Document: NRC Regulatory Guide
Document ID: 5f799693-27fd-4e13-a5e1-4c02f393d90a
Document Type: regulatory_guide
Title: Best-Estimate Calculations of Emergency Core Cooling System Performance + HISTORY –HISTORY 04/2013 – Periodic Review of Revision 0 – Reviewed with issues identified for future consideration 03/1987 – Draft RS 701-4, Proposed Revision 0
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739584.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.157
CFR Part: 
CFR Title: 

Content:
U.S. NUCLEAR REGULATORY COMMISSION REGULATORY May 1989 GUIDE OFFICE OF NUCLEAR REGULATORY RESEARCH REGULATORY GUIDE 1.157 (Task RS 701-4) BEST-ESTIMATE CALCULATIONS OF EMERGENCY CORE COOLING SYSTEM PERFORMANCE A. INTRODUCTION Section 50.46, "Acceptance Criteria for Emer gency Core Cooling Systems for Light-Water Nuclear Power Reactors," of 10 CFR Part 50, "Domestic Li censing of Production and Utilization Facilities," re quires that light-water nuclear reactors fueled with uranium oxide pellets within cylindrical zircaloy clad ding be provided with emergency core cooling systems (ECCS) that are designed in such a way that their calculated core cooling performance after a postu lated loss-of-coolant accident (LOCA) conforms to certain criteria specified in paragraph 50.46(b). Para graph 50.46(b)(1) requires that the calculated maxi mum temperature of fuel element cladding not be ~ greater than 2200'F. In addition, paragraphs 50.46(b) (2) through (b) (5), which contain required limits for calculated maximum cladding oxidation and maximum hydrogen generation, require that calcu lated changes in core geometry remain amenable to cooling and that long-term decay heat removal be provided. On September 16, 1988, the NRC staff amended the requirements of § 50.46 and Appendix K, "ECCS Evaluation Models" (53 FR 35996), so that these regulations reflect the improved understand ing of ECCS performance during reactor transients that was obtained through the extensive research performed since the promulgation of the original requirements in January 1974. Paragraph 50.46(a)(1) now permits licensees or applicants to USNRC REGUIATORY GUIDES Regulatory Guides are Issued to describe and make available to the pub lic methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate techniques used by the staff in evaluating specific problems or postulated accidents, or to pro vide guidance to applicants. Regulatory Guides are not