United States Nuclear Regulatory Commission - Protecting People and the Environment

General Information or Other Event Number: 37703
REP ORG: FIRSTENERGY NUCLEAR OPERATING CO. NOTIFICATION DATE: 01/31/2001
LICENSEE: INGERSOLL-DRESSER PUMP COMPANY NOTIFICATION TIME: 13:09[EST]
CITY: SHIPPINGPORT REGION: 1 EVENT DATE: 11/27/2000
COUNTY: STATE: PA EVENT TIME: 12:00[EST]
LICENSE#: AGREEMENT: N LAST UPDATE DATE: 01/31/2001
DOCKET: PERSON ORGANIZATION
DANIEL HOLODY R1
VERN HODGE NRR
NRC NOTIFIED BY: L.W. MYERS
HQ OPS OFFICER: DOUG WEAVER
EMERGENCY CLASS: N/A
10 CFR SECTION:
CCCC 21.21 UNSPECIFIED PARAGRAPH

EVENT TEXT

PART 21 REPORT ON CAP SCREW FAILURE USED IN AN AUXILIARY FEEDWATER PUMP AT THE BEAVER VALLEY POWER STATION UNIT ONE

One of the four cap screws on the collar of the hydraulic balancing drum of the steam-driven Auxiliary Feedwater pump (AFP) 1FW-P-2 failed. The head of the screw broke off and became lodged in the area between the stuffing box extension and the balancing drum collar, preventing 1FW-P-2 from starting on 11/27/00. The root cause of the cap screw failure was material defect. Final metallurgical analysis revealed that the failure was due to intergranular failure. The defects noted in the fastener surface were attributed to the original manufacture of the cap screw. The probable cause of the failure was the propagation of manufacturing cracks under static preload, which caused tensile stress of approximately 88% of the yield stress of the cap screw. Hydrogen absorption and diffusion into regions of high stress caused propagation of the cracks. The failure was a time delayed process.

The material defect led to the failure of one AFP cap screw which prevented the AFP from starting. Failure of one or more Auxiliary Feedwater Pumps to start when required, would result in a major degradation of essential safety related equipment, and the required Auxiliary Feedwater System may not have been able to perform its safety related function, which would constitute a substantial safety hazard.

Though not attributed as part of root cause for the one cap screw failure, two related noteworthy non-compliant issues were identified with the four cap screws found on the 1FW-P-2 AFP collar. An emission spectrograph test run on a cap screw showed a chromium content of 0.148% (indicating the screw was carbon steel). The vendor Material Release for 1FW-P-2 (MR 912004) shows that the cap screws are 410 stainless steel that should have contained 12% chromium. FENOC is not able to conclude whether operating with carbon steel cap screws (in place of the required stainless steel) could have caused the AFP to fail.

Though not attributed as part of root cause for the one cap screw failure, two related noteworthy non-compliant issues were identified with the four cap screws found on the 1FW-P-2 AFP collar. An emission spectrograph test run on a cap screw showed a chromium content of 0.148% (indicating the screw was carbon steel). The vendor Material Release for 1FW-P-2 (MR 912004) shows that the cap screws are 410 stainless steel that should have contained 12% chromium. FENOC is not able to conclude whether operating with carbon steel cap screws (in place of the required stainless steel) could have caused the AFP to fail.

THE LICENSEE ALSO SUBMITTED THE FOLLOWING INFORMATION RELATED TO THE REPLACEMENT SCREWS THAT WERE ORDERED FROM FLOWSERVE CORPORATION AND MANUFACTURED BY U.S. BOLT.

The specified maximum hardness value was exceeded for 16 of 20 cap screws supplied for use on a balancing drum located on the Auxiliary Feedwater Pump (AFP) shaft. Exceeding the hardness limit makes these cap screws susceptible to stress corrosion cracking. Therefore, the defect, if gone undetected and installed, could have caused these cap screws to fail during their operating life. A failed cap screw could jam and prevent a standby AFP from starting. Failure of one or more AFPs to start when required, would result in a major degradation of essential safety related equipment, and the required Auxiliary Feedwater System may not have been able to perform its safety related function, which would constitute a significant safety hazard. As such, the defect is reportable pursuant to 10CFR Part 21 requirements.

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