05000529/LER-2014-001, Regarding Inoperable Essential Spray Pond Train Due to Corrosion on the Diesel Generator Fuel Oil Cooler Cover
| ML14225A537 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 08/11/2014 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06922-DCM/DJH LER 14-001-00 | |
| Download: ML14225A537 (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 |
| 5292014001R00 - NRC Website | |
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DWIGHT C. MIMS Senior Vice President, Nuclear Regulatory & Oversight Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7605 Tel 623 393 5403 102-06922-DCM/DJH August 11, 2014 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Unit 2 Docket No. STN 50-529 / License No. NPF 51 Licensee Event Report 2014-001-00 Enclosed please find Licensee Event Report (LER) 50-529/2014-001-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports a condition prohibited by Technical Specification 3.7.8, Essential Spray Pond (ESP)
System, that resulted from corrosion on the cover of the Unit 2 train A emergency diesel generator fuel oil cooler that rendered train A ESP inoperable. It was preliminarily determined that this event represented a condition that could have prevented the fulfillment of a safety function. A final disposition will be provided in a supplement to this LER which will be submitted upon completion of the event investigation.
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.
Arizona Public Service Company makes no commitments in this letter. If you have questions regarding this submittal, please contact Mark McGhee, Regulatory Affairs Department Leader, at (623) 393-4972.
Sincerely, DCM/DJH/hsc Enclosure cc:
M. L. Dapas B. K. Singal M. M. Watford M. A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager NRC NRR Project Manager NRC Senior Resident Inspector PVNGS A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- Wolf Creek
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 (02-2014)
, the digits/characters foNRC 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 2 05000529 1 OF 4
- 4. TITLE Inoperable Essential Spray Pond Train Due to Corrosion on the Diesel Generator Fuel Oil Cooler Cover
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MOT AY YEAR j SEQUENTIAL REV MOTjAY YA FACILITY NAME DOCE NUMBER SNUMBER NO.
MONT DAY YEAR FACILITY NAME DOCKET NUMBER 06 11 2014 2014 -
001
- - 00 08 11 2014
- 9. OPERATING MODE
- 1. 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)
El 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A) 1E 20.2203(a)(1)
IZ 20.2203(a)(4)
El 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)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 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)
[E 50.46(a)(3)(ii)
[] 50.73(a)(2)(v)(B)
E] 73.71 (a)(5) 10E 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER
[
20.2203(a)(2)(vi)
I]
50.73(a)(2)(i)(B)
[I 50.73(a)(2)(v)(D)
Specify in Abstract below or in
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT TELEPHONE NUMBER (Include Area Code)
Mark McGhee, Department Leader Nuclear Regulatory Affairs 623-393-4972CAUSE SYSTEM COMPONENT MANUFACTURER REPO X
CAUSE
SYSTEM COMPONENT MANU-FACTURER PORTABLE LB MNFAT~e.RI TO EPIX jiTO EI A
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MOT AY YA SUBMISSION YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
El NO DATE 12 5
2014 0BSTRACT (Limit to 1400 spaces, i.e.. approximatelv 15 single-spaced t.pewritten lines)
On June 6, 2014, following planned maintenance on the train A emergency diesel generator (EDG) fuel oil (FO) cooler, essential spray pond (ESP) system water leakage was found on the FO cooler upper cover. The FO cooler upper cover was replaced with a new cover and the EDG and ESP systems were returned to service. A visual inspection of the removed
- - over identified corrosion related degradation of the cast iron cover. On June 11, 2014, an engineering analysis was
,ompleted to determine the required minimum wall thickness for the pressure boundary of the FO cooler upper cover.
Measurements of the FO cooler upper cover wall thickness were found to be below the minimum wall thickness needed to maintain structural integrity for the full range of its design basis requirements. Consequently, it was determined the train A ESP system had been inoperable in excess of the completion time allowed by TS LCO 3.7.8. The train A FO cooler upper cover was degraded when train B ESP was removed from service for maintenance in March 2014. Therefore, it was preliminarily determined that this event also represents a safety system functional failure.
On June 28 and 29, 2014, to address the extent of condition, the remaining five FO cooler upper covers (trains A and B for Units 1 and 3 and train B for Unit 2) were replaced with new covers.
The event investigation is still in progress, and the results will be reported in a supplement to this Licensee Event Report. No previous similar events have been reported to the NRC by PVNGS in the prior three years.
NRC FORM 366 (02-2014)
1. REPORTING REQUIREMENT(S)
This Licensee Event Report is being submitted pursuant to 10 CFR 50.73 (a)(2)(i)(B), to report a condition prohibited by Technical Specification (TS) 3.7.8, Essential Spray Pond (ESP) System. On June 11, 2014, engineering personnel determined corrosion on the Unit 2 train A emergency diesel generator (EDG) fuel oil (FO) cooler upper cover resulted in the cover wall thickness being below the minimum needed to maintain structural integrity for the full range of its design basis requirements. Consequently, train A ESP had been inoperable for a period in excess of the allowed completion time of TS Limiting Condition of Operation (LCO) 3.7.8.
