United States Nuclear Regulatory Commission - Protecting People and the Environment

Sensitivity Studies of Failure of Steam Generator Tubes during Main Steam Line Break and Other Secondary Side Depressurization Events (NUREG/CR-6935)

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Publication Information

Manuscript Completed: December 2006
Date Published: May 2007

Prepared by:
S. Majumdar, K. Kanza, J. Oras, J. Franklin, and C. Vulyak, Jr.

Nuclear Energy Division
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439

E. Reichelt, NRC Project Manager

Prepared for:
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6588

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Abstract

This report summarizes sensitivity studies conducted on the failure of flawed steam generator tubes in a Westinghouse Model 51 steam generator (SG) during main steam line break (MSLB) and feed water line break (FWLB) events. The results of thermal hydraulic transient analysis of temperature and pressure pulse loading during the MSLB and FWLB events were obtained from a recent Nuclear Regulatory Commission (NRC) report. A simplified but conservative finite element model of the tube support plates (TSPs) and their supports and SG tubes was used to analyze the loads transferred to the SG tubes from the TSPs during the transients. Fracture mechanics analyses were conducted to determine the stability of postulated cracks in the SG tubes on the top of the tube sheet and the TSPs. The potential for crack growth during repeated application of the pressure pulse was explored. Tests on SG tubes subjected to bending load and internal pressure showed that the effect of bending on burst pressure is negligible for the type of bending-to-direct-axial-stress ratio that is expected during a MSLB.

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