05000482/LER-2019-002, Emergency Diesel Generator Inoperable Due to Temperature Control Valve Failure

Emergency Diesel Generator Inoperable Due to Temperature Control Valve Failure

ML19295D729
Person / Time
Site:	Wolf Creek
Issue date:	10/14/2019
From:	Bayer R Wolf Creek
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
WO 19-0049 LER 2019-002-00
Download: ML19295D729 (5)

LER-2019-002, Emergency Diesel Generator Inoperable Due to Temperature Control Valve Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
4822019002R00 - NRC Website

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'NUCLEAR OPERATING CORPORATION Robert J. Bayer Plant Manager U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 October 14, 2019 WO 19-0049

Subject:

Docket No. 50-482:

Licensee Event Report 2019-002-00, "Emergency Diesel Generator Inoperable Due to Temperature Control Valve Failure" To Whom It May Concern:

The enclosed Licensee Event Report (LER) 2019-002-00 is being submitted pursuant to 10 CFR 50. 73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications, 10 CFR 50.73(a)(2)(v)(A) as an event or condition that could have prevented fulfillment of a safety function needed to shut down the reactor and maintain it in a safe shutdown condition, and 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident.

This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4015, or Ron Benham at (620) 364-4204.

RJB/rlt

Enclosure:

LER 2019-002-00 cc:

S. A. Morris (NRC), w/e N. O'Keefe (NRC), w/e B. K. Singal (NRC), w/e Senior Resident Inspector (NRG), w/e Sincerely, P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020

/

(04-2018)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection.

3.Page Wolf Creek Generating Station 05000 482 1

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4. Title Emergency Diesel Generator Inoperable Due to Temperature Control Valve Failure

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Month Day Year I

Sequential I Rev Facility Name Docket Number Year Number No.

Month Day Year 05000 Facility Name Docket Number 08 19 2019 2019 -

002 -

00 10 14 2019 05000

9. Operating Mode

11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: {Check all that apply)

D 20.2201(b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(viii)(A)

D 20.2201(d)

D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(iii)

D 50.73(a)(2)(ix)(A)

D 20.2203(a)(2)(i)

D 50.36(c)(1 )(i)(A)

D 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

10. Power Level D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(v)(A)

D 73.71(a)(4)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50. 73(a)(2)(v)(B)

D 73.71 (a)(5)

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

D 50.73(a)(2)(v)(C)

D 73.77(a)(1) 100 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(D)

D 73.77(a)(2)(i)

D 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 73.77(a)(2)(ii)

D 50.73(a)(2)(i)(C)

D Other (Specify in Abstract below or in A review of operating experience discovered that Wolf Creek Nuclear Operating Corporation (WCNOC) personnel had been procuring the power pills commercial grade and then doing commercial grade dedication in-house. This is an outlier in the industry. Most of the industry procures the power pills as safety-related components from the vendor. As part of the commercial grade dedication process, WCNOC had been performing acceptance testing, as well as annual shelf-life testing. The manufacturer does not have a shelf-life requirement for these components. Rather, the industry accepted critical test of these components is to perform testing within 4 weeks prior to installation.

The commercial grade dedication test instructions state to use a thermal water bath for the test fixture to achieve different temperatures but does not specify what type of water or how to cool the bath. Reviews of past testing work orders and discussions with the craft, revealed that for the performance of the acceptance and shelf-life testing, tap water had been used for the heated thermal bath, and the thermal bath was cooled using ice placed in the water. Per discussions with the vendor and other industry personnel, using ice to cool the bath, as well as the use of impure tap water, are not good maintenance practices and could contribute to prematurely aging the rubber diaphragm.

The onsite dedication acceptance and annual shelf life testing submits the rubber diaphragms to additional thermal cycles.

The additional thermal cycles and subsequent drying out of the rubber diaphragm leads to accelerated degradation and embrittlement of the rubber elastomers. Disassembly investigation of the failed power pills from the intercooler water heat exchanger temperature control valve revealed that the rubber diaphragms did indeed have indications of pitting and erosion which caused the metal/wax solution to leak out thus preventing the valve from actuating.

A review of the stock item history for the failed power pills revealed that these had been installed for 3.8 years, and prior to installation had been subjected to 4 tests by WCNOC personnel. These temperature control valves are rebuilt with a frequency of 4.5 years, which is consistent with the industry recommended replacement frequency for these power pills of 3-5 years An extent of condition review shows that these power pills are used in the equivalent application for the 'B' EOG, and in two other valves for both trains of EDGs Uacket water heat exchangers and lube oil coolers). All of the power pills used in valves for both EDGs will be replaced with new ones procured as safety related during their scheduled maintenance outages in 2020.

Upon completion of the previous successful 'A' EOG operability run on July 15, 2019, the power pills would have returned to ambient temperature. Due to the probable failure mechanism of accelerated aging, it was likely that going through the temperature changes associated with starting and running the EOG on August 19, 2019 was the proximate cause of the failure of the power pills. Therefore, once the power pills returned to ambient temperature following the test on July 15, 2019, they would have been susceptible to failure at any time the 'A' EOG would have been called upon. As such, it is likely that the 'A' EOG would not have been able to perform its intended function to provide emergency A/C power for its 7-day mission time between July 15, 2019, and its successful restoration on August 20, 2019.

BASIS FOR REPORTABILITY Because the 'A' EOG was not capable of performing its intended function between July 15, 2019 and August 20, 2019, it was inoperable for longer than the time allowed by TS 3.8.1 Condition B. Therefore, this event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as an event or condition prohibited by TS. In addition, the 'B' EOG was out of service for normally scheduled maintenance for approximately 2 days from July 29, 2019 until July 31, 2019. Therefore, this event is also being reported in accordance with 10 CFR 50.73(a)(2)(v) as an event or condition that could have prevented fulfillment of a safety function of structures or systems that are needed to (A) shutdown the reactor and maintain it in a safe shutdown condition, and (D) mitigate the consequences of an accident.

CORRECTIVE ACTIONS

Immediate:

The power pills were replaced in the intercooler heat exchanger temperature control valve for the 'A' EOG and the EOG was returned to service on August 20, 2019.

Planned:

A purchase order has been issued to procure new power pills as safety related components directly from the vendor. The existing stock of power pills will be discarded as the new ones are received. All of the power pills currently installed will be replaced during maintenance outages in 2020.

Completed:

The pre-installation testing work instructions have been enhanced to clarify that demineralized water shall be used for the thermal bath, and to not use ice to cool the thermal bath. The annual shelf life testing PM has been deleted.

SAFETY SIGNIFICANCE

Both offsite power sources remained operable during the time between the successful run of the 'A' EOG on July 15, 2019 and the restoration of the 'A' EOG following the TCV failure on August 20, 2019. As prerequisites to performing maintenance on the 'B' EDG on July 29, 2019, entry into the Wolf Creek switchyard was restricted, and any work which could challenge the operability of either of the offsite sources of power was minimized. In addition, the station blackout diesel generators were available, and these can provide reliable power to either Class 1 E 4.16 kV bus. Due to the operability of both redundant offsite sources of power, as well as the availability of the SBO DGs, there was no adverse impact on the public health or safety.

OPERATING EXPERIENCE/PREVIOUS EVENTS A review of the past three years at WCGS identified no similar events with the temperature control valves on any of the heat exchangers for either of the EDGs. These are the only applications at WCGS which use the temperature control valves with these power pills. Page 4

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