05000482/LER-2010-003, For Wolf Creek Regarding Post Fire Safe Shutdown Issue with the B Emergency Diesel Generator Voltage Control Circuitry
| ML101060264 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 04/08/2010 |
| From: | Hedges S Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 10-0023 LER 10-003-00 | |
| Download: ML101060264 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 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)(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 |
| 4822010003R00 - NRC Website | |
text
W0LF CREEK
'NUCLEAR OPERATING CORPORATION Stephen E. Hedges Site Vice President April 08, 2010 WO 10-0023 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Docket No. 50-482: Licensee Event Report 2010-003-00, "Post Fire Safe Shutdown Issue with the B Emergency Diesel Generator Voltage Control Circuitry" Gentlemen:
The enclosed Licensee Event Report (LER) is being submitted pursuant to 10 CFR 50.73(a)(2)(ii)(B) regarding an unanalyzed condition that could potentially affect post fire safe shutdown equipment at Wolf Creek Generating Station.
Commitments made by Wolf Creek Nuclear Operating Corporation in the enclosed LER are identified in the Attachment to this letter.
If you have any questions concerning this matter, please contact me at (620) 364-4190, or Mr.
Richard D. Flannigan at (620) 364-4117.
Sincerely, tep / n E. Hedges SEH/rlt Attachment List of Regulatory Commitments Enclosure Licensee Event Report 2010-003-00 cc:
E. E. Collins (NRC), w/a, w/e G. B. Miller (NRC), w/a, w/e B. K. Singal (NRC), w/a, w/e Senior Resident Inspector (NRC), w/a, w/e P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HC/VET
Attachment to WO 10-0023 Page 1 of 1 LIST OF REGULATORY COMMITMENTS The following table identifies those actions committed to by WCNOC in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
Please direct questions regarding these commitments to Mr. Richard Flannigan at (620) 364-4117.
REGULATORY COMMITMENT DUE DATE/EVENT A postf ire safe shutdown (PFSSD) analysis of 12/17/2010 circuits/components in the control room that could affect OFN RP-01 7 components credited for PFSSD in the event of a control room fire will be performed.
A permanent modification will be made to address the 07/28/2011 PFSSD issue currently covered by temporary modification.
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME f
- 2. DOCKET NUMBER
- 3. PAGE WOLF CREEK GENERATING STATION 05000 482 1 OF 4
- 4. TITLE Post Fire Safe Shutdown Issue with the B Emerqencv Diesel Generator Voltaqe Control Circuitry
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 02 09 2010 2010
- - 003 -
00 04 08 2010 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
[1 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1E 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
[E 50.73(a)(2)(viii)(A)
[I 20.2203(a)(1)
El 20.2203(a)(4) 0 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL E[] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
-] 50.73(a)(2)(x)
E] 20.2203(a)(2)(iii)
El 50.36(c)(2)
[l 50.73(a)(2)(v)(A)
El 73.71(a)(4)
[] 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 100 [E 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[E 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 NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER
--ACILITY NAME ITELEPHONE NUMBER (include Area Code)
Richard D. Flannigan, Manager Regulatory Affairs 1(620) 364-4117CAUSE SYSTEM COMPONENT FACTURE R
TOEPORTBL
CAUSE
SYSTEM COMPONENT MN-RPRAL FACTURER TO EPIX FACTURER TO EPIX
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR SUBMISSION El YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On February 9, 2010, engineering reviewed procedure STN RP-002, "Miscellaneous ISO/BYPASS Switch Testing," for an on-going Technical Specification Equipment Outage (TSEO) on the Train B Diesel Generator (DG). During this review, the system engineer identified that a fire induced hot short could energize the unit parallel relay and place the generator in droop mode of operation. In addition, other circuit issues were identified that could adversely affect the DG voltage regulator. This issue could have prevented operation of the Train B DG if a fire occurred in the control room involving these circuits. This could have prevented a safe shutdown of the plant if a severe fire occurred in the control room that also disabled off-site power. No fire actually occurred and this is a historical design issue that has been in place since construction.
A temporary modification was prepared and implemented prior to the Train B DG being returned to service.
NRC FORM 366 (9-2007)U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE I SEQUENTIAL I REV WOLF CREEK GENERATING STATION 05000 482 YEAR NUMBER NO.
2 OF 4
2010
-- 003 00
BACKGROUND INFORMATION
In order to achieve safe shutdown following a fire in the control room, AC power is required to be available to energize pump motors, valve motors and other equipment. Per Appendix R, off-site power is assumed to be lost in the event of a control room fire. At Wolf Creek, Train B was chosen as the credited Train for a control room fire. Train B diesel generator (DG) was designed with control room isolation capability and is considered the assured AC power supply following a control room fire. The Train A diesel generator was not designed with any control room fire isolation capability and is therefore considered unavailable during a control room fire.
PLANT CONDITIONS PRIOR TO EVENT MODE-i1 Power - 100
EVENT DESCRIPTION
During a review of procedure STN RP-002 by the DG system engineer, in support of an ongoing 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Train B Diesel Generator (DG) [EIIS Code: EK] Technical Specification Equipment Outage (TSEO), it was noticed that the unit parallel relay (UPR) [EIIS Code: EK-RLY] is not isolated from the effects of a control room fire. A short circuit between two conductors or a proper polarity external hot short in contact with one of the conductors could bypass the Train B DG unit parallel hand switch [EIIS Code: EK-HS], located in the control room, and energize the UPR.
