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 STATES
{{#Wiki_filter:UNITED STATES


NUCLEAR REGULATORY COMMISSION
===NUCLEAR REGULATORY COMMISSION===
OFFICE OF NUCLEAR REACTOR REGULATION


OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC  20555-0001


WASHINGTON, DC 20555-0001 July 31, 2006 NRC INFORMATION NOTICE 2006-17:               RECENT OPERATING EXPERIENCE OF
===July 31, 2006===
NRC INFORMATION NOTICE 2006-17:  


===RECENT OPERATING EXPERIENCE OF===
SERVICE WATER SYSTEMS DUE TO
SERVICE WATER SYSTEMS DUE TO


EXTERNAL CONDITIONS
===EXTERNAL CONDITIONS===


==ADDRESSEES==
==ADDRESSEES==
Line 38: Line 41:
addressees of operating experience within the past few years affecting the operability of the
addressees of operating experience within the past few years affecting the operability of the


service water system at several nuclear power plants. The NRC expects that recipients will
service 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, to
review the information for applicability to their facilities and consider actions, as appropriate, to


avoid similar problems. However, suggestions contained in this IN are not NRC requirements;
avoid similar problems. However, suggestions contained in this IN are not NRC requirements;
therefore, no specific action or written response is required.
therefore, no specific action or written response is required.


Line 48: Line 51:
During 2004 through 2005, 15 events occurred related to blockages in service water systems.
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 events
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 events


were of low safety significance but illustrate the susceptibility of the safety-significant service
were 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 Fort
water system. For instance, in September 2005, NRC inspectors identified a condition at Fort


Calhoun that allowed small rocks to regularly enter the raw water system, contribute to tripping
Calhoun that allowed small rocks to regularly enter the raw water system, contribute to tripping
Line 59: Line 62:


Report 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)
Report 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)
Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a service
Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a service


water accumulator outlet line at Salem to be nearly full of silt (NRC Inspection
water accumulator outlet line at Salem to be nearly full of silt (NRC Inspection
Line 69: Line 72:
On December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware River
On December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware River


upstream of the Salem and Hope Creek Generating Stations. To mitigate the potential for oil
upstream of the Salem and Hope Creek Generating Stations. To mitigate the potential for oil


intrusion into the cooling water systems, the licensee placed booms around the intake
intrusion into the cooling water systems, the licensee placed booms around the intake


structures at both stations. The booms are effective at controlling oil that is at or near the
structures 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
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
"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
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
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
refueling outage. The licensee restarted both Salem units after review of heat exchanger


performance and monitoring of the oil spill.
performance and monitoring of the oil spill.
Line 92: Line 95:
unexpected pressure drop in both loops of service water, high differential pressure alarms on
unexpected 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
both strainers, and isolation of the nonessential service water loads. Both trains exceeded the


differential pressure operability limit of 15 psid. Backwash automatically initiated and
differential pressure operability limit of 15 psid. Backwash automatically initiated and


successfully cleaned the Loop A strainer, but the analogous action for Loop B did not succeed
successfully 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
in cleaning the strainer. Operators opened the strainer bypass valve to restore service water


flow and subsequently cleaned both strainers.
flow and subsequently cleaned both strainers.
Line 104: Line 107:
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
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 differential
both Loops A and B. The automatic backwash did not sufficiently decrease the differential


pressure, and operators bypassed the strainer. Following these actions, the service water
pressure, and operators bypassed the strainer. Following these actions, the service water


system header pressures returned to normal. During the event, operators declared both loops
system header pressures returned to normal. During the event, operators declared both loops


of service water inoperable. Both loops exceeded the strainer differential pressure structural
of 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
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 loops
debris (small rocks and sediment) introduced by the start of the fourth pump. With both loops


of service water inoperable, operators declared both emergency diesel generators inoperable.
of service water inoperable, operators declared both emergency diesel generators inoperable.
Line 129: Line 132:
identified that a centrifugal charging pump backup cooling line from the essential raw cooling
identified that a centrifugal charging pump backup cooling line from the essential raw cooling


water system was completely blocked with silt. Approximately 2.5 gallons of muddy paste
water system was completely blocked with silt. Approximately 2.5 gallons of muddy paste


passed through the 1-inch drain valve before the valve became blocked. The line had to be
passed 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
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, ADAMS
backup source of cooling water (NRC Inspection Report 50-390, 391/2004-05, ADAMS
Line 144: Line 147:
In both events, for a few minutes service water flow was lost to the nonessential header and
In both events, for a few minutes service water flow was lost to the nonessential header and


greatly reduced to the essential headers. In each case, the successful Loop A automatic
greatly 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 filtering
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 filtering


