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:
ontributors to the overall calculational uncertainty should also be considered in the uncertainty analysis. 4.3.1 Initial and Boundary Conditions and Equipment Availability When a plant input model is prepared, certain relationships describing the plant boundary and initial conditions and the availability and performance of equipment are defined. These include factors such as initial power level, pump performance, valve activa tion times, and control systems functioning. Uncer tainties associated with the boundary and initial con ditions and the characterization and performance of equipment should be accounted for in the uncertainty evaluation. It is also acceptable to limit the variables 1.157-13 to be considered by setting their values to conserva tive bounds. 4.3.2 Fuel Behavior Variability of the results of plant transient calcu lations can result from uncertainties associated with fuel behavior, which are not included in the compari sons of code results with integral experiments since most integral tests use electrically heated rods. This uncertainty includes many effects such as fuel con ductivity, gap width, gap conductivity, and peaking factors. These uncertainties should be quantified and used in the determination of the overall calculational uncertainty. 4.3.3 Other Variables There may be individual models within the best estimate code whose effect may not have been evalu ated by the comparison to the integral systems data. For example, since most integral systems experiments use electrically heated rods, uncertainties associated with the prediction of core decay heat and cladding metal/water reaction have not been evaluated. In ad dition, to demonstrate the overall adequacy of the predictive ability of the best-estimate code, it may be necessary to use empirically arrived at break discharge coefficients to obtain a reasonable break flow. The uncertainties in the individual models that have not been evaluated by comparison to integral systems data should