05000528/LER-2012-004, Regarding Essential Spray Pond Pump Actuation Due to a Control Room Essential Filtration Actuation Signal
| ML12310A363 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 10/29/2012 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06603-DCM/FJO LER 12-004-00 | |
| Download: ML12310A363 (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 |
| LER closed by | |
| IR 05000528/2013002 (14 May 2013) | |
| 5282012004R00 - NRC Website | |
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- Ae A
subsidiary of Pinnacle West Capital Corporation Palo Verde Nuclear Generating Station Dwight C. Mims Senior Vice President Nuclear Regulatory and Oversight Tel. 623-393-5403 Fax 623-393-6077 Mail Station 7605 P.O. Box 52034 Phoenix, Arizona 85072-2034 102-06603-DCM/FJO October 29, 2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Unit 1 Docket No. STN 50-528 License No. NPF-41 Licensee Event Report 2012-004-00 Enclosed please find Licensee Event Report (LER) 50-528/2012-004-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports the automatic actuation of the Unit 1 train A and train B essential spray pond system pumps that occurred as a result of a control room essential filtration actuation signal.
In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the Nuclear Regulatory Commission (NRC) Regional Office, NRC Region IV and the Senior Resident Inspector. If you have questions regarding this submittal, please contact Mark McGhee, Operation Support Manager, Regulatory Affairs, at (623) 393-4972.
Arizona Public Service Company makes no commitments in this letter.
Sincerely, DCM/FJO/hsc Enclosure cc:
E. E. Collins Jr.
L. K. Gibson M. A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager (electronic / paper)
NRC Senior Resident Inspector for PVNGS A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak ° Diablo Canyon ° Palo Verde
- San Onofre ° South Texas ° Wolf Creek
I NRC FORM 366 U.S. NUCLEAR REGL.LATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Palo Verde Nuclear Generating Station (PVNGS) Unit 1 05000528 1 OF 5
- 4. TITLE Essential Spray Pond Pump Actuation Due to a Control Room Essential Filtration Actuation Signal
- 5. EVENT DATE
- 6. LER NUMBER__
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED 0 29 21I" I
I "FACILITY NAME DOCKETocE NUMBERNBE MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FCLT AEDCENME NUMBER NO.
FACILITY NAME DOCKET NUMBER 08 29 2012 2012 - 004 -
00 10 29 2012
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITrED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
EO 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) 1 0
20.2201(d)
[E 20.2203(a)(3)(ii)
[I 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[I 20.2203(a)(1)
[I 20.2203(a)(4)
[I 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[I 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL E] 20.2203(a)(2)(ii)
[1 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
[I 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71 (a)(4)
El 20.2203(a)(2)(iv)
[I 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71 (a)(5) 100 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
[I OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in (CREFAS) to limit radiation exposure to control room personnel following a fuel handling accident.
The CREFAS actuation isolates normal ventilation to the control room and starts the train A and train B control room essential air filtration units (AFU) which provide cooled and filtered air to the control room. The CREFAS also starts both train A and train B essential chilled water (EC) systems (EIIS Code: KM), essential cooling water (EW) systems (EIIS Code: BI) and essential spray pond (SP) systems (EIIS Code: BS) to support the control room essential ventilation system functions. The SP system removes heat from the EW system which in turn removes heat from the EC system. The EC system provides chilled water to the control room essential AFU cooling coils to maintain controlled temperatures in the control room during post accident conditions. The SP system is also the ultimate heat sink.
- 3.
INITIAL PLANT CONDITIONS
On August 29, 2012, Palo Verde Unit 1 was in Mode 1 (Power Operation), at 100 percent power and at normal operating temperature and normal operating pressure.
There were no structures, systems, or components inoperable at the time of the event that contributed to the event.
4. EVENT DESCRIPTION
On August 29, 2012, the Unit 1 control room received a RU-145 high radioactivity alarm.
This resulted in a train A and B FBEVAS actuation and a train A and B CREFAS actuation.
The CREFAS actuations started both trains of the EC, EW and SP systems in support of the control room essential ventilation system functions. Plant equipment that was required to start for the FBEVAS and CREFAS actuations was verified by operations to start and operate as expected. Radiation protection personnel performed alternate sampling of the fuel building ventilation exhaust and evaluated other radiation monitor readings and determined the RU-145 alarm condition was invalid. Operations personnel then performed procedures to bypass the BOP-ESFAS input from RU-1 45 and restore the actuated plant equipment to normal alignments.
