05000530/LER-2011-001, For Palo Verde, Unit 3, Regarding Reactor Trip Due to Failed Open Main Feedwater Pump a Minimum Flow Recirculation Valve
| ML110900061 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 03/21/2011 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06334-DCM/JR LER 11-001-00 | |
| Download: ML110900061 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) |
| 5302011001R00 - NRC Website | |
text
10 CFR 50.73 AM*
A subsidiary of Pinnacle West Capital Corporation Palo Verde Nuclear Generating Station Dwight C. Mims Senior Vice President Regulatory Affairs and Oversight Tel. 623-393-5403 Fax 623-393-6077 Mall Station 7605 P.O. Box 52034 Phoenix, Arizona 85072-2034 102-06334-DCM/JR March 21, 2011 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Unit 3 Docket No. STN 50-530 License No. NPF-74 Licensee Event Report 2011-001-00 Enclosed please find Licensee Event Report (LER) 50-530/2011-001-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports an automatic actuation of the reactor protection system (reactor trip) and auxiliary feedwater actuation signal subsequent to a failed open main feedwater pump minimum flow recirculation valve.
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 Marianne Webb, Section Leader, Regulatory Affairs, at (623) 393-5730.
Arizona Public Service Company makes no commitments in this letter.
Sincerely, DCM/TNW/MNW/JRPgat Enclosure cc:
E. E. Collins Jr.
L. K. Gibson J. R. Hall M. A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager for PVNGS (electronic / paper)
NRC NRR Senior Project Manager (electronic / paper)
NRC Senior Resident Inspector for PVNGS A member of the STARB (Strategic Teaming and Resource Sharing) Alliance Callaway - Comanche Peak - Diablo Canyon
- Palo Verde
- San Onofre
- South Texas
- Wolf Creek
NRC FORM 366 U.S. NUCLEAR REGULATORY 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 3 05000530 1 OF 4
- 6. TITLE Unit 3 Reactor Trip Due to Failed Open Main Feedwater Pump A Minimum Flow Recirculation Valve
- 5. EVENT DATE
- 6. LER NUMBER
[
- 7. REPORT DATE 1
- 8. OTHER FACILITIES INVOLVED MONTH I DAY I
I SEQUENTIAL REV I
FACILITY NAME 01 1 19 12011 1 -FACI20 1
1 NAME k. OPERATING MODE 1
- 10. POWER LEVEL 100
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that EO 20.2201(b)
[1 20.2201(d)
[I 20.2203(a)(1)
[I 20.2203(a)(2)(i)
[I 20.2203(a)(2)(ii)
El 20.2203(a)(2)(iii)
O 20.2203(a)(2)(iv)
O 20.2203(a)(2)(v)
El 20.2203(a)(2)(vi)
[I 20.2203(a)(3)(i) o 20.2203(a)(3)(ii)
El 20.2203(a)(4) o 50.36(c)(1)(i)(A)
El 50.36(c)(1)(ii)(A) o 50.36(c)(2)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(i)(A) o 50.73(a)(2)(i)(B)
[I 50.73(a)(2)(i)(C)
Ol 50.73(a)(2)(ii)(A)
[O 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(iii) 10 50.73(a)(2)(iv)(A) ol 50.73(a)(2)(v)(A)
[I 50.73(a)(2)(v)(B)
[o 50.73(a)(2)(v)(C)
[o 50.73(a)(2)(v)(D)
El 50.73(a)(2)(vii)
E] 50.73(a)(2)(viii)(A)
[] 50.73(a)(2)(viii)(B)
E] 50.73(a)(2)(ix)(A)
[I 50.73(a)(2)(x)
[I 73.71(a)(4)
El 73.71(a)(5)
El OTHER Specify in Abstract below or in Each MFWP is a turbine-driven pump capable of supplying 65 percent of main feedwater system capacity. There are two MFWPs which serve both SGs. The MFWP mini-flow valves assure there is always adequate flow through the MFWPs to prevent pump damage.
