05000457/LER-2011-002, Regarding Auxiliary Feedwater System Incomparability Due to Additional Asiatic Clam Shells in Essential Service Water Supply Piping
| ML11263A185 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 09/12/2011 |
| From: | Enright D Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BW110089 LER 11-002-00 | |
| Download: ML11263A185 (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 |
| 4572011002R00 - NRC Website | |
text
Exeln Exelon Generation Company, LLC www.exeloncorp.com Braidwood Station Nuclear 35100 South Route 53, Suite 84 Braceville, IL 60407-9619 10 CFR 50.73 September 12, 2011 BW1 10089 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Unit 2 Facility Operating License No. NPF-77 NRC Docket No. STN 50-457
Subject:
Licensee Event Report 2011-002 Unit 2 - Auxiliary Feedwater System Inoperability Due to Additional Asiatic Clam Shells in Essential Service Water Supply Piping The enclosed Licensee Event Report is being submitted in accordance with 10 CFR 50.73, "Licensee Event Report System."
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Chris VanDenburgh, Regulatory Assurance Manager, at (815) 417-2800.
Respectfully, Daniel J. Enright Site Vice President Braidwood Station
Enclosure:
LER 2011-002-00 cc: NRR Project Manager - Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety US NRC Regional Administrator, Region III US NRC Senior Resident Inspector (Braidwood Station)
Illinois Emergency Management Agency - Braidwood Representative
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 digits/characters for each block) information collection.
- 3. PAGE Braidwood Station, Unit 2 05000457 1 of 4
- 4. TITLE Auxiliary Feedwater System Inoperability Due to Additional AsiaticClam Shells in Essential Service Water Supply Piping
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REVMONTH DAY YEAR N/A N/A NUMBER NO.
MONT__
DAYYEARN/AN/A FACILITY NAME DOCKET NUMBER 07 14 2011 2011 002 00 09 12 2011 N/A N/A
- 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) 0l 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
[1 20.2201(d) 0l 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)
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)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4) 100 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
Z 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
M 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in At 1418, Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.7.5, "Auxiliary Feedwater (AF)
System," Condition A, "One AF train inoperable" was entered for the 2A AF train. Troubleshooting was initiated to perform additional flushing of the suction piping. At 1151 on July 16, 2011, the 2A AF was declared operable and LCO 3.7.5, Condition A was exited.
TS LCO 3.7.5, Condition A requires restoring the AF train to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This condition existed for a longer period of time than is allowed by LCO 3.7.5 Condition A; therefore, this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by Technical Specifications.
Additionally, as there were time periods between May 9, 2011 and July 14, 2011 where the 2B AF train was declared inoperable for testing or maintenance, this event is also being reported pursuant to 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of a system's safety function.
Cause of Event
The investigation identified two apparent causes:
- 1. Failure to perform a complete borescope inspection of the piping to verify no additional relic clam shells remained in the 2A AF suction piping allowed for continued inoperability of the system.
Clam shells were previously discovered in the 2A AF suction line from SX and no borescope inspection was performed to verify all shells were removed from the system.
The borescope inspection to verify operability performed on July 15, 2011, showed shells had settled in the bends of the piping near the 2AF01 7A and 2AF006A valves and surrounding the drain. A borescope inspection of the entire pipe when the clam shells were initially discovered would have identified the need to perform more effective flushing.
- 2.
Inadequate flushing techniques to remove shells from the 2A AF suction piping allowed for a significant amount of clam shells to remain in the system.
No flow criterion was established for acceptability of the flushing technique in providing reasonable assurance for operability. No quantitative analysis was performed to evaluate what velocity would be adequate to flush the clam shells from the system and therefore, it was not realized that the flows established during troubleshooting flushes were not adequate.
The only mechanism that could be used to remove clam shells from the 2A AF suction piping as it was designed was through the drain line. The original piping configuration did not include a drain of sufficient size to permit achievement of the nominal flushing flow velocities since the volume of piping between the 2AF01 7A and 2AF006A was designed to be maintained in a "dry layup" condition.
). Safety Consequences:
There were no actual safety consequences impacting plant or public safety as a result of this event. Braidwood Station has not experienced an actual event that required the AF system to perform its safety function with flow supplied by the SX system. Flow to the AF system from the CSTs would not have been impacted by Asiatic clams in the SX system. Therefore, the existence of the clams in the SX supply line has not impacted AF flow to the SGs.
In a design basis accident, an Engineered Safety Feature (ESF) signal will actuate the AF system, and the AF pumps will initially draw condensate from the CST. If the CST becomes depleted or unavailable coincident with AF ESF actuation, a low suction header pressure signal opens valves 2AF017A and 2AF006A, allowing pump supply from SX. Upon this action, the clam shells in the piping between valves 2AF01 7A and 2AF006A would pass through the 2A AF pump and on to the 2A Train AF control valves (2AF005A-D). The presence of the Asiatic clam shells in the 2A SX supply header had the potential to be transported through the 2A AF system and block flow through the AF control valves. While this condition affected the 2A Train AF, there were four time periods since
May 9, 2011, where the 2B AF train was declared inoperable for testing or maintenance. Therefore, this event represents a safety system functional failure.
From a risk perspective, the loss of function would only occur if, during a design basis accident, the CSTs were lost, 2B AF train fails or is unavailable due to maintenance, and the clam shells propagated through the system causing a loss of the 2A AF train. The probability of these three events occurring concurrently is considered unlikely. The potential impact of clam shells in the 2A Train AF is considered as a low safety significance due to the low probability associated with events that would require use of SX as a suction source for the AF system.
During the time of past inoperability of the 2A AF pump (May 9, 2011 to July 14, 2011), there were four instances where the 2B AF pump was inoperable but available: for performance of surveillance testing; for SX supply to the 2B AF pump suction line flushing for extent of condition; and for performance of valve strokes. At all times during this time period, although the 2B AF pump was inoperable, it was available to perform its design basis function based on the pre-determined and pre-briefed risk management actions established to maintain component availability.
E. Corrective Actions
Corrective actions taken include:
Flushing of the 2A AF suction piping between the 2AF006A and 2AF01 7A valves using improved flushing techniques (i.e., removing the drain line and completely draining the pipe between flushes).
Performing a complete inspection of the 2A AF suction piping for remaining clam shells.
Completion of the extent of condition flushing activities for the 1A, 1 B and 2B AF trains.
F. Previous Occurrences
There has been two previous, similar Licensee Event Reports identified at the Braidwood Station in the past three years:
Licensee Event Report Number 2008-001 - 2A Essential Service Water Train Inoperable Due to Strainer Fouling from Bryozoa Deposition and Growth Licensee Event Report Number 2011-001 - Asiatic Clam Shells in Essential Service Water Supply Piping to the 2A Auxiliary Feedwater Pump Resulted in Auxiliary Feedwater System Inoperability
Component Failure Data
Manufacturer Nomenclature Model Mfgc. Part Number N/A N/A N/A N/A