Information Notice 2006-17, Recent Operating Experience of Service Water Systems Due to External Conditions: Difference between revisions

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{{#Wiki_filter:UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, DC  20555-0001July 31, 2006NRC INFORMATION NOTICE 2006-17: RECENT OPERATING EXPERIENCE OFSERVICE WATER SYSTEMS DUE TO
[[Issue date::July 31, 2006]]


NRC INFORMATION NOTICE 2006-17: RECENT OPERATING EXPERIENCE OFSERVICE WATER SYSTEMS DUE TO EXTERNAL CONDITIONS
===EXTERNAL CONDITIONS===


==ADDRESSEES==
==ADDRESSEES==
All holders of operating licenses for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.
All holders of operating licenses for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removed
 
from the reactor vessel.


==PURPOSE==
==PURPOSE==
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to informaddressees of operating experience within the past few years affecting the operability of theservice water system at several nuclear power plant The NRC expects that recipients will review the information for applicability to their facilities and consider actions, as appropriate, toavoid similar problem However, suggestions contained in this IN are not NRC requirements;therefore, no specific action or written response is required.
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to informaddressees of operating experience within the past few years affecting the operability of theservice water system at several nuclear power plants.  The NRC expects that recipients will
 
review the information for applicability to their facilities and consider actions, as appropriate, toavoid similar problems.  However, suggestions contained in this IN are not NRC requirements;therefore, no specific action or written response is required.


==DESCRIPTION OF CIRCUMSTANCES==
==DESCRIPTION OF CIRCUMSTANCES==
During 2004 through 2005, 15 events occurred related to blockages in service water systems. These events were primarily self-revealin The various blocking agents included silt, sand, small rocks, grass or weeds, frazil ice, and small aquatic fauna, such as fis All these eventswere of low safety significance but illustrate the susceptibility of the safety-significant service water syste For instance, in September 2005, NRC inspectors identified a condition at FortCalhoun that allowed small rocks to regularly enter the raw water system, contribute to trippingof a pump and strainer motors, and interfere with traveling screen operation (NRC InspectionReport 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)
During 2004 through 2005, 15 events occurred related to blockages in service water systems. These events were primarily self-revealing.  The various blocking agents included silt, sand, small rocks, grass or weeds, frazil ice, and small aquatic fauna, such as fish.  All these eventswere of low safety significance but illustrate the susceptibility of the safety-significant service
Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a servicewater accumulator outlet line at Salem to be nearly full of silt (NRC InspectionReport 50-272/2005-03, ADAMS Accession No. ML052090344). Salem - Hope Creek Nuclear Power PlantsOn December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware Riverupstream of the Salem and Hope Creek Generating Station To mitigate the potential for oilintrusion into the cooling water systems, the licensee placed booms around the intakestructures at both station The booms are effective at controlling oil that is at or near the  surface; however, the effectiveness of the booms was lessened because the spilled oil was"heavy" crude and was suspended at varying depths in the rive On December 3, 2004, the licensee commenced shutdown of both Salem units due to the conditions on the rive There were no issues associated with the shutdown Hope Creek was already shut down for a refueling outag The licensee restarted both Salem units after review of heat exchanger performance and monitoring of the oil spill. Cooper Nuclear StationOn November 20, 2004, the service water system was clogged with sediment, resulting in anunexpected pressure drop in both loops of service water, high differential pressure alarms on both strainers, and isolation of the nonessential service water load Both trains exceeded the differential pressure operability limit of 15 psi Backwash automatically initiated andsuccessfully cleaned the Loop A strainer, but the analogous action for Loop B did not succeed in cleaning the straine Operators opened the strainer bypass valve to restore service water flow and subsequently cleaned both strainers.On October 20, 2005, while preparing for online maintenance of the service water system,operators started a fourth service water pump and received high differential pressure alarms on both Loops A and The automatic backwash did not sufficiently decrease the differentialpressure, and operators bypassed the straine Following these actions, the service water system header pressures returned to norma During the event, operators declared both loopsof service water inoperabl Both loops exceeded the strainer differential pressure structural integrity limit of 15 psi The high differential pressure across the strainers was the result of debris (small rocks and sediment) introduced by the start of the fourth pum With both loopsof service water inoperable, operators declared both emergency diesel generators inoperabl In 2005, the NRC Region IV office organized a special inspection based on the repetitive natureof this type of event (NRC Inspection Report 50-298/2005-15, ADAMS Accession No. ML061160027).Watts Bar Nuclear PlantOn November 22, 2004, while performing a manual valve exercising procedure, the licenseeidentified that a centrifugal charging pump backup cooling line from the essential raw coolingwater system was completely blocked with sil Approximately 2.5 gallons of muddy pastepassed through the 1-inch drain valve before the valve became blocke The line had to be cleared mechanicall This line is significant in that this is the only high head pump with a backup source of cooling water (NRC Inspection Report 50-390, 391/2004-05, ADAMSAccession No. ML050280344).
 
