Document: NRC Regulatory Guide
Document ID: da2e0703-3488-44b0-b6d0-089aac7cae3d
Document Type: regulatory_guide
Title: Format and Content of Plant-Specific Pressurized Thermal Shock Safety Analysis Reports for Pressurized Water Reactors
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740028.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.154
CFR Part: 
CFR Title: 

Content:
sentatioh of each variable as a distribution w i t h 5th and 95th percentiles as previously identified. The shapes of the distributions selected should be discussed. 2. Select a random value from each distribution - A random sampling code should be used to sample from each of the distributions. 3. Calculate a through-wall crack frequency estimate based on values obtained in the previous step - In this step, the through-wall crack frequency i s obtained based on the randomly selected variables. This requires under- standing the form of the relationship between each input variable and through- wall crack frequencies. For some variables such as initiating event and branch frequencies and flaw density, this is simple since the through-wall crack frequency i s directly proportional to the value of these parameters over the range of variable val ues considered. Other vari abl es such as temperature and pressure may require the development of an appropriate relationship. In such cases i n which the effect of a variable change may be dependent on the value of another variable, response-surface techniques may be used to estimate important interaction effects. 4. Summarize the resulting estimates and approximate frequency distribu- tion - Steps 2 and 3 are repeated until a statistically valid number of t r i a l s have been- performed. A distribution of through-wall crack frequencies i s then produced from the results of the trials. The 95th and 5th percentiles and the mean (expected value) of this distribution should be identified and discussed. 7.2.2 Model i ng Uncertai nties (Bi ases) During the process of performing the PTS analysis, the analyst will make simplifying assumptions i n order to make the analysis tractable. Such assump- tions include decisions on thermal-hydraulic models, fracture mechanics models, grouping of sequences both for thermal-hydraulic analysis and fracture mechanics analysis, nodalization i n the thermal-hydraulic models, etc. These assumptions