TRAC-PF1 analyses of potential pressurized-thermal-shock transients at a combustion-engineering PWR

The study identified the importance of the initial plant conditions and loop flows to the PTS issue. If the plant was initially at hot-zero power (rather than full power), the same accident initiator could produce significantly lower downcomer temperatures because of the reduced decay heat and stored energy. Flow stagnation in all reactor coolant loops, which occurred in one transient, could lead to a vessel wall temperature that approached the relatively cold high-pressure-injection fluid temperature. However, routine operator actions would reduce the consequences of any of these simulated accidents if the pressure-temperature relationships prescribed in the operator guidelines are followed. ORNL will extend the results of the Los Alamos study by determining the probability of vessel failure and accident occurrence for an overall assessment of PTS risk. (orig./HP)