water system.  For instance, in September 2005, NRC inspectors identified a condition at FortCalhoun that allowed small rocks to regularly enter the raw water system, contribute to trippingof a pump and strainer motors, and interfere with traveling screen operation (NRC InspectionReport 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)
Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a servicewater accumulator outlet line at Salem to be nearly full of silt (NRC InspectionReport 50-272/2005-03, ADAMS Accession No. ML052090344). Salem - Hope Creek Nuclear Power PlantsOn December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware Riverupstream of the Salem and Hope Creek Generating Stations.  To mitigate the potential for oilintrusion into the cooling water systems, the licensee placed booms around the intakestructures at both stations.  The booms are effective at controlling oil that is at or near the  surface; however, the effectiveness of the booms was lessened because the spilled oil was"heavy" crude and was suspended at varying depths in the river.  On December 3, 2004, the
 
licensee commenced shutdown of both Salem units due to the conditions on the river.  There
 
were no issues associated with the shutdowns.  Hope Creek was already shut down for a
 
refueling outage.  The licensee restarted both Salem units after review of heat exchanger
 
performance and monitoring of the oil spill. Cooper Nuclear StationOn November 20, 2004, the service water system was clogged with sediment, resulting in anunexpected pressure drop in both loops of service water, high differential pressure alarms on
 
both strainers, and isolation of the nonessential service water loads.  Both trains exceeded the
 
differential pressure operability limit of 15 psid.  Backwash automatically initiated andsuccessfully cleaned the Loop A strainer, but the analogous action for Loop B did not succeed
 
in cleaning the strainer.  Operators opened the strainer bypass valve to restore service water
 
flow and subsequently cleaned both strainers.On October 20, 2005, while preparing for online maintenance of the service water system,operators started a fourth service water pump and received high differential pressure alarms on
 
both Loops A and B.  The automatic backwash did not sufficiently decrease the differentialpressure, and operators bypassed the strainer.  Following these actions, the service water
 
system header pressures returned to normal.  During the event, operators declared both loopsof service water inoperable.  Both loops exceeded the strainer differential pressure structural
 
integrity limit of 15 psid.  The high differential pressure across the strainers was the result of
 
debris (small rocks and sediment) introduced by the start of the fourth pump.  With both loopsof service water inoperable, operators declared both emergency diesel generators inoperable.  In 2005, the NRC Region IV office organized a special inspection based on the repetitive natureof this type of event (NRC Inspection Report 50-298/2005-15, ADAMS Accession No. ML061160027).Watts Bar Nuclear PlantOn November 22, 2004, while performing a manual valve exercising procedure, the licenseeidentified that a centrifugal charging pump backup cooling line from the essential raw coolingwater system was completely blocked with silt.  Approximately 2.5 gallons of muddy pastepassed through the 1-inch drain valve before the valve became blocked.  The line had to be
 
cleared mechanically.  This line is significant in that this is the only high head pump with a
 
backup source of cooling water (NRC Inspection Report 50-390, 391/2004-05, ADAMSAccession No. ML050280344).


