05000457/LER-2011-001, For Braidwood Station, Unit 2, Regarding Asiatic Clam Shells in Essential Service Water Supply Piping to the 2A Auxiliary Feedwater Pump Resulted in Auxiliary Feedwater Inoperability
| ML112010177 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 07/19/2011 |
| From: | Enright D Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BW110080 LER 11-001-00 | |
| Download: ML112010177 (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 |
| 4572011001R00 - NRC Website | |
text
10 CFR 50.73 July 19, 2011 BW110080 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 2011-001 Unit 2 - Asiatic Clam Shells in Essential Service Water Supply Piping to the 2A Auxiliary Feedwater Pump Resulted in Auxiliary Feedwater System Inoperability 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 2011-001-00 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 SY OMS: 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/Privacy Section (T-5 F53). U.S. Nuclear Regulatory Commission.
DC 20555-0001.
or by internet e-mail to LICENSEE EVENT REPORT (LER) infocollects.resource@nrc.gov. and to the Desk Officer. Office of Information and Regulatory Affairs. NEOB-10202. (3150..Q104). Office of Management and Budget. Washington. DC 20503. If a means used to impose an Information (See reverse for required number of collection does not display a currently valid OMS control number. the NRC may digits/characters for each block) not conduct or sponsor. and a person is not required to respond to. the information collection.
- 13. PAGE Braidwood Station, Unit 2 05000457 1 of 4
- 4. TITLE Asiatic Clam Shells in Essential Service Water Supply Piping to the 2A Auxiliary Feedwater Pump Resulted in Auxiliary Feedwater System Inoperability
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR I SEQUENTIALIREV MONTH DAY YEAR N/A N/A NUMBER NO.
FACILITY NAME DOCKET NUMBER 05 20 2011 2011. 001.
00 07 19 2011 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) o 20.2201(b) o 20.2203(a)(3)(i) o 50.73(a)(2)(i)(C) o 50.73(a)(2)(vii) 1 o 20.2201(d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2203(a)(1) o 20.2203(a)(4)
!EJ 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(2)(i) o 50.36(c)(1)(i)(A) o 50.73(a)(2)(iii) o 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1 )(ii)(A) o 50.73(a)(2)(iv)(A) o 50.73(a)(2)(x) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 50.73(a)(2)(v)(A) o 73.71(a)(4) 100 o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii)
!EJ 50.73(a)(2)(v)(B) o 73.71(a)(5) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(C) o OTHER o 20.2203(a)(2)(vi)
!EJ 50.73(a)(2)(i)(B) o 50.73(a)(2)(v)(D)
Specify in Abstract below or in 2011 001 00 On May 20, 2011, the evaluation of past operability concluded Unit 2 Train A of AF was not operable with this larger quantity of shells. The clam shells which were identified in the suction piping between the 2AF006A and 2AF017A valves had the potential to be transported through the 2A AF system and block flow through the AF flow control valves (2AF005A-D). The extent of condition has been evaluated for Unit 2 Train B of AF, and for Unit 1 Trains A and B, and it has been determined that the only affected train was 2A. This was determined to be an eight hour reportable event under 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition that significantly degraded plant safety. An Event Notification Report was made at 2257 Eastern Daylight Time on May 20, 2011.
Technical Specifications Limiting Condition for Operation (LCO) 3.7.5, "Auxiliary Feedwater (AF) System," Condition A, "One AF train inoperable" 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 />. It is reasonable to conclude that 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. As there were time periods during the past three years where the 2B AF train was coincidently out of service for testing or maintenance, this event is also being reported pursuant to 10 CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition that significantly degraded plant safety, and 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of a system's safety function.
On July 14, 2011, as a confirmatory action from the previous events, additional flushing of the line between the 2AF017A and 2AF006A valves resulted in additional shells being flushed out of the AF system. The amount of shells collected was greater than the amount collected from the May 9, 2011 flushing. Based on the amount of shells collected, operability of the 2A AF could not be supported. An investigation is ongoing, and either this Licensee Event Report (LER) will be supplemented, or a separate LER will be submitted.
C.
Cause of Event
This investigation identified two root causes:
1.
Historical inadequate chemical feed (CF) biocide treatment of SX prevented the termination of Asiatic clam larvae, allowing Asiatic clams to grow in the low flow section of the SX header to 2A AF suction.
Prior to 1995, biocide feed to SX was inconsistent due to chemical feed system problems. However, after 1998 biocide feed became more consistent and then became very consistent with the installation of a new chemical feed system in 2000.
It has been shown that continuous biocide injection is required to effectively terminate Asiatic clams and their larvae. The history of the chemical addition system can be used to age the clams. An adult clam is killed by a consistent (uninterrupted) application of biocide for approximately 12 to 14 days. Therefore, the clams must have lived during a period when there was not continuous chlorination. The clams lived for about one year based on their size, so that the most recent time period when the clams could have lived would be before 2000, prior to the time when the new chemical feed system started to provide consistent chem ical feed.
2.
Historical ineffective Problem Identification and Resolution associated with discoveries of Asiatic clam shells in the 2A AF suction allowed the condition to remain unanalyzed and uncorrected.
A review identified a number of historical issues involving clams and other debris clogging the Train 2A AF suction drain valve and sight glass. Actions taken focused on removing the debris. There where no attempts to perform a complete system flush to ensure all clam shells were removed from the system.
D.
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 steam generators.
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 2AF017A and 2AF006A would pass through the 2A AF pump and on to the Train A 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 AF train, there were time periods during the past three years where the 2B AF train was coincidently out of service for testing or maintenance. During these periods, the AF system safety function would have been unavailable. 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 CST 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 claim shells in the 2A AF train 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.
E. Corrective Actions
Corrective actions include:
Flushing of the line between the 2AF006A and 2AF017A valves was performed to remove shells.
Revising the service water heat exchanger inspection guide to incorporate additional guidance on actions to be taken upon the discovery of macrofouling and biological fouling of GL 89-13 systems. Guidance to ensure debris potentially affecting system operability is entered into the corrective action process for appropriate evaluation and resolution.
Revising the AF 1/2AF006A1B and 1/2AF017A1B valve stroke surveillance to provide a location for documentation of the discovery of debris in the site glass or the drain, and instructions clarifying entering the discovery of debris into the corrective action process.
Previous Occurrences
There has been one previous, similar Licensee Event Report 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
~. Component Failure Data:
Manufacturer N/ANomenclature N/A Model N/A Mfg. Part Number N/A