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:
radiological consequences from the MHA LOCA. The following assumptions are acceptable for evaluating the consequences of leakage from ESF components outside the primary containment for BWRs and PWRs: A-4.1 With the exception of noble gases, all fission products released from the fuel to the containment (as defined in Tables 1 and 2 of this guide) should be assumed to instantaneously and homogeneously mix in the primary containment sump water (in PWRs) or suppression pool (in BWRs) at the time of release from the core. In lieu of this deterministic approach, suitably conservative mechanistic models for the transport of airborne activity in containment to the sump water may be used. Note that many of the parameters that make spray and deposition models DG-1389, Appendix A, Page A-5 conservative in estimating containment airborne leakage are nonconservative in estimating the buildup of sump activity. A-4.2 The leakage should be taken as 2 times1 the sum of the simultaneous leakage from all components in the ESF recirculation systems above which the technical specifications, or licensee commitments to Item III.D.1.1 of NUREG-0737, “Clarification of TMI Action Plan Requirements,” issued November 1980 (Ref. A-9), would require declaring such systems inoperable. Design leakage from any systems not included in technical specifications that transport primary coolant sources outside of containment should be added to the total leakage. The applicant should justify the design leakage used. The leakage should be assumed to start at the earliest time the recirculation flow occurs in these systems and end at the latest time the releases from these systems are terminated and should account for the ESF leakage at accident conditions. Consideration should also be given to design leakage through valves isolating ESF recirculation systems from tanks vented to the atmosphere (e.g., emergency core cooling system pump miniflow return to the refueling water storage tank). A-4.3 With