05000298/LER-2011-007, For Cooper Nuclear Station, Regarding Primary Containment Lost Safety Function Due to Open Drywell Vacuum Breaker
| ML12024A321 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 01/12/2012 |
| From: | Dori Willis Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2012008 LER 11-007-00 | |
| Download: ML12024A321 (6) | |
| 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)(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 |
| 2982011007R00 - NRC Website | |
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N Nebraska Public Power District Always there when you need us NLS2012008 January 12, 2012 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2011-007-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
is to forward Licensee Event Report 2011-007-00.
Demetrius L. Willis General Manager of Plant Operations hJo Attachment cc:
Regional Administrator w/attachment USNRC - Region IV Cooper Project Manager w/attachment-USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/attachment USNRC - CNS SRAB Administrator w/attachment NPG Distribution w/attachment INPO Records Center w/attachment SORC Chairman w/attachment CNS Records w/attachment COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com Ea2;)
1-4 (LfC
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/31/2013 (10-2010)
Estimated burden per response to comply with this mandatory information collection request: 80 hrs. Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA/Privacy Service Branch (T-5 F53), U.S. Nuclear Regulatory Commission, LICENSEE EVENT REPORT (LER)
Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs NEOB-10202, (See reverse for required number of (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means digits/characters for each block) used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Cooper Nuclear Station 05000298 1 of 4
- 4. TITLE Primary Containment Lost Safety Function due to Open Drywell Vacuum Breaker
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH i DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
05000 I
FACILITY NAME DOCKET NUMBER 11 22 2011 2011 007-00 01 12 2012 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 6: (Check all that annlv) 1 El 20.2201(b)
[] 20.2203(a)(3)(i)
[L 50.73(a)(2)(i)(C)
EL 50.73(a)(2)(vii)
I] 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)
LI 20.2203(a)(4)
EL 50.73(a)(2)(ii)(B)
EL 50.73(a)(2)(viii)(B)
EL 20.2203(a)(2)(i)
LI 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
EL 50.73(a)(2)(ix)(A)
EL 20.2203(a)(2)(ii)
EL 50.36(c)(1)(ii)(A)
EL 50.73(a)(2)(iv)(A)
[L 50.73(a)(2)(x)
- 10. POWER LEVEL EL 20.2203(a)(2)(iii)
[L 50.36(c)(2)
[] 50.73(a)(2)(v)(A)
LI 73.71(a)(4) 100 LI 20.2203(a)(2)(iv)
LI 50.46(a)(3)(ii)
LI 50.73(a)(2)(v)(B)
LI 73.71(a)(5)
LI 20.2203(a)(2)(v)
[E 50.73(a)(2)(i)(A)
[L 50.73(a)(2)(v)(C)
EL OTHER Li 20.2203(a)(2)(vi)
Li 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify in Abstract below or in PLANT STATUS Cooper Nuclear Station (CNS) was in Mode 1, Power Operation, at 100 percent power at the time of the event.
BACKGROUND The function of the Torus to Drywell Vacuum Breaker [EIIS:VACB] is to relieve vacuum in the drywell. There are 12 internal vacuum breakers which allow air and steam flow from the suppression chamber (torus) to the drywell when the drywell is at a negative pressure. Torus to Drywell Vacuum breakers prevent an excessive negative differential pressure across the drywell boundary. Each vacuum breaker is a self-actuating valve [EllS:V], similar to a check valve, which can be remotely operated for testing purposes.
A negative differential pressure across the drywell wall is caused by rapid depressurization of the drywell. Design Bases Accident (DBA) analyses assume the vacuum breakers to be closed initially and to remain closed and leak tight, until the suppression pool is at a positive pressure relative to the drywell. The requirement that the vacuum breakers be closed ensures that there is no excessive bypass leakage should a Loss of Coolant Accident (LOCA) occur.
The function of the primary containment [EIIS:NH] is to isolate and contain fission products released from the Reactor Primary System following a design basis LOCA and to confine the postulated release of radioactive material. The safety design basis for the primary containment is that it must withstand the pressures and temperatures of the limiting DBA without exceeding the design leakage rate. The leakage from the drywell to the suppression chamber must be limited to ensure the pressure suppression function is accomplished and the suppression chamber pressure does not exceed design limits.
The vacuum breaker has a safety function in the closed position to limit the amount of bypass flow to ensure proper containment response on a postulated LOCA event and an open safety function post LOCA to limit negative differential pressure between the drywell and the suppression chamber. With the valve partially open, the LOCA containment response cannot be assured.
