05000528/LER-2012-001, For Palo Verde, Unit 1, Regarding Technical Specification LCO 3.1.7 Incorrect Pdil Setpoint Values
| ML12139A130 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/04/2012 |
| From: | Mims D Arizona Public Service Co, Pinnacle West Capital Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06521-DCM/TNW/MAM/DFH LER 12-001-00 | |
| Download: ML12139A130 (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 |
| 5282012001R00 - NRC Website | |
text
10 CFR 50.73 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 102-06521 -DCM/TNW/MAM/DFH May 4, 2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Units 1, 2, and 3 Docket No. STN 50-528, STN 50-529, and STN 50-530 License No. NPF-41, NPF-51, and NPF-79 Licensee Event Report 2012-001-00 Enclosed, please find Licensee Event Report (LER) 50-528/2012-001-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports a condition prohibited by Technical Specification (TS) 3.1.7, Regulating Control Element Assembly (CEA) Insertion Limits, when the power dependent insertion limit alarm circuit was determined to be inoperable for a period greater than allowed by TS.
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, Operations Support Manager, Regulatory Affairs, at (623) 393-4972.
Arizona Public Service Company makes no commitments in this letter.
DCM/TNW/MAM/DFH/hsc Enclosure cc:
E. E. Collins Jr.
B. K. Singal L. K. Gibson J. R. Hall M. A. Brown Sincerely, 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: 10/3112013 (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 Technical Specification LCO 3.1.7 Incorrect PDIL Setpoint Values
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY1' NAE OCKE TNUMB MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR (PVNGS) N it 2 050052 NUMBER()
Unit 2 05000529 FACILITY NAME DOCKET NUMBER 04 19 2005 2012 - 001 -
00 05 7
2012 (PVNGS) Unit 3 05000530
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
[I 50.73(a)(2)(vii) 1/1/1 El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
E] 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
[] 50.73(a)(2)(viii)(B)
E] 20.2203(a)(2)(i)
[E 50.36(c)(1)(i)(A)
E] 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 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)
[1 73.71(a)(4)
[I 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5) 100/100/95 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[E 50.73(a)(2)(v)(C)
[I OTHER [I 20.2203(a)(2)(vi) 0 50.73(a)(2)(i)(B)
[E 50.73(a)(2)(v)(D)
Specify in Abstract below or in The PDIL alarms are generated using the PDIL alarm setpoint programmed into the software of the plant monitoring system (PMS) computers. The PMS is comprised of two independent computer systems designated as the plant computer (PC) and the core monitoring computer (CMC). The PC and CMC functions related to the PDIL alarm circuits are fully redundant and each provides the same alarm capabilities.
CEA position indication is provided by three separate instruments for each of the CEAs. Two safety-related reed switch position transmitter (RSPT) indications and one computer generated pulse counter position indication are provided for each CEA. The RSPTs measure CEA position via magnetically actuated reed switches located on the CEDM housing and input to the plant protection system to provide safety related reactor protection system functions and CEA position indications in the Control Room. The PMS computers generate pulse counter CEA position indications by counting CEDM coil movement electrical pulses at the CEDMCS cabinets and provide indications and alarms in the control room and CEA positions for use in the core operating limit supervisory system (COLSS) calculations. Each pulse that is counted indicates 0.75 inches of CEA travel. The pulse counted CEA positions are used as inputs for the PDIL alarm circuits.
- 3.
INITIAL PLANT CONDITIONS
On March 8, 2012, all three units were in Mode 1, with Units 1 and 2 operating at 100 percent power and Unit 3 at 95 percent power during power coast down for a scheduled refueling outage. There were no structures, systems, or components inoperable at the time of the event that contributed to the event.
- 4.
EVENT DESCRIPTION
On March 8, 2012, at 1752, all Palo Verde units entered TS LCO 3.1.7, Regulating CEA Insertion Limits, Condition D, when the PDIL alarm setpoint for each unit was determined to be non-conservative.
