Document: NUREG-0800
Document ID: 28c03fd2-3542-41ec-bfd7-5df2087c4ee6
Document Type: srp
Title: FUEL SYSTEM DESIGN
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070407.pdf
Revision Date: 2023-06
Chapter: 4
Section ID: 4.2
CFR Part: 
CFR Title: 

Content:
res. (1) The uniform strain of the cladding should not exceed 1%. In this context, uniform strain (elastic and inelastic) is defined as transient-induced deformation with gage lengths corresponding to cladding dimensions; steady-state creepdown and irradiation growth are excluded. Although observing this strain limit may preclude some PCI failures, it will not preclude the corrosion-assisted failures that occur at low strains, nor will it preclude highly localized overstrain failures. (2) Fuel melting should be avoided. The large volume increase associated with melting may cause a pellet with a molten center to exert a stress on the cladding. Such a PCI is avoided by avoiding fuel melting. Note that this same criterion was invoked in paragraph (e) to ensure that overheating of the cladding would not occur. (h) Bursting: To meet the requirements of 10 CFR 50.46 as it relates to ECCS performance evaluation, a calculation of the swelling and rupture of the cladding resulting from the temperature distribution in the cladding and from pressure differences between the inside and outside of the cladding should be included in the ECCS evaluation model. Regulatory Guide 1.157 provides guidelines for performing a realistic (i.e., best-estimate) model to calculate the degree of cladding swelling and DRAFT Rev. 3 - April 1996 4.2-8 rupture. Alternatively, Appendix K of 10 CFR 50 presents acceptable features of an evaluation model for predicting the degree of swelling and rupture in the Zircaloy cladding. To meet the requirements of Appendix K of 10 CFR Part 50 (Ref. 9) as it relates to the incidence of rupture during a LOCA, a rupture temperature correlation must be used in the LOCA ECCS analysis. Zircaloy cladding will burst (rupture) under certain combinations of temperature, heating rate, and differential pressure. Although fuel suppliers may use different rupture-temperature 39 vs differential-pressure curves, an acceptable curve should be similar to the one described in