Document: NUREG-0800
Document ID: 42f941d3-4815-4bc5-bf81-f2dab04a7aa7
Document Type: srp
Title: SECONDARY CONTAINMENT FUNCTIONAL DESIGN
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070459.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.2.3
CFR Part: 
CFR Title: 

Content:
e or maintain the secondary containment volume at a negative pressure. All primary containment leakage may not be collected because (1) direct primary containment leakage can occur while the secondary containment is being depressurized and (2) 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 an outward positive differential pressure exists across the secondary containment boundary. The secondary containment can experience a positive pressure transient following a postulated loss-of-coolant accident 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. In this regard, a "positive" pressure is defined as any pressure greater than -0.063 kPa [-0.25 in. w.g. (water gauge)] , to account for wind loads and the 73 uncertainty in the pressure measurements. Whenever the pressure in the secondary containment volume exceeds -0.063 kPa (-0.25 in. w.g.) , the leakage-prevention function of the secondary 74 containment is assumed to be negated. Since leakage from the secondary containment during positive pressure periods cannot be determined, the conservative assumption is made that, all 75 primary containment leakage is released directly to the environment during these time periods. Therefore, it becomes necessary to determine the time periods during which these threshold conditions exist. 6.2.3-13 DRAFT Rev. 3 - April 1996 The existence and duration of periods of positive pressure within the secondary containment should be based on analyses of the secondary containment pressure response to postulated loss-of-coolant accidents within the primary