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:
oads, 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 described in Subsection II.1 of this appendix, and the resulting loads should be added by the square-root- of-sum-of-squares method. These combined loads should be compared with the component strengths described in Subsection III according to the acceptance criteria in Subsection IV. 4.2-31 Revision 3 - March 2007 III. DETERMINATION OF STRENGTH 1. Grids All modes of loading (e.g., in-grid and through-grid loadings) should be considered, and the vendor’s laboratory grid strength tests should represent the most damaging mode. Test procedures and results should be reviewed to assure that the appropriate failure mode is being predicted. The review should also confirm that (1) the testing impact velocities correspond to expected fuel assembly velocities and (2) the crushing load P(crit) has been suitably selected from the load-versus-deflection curves. Because of the potential for different test rigs to introduce measurement variations, the review of the test procedure will evaluate the grid strength test equipment. The consequences of grid deformation are small. Gross deformation of grids in many PWR assemblies would be needed to interfere with control rod insertion during an SSE (i.e., buckling of a few isolated grids could not displace guide tubes significantly from their proper location), and grid deformation (without channel deflection) would not affect control blade insertion in a BWR. In a LOCA, gross deformation of the hot channel in either a PWR or a BWR would result in only small increases in peak cladding temperature. Therefore, average values are appropriate, and the allowable crushing load P(crit) should be the 95- percent confidence level on the true mean as taken from the distribution of measurements on unirradiated production grids at (or corrected to)