two standards.In this paper,the stress intensity factor was calculated using the methods of the two standards separately,and the detection ability of the in-service hydraulic test required by the RSE-M standard for defects was analyzed using fracture mechanics.During the defect evaluation,a more realistic calculation method was employed,which took into account a safety factor of 1.Additionally,the analysis also considered the impact of neutron irradiation on the toughness of the pressure vessel’s reactor-type cylinder material,as well as the inhomogeneous distribution of neutron fluence within the vessel wall thickness.The analysis primarily focused on calculating TypeⅠfailure,assuming that the defects were planar and perpendicular to the direction of maximum stress.Both the methods outlined in ASMEⅪand the RSE-M standard were utilized to calculate the KⅠvalue.Furthermore,the limiting defects under conditions of 1.2 times the design pressure and operating pressure were calculated separately.The analysis results show that it is impossible to maintain both high detection capabilities of defects and equipment loads at a designed safety coefficient in regular hydraulic tests at 1.2 times of design pressure.Based on long-term operational experience,with the implementation of appropriate non-destructive inspection,the role of the regular hydraulic test at 1.2 times of design pressure in the RSE-M standard is limited in the regular evaluation of the pressure-bearing capacity of ClassⅠnuclear safety equipment,while it reduces the operational safety coefficient of pressure vessels and increases the risk of equipment fatigue damage and crack propagation.Taking into account the pros and cons of implementing the regular hydraulic test,it is recommended to cancel the ten-year cycle of the 1.2 times design pressure regular hydraulic test and replace it with a shorter test cycle for a seal test.