EVENT DESCRIPTION
On November 22, 2011, during performance of surveillance 6.2REC.101, the Master Control Switch (PC-SW-CSVB) for the 12 Torus to Drywell Vacuum Breakers was inadvertently bumped.
While performing the surveillance, a rolling podium was moved in front of panel VBD-J to allow the Control Room operator to perform a manipulation on panel VBD-M.
While moving the rolling podium, the top corner of the podium inadvertently came into contact with the Master Control Switch for the Torus to Drywell Vacuum Breakers. Contact between the rolling podium and the Master Control Switch was sufficient to cause the switch, normally in the closed position, to move to the open position. Consequently, an alarm was received indicating one
(PC-AO-NRV27) of the 12 Torus to Drywell Vacuum Breakers was at least partially open. This open indication was likely the result of residual pressurized air in the test actuator and associated instrument air line which was sufficient to move the valve test actuator and reposition the vacuum breaker off the contact points that operate the indicator light.
The Control Room operator, along with a peer, observed that the rolling podium contacted the Master Control Switch and repositioned the Master Control Switch to its normally closed position, closing PC-AO-NRV27. PC-AO-NRV27 was open approximately 5 seconds.
The Control Room Supervisor declared the Torus to Drywell Vacuum Breaker inoperable at 1353 hours0.0157 days <br />0.376 hours <br />0.00224 weeks <br />5.148165e-4 months <br /> and entered Technical Specification Limiting Condition of Operation (LCO) 3.6.1.8, Condition B, Required Action B.1, which requires the valve to be closed within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
Concurrently, Primary Containment was declared inoperable and LCO 3.6.1.1, Condition A, Action A.1, was entered, which requires restoration of Primary Containment within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. After the Torus to Drywell Vacuum Breaker was closed, the Control Room Supervisor declared the Torus to Drywell Vacuum Breaker and Primary Containment operable and exited LCO 3.6.1.8 and 3.6.1.1, respectively.
The rolling podium has an upper platform that is used to place documents during the performance of work evolutions. The rolling podium is designed such that the bottom base platform and the upper platform could contact a vertical surface simultaneously. The Master Control Switch protrudes from the control panel. The rolling podium had been previously adjusted to a height that is the same elevation as the Master Control Switch.
The rolling podium did not meet the requirements of CNS' Seismic Housekeeping procedure.
For compliance with this procedure, the rolling podium must be a "tended" item (i.e., a temporary item needed to support on-going work) or stowed no closer than 4 feet from any electrical control panel in the Control Room with the wheels in the locked position. Operations personnel confirmed that the rolling podium has been stowed in the Control Room when not "tended" and has been stowed within 4 feet from the electrical control panels. Therefore, it was incorrectly presumed that the rolling podium complied with the Seismic Housekeeping procedure. Compliance with the procedure was not questioned until the inadvertent bump of the Master Control Switch caused an unplanned LCO.
The podium was removed from the Control Room on November 30, 2011.
BASIS FOR REPORT CNS is reporting this event as a condition which could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident, per 10 CFR 50.73(a)(2)(v)(D), due to the function of Primary Containment being potentially degraded. CNS also reported this event per Event Notification 47471.
SAFETY SIGNIFICANCE
The safety significance associated with this condition is low due to the short duration the Torus to Drywell Vacuum Breaker was open. The potential impact of this condition is limited to LOCAs located in containment. The probability of a LOCA occurring during the approximate 5 second interval of time the Torus to Drywell Vacuum Breaker Master Control Switch was positioned to open is considered negligible. Therefore, it is concluded that this condition had low safety significance.
CAUSE
CNS determined the root cause of this event is the design of the rolling podium was deficient with respect to its use in the Control Room.
CORRECTIVE ACTION
To prevent recurrence of this event, the rolling podium will be replaced with one designed such that it cannot contact the switches and instrumentation.
PREVIOUS EVENTS A previous similar event involving the inadvertent contact of a switch in the Control Room occurred on August 27, 2011. A Gaitronics handset was dropped and contacted the "A" side Automatic Depressurization System (ADS) inhibit switch. This contact was sufficient to move the switch from the AUTO position to the INHIBIT position. The Control Room Supervisor was immediately informed and direction was given to place the switch back to AUTO. The "B" side of the ADS remained operable thus maintaining safety function of the ADS.
ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS© 4 ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS©4 Correspondence Number:
NLS2012008 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory
commitments
Please notify the Licensing Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.
COMMITMENT
COMMITTED DATE
COMMITMENT
NUMBER OR OUTAGE None
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