==DISCUSSION==
==DISCUSSION==
Cooper Nuclear StationIn both events, for a few minutes service water flow was lost to the nonessential header andgreatly reduced to the essential header In each case, the successful Loop A automatic backwash precluded the need for a manual scram, which would have been required if the loss of turbine equipment cooling water had been prolonge In each event, the Loop B filteringfunction was overwhelmed by the inrush of sedimen The Loop B automatic backwash function failed due to the lack of downstream pressure, which provides the motive force for the backwashing operatio The licensee believes that the contributing external factor was the lowlevel of the Missouri River, the source of the service water syste Both of these events occurred during autumn, following the navigation seaso A weir wall is installed in the river in front of the intake structur The low river level caused an increased portion of the water that flows into the intake structure to go around (rather than over) the weir wall and jet into the service water ba This circuitous flow entrained more sand due to the high flow and deposited it in the intake structure near the service water pump intakes in the low-flow areas.At the time of the October 2005 event, the licensee had not completed its actions to modify thesetpoint for automatic backwash of the strainer, alter the strainer intermittent backwashfrequency, modify the strainer differential pressure alarm setpoint, and implement weir-wall and traveling-screen modifications.NRC inspectors noted that the licensee had not performed certain actions committed to in itsresponse to NRC Generic Letter (GL) 89-13, "Service Water System Problems AffectingSafety-Related Equipment," specifically to periodically monitor silt levels and to periodically examine the intake structure basin for silt, debris, and deterioration (including corrosion), using divers or by dewatering the intake structure ba At the time of the event, the licensee had not examined the intake structure bay to assess its conditio Watts Bar Nuclear PlantThe licensee generated 13 problem evaluation reports from early 2002 through late 2005 forblockages identified in raw cooling water line The licensee identified silt accumulation in portions of systems providing raw cooling water for both essential and nonessential purposesand for high pressure water for fire protectio These accumulations were identified in both stagnant and active cooling water lines, typically in system low points and in piping with lowwater velocit In 1999 and 2002, clam accumulations resulted from missed biocide treatment The licensee implemented periodic ultrasonic testing and flushing to identify and minimize blockages due to silt and clam accumulation The initial frequency of ultrasonic testing was every 6 months, later shortened to every 3 month However, the licensee determined that thisprogram did not cover all susceptible lines and components.The centrifugal charging pump backup cooling line was not included in the ultrasonic testingmonitoring progra In 2000, a maintenance rule panel review left the flushing frequency for this line at 18 months, not recognizing the consequences of silt accumulatio This conclusion was consistent with the general site perception that silt accumulation was not a significantproble The blockage was found by means of an 18-month manual valve tes Most other lines were being flushed or tested every 3 month This issue resulted in a White finding in the NRC's Significance Determination Process. Raw water systems draw from a section of the Tennessee River downstream of the Watts Barda The suspended solids count in the river water increases after periods of heavy rains upstrea The suspended solids are transported into the affected systems where they settle atpoints with low fluid velocitie The licensee's corrective actions for the violation included increasing the frequency of ultrasonictesting, developing higher velocity flush procedures, and modifying systems to improve flushing. Lessons learned included the following observations:*Silt accumulation in smaller diameter lines may not flush as readily as in larger diameterlines.*Silt accumulates in stagnant lines off the main headers.
Cooper Nuclear StationIn both events, for a few minutes service water flow was lost to the nonessential header andgreatly reduced to the essential headers.  In each case, the successful Loop A automatic
 
backwash precluded the need for a manual scram, which would have been required if the loss of turbine equipment cooling water had been prolonged.  In each event, the Loop B filteringfunction was overwhelmed by the inrush of sediment.  The Loop B automatic backwash function
 
failed due to the lack of downstream pressure, which provides the motive force for the
 
