Document: NRC Regulatory Guide
Document ID: 4d46a966-d280-43da-9b03-8b0abe7b29ce
Document Type: regulatory_guide
Title: Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2120/ML21204A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.183
CFR Part: 
CFR Title: 

Content:
nsee’s most recent site-specific probabilistic seismic hazard is greater than 0.4g, the justification should include (1) discussion of seismic capacity and margin present in relevant SSCs, including the condenser, based on their design code(s) of record, (2) Individual Plant Examination for External Events insights described above, (3) walkdown(s) of the SSCs in the alternate pathway including the condenser, performed by knowledgeable licensee staff to ensure that items adversely affecting the seismic capacity of relevant SSCs (e.g., loose or missing anchorages and degraded pipe supports) are identified and corrected, and (4) confirmatory calculations for a sample of piping supports to verify that they provide acceptable flexibility at terminal ends of piping and major branch connections. The extent of the selected samples should be justified based on the plant-specific seismic hazard and quality assurance applied to design and fabrication. Details of the walkdown(s), including qualification of licensee staff performing them, should be retained in archival documentation. A-5.6 Aerosol deposition in horizontal volumes that meet Regulatory Positions A-5.4 or A-5.5 may be credited as described below.4 For BWR designs other than plants with Mark I, II, or III containment design, other models of aerosol deposition will be considered on a case-by-case basis. A-5.6.1 SAND 2008-6601 Model: Section 6.4 of Reference A-11 describes an acceptable model for estimating the aerosol deposition between closed MSIVs and downstream of the MSIVs. Table A-1 below provides the removal coefficients recommended by Reference A-11 and given in Table 6-1. Table A-1. BWR Main Steamline and Condenser Removal Coefficients (hr-1) Time (hr) Inboard Between MSIVs Outboard Condenser 0 - 10 0.0 1.8 1.0 0.015 10+ 0.0 1.0 0.7 0.012 A-5.6.2 Re-Evaluated AEB 98-03 with multi-group method: Aerosol deposition removal coefficients for the main steamline piping between the MSIVs and downstream of the MSIVs