05000298/LER-2014-002, Regarding Jacket Water Leak Into Emergency Diesel Generator Engine Results in Condition Prohibited by Technical Specifications and Loss of Safety Function
| ML14105A017 | |
| Person / Time | |
|---|---|
| Site: | Cooper  (DPR-046) |
| Issue date: | 04/11/2014 |
| From: | Limpias O Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2014033 LER 14-002-00 | |
| Download: ML14105A017 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 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)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2982014002R00 - NRC Website | |
text
H Nebraska Public Power District Always there when you need us NLS2014033 April 11, 2014 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2014-002-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2014-002-00.
There are no new commitments contained in this letter.
- Sincere, 0 c
. Limpias(/
Vice President Nuclear-Chief Nuclear Officer Jo Attachment: Licensee Event Report 2014-002-00 cc:
Regional Administrator w/attachment NPG Distribution w/attachment USNRC - Region IV Cooper Project Manager w/attachment INPO Records Center w/attachment USNRC - NRR Project Directorate IV-1 via ICES entry Senior Resident Inspector w/attachment SORC Chairman w/attachment USNRC - CNS SRAB Administrator w/attachment CNS Records w/attachment COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppdl.com
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-2014)
Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by LICENSEE EVENT REPORT(E) internet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and (See Page 2 for required number of Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB digits/characters for each block) control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Cooper Nuclear Station 05000 298 1 OF
- 4. TITLE Jacket Water Leak into Emergency Diesel Generator Engine Results in Condition Prohibited by Technical Specifications and Loss of Safety Function
- 5. EVENT DATE
- 6. LER NUMBER MONTH DAY YEAR YEAR T NUMBER NO.
10 07 2013 2014 002 00
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER 05000 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
F] 20.2203(a)(3)(i)
[] 50.73(a)(2)(i)(C)
F] 50.73(a)(2)(vii)
E] 20.2201(d)
El 20.2203(a)(3)(ii)
[] 50.73(a)(2)(ii)(A)
[] 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
_ 20.2203(a)(2)(i)
[
50.36(c)(1)(i)(A)
[] 50.73(a)(2)(iii)
[] 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
[
50.36(c)(2)
[] 50.73(a)(2)(v)(A)
[] 73.71(a)(4) 100 El 20.2203(a)(2)(iv)
[
50.46(a)(3)(ii)
[] 50.73(a)(2)(v)(B) 73.71(a)(5)
[] 20.2203(a)(2)(v)
[
50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
[] OTHER E] 20.2203(a)(2)(vi)
[1 50.73(a)(2)(i)(B)
[1 50.73(a)(2)(v)(D)
Specify in Abstract below or in I.
PLANT STATUS Cooper Nuclear Station (CNS) was in Mode 1, Power Operations, at 100% power at the time the condition was discovered on October 7, 2013. Diesel Generator (DG) I was inoperable for the monthly operability test.
BACKGROUND The purpose of the standby (emergency) Alternating Current (AC) power system [EIIS:EK] is to provide a single failure proof source of on-site AC power adequate for maintaining the safe shutdown of the reactor following abnormal operational transients and postulated accidents. This system consists of two independent AC power sources, the Emergency Diesel Generators (EDG) [EIIS:
DG].
Each DG shall be capable of automatic start at any time and capable of continued operation at rated load, voltage, and frequency until manually stopped.
During normal plant operations both DGs are in standby. A DG starts automatically on a loss of coolant accident signal (i.e., low reactor water level signal or high drywell pressure) or on loss of voltage on a critical bus. The DG automatically connects to its respective bus after off-site power is tripped as a consequence of critical bus loss of voltage or degraded voltage.
CNS Technical Specifications (TS) require that two EDGs be operable when the plant is in Modes 1, 2, or 3, and that one DG be operable when the plant is in Modes 4 or 5.
