Document: NUREG-0800
Document ID: 2bca792d-0e88-4e2d-b437-be572ed57a48
Document Type: srp
Title: REVIEW OF TRANSIENT AND ACCIDENT ANALYSIS METHODS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0708/ML070820123.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.0.2
CFR Part: 
CFR Title: 

Content:
hat can be solved more readily and with less computational effort. Examples of common simplifications are incompressible flow models, one- dimensional flow models, common two-phase flow models such as the homogeneous equilibrium model (HEM), drift flux, and the two-fluid model, and simplified reactor kinetics models such as point kinetics or one-dimensional kinetics. Even models commonly thought of as detailed models usually contain simplifying assumptions and averaging procedures applied to first-principles models. Reviewers should confirm that justifications are provided for all simplifications, assumptions, and averaging. The reviewers should confirm that the level of detail in the model is equivalent to or greater than the level of detail required to specify the answer to the problem of interest. For example, a one-dimensional flow model can not provide information about the velocity profile in the vicinity of a pipe bend or the degree of thermal stratification in a horizontal pipe. A detailed, three-dimensional flow model would be needed to provide this type of information. The reviewers should confirm that the equations and derivations are correct. There must be sufficient text to adequately describe the derivation, including all assumptions and equations. The derivations must be sufficiently detailed to allow the reviewers to understand the logical progression of steps involved in the derivation. Simplifying assumptions must have a technical justification and a range of validity associated with them. Models that are typically used in nuclear reactor analysis are highly phenomenological and/or empirical in nature. They are either proposed using 15.0.2-9 March 2007 physical or engineering judgment based on observations of experimental data or derived using averaging procedures applied to detailed first-principle models. These models often represent processes that occur on length and time scales that are too small to be resolved in the computation or processes