Resolution of Generic Safety Issues: Item A-26: Reactor Vessel Pressure Transient Protection (Rev. 2) ( NUREG-0933, Main Report with Supplements 1–34 )

DESCRIPTION

From 1972 to 1983, there had been numerous reported incidents of pressure transients in PWRs where TS pressure and temperature limits were exceeded. The majority of these events occurred while the reactors were in a water solid condition during startup or shutdown and at relatively low reactor vessel temperatures. Since the reactor vessels have less toughness at lower temperatures, they are more susceptible to brittle fracture under these conditions than at normal operating temperatures. In light of the frequency of the reported transients and the associated potential for vessel damage, the NRC concluded that measures should be taken to minimize the number of future transients and reduce their severity. This item was originally identified in NUREG-0371² and was later determined to be a USI in NUREG-0510.¹⁸⁶

CONCLUSION

This USI was RESOLVED with the publication of NUREG-0224 ⁷⁴⁶ and SRP ¹¹ Section 5.2. All operating PWRs were requested to provide an overpressure prevention system that could be used whenever the plants were in a cold shutdown condition. The issue affected all operating and future plants, and MPA B-04 was established by DL/NRR for implementation of the solution at operating PWRs.