Document: NUREG-0800
Document ID: 22c713a3-851c-4195-8d52-e7a90bcbeed0
Document Type: srp
Title: LEAK-BEFORE-BREAK EVALUATION PROCEDURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600396.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.6.3
CFR Part: 
CFR Title: 

Content:
s stability analysis or limit load analysis based on subparagraph 11(C)(vi) below, determine the critical crack size for the postulated throughwall crack using loads from the normal plus safe shutdown earthquake (SSE). Determine the crack size margin by comparing the selected leakage crack size to the critical crack size. Demonstrate that there is a margin of 2 between the leakage crack size and critical crack size. The same load combination method selected in subparagraph 11(C)(v) below must be used to determine the critical crack size. (v) Calculate the margin on the flaw size in terms of applied loads by a crack stability analysis. Demonstrate that the size of leaking cracks will not become unstable if 1.4 times the normal plus Safe Shutdown Earthquake (SSE) loads are applied. Demonstrate that the crack growth is stable and the final crack size is limited such that a double-ended pipe break will not occur. The 1.4 margin should be reduced to 1.0 if the deadweight, thermal expansion, pressure, SSE (inertial), and seismic anchor motion (SAM) loads are combined based on individual absolute values as follows: Combined Deadweight thermal Pressure SSE SAM F = I F I + l F l + I F l + I F I + I F I i Combined i Deadweight i thermal i Pressure i ( M ) = I ( M ) I + l ( M ) l + I ( M ) l + I ( M ) SSE I i SAM + I ( M ) I ____________________________________ Combined 1 Combined 2 Combined 3 Combined ( M ) = / ( M ) + ( M ) + ( M ) 2 2 2 i where F denotes the axial force, M denotes the i-th component of moment (i = 1, 2, 3), M denotes the total moment, and the subscripts denote the loads. An evaluation of seismic anchor motion loads at SSE conditions may be omitted when these are shown to be small at operating basis earthquake (OBE) conditions. (vi) There are certain limitations that currently preclude generic use of limit load analyses to evaluate LBB conditions for eliminating pipe restraints. However, a modified limit-load analysis can be used for austenitic steel piping