Document: NUREG-0800
Document ID: c23d52ec-d83f-4468-b35e-e8c97fdf2f09
Document Type: srp
Title: CONTAINMENT ISOLATION SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070461.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.2.4
CFR Part: 
CFR Title: 

Content:
l permit some degree of control over the containment atmosphere to facilitate personnel access, some plants have used them for containment purging during normal plant operation. Under such conditions, calculated accident doses could be significant. Therefore, the use of these large containment purge and vent lines should be restricted to cold shutdown conditions and refueling operations and they must be sealed closed in all other operational modes. DRAFT Rev. 3 - April 1996 6.2.4-22 The design and use of the purge and vent lines should be based on the premise of achieving acceptable calculated offsite radiological consequences and assuring ensuring that emergency core cooling (ECCS) effectiveness is not degraded by a reduction in the containment backpressure. Purge system designs that are acceptable for use on a nonroutine basis during normal plant operation can be achieved by providing additional purge lines. The size of these lines should be limited such that in the event of a loss-of- coolant accident, assuming the purge valves are open and subsequently close, the radiological consequences calculated in accordance with Regulatory Guides 1.3 and 1.4 would not exceed the 10 CFR Part 100 guideline values. Also, the maximum time for valve closure should not exceed five seconds to ensure that the purge valves would be closed before the onset of fuel failures following a LOCA. Similar concerns apply to vent system designs. The size of the purge lines should be about eight inches in diameter for PWR plants. This line size may be overly conservative from a radiological viewpoint for the Mark III BWR plants and the HTGR plants because of containment and/or core design features. Therefore, larger line sizes may be justified. However, for any proposed line size, the applicant must demonstrate that the radiological consequences following a loss-of-coolant accident would be within 10 CFR Part 100 guideline values. In summary, the acceptability of a specific line size is a