Document: NRC Regulatory Guide
Document ID: ceaeb6d7-d85a-46d3-a1b6-70059a498965
Document Type: regulatory_guide
Title: 12/2001 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0131/ML013100014.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.78
CFR Part: 
CFR Title: 

Content:
HAZARDOUS CHEMICALS THAT REQUIRE CONSIDERATION IN CONTROL ROOM EVALUATIONS (FOR A 50 mg/m3 TOXICITY LIMIT AND STABLE METEOROLOGICAL CONDITIONS) Distance From Control Room (miles)a Weight (1000 lb) Air Exchange Rate 0.015 per hour Air Exchange Rate 0.06 per hour Air Exchange Rate 1.2 per hour 0.3 to 0.5 0.5 to 0.7 0.7 to 1.0 1 to 2 2 to 3 3 to 4 4 to 5 9 35 120 270 1300 3700 8800 2.25 8.75 30 67.5 325 925 2200 0.11 0.43 1.5 3.37 16.25 46.25 110 a All hazardous chemicals present in weights greater than 100 lb within 0.3 mile of the control room should be considered in a control room evaluation.    An air exchange rate of 0.015 (i.e., 0.015 of the control room air by volume is replaced by atmospheric ambient air in one hour) is considered representative of a “tight” control room that has very low-leakage construction features and automatic isolation capabilities. An air exchange rate of 0.06 per hour is considered representative of a control room that has normal leakage construction features and automatic isolation capabilities, whereas an air exchange rate of 1.2 per hour is considered representative of a control room with construction features that are not as efficient for leakage control and without automatic isolation capabilities. If the toxicity limit, air exchange rate, or meteorological conditions are different from the assumptions used in the table, simple calculations using the following procedures can be performed to determine the weights of hazardous chemicals that are to be considered 1.78-16 for the control room evaluation. Note that the weights in the table are based on EXTRAN calculations without the wake effect correction. Toxicity Limit The weights presented in the table are directly proportional to the toxicity limit. If a particular chemical has a toxicity limit of 500 mg/m3, the weights from the table (based on 50 mg/m3) should be