Document: NUREG-0800
Document ID: f972dc01-fc50-4909-b196-900835abafe9
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500523.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
Appendix 7-A Rev. 4 — June 1997 BTP HICB- 2- 1 Branch Technical Position HICB-2 Guidance on Requirements of Motor-Operated Valves in the Emergency Core Cooling System Accumulator Lines A. Background For many postulated loss-of-coolant accidents, the performance of the emergency core cooling system (ECCS) in pressurized water reactor plants depends upon proper functioning of the safety injection tanks (also referred to as "accumulators" or "flooding tanks" in some applications). In these plants, a motor-operated isolation valve (MOIV) and two check valves are provided in series between each safety injection tank and the reactor coolant (primary) system. The MOIVs must be considered to be "operating bypasses" because, when closed, they prevent the safety injection tanks from performing the intended protective function. ANSI/IEEE Std 279, "Criteria for Protection Systems for Nuclear Power Generating Stations," has a requirement for "operating bypasses" which states that the bypasses of a protective function will be removed automatically whenever permissive conditions are not met. IEEE Std 603, "IEEE Standard Criteria for Safety Systems for Nuclear Power Generating Stations," contains a similar requirement. This branch technical position provides specific guidance in meeting the intent of ANSI/IEEE Std 279 or IEEE Std 603 for safety injection tank MOIVs. It should be noted that BTP ICSB-18 (PSB), "Application of the Single-Failure Criterion to Manually Controlled Electrically Operated Valves," also applies to these isolation valves and should be used in conjunction with this position. B. Branch Technical Position The following features should be incorporated into the design of MOIV systems for safety injection tanks to meet the intent of ANSI/IEEE Std 279: 1. Automatic opening of the valves when either primary coolant system pressure exceeds a preselected value (to be specified in the technical specifications), or a safety injection signal is present. Both primary