Document: NUREG-0800
Document ID: 55688d47-80f6-498a-af38-5bfb9d7420aa
Document Type: srp
Title: Revision 3 - March 2007
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070740004.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6
CFR Part: 
CFR Title: 

Content:
ision 3 - March 2007 containment, and other regions of the plant with leakage collection and filtration systems. Depressurization systems as parts of the secondary containment decrease or maintain the secondary containment volume at a negative pressure. All primary containment leakage may not be collected because (a) direct primary containment leakage can occur while the secondary containment is being depressurized and (b) primary containment leakage can bypass the secondary containment through containment penetrations and seals which do not terminate in the secondary containment. Direct leakage from the secondary containment to the environment can occur whenever there is an outward positive differential pressure across the secondary containment boundary. The secondary containment can experience a positive pressure transient following a postulated LOCA in the primary containment as a result of thermal loading and infiltration from the environment and the primary containment that will occur until the depressurization systems become effective. An outward positive differential on the secondary containment wall can also be created by wind loads. A "positive" pressure is defined as any pressure greater than -0.063 kPa (-0.25 inches water gauge), to account for wind loads and the uncertainty in the pressure measurements. Whenever the pressure in the secondary containment volume exceeds -0.063 kPa (-0.25 inches water gauge), the leakage-prevention function of the secondary containment is assumed to be negated. The conservative assumption is that all primary containment leakage is released directly to the environment during such time periods because leakage from the secondary containment during positive pressure periods cannot be determined. Therefore, it becomes necessary to determine the time periods during which these threshold conditions exist. Determination of the duration of periods of positive pressure within the secondary containment should be based on analyses of