ML20138E325
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a UNITED STATES
.j NUCLEAR REGULATORY COMMISSION E
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j WASHINGTON, D.C. 20565 4 001 4
MAR 31 W MEMORANDUM FOR: Herbert N. Berkow, Director Project Directorate II-2
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Division of Reactor Projects I/II
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FROM:
Jack R. Strosnider, Chief Materials and r.hemical Engineering Branch Division of Engineering
SUBJECT:
ST LUCIE UNIT 2: REVIEW OF FLAW EVALUATION FOR INSTRUMENT N0ZZLE PENETRATION IN PRESSURIZER t
On March 28, 1994, pursuant to 10 CFR 50.55a(a)(3), Florida Power and Light Company submitted for staff approval a~ fracture mechanics analysis of the flaw in "C" instrument nozzle in the St. Lucie Unit 2 pressurizer.
During the 1994 refueling outage, the licensee found that boric acid had leaked from the "C" instrument nozzle attached to the pressurizer upper head.
Subsequent. nondestructive examination detected indications in two other similar instrument nozzles. The indications were located in the attachment welds inside of the pressurizer head. The outside diameter of the nozzle is 1.33 inches with a thickness of 0.26 inch. The thickness of the pressurizer
l head is 3.875 inches. The nozzle and pressurizer are made of Inconel 690 and SA-533 Grade B Class I steel plate, respectively.
I The fracture mechanics analysis assumed an initial " corner" crack of 1.0 inch depth in the attachment weld in the inside surface of the pressurizer head.
The assumed depth was greater than the radial extent of the indications detected in the J-groove weld. The crack was assumed to completely penetrate the weld between the nozzle and base metal.
It bounded the observed indications in all four nozzles attachment welds and in the bore region of the l
l nozzles.
I' The analysis was based on the flaw evaluation procedure in IWB-3600 and
{l Appendix A of ASME Section XI. The applied stress intensity-factors, K, were i
calculated and compared to the allowable fracture toughness, K, of the base metal for norwl operating conditions. The acceptance criteriE for the normal i
operating corAitions are limiting when comparing to that of emergency and faulted conditions. Crack growth was calculated based on fatigue crack growth curves for ferritic materials in Appendix A of ASME Section XI. The crack i
growth calculation used 500 cycles of startup and shutdown transients, which were'specified in the design basis for the life of the plant, even though the actual number of cycles were much less than 500.
The analysis showed that the critical flaw depth is 3.1 inches from the inside corner of the nozzle penetration.
It will take more than 6000 cycles of b
startups and shutdowns for an initial crack depth of 1.0 inch to grow to the
.1 critical flaw depth. The crack will not grow to more than 1.035 inches in 4
depth by the end of next operating cycle. The analysis is conservatively i
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l limited to one operating cycle, i
The staff determined that the analysis followed the flaw evaluation procedure -
in IWB-3600 and Appendix A of ASME Section XI. The results satisfied the acceptance criteria of IWB-3600 of ASME Section XI for the applied load from normal operating conditions. Based on its review of the licensee's fracture mechanics analysis, the staff concludes that the structural integrity of the instrument nozzle at the pressurizer satisfies the safety margin of ASME Section XI for one fuel cycle.
In addition to the fracture mechanics analysis, the licensee is repairing all four nozzles with an Inconel 690 pad welded to the nozzle at outside surface 1
of the pressurizer head to prevent further leakage.
The nozzle inside of the penetration will be severed thereby making the Inconel 690 welded pad the new pressure boundary.
r This completes our effort for TAC M89C90.
ORIGINAL SIGNED BY:
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EDMUND J.SULLIVAN fm Jack R. Strosnider, Chief Materials and Chemical Engineering Branch Division of Engineering cc: B. D. Liaw J. Norris DISTRIBUTION Central Files EMCB RF/PF KWichman JTsao RHermann WKoo D
B SC:E BC:EMCB JTsao:jt KWichman yJStrosnider J $/ /94 J /3//94 3/3l /94 Official Record Copy Document Name:g:\\tsao\\stlucie. pre
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