Part 21 Report - 2003-001-00
Jeffrey T. Gasser Southern Nuclear
Vice President Operating Company. Inc.
40 Inverness Center Parkway
Post Office Box 1295
Birmingham, Alabama 35201
Fax 205.992.0403 SOUTHERN
Energy to Serve Your World
December 20, 2002 LCV-1640
Docket Nos. 50-425
U.S. Nuclear Regulatory Commission
ATTN: Document Control Desk
Washington, D.C. 20555
Ladies and Gentlemen:
VOGTLE ELECTRIC GENERATING PLANT
LICENSEE EVENT REPORT 2-2002-00l
UNSTAKED CAPSCREWS RENDERS RESDUAL
HEAT REMOVAL PUMP INOPERABLE
In accordance with the reqwrements of 10 CFR 50.73, Southern Nuclear Operating Company hereby submits a Vogtle Electric Generating Plant licensee event report for a condition that was discovered on October 22, 2002.
Please contact this office if you have any questions.
Jeffrey T. Gasser
Enclosure: LER 2-2002-00l
xc: Southern Nuclear Operating Company
Mr. G. R. Frederick
Mr. M. Sheibani
SNC Document Management
U.S. Nuclear Regulatorv Commission
Mr. L. A. Reyes, Regional Administrator
Mr. F. Rinaldi, Project Manager, NRR
Mr. J. Zeiler, Senior Resident Inspector, Vogtle
FOR NRC FORM 368 - SEE ATTACHED/LINKED PDF AT BOTTOM
On October 22,2002, while defueled, residual heat removal (RHR) pump A was started for dynamic fill and vent of the RHR system. Moments later, the pump tripped. An investigation determined that a back Casing ring capscrew had come loose and lodged between the impeller and the back casing ring. It was found that the pump was last operated on October 11,2002, when the unit was in Mode 6 (Refueling). It is believed that the Capscrew came loose and lodged between the impeller and the back Casing ring as the pump was being placed into standby status on October 11th. Because two pumps are required to be operable at certain times in Mode 6, this represented operation in a condition prohibited by the Technical Specifications. Because the other RHR pump was also found to have inadequately staked capscrews, this represented a condition that could have prevented the fulfillment of the safety function of a system needed to remove residual heat. This condition is also reportable per 10 CFR21.21 because similar back casing rings with inadequately staked capscrews were found in the warehouse.
The root cause of this event was determined to be the failure of the manufacturer to properly stake the back casing ring capscrews. The capscrews on the back Casing rings for both Unit 2 RHR pumps were properly staked prior to the pumps being returned to service and the Unit retuning to Mode 6.
A. REQUIREMENT FOR REPORT
This event is reportable per 10 CFR 50.73 (a)(2)(1)(B) because the unit was operated in a condition prohibited by the Technical Specifications (TS) for a period of6 hours and 31 niinutes. It is also reportable per 10 CFR 50.73 (a)(2)(v)(B) because a condition existed that could have prevented the fulfillment of the safety fimetion of a system needed to remove residual heat. Furthermore, this report is being made per the requirements of 10 CFR 21.21 because defective components were procured whose use could have led to the creation of a substantial safety hazard.
B. UNIT STATUS AT TIME OF EVENT
At the time of the discovery of this event, Unit 2 was deflieled at 0 percent of rated thermal power. Personnel were preparing for fill and vent of the residual heat removal (RHR) system. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C. DESCRIPTION OF EVENT
On October 22,2002, while deflieled, residual heat removal (RHR) pump A was started for dynamic fill and vent of the RHR system. Moments later, the pump tripped.
Personnel found that the pump shaft could not be hand turned. An investigation determined that a back casing ring capscrew had come loose and lodged between the impeller and the back casing ring.
It was found that the pump was last operated on October 11,2002, when the unit was in Mode 6 (Refueling). It is believed that the capserew came loose and lodged between the impeller and the back casing ring as the pump was being placed into standby status on October 11th.
D. CAUSE OF EVENT
The root cause of this event was determined to be the failure of the manufacturer to properly stake the back casing ring eapserews. Each eapscrew is torqued and staking performed as a redundant measure to hold the eapserews in place. Although staking had been performed for the back casing rings inspected, it was inadequate to prevent at least one of the capscrews from backing out of the casing ring after it had lost its torque and become loose.
RHR pump B was inspected and fowid to have a similar condition. Spare back casing rings in the warehouse were also inspected and found to have a similar condition of inadequately staked
E. ANALYSIS OF EVENT
From the period of time when RHR pump A was stopped on October 11,2002, at 1017 EST, until the reactor Cavity water level was raised to 23 feet above the vessel flange at 1648 EST, Unit 2 operated in a condition proln~ited by TS 3.9.6 because two RHR pumps were not maintained operable. However, the system safety fimction continued to be met because RHR pump B remained operable.
The spare back casing rings in the Warehouse were not placed into service with the inadequately staked capserews and did not ereate a substantial Safety hazard.
In addition, the improperly staked capserews on both RHR pumps represent a condition that could have prevented flilfiliment of a safety flinction of a system needed to remove residual heat. Discussions with pump vendor personnel determined that there are approximately 60 of these pumps in service in the nuclear industry, most with several years of service, and that this was the first failure of this type. Additionally, 15 of ihese pumps, including the 4 in Units 1 & 2, have undergone a coupling modification in recent years that replaced the back casing ring. However, it is not known if the back casing ring defect is limited to only those casing rings that were procured for the modifications or if the original pump back casing rings also possess this defect. Nonetheless, this was the first failure of this type for any of the 60 pumps, providing assurance that this event was an isolated occurrence and that RHR pump B was unlikely to also fail due to this mechanism.
It is not known if the Unit 1 RHR pumps have a similar condition of im properly staked capserews.
However, the following facts are known:
As described above, the unlikeliness of this occurrence is reflected in the hundreds of pump service years by this type of pump in the nuclear industry, with no similar events. Per discussion with the vendor, a loose capserew is more likely to be discharged from an operating pump rather than be cauglit in the impeller, as occurred here. Plans are underway to develop a methodology to ensure the Unit 1 RHR pumps remain operable following each run to ensure that no capserews have jammed the impellers.
These facts provide assurance that the Unit 1 pumps will continue to flinction until they are inspected during the Fall 2003 reflieling outage.
Based on these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
This event represents a safety system flinctional failure.
F. CORRECTIVE ACTIONS
1) The capscrews on the back casing rings for both Unit 2 RHR pumps were properly staked prior to the pumps being returned to service and the Unit returning.to Mode 6.
2) The supplier of the spare back casing rings in the w&ehouse was advised of the defect. The Casing rings themselves were returned to the vendor for reworking.
3) A methodology will be developed by January 20,2003, to ensure the Unit I RHR pumps remain operable afler each pump run to ensure the impellers have not become jammed.
4) Each pump's back casing rings will be inspected during the Fall 2003 reflieling outage and appropriate actions will be taken as necessary.
G. ADDITIONAL INFORMATION
1) Failed Components:
RHR pump manufactured by Ingersoll-Rand, Model number 8X2OWDF.
Back casing ring part number: 6B.
2) Previous Similar Events:
There have been no previous similar events in the last two years.
3) Energy Industry Identification System Code:
Residual Heat Removal System - BP
Reactor Coolant System - AB
Page Last Reviewed/Updated Friday, January 31, 2020