05000298/LER-2012-004, Regarding Isolation of Shutdown Cooling Results in Loss of Safety Function
| ML12348A032 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/06/2012 |
| From: | O'Grady B Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2012126 LER 12-004-00 | |
| Download: ML12348A032 (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)(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 |
| 2982012004R00 - NRC Website | |
text
H Nebraska Public Power District Always there when you need us NLS2012126 December 6, 2012 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2012-004-00 Cooper Nuclear Station, Docket No. 50-298, DPR-46
Dear Sir or Madam:
The purpose of this correspondence is to forward Licensee Event Report 2012-004-00.
There are no new commitments contained in this letter.
Sincerely, Brian J. O'Grady Vice President Nuclear-Chief Nuclear Officer
/Jo Attachment: Licensee Event Report 2012-004-00 cc:
Regional Administrator w/attachment NPG Distribution w/attachment USNRC - Region IV Cooper Project Manager w/attachment INPO Records Center w/attachme USNRC - NRR Project Directorate IV-I via ICES entry Senior Resident Inspector w/attachment SORC Chairman w/attachment USNRC - CNS SRAB Administrator w/attachment CNS Records w/attachment nt COOPER NUCLEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com I ý11/
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 Isolation of Shutdown Cooling Results in Loss of Safety Function
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
05000 t
jFACILITY NAME DOCKET NUMBER 10 14 2012 2012 004-00 12 06 2012 i
05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 6: (Check all that aoolv) 3 El 20.2201(b)
[I 20.2203(a)(3)(i)
E] 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
El 20.2201(d)
[] 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
[] 20.2203(a)(4)
E3 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
E) 20.2203(a)(2)(i)
[l 50.36(c)(1)(i)(A)
E3 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
El 20.2203(a)(2)(ii)
[L 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
C3 50.73(a)(2)(x)
- 10. POWER LEVEL Li 20.2203(a)(2)(iii)
Li 50.36(c)(2)
EL 50.73(a)(2)(v)(A)
EL 73.71(a)(4) 000
[]
20.2203(a)(2)(iv)
Ei 50.46(a)(3)(ii)
[D 50.73(a)(2)(v)(B)
[L 73.71(a)(5)
El 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A)
Ei 50.73(a)(2)(v)(C)
El OTHER Li 20.2203(a)(2)(vi)
Li 50.73(a)(2)(i)(B)
Li 50.73(a)(2)(v)(D)
Specify in Abstract below or in PLANT STATUS Cooper Nuclear Station (CNS) was at 29 psig reactor pressure, in Mode 3, Hot Shutdown, at the time of the event. Shutdown Cooling (SDC) was not in-service at the time. Plant cooldown was in progress through the Main Condenser. Main Turbine bypass valves controlled temperature and pressure steady.
BACKGROUND The safety objective of the Residual Heat Removal (RHR) system [EIIS:BO] is to provide core cooling, in conjunction with other Emergency Core Cooling Systems, and to provide containment cooling as required during abnormal operational transients and postulated accidents. The RHR system consists of two heat exchangers [EIIS:HX], four main system pumps [EllS:P], and associated piping, valves [EIIS:V], controls and instrumentation. Irradiated fuel in the shutdown reactor core generates heat during the decay of fission products and increases the temperature of the reactor coolant. The decay heat must be removed to reduce the temperature of the reactor coolant less than or equal to 212 degrees Fahrenheit in preparation for performing Refueling or Cold Shutdown maintenance operations, or the decay heat must be removed for maintaining the reactor in the Hot Shutdown condition.
SDC is a subsystem of RHR and is placed in operation during a normal reactor shutdown and cooldown. Reactor Coolant is pumped by the RHR main system pumps from one recirculation loop through the RHR heat exchangers prior to returning to the reactor vessel through connections to the recirculation loop(s).
Pressure switches [EIIS:PS] RR-PS-128A and RR-PS-128B function to protect SDC suction piping from overpressure. Isolation valves [EIIS:ISV] RHR-MO-17 and RHR-MO-18 are interlocked to close and remain closed on a reactor pressure greater than 72 psig.
EVENT DESCRIPTION
On October 14, 2012, CNS was in Mode 3 with reactor pressure at 29 psig, and reactor coolant temperature at 273 degrees Fahrenheit. Operations personnel were flushing the B loop of RHR in accordance with the station procedure in preparation for the start of the SDC mode of operation.
Per station procedure, the radwaste discharge valve (RHR-MOV-MO57) was slowly throttled open to perform a slow and controlled heatup of RHR piping. Due to existing reactor temperature and pressure, flashing of the hot reactor coolant to steam occurred, causing a pressure spike that exceeded 72 psig. This occurred because the distance that RHR-MOV-M057 can be throttled open is dependent upon the temperature of the incoming reactor coolant. Consequently, an annunciator alarm was received in the Control Room at 01:17 indicating there had been a high pressure event that automatically closed RHR-MO-17 and RHR-MO-18 isolating the RHR SDC loop.
The RHR system was subsequently vented and the flush was re-performed successfully at 02:48.
BASIS FOR REPORT This event is reportable under 10 CFR 50.73(a)(2)(v)(B) due 60 days from day of discovery, i.e.,
by December 13, 2012. This was a condition which could have prevented the fulfillment of the safety function of structures or systems that are needed to remove residual heat.
SAFETY SIGNIFICANCE
This event is considered to have minimal safety significance because all RHR pumps and associated equipment required for SDC operation remained available. Isolation of the RHR SDC suction valves occurred due to a momentary isolation signal received while performing system alignment and flushing in preparations for start of SDC operation. This isolation was momentary and did not impact the ability to restore the valves to the open position and place SDC in service.
This is a Safety System Functional Failure.
CAUSE
CNS determined that the station procedure provides insufficient guidance to avoid automatic closure of RHR-MO-17 and RHR-MO-18 during SDC heatup and flush when the reactor temperature is higher than 212 degrees Fahrenheit.
CORRECTIVE ACTION
To prevent recurrence of this event, the procedure will be revised so that the isolation of RHR-MO-17 and RHR-MO-18 is an expected effect that will occur during SDC heatup and flush; and provide more specific instructions concerning throttling time versus reactor vessel conditions.
PREVIOUS EVENTS On November 7, 2009, isolation signals from pressure switches in the Recirculation System caused SDC suction isolation valves to close, which initiated a trip of the operating RHR Pump D. The event was reported under LER 2009-003-00, Isolation of Residual Heat Removal Shutdown Cooling, dated January 4, 2010.
On September 26, 2009, isolation valves closed while performing the procedure for SDC flush.
The procedure was revised to instruct slowly opening RHR-MO-57.
On October 28, 2003, RHR loop A tripped twice while attempting to place in SDC. The condition was attributed to pressure perturbations caused by inadequate flushing of the system.
On June 15, 2003, RHR loop B was in SDC. During the initial pump start of RHR, the SDC suction header high pressure alarm activated; also on May 27, 2003, RHR loop A was in SDC, the SDC suction header high pressure alarm activated. Both events were unexpected Control Room alarms.