backwashing operation.  The licensee believes that the contributing external factor was the lowlevel of the Missouri River, the source of the service water system.  Both of these events
 
occurred during autumn, following the navigation season.  A weir wall is installed in the river in
 
front of the intake structure.  The low river level caused an increased portion of the water that
 
flows into the intake structure to go around (rather than over) the weir wall and jet into the
 
service water bay.  This circuitous flow entrained more sand due to the high flow and deposited
 
it in the intake structure near the service water pump intakes in the low-flow areas.At the time of the October 2005 event, the licensee had not completed its actions to modify thesetpoint for automatic backwash of the strainer, alter the strainer intermittent backwashfrequency, modify the strainer differential pressure alarm setpoint, and implement weir-wall and
 
traveling-screen modifications.NRC inspectors noted that the licensee had not performed certain actions committed to in itsresponse to NRC Generic Letter (GL) 89-13, "Service Water System Problems AffectingSafety-Related Equipment," specifically to periodically monitor silt levels and to periodically
 
examine the intake structure basin for silt, debris, and deterioration (including corrosion), using
 
divers or by dewatering the intake structure bay.  At the time of the event, the licensee had not
 
examined the intake structure bay to assess its condition.  Watts Bar Nuclear PlantThe licensee generated 13 problem evaluation reports from early 2002 through late 2005 forblockages identified in raw cooling water lines.  The licensee identified silt accumulation in
 
portions of systems providing raw cooling water for both essential and nonessential purposesand for high pressure water for fire protection.  These accumulations were identified in both
 
stagnant and active cooling water lines, typically in system low points and in piping with lowwater velocity.  In 1999 and 2002, clam accumulations resulted from missed biocide treatments.
 
The licensee implemented periodic ultrasonic testing and flushing to identify and minimize
 
blockages due to silt and clam accumulations.  The initial frequency of ultrasonic testing was
 
every 6 months, later shortened to every 3 months.  However, the licensee determined that thisprogram did not cover all susceptible lines and components.The centrifugal charging pump backup cooling line was not included in the ultrasonic testingmonitoring program.  In 2000, a maintenance rule panel review left the flushing frequency for
 
this line at 18 months, not recognizing the consequences of silt accumulation.  This conclusion
 
was consistent with the general site perception that silt accumulation was not a significantproblem.  The blockage was found by means of an 18-month manual valve test.  Most other
 
lines were being flushed or tested every 3 months.  This issue resulted in a White finding in the
 
NRC's Significance Determination Process. Raw water systems draw from a section of the Tennessee River downstream of the Watts Bardam.  The suspended solids count in the river water increases after periods of heavy rains
 
upstream.  The suspended solids are transported into the affected systems where they settle atpoints with low fluid velocities. The licensee's corrective actions for the violation included increasing the frequency of ultrasonictesting, developing higher velocity flush procedures, and modifying systems to improve flushing. Lessons learned included the following observations:*Silt accumulation in smaller diameter lines may not flush as readily as in larger diameterlines.*Silt accumulates in stagnant lines off the main headers.
 
*Lines with a vertical drop off the main headers are more susceptible to silt accumulationthan lines with horizontal legs off the main headers.RELEVANT GENERIC COMMUNICATIONS
 
NRC Generic Letter 89-13, "Service Water System Problems Affecting Safety-RelatedEquipment"NRC GL 89-13 lists the following five recommendations for licensees:*Significantly reduce the incidence of flow blockage problems resulting from biofouling.*Conduct a test program to verify the heat transfer capability of all safety-related heatexchangers cooled by service water, including initial and periodic retesting.*Ensure by a routine inspection and maintenance program for open-cycle service watersystem piping and components that corrosion, erosion, protective coating failure, silting,and biofouling cannot degrade the performance of the safety-related systems suppliedby service water.*Confirm that the service water system will perform its intended function in accordancewith the licensing basis for the plant.*Confirm that maintenance practices, operating and emergency procedures, and trainingthat involves the service water system are adequate for ensuring that safety-relatedequipment cooled by the service water system will function as intended and thatoperators of this equipment will perform effectively.NRC Information Notice 2004-07:  "Plugging of Safety Injection Pump Lubrication Oil Coolerswith Lakeweed" NRC IN 2004-07 also discusses operating experience related to service water systemsusceptibilities due to external events.CONCLUSION
 
