Document: NUREG-0800
Document ID: 3ea2f0ac-4d7e-464a-b1c4-390c3970f642
Document Type: srp
Title: provides specific thermal-hydraulic criteria.  The available radioactive fission product
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070740002.pdf
Revision Date: 2023-06
Chapter: 4
Section ID: 4.4
CFR Part: 
CFR Title: 

Content:
t. 3. Uncertainty Allowances The fuel assembly structural models and analytical methods are likely to be conservative; input parameters are also conservative. However, to ensure that the fuel assembly analysis does not introduce any nonconservatisms, two precautions should be taken—(1) if it is not explicitly evaluated, impact loads from the PWR LOCA analysis should be increased by about 30 percent to account for a pressure pulse, which is associated with steam flashing that affects only the PWR fuel assembly analysis and (2) conservative margin should be added if any part of the analysis (PWR or BWR) exhibits pronounced sensitivity to input variations. Variations in resultant loads should be determined for positive variations in input amplitude and frequency of 10 percent; variations in amplitude and frequency should be made separately, not simultaneously. A factor should be developed for resultant load magnitude variations of more than 15 percent. For example, if +10-percent variations in input magnitude or frequency produce a maximum resultant increase of 35 percent, the sensitivity factor would be 1.2. Since resonances and pronounced sensitivities may be plant dependent, the sensitivity analysis should be performed on a plant-by-plant basis until the reviewer is confident that further sensitivity analyses are unnecessary or it is otherwise demonstrated that the analyses performed are bounding. 4. Audit The reviewer should perform independent audit calculations for a typical full- sized core to verify that the overall structural representation is adequate. An independent audit code (NUREG/CR-1019) should be used for this audit during the generic review of the analytical methods. 5. Combination of Loads To meet the requirements of GDC 2, as it relates to combining loads, an appropriate combination of loads from natural phenomena and accident conditions must be made. Loads on fuel assembly components should be calculated for each input (i.e., seismic and LOCA) as