function was overwhelmed by the inrush of sediment. The Loop B automatic backwash function
function 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
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 low
backwashing operation. The licensee believes that the contributing external factor was the low


level of the Missouri River, the source of the service water system. Both of these events
level 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
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
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
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
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.
it in the intake structure near the service water pump intakes in the low-flow areas.
Line 182: Line 185:
examine the intake structure basin for silt, debris, and deterioration (including corrosion), using
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
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.
examined the intake structure bay to assess its condition.
Line 189: Line 192:
The licensee generated 13 problem evaluation reports from early 2002 through late 2005 for
The licensee generated 13 problem evaluation reports from early 2002 through late 2005 for


blockages identified in raw cooling water lines. The licensee identified silt accumulation in
blockages identified in raw cooling water lines. The licensee identified silt accumulation in


portions of systems providing raw cooling water for both essential and nonessential purposes
portions of systems providing raw cooling water for both essential and nonessential purposes


and for high pressure water for fire protection. These accumulations were identified in both
and 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 low
stagnant and active cooling water lines, typically in system low points and in piping with low


water velocity. In 1999 and 2002, clam accumulations resulted from missed biocide treatments.
water velocity. In 1999 and 2002, clam accumulations resulted from missed biocide treatments.


The licensee implemented periodic ultrasonic testing and flushing to identify and minimize
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
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 this
every 6 months, later shortened to every 3 months. However, the licensee determined that this


program did not cover all susceptible lines and components.
program did not cover all susceptible lines and components.
Line 209: Line 212:
The centrifugal charging pump backup cooling line was not included in the ultrasonic testing
The centrifugal charging pump backup cooling line was not included in the ultrasonic testing


monitoring program. In 2000, a maintenance rule panel review left the flushing frequency for
monitoring 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
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 significant
was consistent with the general site perception that silt accumulation was not a significant


problem. The blockage was found by means of an 18-month manual valve test. Most other
problem. 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
lines were being flushed or tested every 3 months. This issue resulted in a White finding in the


NRCs Significance Determination Process.
NRCs Significance Determination Process.
Line 223: Line 226:
Raw water systems draw from a section of the Tennessee River downstream of the Watts Bar
Raw water systems draw from a section of the Tennessee River downstream of the Watts Bar


dam. The suspended solids count in the river water increases after periods of heavy rains
dam. 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 at
upstream. The suspended solids are transported into the affected systems where they settle at


points with low fluid velocities. The licensees corrective actions for the violation included increasing the frequency of ultrasonic
points with low fluid velocities. The licensees corrective actions for the violation included increasing the frequency of ultrasonic
Line 232: Line 235:


Lessons learned included the following observations:
Lessons learned included the following observations:
*       Silt accumulation in smaller diameter lines may not flush as readily as in larger diameter
*
Silt accumulation in smaller diameter lines may not flush as readily as in larger diameter


lines.
lines.


*       Silt accumulates in stagnant lines off the main headers.
*
Silt accumulates in stagnant lines off the main headers.


*       Lines with a vertical drop off the main headers are more susceptible to silt accumulation
*
Lines with a vertical drop off the main headers are more susceptible to silt accumulation


than lines with horizontal legs off the main headers.
than lines with horizontal legs off the main headers.
Line 248: Line 254:


NRC GL 89-13 lists the following five recommendations for licensees:
NRC GL 89-13 lists the following five recommendations for licensees:
*       Significantly reduce the incidence of flow blockage problems resulting from biofouling.
*
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 heat
*
Conduct a test program to verify the heat transfer capability of all safety-related heat


exchangers cooled by service water, including initial and periodic retesting.
exchangers cooled by service water, including initial and periodic retesting.


*       Ensure by a routine inspection and maintenance program for open-cycle service water
*
Ensure by a routine inspection and maintenance program for open-cycle service water


system piping and components that corrosion, erosion, protective coating failure, silting, and biofouling cannot degrade the performance of the safety-related systems supplied
system piping and components that corrosion, erosion, protective coating failure, silting, and biofouling cannot degrade the performance of the safety-related systems supplied
Line 260: Line 269:
by service water.
by service water.


*       Confirm that the service water system will perform its intended function in accordance
*
Confirm that the service water system will perform its intended function in accordance


with the licensing basis for the plant.
with the licensing basis for the plant.


*       Confirm that maintenance practices, operating and emergency procedures, and training
*
Confirm that maintenance practices, operating and emergency procedures, and training


that involves the service water system are adequate for ensuring that safety-related
that involves the service water system are adequate for ensuring that safety-related
Line 272: Line 283:
operators of this equipment will perform effectively.
operators of this equipment will perform effectively.


