05000321/LER-2014-001
| Edwin I. Hatch Nuclear Plant Unit 1 | |
| Event date: | 03-14-2014 |
|---|---|
| Report date: | 06-05-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3212014001R01 - NRC Website | |
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CONTINUATION SHEET
1. FACIUTY NAME 3. PAGE 2. DOCKET 6. LER NUMBER
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On March 14, 2014 at 11:50 AM, with Units 1 and 2 operating at 100 percent rated thermal power (RTP), fire vulnerabilities due to unfused ammeter cables were identified by engineering as a result of a review being performed in response to industry operating experience. The review and evaluation were performed after several other utilities had identified possible fire vulnerabilities from unfused ammeters on batteries and battery chargers that would compromise Safe Shutdown (SSD) capabilities.
It was concluded that Hatch Units 1 and 2 have unfused ammeters on non-safety related reactor protection system (RPS) batteries and battery chargers whose cabling passes through fire areas containing SSD equipment.
Specifically, the non-safety ammeter circuits for the non-safety related reactor protection system (RPS) batteries 1R42S017A, 1R42S017B, 2R42S017A, and 2R42S017B, and associated battery chargers are unfused, and a postulated fire could result in concurrent shorts of an unfused DC ammeter cable and a DC cable of opposite polarity.
Due to a lack of overcurrent protection on the ammeter cables, the resultant excessive current flow and overheating of the ammeter cable could result in a secondary fire in another fire area that could adversely affect fire safe shutdown capability and create an unanalyzed condition with respect to 10 CFR 50 Appendix R analysis requirements.
Therefore Hatch Units 1 and 2 had fire vulnerabilities creating an unanalyzed condition with respect to 10 CFR 50 Appendix R analysis requirements. There are no structures, components, or systems that are inoperable that contributed to this conclusion.
The ammeter circuits for non-safety related RPS batteries and associated battery chargers have positive and negative cabling, associated with the same battery, that pass through fire areas that contain fire safe shutdown equipment.
The fire areas of concern are limited to the Control Building and are fire areas 0001, 0014, 0024, 0040, 1009, 1010, 1013, 1015, 2008, 2009, 2010, 2013, and 2015.
The extent of condition is limited to DC ammeter circuits due to their unique design where ammeter circuits were not required to be fused when tapped off of a shunt. A review by Fire Protection Engineering concluded that for all batteries except 1/2R42S017A/B, there are no unfused ammeter cables that pass through fire areas that contain a negative conductor from the same battery that could short to the ammeter cable causing overheating of the ammeter cable in a secondary fire area(s). Therefore, no single initiating fire can produce a secondary fire(s) and thus there are no areas where both SSD paths are compromised, for the remaining batteries.
CAUSE OF EVENT
This is a legacy analysis error where unfused DC ammeter circuits, and the secondary fires they could produce, were not addressed for the non-safety ammeter circuits for the Units 1 and 2 non-safety RPS batteries and battery chargers during the implementation of 10 CFR 50 Appendix R. As a result the equipment design issue was not recognized as an unacceptable configuration. The design issue was associated with an evolving industry understanding of the Appendix R common enclosure scope. Specifically, ammeter circuits were not required to be fused in the original design of the plant nor included within the original scope of Appendix R evaluation of common enclosure type circuits.
Recent industry operating experience resulted in re-evaluating the implications of unfused ammeter circuits whose connecting cables were routed through safe shutdown paths which resulted in the recognition of the current condition.
Since the vulnerability could result in a condition such that the required degree of separation for redundant safe shutdown trains would be adversely impacted, this event represents an unanalyzed condition that significantly degraded plant safety and is reportable pursuant to 10 CFR 50.73(a)(2)(ii)(B).
There were no actual safety consequences of this condition. This is a postulated event and as such did not adversely affect the safe operation of the plant or the safety of the public. The actual safety impact of this condition has very low safety significance. The combined effect of the cables having thermoset insulation, the administrative controls of the fire protection program, the availability of fire detection and suppression systems, and the trained on-site fire brigade make it highly unlikely that a fire could progress to the event postulated in this scenario prior to the time when the corrective actions were implemented to remove the vulnerability. A consequential secondary fire due to overheating of the unfused ammeter cables is highly unlikely due to the combination of conditions necessary to initiate the overheating event.
CORRECTIVE ACTIONS
Immediate hourly fire watches were initiated and subsequently the affected circuits' leads were lifted to remove the vulnerabilities. Work orders are in place to implement design changes to install fuses in the ammeter circuits for the non-safety RPS batteries and battery chargers on both units. Revisions to current procedures will be performed that provide guidance that ensures future design changes have properly addressed DC ammeter cables and their potential to create secondary fires during a fire event.
ADDITIONAL INFORMATION
Other Systems Affected: None.
Failed Components Information:
Master Parts List Number:
1R42S017A EllS System Code: El 1R42S017B 2R42S017A 2R42S017B Reportable to Epix: Yes Manufacturer: C and D (C179) Model Number: 3DCU-7 (U1) Root Cause Code: - B Model Number: 3DCU-9 (U2) EIIS Component Code: II Commitment Information: This report does not create any new licensing commitments.
Previous Similar Events: None.