05000425/LER-2002-001, Re Unstaked Capscrews Renders Residual Heat Removal Pump Inoperable
| ML023650495 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  (NPF-081) |
| Issue date: | 12/20/2002 |
| From: | Gasser J Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LCV-1640 LER 02-001-00 | |
| Download: ML023650495 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 4252002001R00 - NRC Website | |
text
I; Jeffrey T. Gasser Vice President Southern Nuclear Operating Company, Inc.
40 Inverness Center Parkway Post Office Box 1295 Birmingham, Alabama 35201 Tel 205.992 7721 Fax 205.992.0403 SOUTHERN A COMPANY Energy to Serve Your World'l 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 2-2002-001 UNSTAKED CAPSCREWS RENDERS RESIDUAL HEAT REMOVAL PUMP INOPERABLE In accordance with the requirements 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.
Sincerely, Jeffrey T. Gasser JTG/NJS Enclosure: LER 2-2002-001 xc:
Southern Nuclear Operating Company Mr. G. R. Frederick Mr. M. Sheibani SNC Document Management U. S. Nuclear Regulators Commission Mr. L. A. Reyes, Regional Administrator Mr. F. Rinaldi, Project Manager, NRR Mr. J. Zeiler, Senior Resident Inspector, Vogtle
4-;
Abstract
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 1 th. 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 CFR 21.21 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 returning to Mode 6.
NRC FORM 388A (1-2001)(1-001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION 1 FACILITY NAME (1)
I DOCKET l
EAR lSEQUENWL REVON Wf RNUMB8ER Vogtle Electric Generating Plant - Unit 2 05000-425 2002 001 00 2 C TEXT Iff more space is required, use additional copies of NRC Form 366A) ( 17 A. REQUIREMENT FOR REPORT This event is reportable per 10 CFR 50.73 (a)(2)(i)(B) because the unit was operated in a condition prohibited by the Technical Specifications (TS) for a period of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and 31 minutes. 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 function 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 defueled 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 defueled, 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 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.
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 capscrews. Each capscrew is torqued and staking performed as a redundant measure to hold the capscrews 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.U.S. NUCLEAR REGULATORY COMMI:
(1-2X01)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME 11)
DOCKET LER NUMBER 16)
PAG YEAR SEQUENTnAL REVISION YEAR NUMBER Vogtle Electric Generating Plant - Unit 2 05000-425
'2002 001 00 3 01 TEXT Of more space is equired, use addiional copies of NRC Form 366AJ 117 RHR pump B was inspected and found 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 capscrews.
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 prohibited by TS 3.9.6 because two RHR pumps were not maintained operable.' However, the system safety function 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 capscrews and did not create a substantial safety hazard.
In addition, the improperly staked capscrews on both RHR pumps represent a condition that could have prevented fulfillment of a safety function 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 these 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 improperly staked capscrews.
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 capscrew is more likely to be discharged from an operating pump rather than be caught 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 capscrews have jammed the impellers.
These facts provide assurance that the Unit 1 pumps will continue to function until they are inspected during the Fall 2003 refueling outage.
SSION IRC Form 366A (1.2001)U.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME III DOCKET LER NUMBER (6)
PAGE 13l IYEAR ISEQUEMTAL REMO Vogtle Electric Generating Plant - Unit 2 05000-425 2002 001 00 4 OF 4 TEXT Of mole space is required, use additonel copies of NRC Foim 366AJ 117 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 functional 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 warehouse 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 1 RHR pumps remain operable after 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 refueling outage and appropriate actions will be taken as necessary.
G. ADDITIONAL INFORMATION
- 1) Failed Components:
RHR pump manufactured by Ingersoll-Rand, Model number 8X20WDF.
Back casing ring part number: 6B.
Capscrew: 118C.
- 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 KRC Form 326A (1-2001)