On August 31, 2012, troubleshooting determined the RU-145 high alarm was caused by the loss of the monitor's 24 VDC low voltage power supply. The loss of the 24 VDC resulted in two relays activating at the RU-145 equipment skid, located in the fuel building. Relay K201 turned on the monitor check source which is intended to raise the monitor's output 3 to 4 decades to confirm that the detector is capable of detecting radiation. During the normal check source activation sequence, the monitor's software first inhibits any trip functions and then activates the check source. However, when relay K201 activated due to the loss of 24 VDC, the software, which was functioning normally, was bypassed so that no software
based trip inhibit function was activated and the increased monitor output caused a high alarm trip which initiated a FBEVAS and CREFAS. Relay K205 also activated, which turned Qff the monitor's sample pump and caused a low flow/equipment failure alarm. This condition resulted in RU-1 45 no longer performing its function of monitoring the fuel building ventilation exhaust for radioactivity. The fuel building ventilation exhaust high range monitor, RU-1 46, remained available to monitor the fuel building ventilation exhaust.
The RU-1 45 low voltage power supply was replaced and the monitor was returned to service.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
RU-1 45 is the low range portion of the fuel building ventilation exhaust post accident monitor. The primary function of this monitor is to provide the FBEVAS engineered safety feature actuation on high alarm. The other purpose of this monitor is to assess releases through the fuel building ventilation exhaust under both normal and post accident conditions.
With RU-1 45 failed, the high range monitor, RU-146, remained available to monitor the fuel building ventilation exhaust. The spent fuel pool area radiation monitor, RU-31, and the new fuel storage area monitor, RU-1 9, were available to alert operators to a high radiation level condition in the fuel building, and RU-31 provides a redundant and diverse actuation of FBEVAS. No fuel handling was in progress during the event or following the event while RU-145 was out of service. The action requirements of the PVNGS Offsite Dose Calculation Manual for failure of RU-145 were met during this event. No Technical Specification or Technical Requirements Manual requirements were affected by this event.
Actuation of the fuel building essential ventilation, control room essential ventilation, EC, EW, and SP systems did not affect the capability of these systems to perform their safety functions.
There were no inoperable structures, systems, or components at the time of the event that contributed to this event. The event did not result in any challenges to the fission product barriers or result in the release of radioactive materials. There were no actual safety consequences as a result of this event. The condition did not result in a safety system functional failure as described by 10 CFR 50.73 (a)(2)(v).
6. CAUSE OF THE EVENT
The direct cause of the RU-1 45 high alarm was loss of the monitor's 24 VDC low voltage power supply voltage which caused the monitor check source feature to activate.
The event investigation team determined that a random failure of a zener diode in the RU-145 low voltage power supply caused the loss of the 24 VDC low voltage source.
- 7.
CORRECTIVE ACTIONS
The following immediate actions were performed:
" Plant equipment that was required to start for the FBEVAS and CREFAS actuation signals was verified by operations to start and operate as expected.
" Radiation protection personnel performed alternate sampling of the fuel building ventilation exhaust and evaluated other radiation monitor readings and determined the RU-145 alarm condition was invalid.
" Operations placed the BOP-ESFAS input from RU-145 in bypass which disabled the FBEVAS actuation function of the monitor and allowed reset of all actuations.
" Operations personnel restored plant equipment to normal alignments.
The investigation team determined that zener diodes have no known wear-out mechanisms and are reliable components in low voltage power supply applications. Existing preventive maintenance requirements for the radiation monitoring system replace the power supply boards at a 7.5 year interval. This failure was the first of this type in the radiation monitoring system at PVNGS with greater than 25 years of operation. Therefore, no additional preventive maintenance or other corrective actions were determined to be necessary to minimize the potential for recurrence of this event.
Any additional corrective actions taken as a result of this event will be implemented in accordance with the PVNGS corrective action program. If information is subsequently developed that would significantly affect a reader's understanding or perception of this event, a supplement to this LER will be submitted.
- 8.
PREVIOUS SIMILAR EVENTS
PVNGS has not reported a similar event of a system actuation that resulted in the actuation of the SP in the past three years.PRINTED ON RECyCLED PAPER