The above events involve instances in which sediment and debris has blocked flow in one ormore service water lines.  A number of the events described above involved the failure to take
 
adequate and timely corrective actions that could have prevented the event from occurring. Often there were multiple previous occurrences that could have alerted licensees to take more
 
aggressive or broader corrective actions.
 
==CONTACT==
This information notice requires no specific action or written response.  Please direct anyquestions about this matter to the technical contacts listed below./RA/Ho K. Nieh, Acting DirectorDivision of Policy and Rulemaking
 
Office of Nuclear Reactor RegulationTechnical Contacts:  John D. Hanna, NRC/RIVJonathan Bartley, NRC/RII402-426-9611423-365-5487 E-mail:  jdh1@nrc.govE-mail:  jhb1@nrc.govC. Vernon Hodge, NRR/DIRS301-415-1861 E-mail:  cvh@nrc.govNote:  NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collections.
 
==CONTACT==
This information notice requires no specific action or written response.  Please direct anyquestions about this matter to the technical contacts listed below./RA/Ho K. Nieh, Acting DirectorDivision of Policy and Rulemaking
 
Office of Nuclear Reactor RegulationTechnical Contacts:  John D. Hanna, RIVJonathan Bartley, RII402-426-9611423-365-5487 E-mail: jdh1@nrc.govE-mail: jhb1@nrc.govC. Vernon Hodge, NRR301-415-1861 E-mail: cvh@nrc.govNote: NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collections.DISTRIBUTIONIN File
 
ADAMS ACCESSION NUMBER:  ML061510292OFFICEIOEB:DIRSTECH EDITORRIV:DRP:RPB-E/FCSADRO:DORL:LPL4NAMECVHodgeHChang        (by e-mail)JDHanna      (by e-mail)BJBenneyDATE7/11/200606/14/20065/18/20067/12/2006OFFICERII:DRP:RPB6:WBROADRO:DORL:LPL2-2ADRO:DORL:LPL1-2TL:IOEB:DIRSNAMEJHBartley (by email)DVPickettSNBaileyICJungDATE  6/29/2006  7/18/20067/ 19 /20067/20/2006OFFICEPGCB:DPRLA:PGCB:DPRBC:PGCB:DPRD:DPR(A)NAMEDBeaulieuCHawes via e-mailCJacksonHNieh (JLubinski)DATE07/28/200607 /28 /200608/01/200608/01/2006OFFICIAL RECORD COPY


*Lines with a vertical drop off the main headers are more susceptible to silt accumulationthan lines with horizontal legs off the main headers.RELEVANT GENERIC COMMUNICATIONS NRC Generic Letter 89-13, "Service Water System Problems Affecting Safety-RelatedEquipment"NRC GL 89-13 lists the following five recommendations for licensees:*Significantly reduce the incidence of flow blockage problems resulting from biofouling.*Conduct a test program to verify the heat transfer capability of all safety-related heatexchangers cooled by service water, including initial and periodic retesting.*Ensure by a routine inspection and maintenance program for open-cycle service watersystem piping and components that corrosion, erosion, protective coating failure, silting,and biofouling cannot degrade the performance of the safety-related systems suppliedby service water.*Confirm that the service water system will perform its intended function in accordancewith the licensing basis for the plant.*Confirm that maintenance practices, operating and emergency procedures, and trainingthat involves the service water system are adequate for ensuring that safety-relatedequipment cooled by the service water system will function as intended and thatoperators of this equipment will perform effectively.NRC Information Notice 2004-07: "Plugging of Safety Injection Pump Lubrication Oil Coolerswith Lakeweed" NRC IN 2004-07 also discusses operating experience related to service water systemsusceptibilities due to external events.CONCLUSION The above events involve instances in which sediment and debris has blocked flow in one ormore service water line A number of the events described above involved the failure to take adequate and timely corrective actions that could have prevented the event from occurring. Often there were multiple previous occurrences that could have alerted licensees to take more aggressive or broader corrective action IN 2006-17  }}
}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 18:25, 6 April 2018