During an emergency start of the DG due to an undervoltage or safety injection signal, the UPR would be de-energized, which is the desired state. However, during implementaton of post fire safe shutdown (PFSSD) per procedure OFN RP-017, "Control Room Evacuation," operator action could potentially reenergize the UPR if the hot short persists.
With the UPR energized, a number of contacts change state. In particular, the governor droop control contact will open when the UPR is energized. This places the governor in the droop mode of operation, which is undesired for PFSSD. This could adversely impact the ability to properly operate the Train B DG.
As a result of the review, engineers also noticed that a hot short in the control room voltage control circuit could signal the voltage regulator to reduce or increase the terminal voltage. The input voltage to this circuit is 125 VDC. A 125 VDC short of the proper polarity on particular conductors will energize the associated relay and send a signal to the electronic voltage adjuster or the electronic base adjuster. This would have a competing effect when loads are added to the DG as the automatic voltage adjuster tries to compensate for the added loads. If the hot short is signaling the adjuster to lower the voltage, then the machine terminal voltage may not be sufficient for the added loads. This potentially could affect the ability to energize the NB02 bus using the Train B EDG if a severe fire occurred in the control room.
1U.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REV WOLF CREEK GENERATING STATION 0 5000 482 1 YEAR NUMBER NO.
3 OF 4
2010
-- 003 001 In addition, engineers also identified that the null meter and the voltage regulator selector switch [EIIS Code: EK-HS], located in the control room, are not adequately isolated from the effects of a control room fire. The voltage potential normally carried by the cable connected to the control room mounted null meter is 15 VDC. A fire in the control room could cause a 125 VDC or 120 VAC hot short to come in contact with this cable, potentially causing damage to the voltage error detector card or the firing circuit input card. If this were to occur, the Train B DG may not function properly.
In addition, engineers also identified that the null meter and the voltage regulator selector switch [EIIS Code: EK-HS], located in the control room, are not adequately isolated from the effects of a control room fire. The voltage potential normally carried by the cable connected to the control room mounted null meter is 15 VDC. A fire in the control room could cause a 125 VDC or 120 VAC hot short to come in contact with this cable, potentially causing damage to the voltage error detector card or the firing circuit input card. If this were to occur, the Train B DG may not function properly.
BASIS FOR REPORTABILITY This condition is reportable pursuant to 10 CFR 50.73(a)(2)(ii)(B) for any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety. Additionally, WCNOC made an eight hour Emergency Notification System call, Event Notification 45692, in accordance with 10 CFR 50.72(b)(3)(ii)(B).
ROOT CAUSE The apparent cause for this event is inadequate review of control room circuitry for impact on PFSSD following a control room fire. The issues described in this LER were inherent in the original design of the plant. Since approval of the original safe shutdown strategy for a control room fire, a detailed circuit analysis for equipment required to achieve and maintain safe shutdown in the event of a control room fire was not completed. Instead, corrective actions to address specific identified issues regarding the control room fire safe shutdown strategy were addressed.
CORRECTIVE ACTIONS
A change was made to procedure OFN RP-01 7 that would de-energize the UPR and take the governor out of droop mode of operation. To address the issues with the UPR and a 125 VDC hot short, procedure OFN RP-01 7 was revised to have operators actuate the emergency start switch as a required action during the startup of the Train B DG.
A temporary modification was installed which bypassed the control room circuitry for the null meter and hand switch NEHS0012A.
IU.S. NUCLEAR REGULATORY COMMISSION (9-2007)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEQUENTIAL REV WOLF CREEK GENERATING STATION 05000 482 YEAR NUMBER NO.
4 OF 4
I2010
-- 003--
00 A PFSSD analysis of circuits/components in the control room that could affect OFN RP-01 7 components credited for PFSSD in the event of a control room fire will be performed and completed by 12/17/2010.
A modification to permanently address the PFSSD issue currently covered by temporary modification will be implemented by 7/28/2011.
SAFETY SIGNIFICANCE
This issue has low safety significance. A fire in the control room of such magnitude and severity as to cause an evacuation and plant shutdown is extremely unlikely. Based on the Fire Hazards Analysis (E-1 F9905), the combustible loading in the control room is low and interior finish materials meet or exceed the surface flammability requirements of applicable standards. Cables entering the control room are IEEE 383 rated. Large concentrations of cables in the control room trenches are protected with an automatic Halon extinguishing system and automatic smoke detectors are located in the control cabinets and trenches.
OPERATING EXPERIENCE/PREVIOUS EVENTS LER 2005-005-00 reported a condition where a postulated fire could cause the loss of the centrifugal charging pump's capability to successfully inject borated water into the reactor. This condition was caused by the original Electrical Fire Hazards Analysis (EFHA) having non-validated assumptions and being insufficiently documented.
LER 2005-007-00 reported a condition where a postulated fire could cause the loss of field flashing for the Train B Diesel Generator. This condition was caused by the original EFHA completed for the Wolf Creek Generating Station not identifying that field flashing may not be available if a fire occurs in the control room.
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