EVENT DESCRIPTION
On October 7, 2013, at 09:11, DGI was declared inoperable for the performance of the monthly operability test and TS Limiting Condition for Operation (LCO) 3.8.1, Condition B, was entered. During the monthly operability test, indications of water intrusion into the DGI lubricating oil system [EIIS:LA] were observed.
Troubleshooting commenced and found the source of water intrusion was the I-Left cylinder. With the DGI water jacket pressurized, water was observed running out of the bottom of the I-Left cylinder liner [EIIS:LNR). Using a borescope through the fuel injector bore in the cylinder head, a crack in the liner wall was visible near the top of the liner.
As directed by TS LCO 3.8.1, Condition B, Required Action B.3.1, a common cause failure analysis was completed for DG2. This analysis found DG2 continued to be operable, as there were no indications of a similar high sodium content in the DG2 lube oil which indicates no leakage ofjacket water into the DG2 lube oil.
The cracked liner was removed and shipped to Lucius Pitkin, Incorporated, for metallurgical examination. The examination results provided to CNS in February 2014 found that the tensile strength of the liner in the area of the crack was 15% lower than specification.
A slight increase in assembly stresses imposed by the installation of a new cylinder head in October 2011 caused a fatigue crack to initiate in the liner with lower than expected tensile strength. The crack then propagated through the liner wall and allowed the jacket water to leak into the DGI cylinder.
The I-Left liner was installed in 1997 and a torque specification of 1450 ft-lbf was used to bolt the cylinder head. When a new cylinder head was installed in October 2011, due to an external jacket water leak on the I-Left cylinder, the I-Left liner was not replaced, and the same torque specification of 1450 ft-lbf was used to bolt the new cylinder head.
During the time frame from October 2011, when the new cylinder head was installed on the 1-Left cylinder, to the discovery of the leak on October 7, 2013, it was determined that DGi was inoperable, resulting in a past operation or condition prohibited by Technical Specifications. A search found that from October 2011 to October 2013, DG2 was inoperable during monthly surveillance runs and during performance of annual maintenance on March 12, 2012 and March 12, 2013. As such, a loss of safety function also occurred.
A new 1-Left liner was installed and DGI was declared operable on October 12, 2013, at 11:04.
BASIS FOR REPORT This event is being reported per 10 CFR 50.73(a)(2)(i)(B) as "any operation or condition which was prohibited by Technical Specifications" and reportable in accordance with 10 CFR 50.73(a)(2)(v) as "any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to...(D) Mitigate the consequences of an accident."
SAFETY SIGNIFICANCE
DG2 was operable and available during the October 7, 2013 thru October 12, 2013 period; therefore, there was no impact to safety.
A conservative estimate for potential initial failure would be October 2011, when the new cylinder head was installed on the 1-Left cylinder. The duration of both DGs being inoperable was short and the exposure window was small; therefore, the potential safety impact was negligible.
This event is a safety system functional failure.
CAUSE
The root cause of the event was that the subpar mechanical properties of the liner caused the cylinder liner to crack which then allowed jacket water to leak into the engine lubrication oil.
CORRECTIVE ACTION
A common cause analysis was performed on DG2, liners pre-dating Change Evaluation Document 1999-0212 were placed on-hold, and an increase in oil sampling frequency was initiated from quarterly to monthly.
To prevent recurrence of this condition, System Engineering shall specify, the test method(s) to ensure that liners currently in inventory have sufficient material tensile strength to conform to the given requirements, and shall oversee testing work that is done to provide that assurance. A report that details the test methods used and the results of testing shall be given to the Corrective Action Review Board for their review prior to any liner from inventory being installed in either DGI or DG2.
PREVIOUS EVENTS On April II, 2012, DGI failed to start after performance of on-line maintenance activities. The failure was due to improper installation of a starting air distributor rotor in October 2011. This was reported under LER 2012-002-00, in accordance with 10 CFR 50.73(a)(2)(i)(B) as "an operation or a condition which was prohibited by Technical Specifications" and also in accordance with 10 CFR 50.73(a)(2)(v) as "any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to...(D) Mitigate the consequences of an accident."