Each mini-flow valve has the capability of providing a flow of approximately 7000 gpm to the main condenser (EIIS Code: SG). The mini-flow valve is designed to fail open on loss of electrical signal or loss of instrument air to ensure that minimum flow is maintained through the MFWP to prevent pump damage on a loss of downstream flowpath during pump operation.
- 3.
INITIAL PLANT CONDITIONS
On January 19, 2011, Palo Verde Unit 3 was in Mode 1 (Power Operation) at 100 percent power at normal operating temperature and normal operating pressure. There were no inoperable structures, systems, or components at the time that contributed to this event.
- 4.
EVENT DESCRIPTION
On January 19, 2011, at 1840, Unit 3 experienced a reactor power cutback (RPCB) (EIIS Code: JD) from 100 percent power to approximately 60 percent power due to MFWP B tripping on low suction pressure. The low suction pressure was experienced by both MFWPs. The MFWP trip logic is designed to trip MFWP B first to prevent simultaneous MFWP trips. The low suction pressure was caused by a failed diaphragm in a pneumatic 3-way precision relay (precision relay) for the mini-flow valve on MFWP A (see diagram) which caused the mini-flow valve to fail open and divert a percentage of feedwater flow from both SGs to the condenser.
The precision relay functions to cause full opening of the mini-flow valve when input control air pressure falls below 3 psig. Control air pressure is normally maintained between 3 to 15 psig.
The failed diaphragm caused air leakage within the precision relay which lowered the input control air pressure to less than 3 psig and actuated the precision relay to open the mini-flow valve.
During this transient, both SG levels decreased to the point that a reactor trip (EIIS Code: JC) occurred at 1841. The SG levels continued to lower following the reactor trip resulting in an AFAS (EIIS Code: JE). Both auxiliary feedwater pumps A and B started and fed SGs in conjunction with MFWP A. The plant was stabilized in Mode 3.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
There were no inoperable structures, systems, or components at the time that contributed to this event. The plant responded as designed for the RPCB, reactor trip and AFAS actuations. The conditional core damage probability for this event was calculated to be NKR, FRUM 366A (10-20107)
PRKINTED ON RECYCLED PAPER
1.26E-6. This 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.
This event did not prevent the fulfillment of a safety function nor did it result in a safety system functional failure as described by 10 CFR 50.73 (a)(2)(v).
- 6.
CAUSE OF THE EVENT
The cause of the event was a failed diaphragm in the precision relay for the mini-flow valve control loop which resulted in the opening of the mini-flow valve on MFWP A. This allowed a percentage of feedwater flow to be diverted to the condenser, resulting in a MFWP B trip and a RPCB followed by a reactor trip and AFAS.
- 7.
CORRECTIVE ACTIONS
The following corrective actions were implemented:
- 1. The Unit 3 MFWP A mini-flow valve control system precision relay was immediately replaced.
- 2. The Unit 3 MFWP B mini-flow valve control system precision relay was replaced on February 18, 2011 as an interim action.
The extent of condition evaluation determined that the subject relays are not installed in the Units 1 and 2 MFWP mini-flow valve control systems. To improve maintenance reliability, a modification replaced these mini-flow valves and control systems during previous outages in Units 1 and 2. The same modification to replace the Unit 3 MFWP mini-flow valves and their control systems is planned during the next refueling outage.
The preventive maintenance process for these relays will be addressed as part of the corrective actions of this investigation. Any additional corrective actions taken as a result of the investigation of this event will be implemented in accordance with the requirements of the Palo Verde corrective action program. If information is subsequently developed which would significantly affect a reader's understanding or perception of this event, a supplement to this LER will be submitted.
- 8.
PREVIOUS SIMILAR EVENTS
No similar conditions have been reported by Palo Verde in the past three years.
N'C. F-URM,36bA (10U-20107),
RliNl I ED:: ON MM'*Tý.LiCU PAPERI: