1 Throughout this report, "lakeweed" is considered a mixture of plant fiber, diatom, algae filament, fungi, protozoa,

and bacteria.

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001

April 7, 2004

NRC INFORMATION NOTICE 2004-07: PLUGGING OF SAFETY INJECTION PUMP

LUBRICATION OIL COOLERS WITH LAKEWEED1

Addressees:

All holders of operating licenses or construction permits 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 alert

addressees to plugging of the high-pressure safety injection pump lubrication oil coolers with

lakeweed, which occurred at the Kewaunee Nuclear Power Plant (KNPP), a pressurized-water

reactor, during full-power operations. The NRC expects recipients to review the information

in this notice for applicability to their facilities and consider actions, as appropriate, to avoid

similar problems. However, suggestions contained in this information notice do not constitute

NRC requirements and, therefore, do not require any specific action or written response.

Description of Circumstances:

At the time of this event, the safety injection pump lubrication (lube) oil coolers at KNPP

were horizontal, straight tube, two-pass heat exchangers with twenty d-inch (0.95-cm)

(outer diameter) tubes per pass. Lubrication oil from the high-pressure safety injection pumps

circulated on the shell side, and service water from Lake Michigan passed through on the tube

(service water) side.

On January 15, 2004, during a routine quarterly maintenance inspection of the “A” safety injection

pump lube oil cooler, visual examination revealed silt and biological blockage (lakeweed)

at 17 of 20 tube pass inlets. The "as-found" tube-side flow measured 3.0 to 3.8 gallons/minute

(gpm) (11.4 to 14.4 liters/minute, lpm) before cleaning, and 5.95 to 6.05 gpm (22.5 to 22.9 lpm)

after cleaning. This concern prompted an investigation into the condition of the “B” safety

injection pump lube oil cooler, during which the licensee determined that 17 of 20 tubes in each

pass of this cooler were also blocked. A flow test, conducted with the cooler's end bell

removed, revealed that there was no flow from 17 of the 20 tubes, as seen from the outlet of the

cooler, and the "as-found" flow rate measured similar to that of the “A” safety injection pump

lube oil cooler. 

ML040770145
IN 2004-07

Page 2 of 3

The licensee and the NRC believe that the small tube diameter and tube sheet design

contributed to the lakeweed fouling on the tube side of the lubrication oil coolers.

The licensee determined that this condition had potentially rendered both safety injection pump

trains inoperable, and this discovery raised doubts regarding the future operability of the safety

injection pumps. As a result, plant operators declared both trains of the high-pressure safety

injection system inoperable at 12:20 a.m. on January 16, 2004, and initiated a plant shutdown at

1:20 a.m. the same day.

Discussion:

Generic Letter (GL) 89-13, “Service Water System Problems Affecting Safety-Related

Equipment,” requested that licensees evaluate system heat exchangers that perform safetyrelated functions. The NRC also requested that licensees initiate a maintenance, test, and

inspection program (as necessary) to comply with GL 89-13 and General Design Criterion

(GDC) 44, “Cooling Water,” as defined by Appendix A to Title 10, Part 50, of the Code of

Federal Regulations (10 CFR Part 50). The GL further stated that licensees’ programs should

account for heat exchanger fouling, plugging, and the potential for reduced flow and heat

removal capability.

With respect to safety injection pump coolers, the operability assessment would (as a minimum)

evaluate the delivered flow with the service water system in accident alignment, service water

temperature at its design limits (upper and lower bounds), and the safety injection pump moving

fluid at accident temperatures for a prolonged period of time (i.e., for the duration of the postaccident function). 

Operating experience at KNPP and another operating plant shows that fouling with lakeweed

is a concern with heat exchangers that have an inner diameter (ID) of less than 1⁄2 inch

(1.27 cm). This concern is heightened if the heat exchanger in question is in a low point

in the system and experiencing low flow. Coolers with higher flow velocities and larger diameter

heat exchanger tubes have been shown to be less susceptible to fouling and flow blockage. 

The higher velocities tend to keep solids suspended, and the larger diameter tubing provides

less potential for the accumulation of lakeweed or other marine organisms at the tube inlets.

Instances of lakeweed fouling of safety-related heat exchangers have occurred at other sites, as

follows (this is not an all-inclusive list):

• Point Beach Nuclear Plant experienced lakeweed clogging of the G1/G2 diesel coolers. 

The heat exchangers had d-inch (0.95-cm) tubes.

• R.E. Ginna Nuclear Power Plant has diesel generator cooling with two lube oil and jacket

water heat exchangers in series, one with d-inch (0.95-cm) tubes, and the other with

1⁄2-inch (1.27-cm) tubes. Ginna has not experienced significant blockage of the larger

tubing but has reported blockage on the smaller tubing and continues to monitor lakeweed

fouling on all the heat exchangers.
IN 2004-07

Page 3 of 3

• Brunswick Steam Electric Plant, Unit 1, noted that cooling flow to both residual heat

removal pump seal coolers was approximately 1 gpm (3.8 lpm). The licensee removed

the coolers from service and found that they were partially filled with silt. The seal

coolers are in a low point of the service water system. Upon opening these coolers, the

licensee frequently discovers lakeweed creating a matte over the inlet tubesheets.

Licensees need to be aware that plugging and blockage of heat exchanger tubing attributable 

to a buildup of silt, sand, or biological material may decrease the ability of the heat exchanger or

cooler to perform its required heat removal function. This may also affect other safety-related

components, such as pumps; emergency diesel generators; and heating, ventilation,

and air conditioning equipment, causing them to potentially fail when called upon to perform

their safety-related function.

This information notice does not require any specific action or written response. If you have any

questions about the information in this notice, please contact one of the technical contacts

identified below or the appropriate project manager in the NRC’s Office of Nuclear Reactor

Regulation (NRR).

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Robert G. Krsek, Region III Jack W. Foster, NRR

(920) 388-3156 (301) 415-3647

Email: rgk@nrc.gov Email: jwf@nrc.gov

John G. Lamb, NRR Steven M. Unikewicz, NRR

(301) 415-1446 (301) 415-3819

Email: jgl1@nrc.gov Email: smu@nrc.gov

Attachment: List of Recently Issued NRC Information Notices
____________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment 1

IN 2004-07

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-06 Loss of Feedwater Isokinetic

Sampling Probes at Dresden

Units 2 and 3

03/26/2004 All holders of operating licensees

for nuclear power reactors except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-05 Spent Fuel Pool Leakage to

Onsite Groundwater

03/03/2004 All holders of operating licensees

for nuclear power reactors (except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel) and for research

and test reactors, and all holders

of fuel storage licenses and

construction permits.

2004-04 Fuel Damage During Cleaning

at a Foreign Pressurized Water

Reactor

02/24/2004 All holders of operating licenses

for light-water reactors, except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor.

2004-03 Radiation Exposures to

Members of the Public in

Excess of Regulatory Limits

Caused by Failures to Perform

Appropriate Radiation Surveys

During Well-logging Operations

02/24/2004 All well-logging licensees.

Note: NRC generic communications may be received in electronic format shortly after they are

issued by subscribing to the NRC listserver as follows:

To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following

command in the message portion:

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