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:
rmine whether the proposed changes are consistent with the principle that adequate defense in depth is maintained to compensate for uncertainties in accident progression and analysis data. Consistency with the defense in depth philosophy is maintained if system redundancy, independence, and diversity are preserved commensurate with the expected accident frequency, consequences of challenges to the system, and uncertainties. For facilities to which the GDC (see Appendix A to 10 CFR Part 50) apply, compliance with these criteria is required. Modifications proposed for the facility generally should not create a need for compensatory programmatic activities (e.g., reliance on manual operator actions, use of potassium iodide as a prophylactic drug) or self-contained breathing apparatus or post-accident entries into vital areas to maintain required equipment qualifications. DG-1389, Page 9 Licensees should evaluate proposed modifications that seek to downgrade or remove required engineered safeguards equipment to confirm that the modification does not invalidate assumptions made in facility PRAs and does not adversely impact the facility’s severe accident management program. 1.1.3 Integrity of Facility Design Basis The DBA source term used for dose consequence analyses is a fundamental assumption and the basis for much of the facility design. Additionally, many aspects of an operating reactor facility are derived from the radiological design analyses that incorporated the TID-14844 accident source term. Although a complete reassessment of all facility radiological analyses would be desirable, the NRC staff determined that recalculation of all design analyses for operating reactors would generally not be necessary. Regulatory Position 1.3 of this guide provides guidance on which analyses should be updated as part of the AST implementation submittal and which may need to be updated in the future as additional modifications are made. This approach for operating reactors