Resolution of Generic Safety Issues: Item B-63: Isolation of Low Pressure Systems Connected to the Reactor Coolant Pressure Boundary ( NUREG-0933, Main Report with Supplements 1–34 )
There are several systems connected to the reactor coolant pressure boundary that have design pressures that are considerably below the reactor coolant system operating pressure. The NRC has required that valves forming the interface between these high and low pressure systems have sufficient redundancy to assure that the low pressure systems are not subjected to pressures which exceed their design limits.
Recently, there has been discussion relative to the adequacy of the isolation of low pressure systems that are connected to the reactor coolant pressure boundary. Past reviews have concentrated on ensuring isolation of the residual heat removal system, which is a low pressure system on almost all PWRs and BWRs. Current reviews of license applications for new plants (CP/OL evaluations) are based on guidelines set forth in the SRP11 supplemented by the staff position, "Leak Testing of Pressure Isolation Valves," which is documented in the proposed Revision 2 to SRP11 3.9.6 issued for public comment in 1980. These guidelines were not available during the reviews of the plants which are currently operating. The next revision of SRP11 3.9.6 will include the staff position on leak testing pressure isolation valves.
To assess the isolation capabilities of low pressure systems, this NUREG-04713 task involves the review of a representative operating plant for each NSSS vendor. Each low pressure system connected to the reactor coolant pressure boundary and penetrating the containment will be examined.
In April 1981, an order was issued168 to all operating reactors to comply with the requirements of the technical resolution for Event V configurations. All other configurations are being addressed by inservice testing SERs and are being issued as license amendments.
This issue has been RESOLVED and requirements have been issued.