Document: NUREG-0800
Document ID: 9f13abda-ee55-4fa1-8276-db55ac2094ef
Document Type: srp
Title: CONTROL ROOM HABITABILITY SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070449.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.4
CFR Part: 
CFR Title: 

Content:
) 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. (4) 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 assuresensures 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. Reference 9 presents the position for dealing with the DRAFT Rev. 3 - April 1996 6.4-14 evaluation of the atmospheric dispersion (X/Q values) for dual inlet systems. With dual inlets placed on plant structures on opposite sides of potential radiation release points (e.g., containment building) and capable of functioning with an assumed single active failure in the inlet isolation system, the following considerations may be applied to the evaluation of the control room X/Q's: (i) Dual inlet designs without manual or automatic selection control - equation (6) of Reference 9 may be used with respect to the least favorable inlet location to estimate X/Q's. The estimated values can be reduced by a factor of 2 to account for dilution effects associated with a dual inlet configuration. This is based upon the dilution derived from drawing in equal amounts of clean and contaminated air through two open inlets. (ii) Dual inlet designs with manual selection control - equation (6) of Reference 9 may be used with respect to the more favorable inlet location to estimate the X/Q's. The