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:
ies are the 15.0.2-8 March 2007 equation of state, the stress tensor, and the heat flux. In order to be able to solve the field equations the unknown quantities must be expressed in terms of the known quantities from the field equations. The equations that relate the unknown quantities to the known quantities are constitutive or closure relationships. These equations are often models or approximations that are much more restrictive in their range of validity than the set of field equations that they are used with. For example, using Newton’s law of cooling as a closure relationship for heat flux from a heat structure to a fluid will limit the application to model situations where radiation heat transfer is not significant even though the field equations are valid. The reviewer must therefore ensure that the field equations of the evaluation model are adequate to describe the set of physical phenomena that occur in the accident and ensure that the closure relationships are valid over the full range of conditions encountered during the accident. The modeling must be consistent with the results of the accident scenario identification process in that there must be models for all important phenomena in the accident scenario. Components and physical phenomena that are identified as being important in the accident scenario identification process must be modeled with a high degree of fidelity. Phenomena of lower importance may be represented by less accurate models. The reviewers should determine if the simplifying assumptions and assumptions used in the averaging procedure are valid for the accident scenario under consideration. Simplifying assumptions and averaging are often applied to detailed physical and mathematical modeling to obtain simplified mathematical models that 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