Document: NUREG-0800
Document ID: 91a12934-f0d9-4573-ad3b-553ab75dabc0
Document Type: srp
Title: FISSION PRODUCT CONTROL SYSTEMS AND STRUCTURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600408.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.5.3
CFR Part: 
CFR Title: 

Content:
auxiliary systems. The exhaust system may also treat the auxiliary building regions that are part of the secondary containment, but if these regions are maintained at a negative pressure during normal operation, it is most likely done with the auxiliary building ventilation system. The ability of the vacuum exhaust and auxiliary building ventilation systems falls under the purview of the organization responsible for the review of reactor accident consequence assessment, specifically design basis containment and ventilation performance. The systems' ability to maintain a negative pressure of sufficient margin under varying wind conditions and operational modes prior to a design basis accident is verified by the same organization. The reviewer also verifies that the systems have the capability to maintain negative pressure following a design basis accident. If an adequate negative differential pressure (0.6 cm, or 0.25 in, water gauge) is achieved within 60 seconds from the time the accident, then no positive pressure time period need be assumed in the dose model. All positive pressure periods at any time in the secondary containment regions are treated as direct outleakage periods following an accident, and no credit is given for filters or recirculation systems. The organization responsible for the review of reactor accident consequence assessment (specifically design basis containment and ventilation performance) verifies the positive pressure periods. The large reactor buildings around older BWR containments are usually maintained at a negative pressure during normal operation, and the dose model used for these cases has not assumed any positive pressure period. B. The exhaust systems used to maintain the negative pressure differential following the accident should be sized to meet the negative pressure criterion for the inleakage rate and the conservatively calculated heat load for the regions 6.5.3-9 Revision 3 - March 2007 served by each rate, and analyses to