NRC Information Notice 2004-07: Plugging of Safety Injection Pump Lubrication Oil Coolers
NRC Information Notice 2004-07: Plugging of Safety Injection Pump Lubrication Oil Coolers


with Lakeweed
with Lakeweed
Line 284: Line 295:
The above events involve instances in which sediment and debris has blocked flow in one or
The above events involve instances in which sediment and debris has blocked flow in one or


more service water lines. A number of the events described above involved the failure to take
more 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.
adequate and timely corrective actions that could have prevented the event from occurring.
Line 293: Line 304:


==CONTACT==
==CONTACT==
This information notice requires no specific action or written response. Please direct any
This information notice requires no specific action or written response. Please direct any


questions about this matter to the technical contacts listed below.
questions about this matter to the technical contacts listed below.


/RA/
/RA/
                                            Ho K. Nieh, Acting Director


===Ho K. Nieh, Acting Director===
Division of Policy and Rulemaking
Division of Policy and Rulemaking


Office of Nuclear Reactor Regulation
===Office of Nuclear Reactor Regulation===
Technical Contacts:  John D. Hanna, NRC/RIV
 
Jonathan Bartley, NRC/RII


Technical Contacts: John D. Hanna, NRC/RIV          Jonathan Bartley, NRC/RII
402-426-9611
423-365-5487 E-mail: jdh1@nrc.gov


402-426-9611                  423-365-5487 E-mail: jdh1@nrc.gov          E-mail: jhb1@nrc.gov
E-mail: jhb1@nrc.gov


C. Vernon Hodge, NRR/DIRS
C. Vernon Hodge, NRR/DIRS


301-415-1861 E-mail: cvh@nrc.gov
301-415-1861 E-mail: cvh@nrc.gov
 
Note:  NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
 
ML061510292 OFFICE
 
IOEB:DIRS
 
TECH EDITOR
 
RIV:DRP:RPB-E/FCS
 
ADRO:DORL:LPL4 NAME
 
CVHodge
 
HChang        (by e-mail)
JDHanna      (by e-mail)
BJBenney
 
DATE
 
7/11/2006
06/14/2006
5/18/2006
7/12/2006 OFFICE
 
RII:DRP:RPB6:WBRO
 
ADRO:DORL:LPL2-2 ADRO:DORL:LPL1-2 TL:IOEB:DIRS
 
NAME
 
JHBartley (by email)
DVPickett
 
SNBailey
 
ICJung
 
DATE
 
6/29/2006
  7/18/2006
7/ 19 /2006
7/20/2006 OFFICE
 
PGCB:DPR
 
LA:PGCB:DPR
 
BC:PGCB:DPR
 
D:DPR(A)
NAME


Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
DBeaulieu


ML061510292 OFFICE      IOEB:DIRS              TECH EDITOR                RIV:DRP:RPB-E/FCS      ADRO:DORL:LPL4 NAME        CVHodge                HChang      (by e-mail)  JDHanna    (by e-mail) BJBenney
CHawes via e-mail


DATE        7/11/2006              06/14/2006                5/18/2006              7/12/2006 OFFICE    RII:DRP:RPB6:WBRO        ADRO:DORL:LPL2-2          ADRO:DORL:LPL1-2        TL:IOEB:DIRS
CJackson


NAME      JHBartley (by email)     DVPickett                  SNBailey                ICJung
HNieh (JLubinski)
DATE


DATE        6/29/2006                7/18/2006                7/ 19 /2006            7/20/2006 OFFICE    PGCB:DPR                LA:PGCB:DPR                BC:PGCB:DPR            D:DPR(A)
07/28/2006
NAME      DBeaulieu                CHawes via e-mail          CJackson                HNieh (JLubinski)
07 /28 /2006
DATE      07/28/2006               07 /28 /2006               08/01/2006             08/01/2006}}
08/01/2006
08/01/2006}}


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

Latest revision as of 08:40, 15 January 2025

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 STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001

July 31, 2006

NRC INFORMATION NOTICE 2006-17:

RECENT OPERATING EXPERIENCE OF

SERVICE WATER SYSTEMS DUE TO

EXTERNAL CONDITIONS

ADDRESSEES

All holders of operating licenses for nuclear power reactors, except those who have

permanently 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 inform

addressees of operating experience within the past few years affecting the operability of the

service 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, to

avoid 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 events

were 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 Fort

Calhoun that allowed small rocks to regularly enter the raw water system, contribute to tripping

of a pump and strainer motors, and interfere with traveling screen operation (NRC Inspection

Report 50-285/2005-11, Agencywide Documents Access and Management System (ADAMS)

Accession No. ML052920543). In June 2005, NRC inspectors found a portion of a service

water accumulator outlet line at Salem to be nearly full of silt (NRC Inspection

Report 50-272/2005-03, ADAMS Accession No. ML052090344).