Recent Operating Experience of Service Water Systems Due to External Conditions
ML061510292
Person / Time
Issue date: 07/31/2006
From: Ho Nieh
NRC/NRR/ADRA/DPR
To:
C. Vernon Hodge, NRR/DIRS/IOEB
References
IN-06-017
Download: ML061510292 (6)
v • d • e


UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, DC 20555-0001July 31, 2006NRC INFORMATION NOTICE 2006-17: RECENT OPERATING EXPERIENCE OFSERVICE WATER SYSTEMS DUE TO

EXTERNAL CONDITIONS

ADDRESSEES

All holders of operating licenses for nuclear power reactors, except those who havepermanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to informaddressees of operating experience within the past few years affecting the operability of theservice water system at several nuclear power plants. The NRC expects that recipients will

review the information for applicability to their facilities and consider actions, as appropriate, toavoid similar problems. However, suggestions contained in this IN are not NRC requirements;therefore, no specific action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

During 2004 through 2005, 15 events occurred related to blockages in service water systems. These events were primarily self-revealing. The various blocking agents included silt, sand, small rocks, grass or weeds, frazil ice, and small aquatic fauna, such as fish. All these eventswere of low safety significance but illustrate the susceptibility of the safety-significant service

water system. For instance, in September 2005, NRC inspectors identified a condition at FortCalhoun that allowed small rocks to regularly enter the raw water system, contribute to trippingof a pump and strainer motors, and interfere with traveling screen operation (NRC InspectionReport 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)

Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a servicewater accumulator outlet line at Salem to be nearly full of silt (NRC InspectionReport 50-272/2005-03, ADAMS Accession No. ML052090344). Salem - Hope Creek Nuclear Power PlantsOn December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware Riverupstream of the Salem and Hope Creek Generating Stations. To mitigate the potential for oilintrusion into the cooling water systems, the licensee placed booms around the intakestructures at both stations. The booms are effective at controlling oil that is at or near the surface; however, the effectiveness of the booms was lessened because the spilled oil was"heavy" crude and was suspended at varying depths in the river. On December 3, 2004, the

licensee commenced shutdown of both Salem units due to the conditions on the river. There

were no issues associated with the shutdowns. Hope Creek was already shut down for a

refueling outage. The licensee restarted both Salem units after review of heat exchanger

performance and monitoring of the oil spill. Cooper Nuclear StationOn November 20, 2004, the service water system was clogged with sediment, resulting in anunexpected pressure drop in both loops of service water, high differential pressure alarms on

both strainers, and isolation of the nonessential service water loads. Both trains exceeded the

differential pressure operability limit of 15 psid. Backwash automatically initiated andsuccessfully cleaned the Loop A strainer, but the analogous action for Loop B did not succeed

in cleaning the strainer. Operators opened the strainer bypass valve to restore service water

flow and subsequently cleaned both strainers.On October 20, 2005, while preparing for online maintenance of the service water system,operators started a fourth service water pump and received high differential pressure alarms on

both Loops A and B. The automatic backwash did not sufficiently decrease the differentialpressure, and operators bypassed the strainer. Following these actions, the service water

system header pressures returned to normal. During the event, operators declared both loopsof service water inoperable. Both loops exceeded the strainer differential pressure structural

integrity limit of 15 psid. The high differential pressure across the strainers was the result of

