05000286/LER-2015-001, Regarding Safety System Functional Failure Due to Inoperable Refueling Water Storage Tank Level Alarms Due to Freezing of the Level Instrument Sensing Lines Caused by a Failed Strip Heater
| ML15069A080 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  (DPR-064) |
| Issue date: | 03/03/2015 |
| From: | Coyle L Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-15-023 LER 15-001-00 | |
| Download: ML15069A080 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2862015001R00 - NRC Website | |
text
En terg Indian Point Energy Center 450 Broadway, GSB P.O. Box 249 Buchanan, N.Y. 10511-0249 Tel (914) 254-6700 Lawrence Coyle Site Vice President NL-15-023 March 3, 2015 U.S. Nuclear Regulatory Commission Document Control Desk 11545 Rockville Pike, TWFN-2 F1 Rockville, MD 20852-2738
SUBJECT:
Licensee Event Report # 2015-001-00, "Safety System Functional Failure Due to Inoperable Refueling Water Storage Tank Level Alarms Due to Freezing of the Level Instrument Sensing Lines Caused by a Failed Strip Heater" Indian Point Unit No. 3 Docket No. 50-286 DPR-64
Dear Sir or Madam:
Pursuant to 10 CFR 50.73(a)(1), Entergy Nuclear Operations Inc. (ENO) hereby provides Licensee Event Report (LER) 2015-001-00. The attached LER identifies an event where both refueling water storage tank level alarms became inoperable as a result of frozen level transmitter sensing lines caused by a failed strip heater, which is reportable under 10 CFR 50.73(a)(2)(v)(D) as a safety system functional failure and 10 CFR 50.73(a)(2)(vii) as a common cause inoperability of independent channels. This condition was recorded in the Entergy Corrective Action Program as Condition Report CR-IP3-2015-00084.
There are no new commitments identified in this letter. Should you have any questions regarding this submittal, please contact Mr. Robert Walpole, Manager, Regulatory Assurance at (914) 254-6710.,,-7 Sincerely, cc:
Mr. Daniel H. Dorman, Regional Administrator, NRC Region I NRC Resident Inspector's Office, Indian Point 3 Ms. Bridget Frymire, New York State Public Service Commission
Abstract
On January 8, 2015, the Refueling Water Storage Tank (RWST) level sensing instrumentation lines (LT-920 and LIC-921) were discovered frozen resulting in inoperable low-low level alarms in the Control Room.
Entered Technical Specification (TS) 3.5.4 (RWST)
Condition C due to both RWST low-low level alarms disabled in the CR.
TS Condition C requires at least one channel of RWST low-low level to be restored to operable in one hour.
Actions initiated to return one RWST level channel to operable.
Entered TS 3.5.4 Condition D (Required Action and associated Completion Time not met)
D.1 be in. Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and D.2 be in Mode 4 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
Commenced unit shutdown per TS for inoperable RWST level alarms.
Repairs and calibrations completed returning the RWST level alarms to operable.
TS 3.5.4 exited and power ascension commenced.
Loss
-.of bbth LT alarms is a safety system functional failure as the alarms are credited for operator manual switchover for recirculation.
Direct cause was failure of the RWST instrument level alarm strip heater to maintain the temperature in the instrument enclosure.
- - Due to the failure of the heat trace circuit EHT34-1 strip heater to function combined with a period of severe cold weather resulted in the sensing lines for the RWST. to freeze.
The apparent cause was a high resistance electrical connection at the strip heater wire lug due to thermal cycling and age. Corrective actions included
- repair/of ring lug to strip heater and calibration of level instrumentation.
Maintenance procedure 0-ELC-419-EHT will be revised to include inspection/repair of strip heater and ring lug connections within instrument enclosures.
An action request (AR) will be initiated for a new model Work Order/PM to inspect strip heater connections and-operation.
The event had no significant effect on public health and safety.
(if more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
The apparent cause of not recognizing the need to station an operator locally to operate the AFW regulating valves prior to isolating the nitrogen supply was inadequate procedural guidance and licensing basis documents.
The cause of the condition reported in LER-2012-001 was not a result of aging instrumentation.
The only similar aspect of this event to LER-2015-001 was adequacy of procedures since there was no PM for strip heaters on TS systems (RWST,
- However, corrective actions for LER-2012-001 would not have prevented this event.
Safety Significance
This event had no significant effect on the health and safety of the public. There were no actual safety consequences for the event because there were no accidents or transients during the time of the event.
Operators would be aware of RWST drain down as a result of an SI actuation..-
--Adequate water inventory in the containment toprovide adequate.ECCS pump suction
- - can be confirmed by recirculation and/or containment sump level indication....
A risk assessment was performed using the zero maintenance probabilistic risk assessment (PRA) model to determine the plant's baseline risk and the estimated increase in Core Damage Probability and Large Early Release Probability due to the unavailability of RWST level indication.
For the approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> period that the RWST level transmitters were out of service, the increase in Core Damage Probability (ICDP) was estimated as 1.39E-7, while the increase in Large Early Release Probability (ILERP) was estimated as 1.59E-9.
Both the ICDP and ILERP values are below the risk significance values of 1E-6 and 1E-7, respectively.
It can therefore be concluded that the risk of the-inoperable RWST level capability for the 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> out of service time had low. safety significance;