Document: NUREG-0800
Document ID: 07e6bf87-51bb-4023-80a2-2a67ca4a9f80
Document Type: srp
Title: Revision 3 - March 2007
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070740319.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6
CFR Part: 
CFR Title: 

Content:
nuously. There is similar disparity in the need for, and use of, containment vent systems at operating plants. Containment purge systems have been used in a variety of ways (e.g., to alleviate certain operational problems like excess air leakage into the containment from pneumatic controllers, to reduce airborne activity within the containment to facilitate personnel access during reactor power operation, and to control the containment pressure, temperature, and relative humidity). Containment vent systems typically relieve the initial containment pressure buildup caused by the heat load imposed on the containment atmosphere during reactor power ascension or periodically relieve the pressure buildup due to the operation of pneumatic controllers. However, the purge and vent lines provide open paths from the containment to the environs. If a LOCA occurs during containment purging when the reactor is at power, the calculated accident doses should be within 10 CFR Part 100 guideline values. The sizing of the purge lines in most plants is based on the need to control the containment atmosphere during refueling operations. This need has resulted in very large lines (about 42 inches in diameter) to penetrate the containment. As normally these are the only lines permitting 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. The design and use of the purge and vent lines should achieve acceptable calculated offsite radiological consequences and ensure that emergency core cooling system (ECCS) effectiveness is not degraded by a reduction in the containment back pressure. Purge system designs