FAILURE PRESSURE INVESTIGATION OF PWR REACTOR COOLANT PIPE

摘要

In the reactor coolant primary loop of a nuclear power plant (NPP), overpressure protection system keeps pressure in the loop within 110% design pressure. But if the system did not work properly, pressure in the loop could rise very high in short time. It would be disastrous if the piping of the loop burst, since radioactive material would release. It is customary to estimate the probability of rupture of primary pressure boundary based on fracture mechanics. In this study, such detailed fracture mechanics failure analysis with postulated initial notch condition is not carried out. Instead, comparative study of primary coolant pipe of different reactor types is carried out based on gross plastic analysis to realistically assess the maximum pressure primary system can sustain. In this paper, burst pressures of three major reactor coolant piping (APR1400, WER1000, and AP1000) are investigated based on non-linear FEA method. For the analysis axisymmetric models is developed to estimate burst pressure. The FEM results are compared with some existing burst pressure predictive formulae to evaluate accuracy of the prediction. In the analysis, the internal pressures are increased until stress across the entire thickness of piping reach the ultimate tensile stress. The value of pressure at that point is assumed as burst pressure. The results from ANSYS software shows that outlet piping of WER1000 can withstand up to the burst pressure of 161.1Mpa, while that for AP1000 is 87.92Mpa, and that of outlet piping of APR1400 is 97.16Mpa. Burst pressures using empirical formulae also give similar trend as FEM results.