During an investigation of an event described in LER 2-2012-001, Palo Verde personnel determined that the Regulating CEA PDIL alarm setpoint was incorrectly set at 144 inches since April 19, 2005, when the specified CEA fully withdrawn position was changed from greater than or equal to (>/=)144.75 inches to >/=147.75 inches.
Changes which altered the fuel configuration began in 1993, when the fuel inconel spacer grid assembly was replaced with a redesigned inconel spacer grid assembly called the Guardian grid. The Guardian grid fuel assembly was installed in Unit 1 during Cycle 5, Unit 2 during Cycle 6 and Unit 3 during Cycle 5. The Guardian grid raised the active fuel region by 1.589 inches. The reload analysis report (RAR) for those fuel cycles concluded that the
change in the location of the active fuel region relative to the core internals would not impact the results for the various accident analyses and no changes to the CEA Insertion Limits were required with the installation of the new Guardian grid fuel assembly.
On April 19, 2005, changes were made to the COLR figures for CEA Insertion Limits versus Thermal Power to revise the CEA Group insertion limits by changing the fully withdrawn position to >/=147.75 inches. The change added a note to the COLR figures which specified the fully withdrawn CEA position as >/=147.75 inches. Corresponding changes should have been made to the PDIL alarm setpoint; however, the PDIL alarm setpoint remained at 144 inches. Since the PDIL alarm setpoint remained unchanged, the PDIL alarm circuit would not provide operators with an alarm when the limit was exceeded.
Corrective actions were performed in all three units to change the PDIL alarm setpoint to 147 inches, which allowed each unit to exit TS LCO 3.1.7 Condition D, on March 11,2012.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
This condition did not adversely affect plant safety or the health and safety of the public. The condition did not result in any challenges to the fission product barriers or result in any releases of radioactive materials. The safety limits for Departure from Nucleate Boiling Ratio (DNBR) and fuel peak centerline temperature were not exceeded as a result of this event.
An engineering evaluation was performed with the minimum PDIL alarm setpoint of 144 inches to determine the impact on CEA scram worth and the potential impact to the safety analysis, as well as the impact to flux distribution on core power peaking. The evaluation determined that the impact of the incorrect PDIL alarm setpoint was bounded by the assumptions made in the safety analyses with respect to CEA positions at 144.75 inches vs.
the specified COLR limit of 147.75 inches and did not impact the safe operation of the units.
Therefore, there were no actual adverse safety consequences as a result of this condition.
Additionally, the condition did not impact the safety related plant protection system functions performed by the core protection calculators (CPCs) and CEA Calculators (CEACs) which provide the Linear Heat Rate and DNBR reactor trip functions. Based upon these conclusions, the incorrect PDIL alarm setpoint did not adversely affect plant safety or the health and safety of the public.
The CEA safety functions were not affected by the inoperable PDIL alarm circuits. The circuits provide an alarm function only and do not fulfill a safety function credited in the safety analysis. Therefore, this event would not have prevented the fulfillment of a safety function to safely shutdown the reactor and 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 cause of the event was a failure to revise the PDIL alarm setpoint in the software for the CMC and PC computers following changes to the COLR requirements which specified the fully withdrawn position for regulating CEAs.
The root cause for failing to change the PDIL alarm setpoint was determined to be the figures for the Core Operating Limits Report (COLR) were not directly tied to any basis document.
Contributing to this event was the lack of clear procedural guidance for making COLR changes.
- 7.
CORRECTIVE ACTIONS
As an immediate corrective action, PDIL alarm setpoint in the software for the CMC and PC for all three units were changed to 147 inches for the PDIL. This corrective action allowed each unit to exit TS LCO 3.1.7 on March 11, 2012.
Additionally, the following corrective actions are planned:
Develop and institute a Safety Analysis Basis Document (SABD) for the COLR.
Revise Setpoint Checklist SABD (SABD-5.04.06) to include the checks on PMS PDIL files.
Enhance procedural guidance for COLR changes.
- 8.
PREVIOUS SIMILAR EVENTS
No prior similar events were identified in which PDIL alarm circuits were inoperable because changes to the COLR were not incorporated into the PDIL alarm setpoint.