Document: NUREG-0800
Document ID: ea7ce8f5-32bf-4d8c-a653-e964bff0ef48
Document Type: srp
Title: EMERGENCY CORE COOLING SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070448.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.3
CFR Part: 
CFR Title: 

Content:
84 DRAFT Rev. 3 - April 1996 6.3-26 BRANCH TECHNICAL POSITION RSB 6-1 CURRENTLY THE RESPONSIBILITY OF THE REACTOR SYSTEMS BRANCH (SRXB)185 PIPING FROM THE RWST (OR BWST) AND CONTAINMENT SUMP(S) TO THE SAFETY INJECTION PUMPS A. Background Current PWRs utilize the refueling water storage tank (RWST) or the borated water storage tank (BWST) as the sole source of water for the safety injection pumps during the first 20 to 40 minutes of any accident that trips a safety injection signal. Since acceptable results of safety analyses of the accidents are based on the operation of a minimum number of these pumps interruption of this water supply for even a short period of time could result in unacceptably high fuel and cladding temperatures if the safety injection pumps fail because of cavitation or overheating. General Design Criteria 35 requires that the emergency core cooling system have suitable redundancy in components and features and suitable interconnections to assure the system safety function can be accomplished assuming a single failure. The principal problem appears to be a definition of single failure. A recent draft of ANSI N658, "Single Failure Criteria for PWR Fluid Systems," (Reference 36) defines an active failure as: (a) "An active failure is a malfunction, exceeluding passive failures, of a component which relies on mechanical movement to complete its intended function upon demand." (b) "Spurious action of a powered component originating within its actuation or control186 system shall be regarded as an active failure unless specific design features or operating restrictions preclude such spurious action." This branch position on the availability of the RWST is based on the above criteria and the recognition that water supplied from the RWST system to the ECCS system is absolutely essential in the event of a LOCA. B. Branch Position 1. The single active failure criterion defined in (a) and (b) above will be applied in evaluating the design of the piping