Document: NRC Regulatory Guide
Document ID: 7bdfde6b-2c09-49db-8a3f-863eab24747e
Document Type: regulatory_guide
Title: Control of Combustible Gas Concentrations in Containment + HISTORY - HISTORY 08/2002 – DG-1117 , Proposed Revision 3 Prior to the issuance of DG-1117, RG 1.7 was entitled "Control of Combustible Gas Concentrations in Containment Following a Loss-of-Coolant Accident," to reflect its narrower original scope
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0222/ML022210067.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.7
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CFR Title: 

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require the equipment for monitoring oxygen to be functional, reliable, and capable of continuously measuring the concentration of oxygen in the containment atmosphere following a beyond design-basis accident for combustible gas control and accident management, including emergency planning. Safety-related oxygen monitoring systems installed and approved by the NRC prior to the effective date 6 of the rule are sufficient to meet this criterion. Non-safety-related oxygen monitors would also meet these criteria if they meet the Category 2 design and qualification criteria of Regulatory Guide 1.97 (Ref. 8) for monitors designated for indicating system operating status. 3. ATMOSPHERE MIXING SYSTEMS The Proposed Section 50.44 would require that all containments have a capability for ensuring a mixed atmosphere. This capability may be provided by an active, passive, or combination system. Active systems may consist of a fan, a fan cooler, or containment spray. For passive or combination systems that use convective mixing to mix the combustible gases, the containment internal structures should have design features that promote the free circulation of the atmosphere. All containment types should have an analysis of the effectiveness of the method used for providing a mixed atmosphere. This analysis should demonstrate that combustible gases will not accumulate within a compartment or cubicle to form a combustible or detonable mixture that could cause loss of containment integrity. Atmosphere mixing systems prevent local accumulation of combustible or detonable gases that could threaten containment integrity or equipment operating in a local compartment. Active systems installed to mitigate this threat should be reliable, redundant, single-failure proof, able to be tested and inspected, and remain operable with a loss of onsite or offsite power. The NRC staff considers atmosphere mixing systems installed and approved by the NRC as of the effective date of the rule to be