debris (small rocks and sediment) introduced by the start of the fourth pump. With both loopsof service water inoperable, operators declared both emergency diesel generators inoperable. In 2005, the NRC Region IV office organized a special inspection based on the repetitive natureof this type of event (NRC Inspection Report 50-298/2005-15, ADAMS Accession No. ML061160027).Watts Bar Nuclear PlantOn November 22, 2004, while performing a manual valve exercising procedure, the licenseeidentified that a centrifugal charging pump backup cooling line from the essential raw coolingwater system was completely blocked with silt. Approximately 2.5 gallons of muddy pastepassed through the 1-inch drain valve before the valve became blocked. The line had to be

cleared mechanically. This line is significant in that this is the only high head pump with a

backup source of cooling water (NRC Inspection Report 50-390, 391/2004-05, ADAMSAccession No. ML050280344).

DISCUSSION

Cooper Nuclear StationIn both events, for a few minutes service water flow was lost to the nonessential header andgreatly reduced to the essential headers. In each case, the successful Loop A automatic

backwash precluded the need for a manual scram, which would have been required if the loss of turbine equipment cooling water had been prolonged. In each event, the Loop B filteringfunction was overwhelmed by the inrush of sediment. The Loop B automatic backwash function

failed due to the lack of downstream pressure, which provides the motive force for the

backwashing operation. The licensee believes that the contributing external factor was the lowlevel of the Missouri River, the source of the service water system. Both of these events

occurred during autumn, following the navigation season. A weir wall is installed in the river in

front of the intake structure. The low river level caused an increased portion of the water that

flows into the intake structure to go around (rather than over) the weir wall and jet into the

service water bay. This circuitous flow entrained more sand due to the high flow and deposited

it in the intake structure near the service water pump intakes in the low-flow areas.At the time of the October 2005 event, the licensee had not completed its actions to modify thesetpoint for automatic backwash of the strainer, alter the strainer intermittent backwashfrequency, modify the strainer differential pressure alarm setpoint, and implement weir-wall and

traveling-screen modifications.NRC inspectors noted that the licensee had not performed certain actions committed to in itsresponse to NRC Generic Letter (GL) 89-13, "Service Water System Problems AffectingSafety-Related Equipment," specifically to periodically monitor silt levels and to periodically

examine the intake structure basin for silt, debris, and deterioration (including corrosion), using

divers or by dewatering the intake structure bay. At the time of the event, the licensee had not

examined the intake structure bay to assess its condition. Watts Bar Nuclear PlantThe licensee generated 13 problem evaluation reports from early 2002 through late 2005 forblockages identified in raw cooling water lines. The licensee identified silt accumulation in

portions of systems providing raw cooling water for both essential and nonessential purposesand for high pressure water for fire protection. These accumulations were identified in both

stagnant and active cooling water lines, typically in system low points and in piping with lowwater velocity. In 1999 and 2002, clam accumulations resulted from missed biocide treatments.

The licensee implemented periodic ultrasonic testing and flushing to identify and minimize

blockages due to silt and clam accumulations. The initial frequency of ultrasonic testing was

every 6 months, later shortened to every 3 months. However, the licensee determined that thisprogram did not cover all susceptible lines and components.The centrifugal charging pump backup cooling line was not included in the ultrasonic testingmonitoring program. In 2000, a maintenance rule panel review left the flushing frequency for

this line at 18 months, not recognizing the consequences of silt accumulation. This conclusion

was consistent with the general site perception that silt accumulation was not a significantproblem. The blockage was found by means of an 18-month manual valve test. Most other

lines were being flushed or tested every 3 months. This issue resulted in a White finding in the

NRC's Significance Determination Process. Raw water systems draw from a section of the Tennessee River downstream of the Watts Bardam. The suspended solids count in the river water increases after periods of heavy rains

upstream. The suspended solids are transported into the affected systems where they settle atpoints with low fluid velocities. The licensee's corrective actions for the violation included increasing the frequency of ultrasonictesting, developing higher velocity flush procedures, and modifying systems to improve flushing. Lessons learned included the following observations:*Silt accumulation in smaller diameter lines may not flush as readily as in larger diameterlines.*Silt accumulates in stagnant lines off the main headers.

