Document: NUREG-0800
Document ID: 1c401e6c-8c2d-47df-b05f-2978939cbd15
Document Type: srp
Title: CONTROL ROOM HABITABILITY SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550069.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.4
CFR Part: 
CFR Title: 

Content:
ethod (i) or (ii) should be used in the case of a radiological release, provided GDC 19 can be satisfied. A substantial time delay should be assumed where manual isolation is assumed, e.g., 20 minutes for the purposes of dose calculations. iv. Dual air inlets for the emergency zone. Several plants have utilized this concept. The viability of the dual inlet concept depends upon whether or not the placement of the inlets ensures that one inlet will always be free from contamination. The assurance of a contamination free inlet depends in part upon building wake effects, terrain, and the possibility of wind stagnation or reversal. For example, in a situation where the inlets are located at the extreme edges of the plant structures (e.g., one on the north side and one on the south side), it is possible under certain low probability conditions for both inlets to be contaminated from the same point source. SRP Section 2.3.4 presents the position for dealing with the evaluation of the atmospheric dispersion (X/Q values) for dual inlet systems. Because damage to the ducting might seriously affect the system capability to protect the operators, the ducting should be seismic Category I and should be protected against tornado missiles. In addition, 6.4-14 Revision 3 - March 2007 the number and placement of dampers should be such as to ensure both flow and isolation in each inlet assuming one single active component-failure (see Appendix A for information on the damper repair alternative). The location of the intakes with respect to the plant security fence should also be reviewed. Evaluation of the design options described above depends on the physical characteristics of the site as well as the plant design and, thus, can be finalized only at the COL stage of review. v. Bottled air supply for a limited time. In some plant designs, the containment pressure is reduced below atmospheric within 1 hour after a DBA. This generally ensures that, after 1 hour, significant radioactive