05000530/LER-2010-002, Condition Prohibited by Technical Specification Resulting from Containment Spray Nozzle Obstruction
| ML103550380 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 12/13/2010 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06295-DCM/DCE LER 10-002-00 | |
| Download: ML103550380 (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 |
| 5302010002R00 - NRC Website | |
text
10 CFR 50.73 LA-A subsidiary of Pinnacle West Capital Corporation Dwight C. Mims Mail Station 7605 Palo Verde Nuclear Vice President Tel. 623-393-5403 P.O. Box 52034 Generating Station Regulatory Affairs and Plant Improvement Fax 623-393-6077 Phoenix, Arizona 85072-2034 102-06295-DCM/DCE December 13, 2010 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 2010-002-00 Attached, please find Licensee Event Report (LER) 50-.530/2010-002-00 which reports a condition prohibited by technical specifications resulting from blockage in seven containment spray system spray nozzles.
In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the 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/DCE/gat Attachment cc:
E. E. Collins Jr.
NRC Region IV Regional Administrator, J. R. Hall NRC NRR Senior Project Manager L. K. Gibson NRC NRR Project Manager J. H. Bashore NRC Senior Resident Inspector (acting) 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)
Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.' Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA/Pnvacy Section (T-5 F53), U.S. Nuclear LICENSEE EVENT REPORT (LER)
Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.gov, and to the Desk Officer, Office of (See reverse for required number of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of sfor each block)
Management and Budget, Washington, DC 20503. If a means used to digits/characters foimpose an information collection does not display a currentjy valid OMB control number, 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
- 4. TITLE Condition Prohibited by Technical Specification Resulting from Containment Spray Nozzle Obstruction
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER NO.
None NUMBER 10 13 2010 2010 002I "
00 12 13 2010 FACILITYNAME DOCKET 10 13 2010 None NUMBER
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check a/ that apply) 0l 20.2201(b)
El 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
ED 50.73(a)(2)(vii)
Defueled [I 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
E] 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[3 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 Cl 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)
[I 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 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) 0 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[I 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
[0 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in
- 1.
REPORTING REQUIREMENT(S)
This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report a condition prohibited by Technical Specification (TS) Limiting Condition for Operation (LCO) 3.6.6, Condition B. Specifically, on October 13, 2010, Palo Verde personnel determined that containment spray (CS) nozzles on each of two separate CS train "A" and "B" spray headers were obstructed. The obstructions existed for a period greater than allowed by Technical Specification (TS) 3.6.6 "Containment Spray System" LCO.
This condition is also being reported under 10 CFR 50.73(a)(2)(vii) as a common cause inoperability of independent trains because both trains contained boric acid deposits that obstructed the spray nozzles.
- 2.
DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The CS System consists of two independent trains of equal capacity, each capable of meeting the design basis requirement. Each train includes a CS pump, a shutdown cooling heat exchanger, spray headers, nozzles, valves, and piping. Each train is powered from a separate Engineered Safety Feature (ESF) bus.
The CS [EIIS: BP] system, as a subsystem of the safety injection system [EIIS: BP], is an ESF designed to ensure that heat removal can be attained during post accident periods. During a Design Basis Accident (DBA), one CS train is required to maintain the containment peak pressure and temperature below the design limits, to remove iodine from the containment atmosphere to maintain concentrations below those assumed in the safety analysis, and to provide hydrogen mixing. To ensure that these requirements are met, assuming the worst case single active failure occurs, two CS trains are required to be operable.
- 3.
INITIAL PLANT CONDITIONS
On October 13, 2010, Palo Verde Unit 3 was defueled. There were no major structures, systems, or components inoperable at the start of the event that contributed to the event.
- 4.
