05000440/LER-2016-003, Regarding Loss of Safety Related Electrical Bus Results in a Loss of Shutdown Cooling
| ML16104A026 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 04/08/2016 |
| From: | FirstEnergy Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML16104A045 | List: |
| References | |
| L-16-109 LER 16-003-00 | |
| Download: ML16104A026 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4402016003R00 - NRC Website | |
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)
, the NRG may not conduct or sponsor, and a nerson is not reouired to resoond to the information collection.
Perry Nuclear Power Plant 05000440 YEAR 2016
- 3. LER NUMBER SEQUENTIAL NUMBER 003 On February 12, 2016, at 0032 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br />, EH11 was re-energized. The following TSs were declared met:
TS 3.4.10, Residual Heat Removal (RHR) Shutdown Cooling System - Cold Shutdown, February 12, 2016 at 1311 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.988355e-4 months <br /> TS 3.8.2, AC Sources - Shutdown,*February 12, 2016 at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> TS 3.8.5, DC Sources - Shutdown, February 12, 2016 at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> TS 3.8.8, Distribution Systems - Shutdown, February 12, 2016 at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> ORM 6.4.8, Emergency Service Water Systems - Shutdown, February 12, 2016 at 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br />
CAUSE OF EVENT
During the performance of simple troubleshooting on February 11, 2016, a Ferraz Shawmut OT-15 fuse in the A phase bus potential transformer secondary fuse location, which supplies the undervoltage and degraded voltage circuitry, was found to exhibit intermittent continuity. Failure analysis and simple troubleshooting methods determined the cause of the loss of the division 1 bus, EH 11, was due to an invalid undervoltage signal caused by the failure of the fuse which supplies the undervoltage and degraded voltage protection circuitry. The failure analysis revealed that the fuse internals were not soldered correctly during the manufacturing process. One of the fuse elements to fuse ferrule connections had flux applied but no solder.
The apparent cause for the loss of division 1 bus, EH11, was a latent manufacturing defect in the A phase bus potential transformer secondary fuse that resulted in a loss of A phase indicated voltage to the undervoltage sensing logic. This latent manufacturing defect led to an intermittent connection which resulted in a loss of sensed bus voltage.
ANALYSIS OF EVENT
The undervoltage signal that the division 1 DG received due to the failed fuse is not a valid actuation of the system. Per NUREG-1022 Rev. 3, Event Report Guidelines 10 CFR 50.72 and 50.73, it states the foHowing:
Valid actuations are those actuations that result from valid signals or from intentional manual initiation, unless it is part of a preplanned test. Valid signals are those signals that are initiated in response to actual plant conditions or parameters satisfying the requirements for initiation of the system. They do not include those that are the result of other signals.
Since at the time of the fuse failure proper three phase bus voltage was present and the signal was from a latent manufacturing defect, this is not a valid actuation.
A qualitative defense-in-depth risk assessment was performed for the February 11, 2016, loss of shutdown cooling event. Based on the conclusions of the condition report investigation, an event of very small risk significance was concluded. Assuming the loss of EH11 could have occurred at any point in time, a delta core damage frequency of 8.2E-08 per year was calculated that also indicates a very small risk significance event.
These conclusions were based on the nature of the failure immediately being identifiable, appropriate levels of defense-in-depth at the time of the loss, and timely and appropriate operator response to the event.
CORRECTIVE ACTIONS
The defective fuse with the intermittent continuity had an Underwriters Laboratories (UL) provided manufacturing/licensing code of FP22-66. The extent of condition has been limited to fuses obtained under a specific batch number. The remaining stock found in maintenance inventory and the warehouse stock had the REV NO.
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U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 _; (11-2015)
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 industiy.
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 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
- by internet e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and 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 currentty valid OMB control number, the NRG may not conduct or sponsor, and a nerson is not reauired to resoond to the information collection.
- 3. LER NUMBER YEAR SEQUENTIAL NUMBER REV NO.
Perry Nuclear Power Plant 05000440 2016 003 same UL manufacturing code associated with the batch number. A sampling of other Ferraz Shawmut OT-15 fuses with or without the same manufacturing code have been examined without any further soldering defects identified. The defective fuse was purchased through United Controls International Inc. (UCI), which performs Commercial Grade Dedication under a 10 CFR Appendix B Program. The defective fuse and failure analysis have been provided to UCI as information for their 10 CFR Part 21 investigation.
I UCI has received eight of the twenty-two fuses that are in the same purchase order. This included the defective fuse. UCI currently considers this issue to be an isolated event as no previous instances of this failure have been observed and dissection of additional fuses of the same part number and from the same manufacturing lot have provided no additional supporting evidence that the manufacturihg error identified a recurring event. UCI is investigating this issue to identify the possible cause.
The follow-up corrective actions are to replace the Ferraz Shawmut OT-15 fuses that were installed under the suspect batch number and to document their laboratory analysis. UCI has subsequently issued a 10 CFR Part 21 evaluation.
PREVIOUS SIMILAR EVENTS
A review of LERs and the corrective action database for the past three years did not have any previous similar events.
COMMITMENTS
There are no regulatory commitments contained in this report. Actions described in this document represent intended or planned actions, are described for the NRC's information, and are not regulatory commitments. 0