Salem - Hope Creek Nuclear Power Plants

On December 2, 2004, crude oil was found leaking from a ship (Athos I) on the Delaware River

upstream of the Salem and Hope Creek Generating Stations. To mitigate the potential for oil

intrusion into the cooling water systems, the licensee placed booms around the intake

structures 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 Station

On November 20, 2004, the service water system was clogged with sediment, resulting in an

unexpected 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 and

successfully 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 differential

pressure, and operators bypassed the strainer. Following these actions, the service water

system header pressures returned to normal. During the event, operators declared both loops

of 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 loops

of 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 nature

of this type of event (NRC Inspection Report 50-298/2005-15, ADAMS Accession

No. ML061160027).

Watts Bar Nuclear Plant

On November 22, 2004, while performing a manual valve exercising procedure, the licensee

identified that a centrifugal charging pump backup cooling line from the essential raw cooling

water system was completely blocked with silt. Approximately 2.5 gallons of muddy paste

passed 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, ADAMS

Accession No. ML050280344).

DISCUSSION

Cooper Nuclear Station

In both events, for a few minutes service water flow was lost to the nonessential header and

greatly 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 filtering

function 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 low

level 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 the

setpoint for automatic backwash of the strainer, alter the strainer intermittent backwash

frequency, 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 its

response to NRC Generic Letter (GL) 89-13, Service Water System Problems Affecting

Safety-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 Plant

The licensee generated 13 problem evaluation reports from early 2002 through late 2005 for

blockages identified in raw cooling water lines. The licensee identified silt accumulation in

portions of systems providing raw cooling water for both essential and nonessential purposes

and 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 low

water 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 this

program did not cover all susceptible lines and components.

The centrifugal charging pump backup cooling line was not included in the ultrasonic testing

monitoring 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 significant

problem. 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

NRCs Significance Determination Process.

Raw water systems draw from a section of the Tennessee River downstream of the Watts Bar

dam. 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 at

points with low fluid velocities. The licensees corrective actions for the violation included increasing the frequency of ultrasonic

testing, 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 diameter

lines.

Silt accumulates in stagnant lines off the main headers.

Lines with a vertical drop off the main headers are more susceptible to silt accumulation

than lines with horizontal legs off the main headers.

RELEVANT GENERIC COMMUNICATIONS

NRC Generic Letter 89-13, Service Water System Problems Affecting Safety-Related

Equipment

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 heat

exchangers cooled by service water, including initial and periodic retesting.

Ensure by a routine inspection and maintenance program for open-cycle service water

system piping and components that corrosion, erosion, protective coating failure, silting, and biofouling cannot degrade the performance of the safety-related systems supplied

by service water.

Confirm that the service water system will perform its intended function in accordance

with the licensing basis for the plant.

Confirm that maintenance practices, operating and emergency procedures, and training

that involves the service water system are adequate for ensuring that safety-related

equipment cooled by the service water system will function as intended and that

operators of this equipment will perform effectively.

NRC Information Notice 2004-07: Plugging of Safety Injection Pump Lubrication Oil Coolers

with Lakeweed

NRC IN 2004-07 also discusses operating experience related to service water system

susceptibilities due to external events.

CONCLUSION

The above events involve instances in which sediment and debris has blocked flow in one or

more 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 any

questions about this matter to the technical contacts listed below.

/RA/

Ho K. Nieh, Acting Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: John D. Hanna, NRC/RIV

Jonathan Bartley, NRC/RII

402-426-9611

423-365-5487 E-mail: jdh1@nrc.gov

E-mail: jhb1@nrc.gov

C. Vernon Hodge, NRR/DIRS

301-415-1861 E-mail: cvh@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections.

ML061510292 OFFICE

IOEB:DIRS

TECH EDITOR

RIV:DRP:RPB-E/FCS

ADRO:DORL:LPL4 NAME

CVHodge

HChang (by e-mail)

JDHanna (by e-mail)

BJBenney

DATE

7/11/2006

06/14/2006

5/18/2006

7/12/2006 OFFICE

RII:DRP:RPB6:WBRO

ADRO:DORL:LPL2-2 ADRO:DORL:LPL1-2 TL:IOEB:DIRS

NAME

JHBartley (by email)

DVPickett

SNBailey

ICJung

DATE

6/29/2006

7/18/2006

7/ 19 /2006

7/20/2006 OFFICE

PGCB:DPR

LA:PGCB:DPR

BC:PGCB:DPR

D:DPR(A)

NAME

DBeaulieu

CHawes via e-mail

CJackson

HNieh (JLubinski)

DATE

07/28/2006

07 /28 /2006

08/01/2006

08/01/2006


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