05000263/LER-2011-006, Regarding Lntake Structure Fire Suppression System Blockage
| ML113050425 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/31/2011 |
| From: | O'Connor T Northern States Power Co, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-MT-11-057 LER 11-006-00 | |
| Download: ML113050425 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| LER closed by | |
| IR 05000263/2011005 (1 February 2012) | |
| 2632011006R00 - NRC Website | |
text
/e Xcel Energy October 31,201 1 Monticello Nuclear Generating Plant 2807 W County Road 75 Monticello, MN 55362 L-MT-11-057 10 CFR 50.73 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 Monticello Nuclear Generating Plant Docket 50-263 Renewed Facility Operating License No. DPR-22 LER 201 1-006, "Intake Structure Fire Suppression Svstem Blockaae" A Licensee Event Report (LER) for this occurrence is attached.
Summary of Commitments ew commitments and no revisions to existing commitments.
Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosure cc:
Regional Administrator, Region Ill, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (10 2010)
LICENSEE EVENT REPORT (LER)
(See reverse for required number of d~g~ts/characters for each block)
APPRoVEDBYOMBNO 3150 0104 EXPIRES IOI~II~OI~
Estimated burden per response to comply w~th 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 estlmate to the Records and FOINPnvacy Service Branch (T 5 F53) U S Nuclear Regulatory Commlsslon Washington DC 20555 0001 or by Internet e mall to infocollects resourceanrc gov and to the Desk Officer Offlce of lnformatlon and Regulatory Affalrs NEOB 10202 (3150 0066) Office of Management and Budget Wash~ngton DC 20503 If a means used to Impose an informatron collect~on does not d~splay a currently valid OM8 control number the NRC may not conduct or sponsor and a person IS not requ~red to respond to the Informatlon collect~on
- 1. FACILITY NAME Mont~cello Nuclear Generat~ng Plant
- 2. DOCKET NUMBER 05000 263
- 3. PAGE 1OF 3
- 4. TITLE lntake Structure Fire Suppression System Blockage
- 5. EVENT DATE MONTH 09
- 6. LER NUMBER
- 12. LICENSEE CONTACT FOR THlS LER
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR g: (Check all that apply)
[7 20 2201(b)
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Spec~fy in Abstract below or In 9. OPERATING MODE Mode 1
- 10. POWER LEVEL 100%
DAY 02 YEAR NAME Carrle Fosaaen YEAR 2011
- 7. REPORT DATE TELEPHONE NUMBER (Include Area Code) 763-295-1 357 2011 - 0 0 6 -
00 SEQUENTIAL NUMBER MONTH 10
- 8. OTHER FACILITIES INVOLVED REV NO FACILITY NAME FACILITY NAME DAY 31 DOCKET NUMBER 05000 DOCKET NUMBER 05000 YEAR 2011 COMPONENT NIA
CAUSE
NIA MANU FACTURER NIA YEAR MANU-FA CTURER NIA SYSTEM NIA ABSTRACT (Llmrt to 1400 spaces, I e, approximately 15 smgle-spaced typewr~tten Ilnes)
On September 2, 201 1, at approximately 1600, Mechanical Maintenance personnel informed Operations that portions of the lntake Structure sprinkler system piping were found to be partially blocked and incapable of passing flow. The lntake Structure sprinkler system is relied upon in part to satisfy an approved exemption to 10 CFR 50 Appendix R, Section lll.G.2.b concerning separation of components in the lntake Structure.
Installation of the lntake Structure sprinkler system in 1983 did not comply with design requirements for providing required pipe slope to ensure proper draining. This condition allowed excessive water to remain in the system which then contributed to accelerated internal corrosion and accumulation of corrosion byproducts in the piping system.
Immediate corrective actions taken included flushing the sprinkler system and performing internal inspections to confirm removal of blockage before returning the system to service.
NRC FORM 366 (10-2010)
REPORTABLE TO EPlX NIA REPORTABLE TO EPlX NIA COMPONENT NIA
- 14. SUPPLEMENTAL REPORT EXPECTED O NO 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE).