EVENT DESCRIPTION
On October 13, 2010, upon completion of Surveillance Test 73ST-9SI02, "CS Nozzle Air Test,"
Engineering personnel determined the following spray nozzles were obstructed:
(1) Train "A" header (100' elevation) 3SI-A-430, on the end of the header (2) Train "A" header (120' elevation) 3SI-A-413, on the end of the header
(3) Train "A" header (120' elevation) 3SI-A-413, second nozzle from the end of the header (4) Train "B" header (100' elevation) 3SI-B-440, first nozzle from the supply header (5) Train "B" header (100' elevation) 3SI-B-441, first nozzle from the supply header (6) Train "B" header (100' elevation) 3SI-B-438, first nozzle from the supply header (7) Train "B" header (100' elevation) 3SI-B-439, on the end of the header Technical Specification (TS) Surveillance Requirement (SR) 3.6.6.6 requires verification that each CS system spray nozzle (total of 620 nozzles) is un.obstructed. The surveillance test for the CS system uses low pressure air to conduct the test. Each obstruction discovered in Unit 3 consisted of boric acid deposit that was friable and fragmented easily while probing the deposit with a pipe cleaner. The boric acid deposits were the result of boric acid residue and borated water that remained in the CS headers from prior overfill events. The borated water subsequently evaporated causing boric acid to precipitate and form obstructions on the nozzles. The nozzles were cleaned and verified to be unobstructed prior to entering Mode 4.
- 5.
ASSESSMENT OF SAFETY CONSEQUENCES
Since the boric acid deposits were friable and easily removed using a pipe cleaner during the inspections, it is expected that CS header water and associated header pressure would dissolve or easily remove the boric acid deposits out of the nozzles, if an actual CS event occurred.
Even if the boric acid deposits were not displaced or dissolved by CS header water pressure and the nozzles remained obstructed, the remaining spray nozzles that were not obstructed in the CS system would have provided the required spray flow. Therefore, each train would have achieved its safety function to rapidly reduce the containment pressure and temperature following a Loss of Coolant Accident (LOCA) or Main Steam Line Break (MSLB) as required by 10 CFR 50 Appendix A General Design Criteria (GDC) 38, Containment Heat Removal. Additionally, each train would have also met its safety function to control the concentrations of fission products, hydrogen, oxygen, and other substances that may be released into the containment atmosphere following a LOCA as required by GDC 41, Containment Atmosphere Cleanup. Therefore, the blockage would not have prevented the fulfillment of any safety function and did not result in a safety system functional failure as defined by 10 CFR 50.73(a)(2)(v). Since the safety functions would have been met, post-accident radiological releases would not have exceeded those evaluated in the associated safety analyses.
The condition described in this LER did not result in any challenges to fission product barriers or in any offsite releases. Therefore, there were no actual adverse safety consequences or implications as a result of this event and the event did not adversely affect the safe operation of the plant or health and safety of the public.
NRC;
- 6.
CAUSE OF THE EVENT
The preliminary root cause of the obstruction was that boric acid residue and borated water remained in the CS headers from prior overfill events. The borated water subsequently evaporated causing boric acid to precipitate and form obstructions in the nozzles.
The root cause investigation is continuing. A supplement to this LER will be provided that will describe the cause of the event.
- 7.
CORRECTIVE ACTIONS
As described above, the obstructed nozzles were cleaned. The nozzles successfully passed the surveillance test procedure prior to entering Mode 4 at the end of the outage. A supplement to this LER will be provided that will describe the actions to prevent recurrence and the extent of condition.
- 8.
PREVIOUS SIMILAR EVENTS
A prior similar event was reported in 2007 under LER 50-530/2007-001-00 in which two CS "A" train nozzles were obstructed by boric acid deposits. The cause of the prior event was a lack of procedural guidance to detect and respond to a CS header overfill event. The respective operator log procedure was revised to require draining of the header if water from the vertical risers approaches the spill over to the CS header. The corresponding safety injection system operating procedure was changed to provide directions for draining the header. Based on experience to that point, the corrective actions did not consider the potential for future nozzle obstruction caused by the borated water that remained in the header.