Document: NUREG-0800
Document ID: d0e1f2cb-f296-449d-9f9a-85a571917a44
Document Type: srp
Title: EMERGENCY CORE COOLING SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340709.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.3
CFR Part: 
CFR Title: 

Content:
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," defines an active failure as: (a) "An active failure is a malfunction, exceeding passive failures, of a com- ponent which relies on mechanical movement to complete its intended function upon demand." (b) "Spurious action of a powered component originating within its actuation 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 systems that connect the safety injection pumps to the RWST (BWST) and the containment sumps. 2. The piping systems including valves, shall be designed to satisfy the requirements listed below without the need to disconnect the power to any valve. 3. The valves and piping between the RWST (or BWST) and the safety injection pumps must be arranged so that no single failure will Prevent the minimum flow to the core required to satisfy 10 CFR Part 50, §50.46. 6.3-14 Rev. 1 - July 1981 4. The valves and piping between the RWST (or BWST) and safety injec- tion pumps must be arranged so that no single active failure will result in damage to pumps such that the minimum flow requirements for long-term core and containment cooling after a LOCA are not satisfied. 5. The valves and piping that connect the RWST (or BWST) and the contain- ment sumps(s) to the safety injection pumps must be arranged so as not to preclude automatic switchover from the injection mode of ECCS operation to recirculation cooling from