Resolution of Generic Safety Issues: Item A-43: Containment Emergency Sump Performance (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–34 )
This issue deals with a concern for the availability of adequate recirculation cooling water following a LOCA when long-term recirculation of cooling water from the PWR containment sump, or the BWR RHR system suction intake, must be initiated and maintained to prevent core-melt. This water must be sufficiently free of LOCA-generated debris and potential air ingestion so that pump performance is not impaired thereby seriously degrading long-term recirculation flow capability. The concern applies to both PWRs and BWRs. The RHR suction strainers in a BWR are analogous to the PWR sump debris screen and adequate recirculation cooling capacity is necessary to prevent core-melt following a postulated LOCA. The issue was declared a USI in January 1979 and published in NUREG-0510.186
The technical concerns evaluated under USI A-43 are as follows:
|(1)||PWR sump (or BWR RHR suction intake) hydraulic performance under post-LOCA adverse conditions resulting from potential vortex formation and air ingestion and subsequent pump failure.|
|(2)||The possible transport of large quantities of LOCA-generated insulation debris resulting from a pipe break to the sump debris screen(s), and the potential for sump screen (or suction strainer) blockage to reduce net positive suction head (NPSH) margin below that required for the recirculation pumps to maintain long-term cooling.|
|(3)||The capability of RHR and containment spray system (CSS) pumps to continue pumping when subjected to possible air, debris, or other effects such as particulate ingestion on pump seal and bearing systems.|
The staff's proposed resolution for USI A-43 was issued for public comment on May 10, 1983. The public comment package included NUREG-0869,1056 the staff's technical findings report NUREG-0897,1057 proposed Regulatory Guide 1.82, Revision 1, and proposed SRP11 Section 6.2.2, Revision 4, "Containment Heat Removal Systems." A summary of the public comments received and the staff's response are contained in Appendix A of NUREG-0869,1056 Revision 1.
In October 1985, the resolution of USI A-43 was presented to the Commission in SECY-85-349.1060 The staff is implementing the resolution of USI A-43 through the following actions:
|(1)||The staff's technical findings (NUREG-0897, Revision 1)1057 were published for use as an information source by applicants, licensees, and the staff.|
|(2)||SRP11 Section 6.2.2 and Regulatory Guide 1.821058 were revised to reflect the staff's technical findings reported in NUREG-0897, Revision 1. This revised licensing guidance applies only to reviews of: (a) future construction permit applications and preliminary design approvals (PDAs); (b) final design approvals (FDAs) for standardized designs which are intended for referencing in future construction permit applications that have not received approval; and (c) applications for licenses to manufacture. This revised guidance became effective 6 months after issuance of Regulatory Guide 1.82, Revision 1.|
|(3)||Generic Letter 85-221059 (for information only) was sent to all holders of an operating license or construction permit outlining the safety concerns regarding potential debris blockage and recirculation failure due to inadequate NPSH. It was recommended (but not required) that licensees utilize Regulatory Guide 1.82,1058 Revision 1, as guidance for conduct of the 10 CFR 50.59 analysis for future plant modifications involving replacement of insulation on primary system piping and/or equipment. If, as a result of NRC staff review of licensee actions associated with replacement or modification to insulation, the staff decides that SRP11 6.2.2, Rev. 4 and/or Regulatory Guide 1.82,1058 Rev. 1, criteria should be (or should have been) applied by the licensees, and the staff seeks to impose these criteria, then NRC will treat such actions as plant-specific backfits pursuant to 10 CFR 50.109.|
Thus, this issue was RESOLVED and new requirements were established.