Additionally, the train A FO cooler upper cover was degraded when train B ESP was removed from service for maintenance in March 2014. While the investigation is still in progress, it has preliminarily been determined that this event also represents a safety system functional failure pursuant to 10 CFR 50.73 (a)(2)(v)(A), (B), and (D) for a condition that could have prevented the fulfillment of a safety function of systems needed to shutdown the reactor and maintain it in a safe shutdown condition, remove residual heat, and mitigate the consequences of an accident. A final disposition will be provided in a supplement to this LER which will be submitted upon completion of the event investigation.
- 2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The ESP system consists of two independent trains each comprised of a spray pond, spray pond pump and piping system and supporting auxiliary equipment that serve as the ultimate heat sink. Each ESP pump circulates cooling water through redundant safety-related flow trains comprised of the essential cooling water (EW) (EIIS: BI) heat exchanger, EDG (EIIS:
EK) jacket water cooler (EIIS: LB), EDG air aftercooler, EDG lube oil cooler (EIIS: LA), and EDG fuel oil (FO) cooler (EIIS: LB). The heat loads in the ESP system are arranged in parallel and each train is independently capable of providing the required heat removal capacity.
As described above, the heat removal function for the heat loads on each of the two safety-related EDGs in each unit is provided by the respective ESP train. Each EDG includes a FO subsystem which delivers fuel oil from an 1100 gallon day tank to the EDG high pressure injection pumps via an engine driven booster pump. Fuel oil supply pressure is maintained at the discharge of the booster pump by a relief valve that acts as a pressure regulator.
When the engine is running at rated speed, excess fuel oil is diverted by the relief valve back to the day tank after passing through the shell side of the EDG FO cooler. The EDG FO cooler function is to remove heat from fuel oil that is recirculated back to the day tank
and is not a critical function for EDG operation. At lower engine loads, when fuel oil consumption is low, the flow rate of fuel oil recirculated back to the day tank increases.
Additional excess fuel oil from the twenty high pressure injection pumps is diverted back to the day tank without passing through the FO cooler. The EDG FO cooler is a four-pass, straight tube heat exchanger with a shell constructed of brass, tubes of copper, and upper and lower cast iron covers. ESP cooling water supply and return flow paths to the FO cooler are through one-inch stainless steel pipes threaded into the FO cooler upper cover. The FO cooler also provides an anchorage point for the ESP supply and return piping for the EDG, and therefore, serves as a seismic restraint for the ESP piping.
- 3.
INITIAL PLANT CONDITIONS
On June 6, 2014, PVNGS Unit 2 was in Mode 1 (Power Operation), at 100 percent power and normal operating temperature and pressure. Plant conditions on June 11, 2014, remained unchanged from the conditions shown for June 6. There were no structures, systems, or components inoperable that contributed to the event.
4. EVENT DESCRIPTION
On June 6, 2014, the Unit 2 train A EDG FO cooler was disassembled during a planned train A ESP and EDG outage. The EDG FO cooler and associated piping showed no signs of leakage prior to commencement of the outage on June 2, 2014. After re-assembly and subsequent system restoration, ESP water was identified leaking from a crack in the FO cooler upper cover outlet nozzle. The FO cooler upper cover was removed from the system and subsequent examination by engineering personnel identified corrosion related degradation of the cast iron cover.
The EDG FO cooler upper cover was replaced with a new cover on June 6, 2014, and the system was restored following completion of the maintenance window.
On June 11, 2014, an engineering analysis was completed to determine the required minimum wall thickness for the pressure boundary of the EDG FO cooler upper cover.
Measurements of the FO cooler upper cover wall thickness were found to be below the minimum wall thickness needed to maintain structural integrity for the full range of its design basis requirements. Based on the results of this analysis, it was determined that the ESP system had been inoperable in excess of the completion time allowed by TS LCO 3.7.8.
Additionally, the train A FO cooler upper cover was degraded when train B ESP was removed from service for maintenance in March 2014.
On June 28 and 29, 2014, the remaining five EDG FO cooler upper covers for Units 1, 2 and 3 (trains A and B for Units 1 and 3 and train B for Unit 2) were replaced with new covers.
The removed cooler upper covers were delivered to a vendor for detailed inspection and analysis. An event investigation is in progress to determine the cause of this condition and establish corrective actions.
5. ASSESSMENT OF SAFETY CONSEQUENCES
This event did not result in a challenge to the fission product barriers or result in the release of radioactive materials. The event did not adversely affect the safe operation of the plant or health and safety of the public, and did not result in a potential transient more severe than those analyzed in the Updated Final Safety Analysis Report.
Since the train A FO cooler upper cover was degraded when train B ESP was removed from service for maintenance in March 2014, this event preliminarily represents a safety system functional failure. A final disposition will be provided in a supplement to this LER which will be submitted upon completion of the event investigation.
6. CAUSE OF THE EVENT
The event investigation is still in progress. The cause of this condition and corrective actions will be reported in a supplement to this LER.
- 7.
CORRECTIVE ACTIONS
As an immediate corrective action the train A EDG FO cooler upper cover was replaced with a new cover. Additionally, the remaining five EDG FO cooler upper covers for PVNGS Units 1, 2 and 3 (two for each unit) were replaced with new covers.
The event investigation is still in progress. The cause of this condition and corrective actions will be reported in a supplement to this LER.
- 8.
PREVIOUS SIMILAR EVENTS
No previous similar events have been reported to the NRC by PVNGS in the prior three years.