05000461/LER-2012-001, Regarding Loss of Secondary Containment Differential Pressure Due to Transformer Trip
| ML12312A466 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 10/26/2012 |
| From: | Noll W Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SRRS 5A.108, U-604100 LER 12-001-00 | |
| Download: ML12312A466 (5) | |
| 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)(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 |
| 4612012001R00 - NRC Website | |
text
ExeLon Generation.
Clinton Power Station 8401 Power Road Clinton, IL 61727 U-604100 10 CFR 50.73 October 26, 2012 SRRS 5A.108 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461
Subject:
Licensee Event Report 2012-001-00 Enclosed is Licensee Event Report (LER) No. 2012-001-00: Loss of Secondary Containment Differential Pressure Due to Transformer Trip. This report is being submitted in accordance with the requirements of 10 CFR 50.73.
There are no regulatory commitments contained in this report.
Should you have any questions concerning this report, please contact Ms. Kathy Ann Baker, Regulatory Assurance Manager, at (217)-937-2800.
Re William G. Noll Site Vice President Clinton Power Station JLP/blf
Enclosures:
Licensee Event Report 2012-001-00 cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Clinton Power Station Office of Nuclear Facility Safety - IEMA Division of Nuclear Safety
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may sfor each block) not conduct or sponsor, and a person is not required to respond to, the digits/characters
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- 3. PAGE Clinton Power Station, Unit 1 05000461 1 OF 4
- 4. TITLE Loss of Secondary Containment Differential Pressure Due to Transformer Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR EUEN NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 09 02 2012 2012 001 00 10 26 2012 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) 1 [1 20.2201(d)
El 20.2203(a)(3)(ii)
[] 50.73(a)(2)(ii)(A)
[I 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)
El 20.2203(a)(2)(i)
[E 50.36(c)(1)(i)(A)
[E 5Q.73(a)(2)(iii)
C3 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 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)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
[j 73.71(a)(4) 097 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
. [E 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in 2012, within the 30 day TS completion time. The Main Control Room Ventilation 'A' Chiller was restarted at 2237. The DG Vent Oil Room 1A Fan was restarted at 0104 on September 3, 2012.
Since the secondary containment differential pressure was greater than the TS required pressure, this event was reported (Event Number: 48269) on September 3, 2012, at 0417 as a condition that could have prevented the fulfillment of a safety function per 10 CFR 50.72(b)(3)(v)(C).
Corrective action program Issue Report 1408282 was initiated to evaluate this event.
A review of the ERAT trip and of the 1Al Bus fed breaker logic indicates that the DC Scout signal used during ground fault tracing actuated the sudden pressure relay logic which then actuated the.
lockout relays.
One lockout relay specifically blocks the synchro-verifier relay logic, thus blocking a fast transfer. This resulted in an automatic slow 1A1 bus transfer from the ERAT to the RAT. The slow transfer resulted in the momentary loss of power on the 1 Al bus and all downstream loads.
During troubleshooting activities for this event, a latent design error was identified on seal-in relays 63SPX and 63FPX. Both relays are Qualitrol Model 909-200-01 AC/DC Seal-In Relays with 125 VDC supply power. The latent design error is a ground wire installed on terminal 13 of the relay. The current vendor manual information states that terminal 13 should not be connected to earth ground when a DC power supply is used. The vendor has acknowledged that spurious operation can occur when this device is used with DC supply power and a ground on terminal 13. All indications show that the latent error has existed since original transformer construction at the factory in 1998. The current ERAT was received and installed in 1998.
C. CAUSE OF EVENT
The cause of this event was due to a latent design error that involved the wiring of terminal 13 to ground for the sudden pressure seal-in relay cards (63SPX). Updated vendor manual information states that terminal 13 should not be connected to earth ground when a DC power supply is used.
The relay manufacturer has acknowledged that spurious operation can occur when this device is used with DC supply power and a ground on terminal 13. The latent error has existed since original transformer construction at the factory.
D. SAFETY CONSEQUENCES
There were no actual nuclear safety consequences related to this event. This event resulted in the loss of secondary containment for approximately 15 minutes, from 2204 to 2219 on September 2, 2012 due to loss of power to the Fuel Building ventilation system and dampers closing. Secondary Containment differential pressure was greater than the 0.25 inches vacuum required by TS 3.6.4.1. The SGTS was manually started during this period and differential pressure was restored to within limits. The SGTS initiates automatically when conditions indicate a release of radioactive material or a loss of coolant accident to ensure that any radioactive materials that leak from the Primary Containment into the Secondary Containment following an accident are filtered by SGTS prior to release to the environment.
This event is considered to be reportable as a loss of safety function under 50.72(b)(3)(v)(C) and 50.73(a)(2)(v)(C) as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.
E. CORRECTIVE ACTIONS
A Temporary Modification under Engineering Change (EC) 390386 was implemented to disable the 63SPX (Qualitrol Model No. 909-200-01) trip function and remove the ground connection from terminal 13 on the seal-in relays (63SPX and 63FPX). The trip function of the 63SPX relay can be restored during the next ERAT maintenance outage. Based on these actions the risk of an invalid ERAT trip has been mitigated.
F. PREVIOUS OCCURRENCES
12/18/2001 - ERAT TRIP - The ERAT and ERAT SVC tripped (with deluge). A Root Cause investigation was performed. The cause of the trip was an internal fault. The cause for the internal fault on the ERAT was a gradual localized breakdown of the insulating oil due to corona discharge from the spliced HV lead. The controller cards, seal-in relays, etc., were not mentioned as contributing factors and no specific issues with the seal-in relays were documented.
3/02/2002 - ERAT TRIP - The ERAT and ERAT SVC tripped (with deluge). The cause of the trip was determined to be a wet seal-in relay card. The control cabinet contained gaps that allowed rain and subsequent deluge water to enter the cabinet. A Work Request was issued to seal the ERAT control cabinet.
G. COMPONENT FAILURE DATA
Manufacturer Qualitrol Corporation Nomenclature Sudden pressure Seal-in relay (63SPX)
Manufacturer Model Number 909-200-01