Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
ef. 20) and the U.S. Department of Energy’s atmospheric dispersion model “SLAB” code (Ref. 21) for denser-than-air releases codes for dense gas transport phenomena. 3.4 Control Room Air Flow The evaluation should consider the air flows for infiltration, makeup, and recirculation for both normal and accident conditions. It should also consider the volume of the CR and all other rooms, including the ventilation systems, that share the same ventilating air during both normal and accident conditions. The CR envelope should be constructed and equipped with a low-leakage ventilation system to stop or reduce inleakage. For example, low-leakage dampers, low-leakage shut-off valves and other low- leakage Heating, Ventilation and Air Conditioning (HVAC) components should be installed on the upstream side of recirculation fans or at locations where negative pressure exists (e.g., fan shaft seals). The inleakage characteristics of the CR envelope during a hazardous chemical challenge should be determined by testing. A comprehensive test of the CR ventilation systems will identify the total inleakage associated within the CR envelope but will not necessary identify all inleakage sources. An effective and NRC staff-accepted method to test CR envelope inleakage is American Society of Testing and Materials (ASTM) Standard E741, “Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution” (Ref. 22). Further, if credit has been taken in the evaluation for the removal of hazardous chemicals by filtration, adsorption, or other means, the applicant or licensee should provide a technical basis for the dynamic removal capability of the removal system considered. 4. PROTECTION MEASURES For adequate safety and protection of the CR operators against the types of accidental releases discussed in Section 3.2 above, the plant design should include features to: (1) provide capability to detect such releases; (2) isolate the CR if there is a