Document: NUREG-0800
Document ID: 2717fe7f-71fd-4f1e-bd08-7685b24763ba
Document Type: srp
Title: Standard Review Plans are prepared for the guidance of the Office of Nuclear Reactor Regulation staff responsible for th
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0301/ML030160606.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15
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n 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 6.3 Degree of conservatism The review process may be simplified if there is a large degree of 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 not be used to justify conservatism in the evaluation model as a whole because other parts of the model may be non-conservative and cause the overall model to be non- conservative. The degree of conservatism in the overall evaluation model must be quantified and documented for the particular application in order to justify a reduction in assessment requirements using this