05000528/LER-2011-005, For Palo Verde, Unit 1, Regarding Manual Reactor Trip Due to Slipped Control Elemental Assemblies
| ML12039A086 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 01/23/2012 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06462-DCM/DCE LER 11-005-00 | |
| Download: ML12039A086 (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) | |
| 5282011005R00 - NRC Website | |
text
10 CFR 50.73 A--
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 102-06462-DCM/DCE January 23, 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 2011-005-00 Enclosed please find Licensee Event Report (LER) 50-528/2011-005-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports a manual actuation of the reactor protective system in response to a control element assembly subgroup that slipped during post-refueling low power physics testing.
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, Department Leader, Regulatory Affairs, at (623) 393-4972.
Arizona Public Service Company makes no commitments in this letter.
Sincerely, DCM/TNW/DCE/gat Enclosure cc:
E. E. Collins Jr.
B. K. Singal L. K. Gibson J. R. Hall M. A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager for PVNGS (electronic / paper)
NRC NRR Project Manager for PVNGS (electronic)
NRC NRR Senior Project Manager (electronic)
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
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.
- 13. PAGE Palo Verde Nuclear Generating Station (PVNGS) Unit 1 05000528 1 OF 5
- 4. TITLE Unit 1 Manual Reactor Trip due to Slipped Control Element Assemblies
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.I FACILITY NAME DOCKET NUMBER 11 22 2011 2011 - 005 -
00 01 23 2012 I
L
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
[I 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
[1 50.73(a)(2)(vii) 2 [E 20.2201(d)
El 20.2203(a)(3)(ii)
E] 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
[I 20.2203(a)(4)
[E 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
[I 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)
ED 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
[E 20.2203(a)(2)(iii)
El 50.36(c)(2)
[] 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 0 El 20.2203(a)(2)(v)
[I 50.73(a)(2)(i)(A) 0l 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 Each CEAC receives reed switch position transmitter inputs for all CEAs. The CEACs compare the positions of all CEAs within each CEA subgroup and determine penalty factors based upon CEA deviations within a subgroup. The CPCs also compute penalties for CEA group out-of-sequence and subgroup deviation conditions.
Low power physics testing is conducted during Mode 2 following refueling outages to verify reactor core operating characteristics are consistent with design predictions and to provide assurance the core can be operated as designed. The low power physics testing procedure provides direction to invoke the low power physics testing special test exceptions under Technical Specification (TS) 3.1.10 that suspends certain limiting conditions for operation (LCOs), including LCO 3.3.3 which normally requires two channels of CEACs to be OPERABLE and LCO 3.1.5, CEA Alignment. Both channels of CEACs are inoperable during low power physics testing. The CPCs will not generate reactor trips based on CEA alignment deviations while CEACs are inoperable.
- 3.
INITIAL PLANT CONDITIONS
On November 22, 2011, Palo Verde Unit 1 was in Mode 2 (Start-up), at less than 1 percent power and at normal operating temperature and normal operating pressure. The reactor was critical and post-refueling low power physics testing was in progress. CEACs were inoperable at the time of the event as directed by the low power physics testing procedure.
There were no other structures, systems, or components inoperable at the time of the event that contributed to the event.
- 4.
EVENT DESCRIPTION
On November 22, 2011, at 1921, CEA regulating group (RG) #2 was being inserted into the reactor while performing post-refueling low power physics testing during the plant start-up following refueling outage 1 R1 6. At that time, the control room staff noted that the four CEAs in RG #2, subgroup #17, slipped approximately 11 tol4 inches below subgroup #18 CEAs, also in RG #2.
In response to the deviation between the RG #2 subgroups, the control room staff manually tripped the reactor as directed by the abnormal operating procedure, CEA Malfunctions, for deviations of CEA subgroups of more than 6.6 inches. An automatic trip was not generated by the CPCs because CEACs were inoperable for performance of the testing.
All CEAs fully inserted and the plant responded to the trip as designed. No other actuations of plant engineered safety features systems occurred or were required.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
This event did not result in a transient more severe than those already analyzed in the PVNGS Updated Final Safety Analysis Report Chapter 15. The transient did not cause a violation of safety limits or the specified acceptable fuel design limits. Because the primary and secondary system pressures stayed below the respective safety valve opening setpoints, design pressures were not challenged.
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 condition. The condition does not represent a reportable safety system functional failure under 10 CFR 50.73 (a)(2)(v).
- 6.
CAUSE OF THE EVENT
An intermittent failure of a power switch assembly which provides electrical power to the control element drive mechanisms resulted in the CEA slippage.
The root cause investigation is in progress. A supplement to this LER will provide the results of the investigation.
- 7.
CORRECTIVE ACTIONS
After troubleshooting was completed, the power switch assembly was replaced. Retesting was completed on November 24, 2011. The unit was subsequently restarted and entered Mode 1 on November 27, 2011.
A supplement to this LER will discuss the corresponding corrective actions to prevent recurrence prescribed by the root cause investigation.
- 8.
PREVIOUS SIMILAR EVENTS
The root cause investigation is in progress. A complete discussion of previous similar events will be provided in a supplement to this LER based on the investigation results.
Preliminarily, the following events related to failures of power switch assemblies were identified. The relationship of these previous events to the event in this LER has not been determined.
LER 50-528/2011-004-00 reported an automatic trip of the Unit 1 reactor that occurred on August 6, 2011, which resulted from a dropped CEA (#37) caused by a loose terminal lug on the corresponding CEA power switch assembly.
On March 4, 2011, Unit 3 CEA #1 dropped into the core because of an age related failure of an electrolytic capacitor on the zero crossing detector card installed in the corresponding power switch assembly. This did not require an automatic or manual trip of the reactor and was not reportable.
On December 4, 2009, during a Unit 3 reactor startup while subcritical, subgroup #15 part-strength CEAs dropped into the core because of an age related failure of an electrolytic capacitor on the zero crossing detector card installed in the corresponding power switch assembly. The decision was made to terminate the start-up by manually tripping the reactor. This condition was not reportable.
Replacements of the electrolytic capacitors on the zero crossing detector cards have been completed in Unit 1 and are scheduled for upcoming refueling outages in Units 2 and 3.