  • Lines with a vertical drop off the main headers are more susceptible to silt accumulationthan lines with horizontal legs off the main headers.RELEVANT GENERIC COMMUNICATIONS

NRC Generic Letter 89-13, "Service Water System Problems Affecting Safety-RelatedEquipment"NRC GL 89-13 lists the following five recommendations for licensees:*Significantly reduce the incidence of flow blockage problems resulting from biofouling.*Conduct a test program to verify the heat transfer capability of all safety-related heatexchangers cooled by service water, including initial and periodic retesting.*Ensure by a routine inspection and maintenance program for open-cycle service watersystem piping and components that corrosion, erosion, protective coating failure, silting,and biofouling cannot degrade the performance of the safety-related systems suppliedby service water.*Confirm that the service water system will perform its intended function in accordancewith the licensing basis for the plant.*Confirm that maintenance practices, operating and emergency procedures, and trainingthat involves the service water system are adequate for ensuring that safety-relatedequipment cooled by the service water system will function as intended and thatoperators of this equipment will perform effectively.NRC Information Notice 2004-07: "Plugging of Safety Injection Pump Lubrication Oil Coolerswith Lakeweed" NRC IN 2004-07 also discusses operating experience related to service water systemsusceptibilities due to external events.CONCLUSION

The above events involve instances in which sediment and debris has blocked flow in one ormore service water lines. A number of the events described above involved the failure to take

adequate and timely corrective actions that could have prevented the event from occurring. Often there were multiple previous occurrences that could have alerted licensees to take more

aggressive or broader corrective actions.

CONTACT

This information notice requires no specific action or written response. Please direct anyquestions about this matter to the technical contacts listed below./RA/Ho K. Nieh, Acting DirectorDivision of Policy and Rulemaking

Office of Nuclear Reactor RegulationTechnical Contacts: John D. Hanna, NRC/RIVJonathan Bartley, NRC/RII402-426-9611423-365-5487 E-mail: jdh1@nrc.govE-mail: jhb1@nrc.govC. Vernon Hodge, NRR/DIRS301-415-1861 E-mail: cvh@nrc.govNote: NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collections.

CONTACT

This information notice requires no specific action or written response. Please direct anyquestions about this matter to the technical contacts listed below./RA/Ho K. Nieh, Acting DirectorDivision of Policy and Rulemaking

Office of Nuclear Reactor RegulationTechnical Contacts: John D. Hanna, RIVJonathan Bartley, RII402-426-9611423-365-5487 E-mail: jdh1@nrc.govE-mail: jhb1@nrc.govC. Vernon Hodge, NRR301-415-1861 E-mail: cvh@nrc.govNote: NRC generic communications may be found on the NRC public Web site,http://www.nrc.gov, under Electronic Reading Room/Document Collections.DISTRIBUTIONIN File

ADAMS ACCESSION NUMBER: ML061510292OFFICEIOEB:DIRSTECH EDITORRIV:DRP:RPB-E/FCSADRO:DORL:LPL4NAMECVHodgeHChang (by e-mail)JDHanna (by e-mail)BJBenneyDATE7/11/200606/14/20065/18/20067/12/2006OFFICERII:DRP:RPB6:WBROADRO:DORL:LPL2-2ADRO:DORL:LPL1-2TL:IOEB:DIRSNAMEJHBartley (by email)DVPickettSNBaileyICJungDATE 6/29/2006 7/18/20067/ 19 /20067/20/2006OFFICEPGCB:DPRLA:PGCB:DPRBC:PGCB:DPRD:DPR(A)NAMEDBeaulieuCHawes via e-mailCJacksonHNieh (JLubinski)DATE07/28/200607 /28 /200608/01/200608/01/2006OFFICIAL RECORD COPY


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