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:
he new material if they determine that there is nothing new that will invalidate the previous approval, including the range of applicability for the analysis method. Otherwise the entire model must be reviewed. For a new model that has not been previously reviewed, the reviewers initiate an evaluation of the entire analytical model. The reviewers should determine if the physical modeling described in the theory manual and contained in the mathematical models is adequate to calculate the physical phenomena influencing the accident scenario for which the code is used. A scenario will have a set of governing physical phenomena that drive the results of the calculation. The key physical phenomena, including constitutive equations needed for model closure, must be defined for the calculation being performed by the code. Physical phenomena that are important for one accident scenario may not be important for a different accident scenario. The key physical phenomena can also be specific to a particular plant design. The mathematical equations that comprise an evaluation model can be characterized as being either a field equation or as a constitutive or closure relationship. Field equations are a set of rigorously derived equations that contain no approximations other than the initial assumptions used in deriving the equations. The range of applicability of the field equations is limited only by the validity of the assumptions used in their derivation. An example of a set of field equations is the set of fluid transport equations for mass, momentum, and energy that are derived from macroscopic balances of these quantities. Although these equations are mathematically exact, the equations contain more unknown quantities than there are equations. Some of these unknown quantities 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