MONTH
- 15. EXPECTED SUBMISSION DATE
CAUSE
DAY SYSTEM NIA NIA I
EVENT DESCRIPTION
On August 26, 201 1, with the plant operating in Mode 1 at 100% power, it was determined during the performance of Surveillance Test Procedure 0323-01, Fire Protection System Sprinkler Functional Test, that blockage existed at valve FP-171-10, Sprinkler Inspectors Test Valve. At this time Operations declared the fire suppression system [KP] non-functional. A 14-day fire protection system impairment and continuous compensatory fire watch, with backup suppression, had been previously established at the commencement of Procedure 0323-01 and remained in effect. Follow-up maintenance activities confirmed the valve was plugged and removed the blockage.
When Surveillance Test Procedure 0323-01 was re-performed on August 28,201 1 as the post-maintenance test, it was determined that additional blockage was present in the piping. Further maintenance activities on September 2, 201 1, identified significant blockage in the fire sprinkler line upstream of valve FP-171-10 as well as in three vertical risers going to sprinkler heads.
At approximately 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br />, following additional inspections of the lntake Structure fire system piping, Maintenance informed Operations that additional portions of the sprinkler suppression piping were blocked. The fire suppression system is relied upon, in part, to satisfy an approved exemption for the plant to 10 CFR 50 Appendix R, Section lll.G.2.b concerning separation of components in the lntake Structure.
EVENT ANALYSIS
This condition is being reported in accordance with 10 CFR 50.73(a)(2)(ii)(B) - Degraded or Unanalyzed Condition..
Radiography was performed at various locations throughout the lntake Structure sprinkler system to determine the extent of blockage. The most remote portion of the sprinkler system was found to be blocked due to an accumulation of what was later determined to be corrosion products.
System design documentation indicates the piping should be sloped downward from the branches to the cross main and continuing back to the sprinkler control valve main drain. Investigation showed that portions of the system were not installed per the design such that the slope did not promote complete draining of the system. Incomplete draining contributed to the overall accumulation of corrosion products.
During system tests or actuations, water surged through the system which both loosened fixed corrosion products and transported existing corrosion products further into remote parts of the system. The corrosion byproducts were further broken down as a function of time, reducing them to fine particles which took on the form of a reddish, brownish, clay-like mud.
Samples of the "mud" were taken at various locations within the system and sent to an independent lab for analysis to determine the makeuplorigin of the blockage. The results indicated the blockage was primarily made up of iron related corrosion products.
YEAR SEQUENTIAL REV
SAFETY SIGNIFICANCE
The Monticello risk assessment group reviewed the event for risk impact. A quantitative bounding PRA analysis was performed by assuming failure of all equipment residing in the lntake Structure, given a fire occurs in the room. The risk associated with degradation of the automatic fire suppression system in the lntake Structure is conservatively below the thresholds of what is considered to be low significance with regard to core damage frequency (< 1.0 E-06), and with regard to large early release frequency (<I
.OE-07).
Although the sprinkler system was assumed to have failed in the PRA analysis, alternative methods were functional and available to mitigate a fire in the lntake Structure.
CAUSE
Installation of the lntake Structure fire sprinkler system in 1983 did not comply with design requirements for providing required pipe slope to ensure proper draining. This condition allowed excessive water to remain in the system which then contributed to accelerated internal corrosion and accumulation of corrosion byproducts.
CORRECTIVE ACTION
The lntake Structure sprinkler system was flushed and returned to service following radiographic and boroscopic inspections to confirm removal of the blockage. Planned long term actions include:
Restore portions of the lntake Structure fire sprinkler system piping not meeting design requirements for slope to compliance with the design requirements.
Perform periodic internal inspections and periodic testing of the lntake Structure fire sprinkler piping to validate that the sprinklers will perform their intended function.
Corrective actions are being tracked under the Monticello Corrective Action Program.
PREVIOUS SIMILAR EVENTS
An extent of condition evaluation for a 2007 Emergency Diesel Generator sprinkler piping blockage identified a potential for this to occur in the lntake Structure, but while identified, flushing of the sprinkler system had not been performed prior to the 201 1 event.
During post maintenance testing in 2009, following reinstallation of the lntake Structure sprinkler piping, no flow was observed in the inspector test valve orifice. The blockage was removed and it was concluded that the sprinkler system remained functional.
There have been no similar licensee event reports in the last three years.