Document: NUREG-0800
Document ID: 643ab154-682e-480f-a57b-a5fd7390a34e
Document Type: srp
Title: REVIEW OF TRANSIENT AND ACCIDENT ANALYSIS METHODS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0535/ML053550265.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.0.2
CFR Part: 
CFR Title: 

Content:
lexity of the event The level of effort involved in applying the development process should be commensurate with the complexity of the evaluation model. At first glance the review process may seem too burdensome to apply to simple events. However, application of the review process to a simple evaluation models will automatically result in a simplified review process. In simple events the number of key physical phenomena should also be small and the code assessment only needs to cover the important phenomena even though the underlying general purpose transient analysis computer program may have models that cover a much wider range of conditions. An example of this is the system evaluation of a PWR pump trip analysis in which the important phenomena may be limited to a few quantities such as single-phase liquid wall drag and heat transfer, and pump inertia. In this case, very little assessment would need to be performed and there may be adequate full scale plant data for the code assessment so there would be no need for a scaling analysis. The other extreme is an evaluation model for a large-break loss-of-coolant accident where the physical phenomena and the mathematical models are complex and cover a wide range of conditions. An extensive code development process and assessment and an extensive review process would be required in this case. 15.0.2-16 Initial Issuance - December 2005 6.3 Degree of conservatism The review process may be simplified if there is a large degree off conservatism in the evaluation model. The intended results of an analysis can be conservative due to a combination of code input and modeling assumptions. The amount of assessment required for a change to an evaluation model may be reduced significantly if the documented degree of conservatism is large or if the new model can be shown to give more conservative results than the previous model. However, conservatism in just one part of the evaluation model such as a heat transfer correlation can