UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

March 26, 2004

NRC INFORMATION NOTICE 2004-06: LOSS OF FEEDWATER ISOKINETIC SAMPLING

PROBES AT DRESDEN UNITS 2 AND 3

Addressees:

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

ceased operation 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 to alert

addressees to recent experience in which feedwater isokinetic sampling probes were broken off

and lost in feedwater spargers. It is expected that recipients will review this information for

applicability to their facilities and consider actions, as appropriate. However, suggestions

contained in this information notice are not NRC requirements; therefore, no specific action or

written response is required. 

Background:

In 1971, to expand its water chemistry program, the Dresden licensee installed three sample

probes in each of the Unit 2 and 3 feedwater and condensate systems. In each unit, the probes

were installed at the discharge of the condensate pump (condensate sample probe), at the

suction of the condensate booster pump (condensate demineralizer effluent sample probe), and

at the discharge of the feedwater heaters to the feedwater spargers in the reactor vessel

(feedwater sample probe). These probes were designed for isokinetic sampling, in which the

water sample drawn in the probe is representative of the fluid in the process stream.

Each stainless steel probe was joined to the condensate or feedwater pipe by a carbon steel

collar. The collar was joined to the probe by a weld on the outside of the collar and to the

condensate or feedwater pipe by a weld to a carbon steel weldolet on the pipe. The collar

allows welding of dissimilar materials in the shop; field welding then only needs to be done on

similar materials. The crevice made by a small clearance between the collar and outside

diameter of the probe is exposed to water flow. Typically, these probes are about 0.3 meter 

(1 foot) long and about 2 centimeters (3/4 inch) in diameter.

In 1977, the nuclear steam supply system vendor, General Electric (GE), issued a generic

communication ("Improved Feedwater Sample Probe," Service Information Letter (SIL) No. 257,

December 30, 1977) to report failures at two boiling water reactor nuclear power plants in which

feedwater probes broke and lodged in downstream valves. The failure mechanism was

determined to be transgranular stress corrosion in the crevice between the collar and the probe. 

GE recommended an improved probe design in which a seal weld would protect the crevice

from the water flow.

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In 1990, GE issued a generic communication ("Improved Recirculation Water Chemistry

Sample Probe," SIL No. 518, August 6, 1990) to document potential failure of a recirculation

system sample probe due to mechanical, high-cycle fatigue induced by flow vibrations.

Description of Circumstances: 

In 2001, the Dresden licensee became aware of GE SIL 257 and planned inspections of the

Unit 2 and Unit 3 feedwater sample probes. 

Dresden Unit 2:

During the refueling outage in 2001 (D2R17), the licensee found the feedwater sample probe

missing. The licensee evaluation determined that the missing probe was most likely in a

feedwater sparger and did not present a safety concern. Another probe was installed to replace

the missing probe in accordance with GE SIL 257.

During the refueling outage in 2003 (D2R18), the licensee found three holes in the N4C 240

sparger nozzle and a sample probe resting in the sparger. The licensee inferred that the probe

was the missing feedwater sample probe and that the probe apparently caused the sparger

damage, although the physical phenomenon acting on the probe that could cause such damage

to the sparger was (and still is) unclear. The licensee removed the resting probe and repaired

the sparger. During a forced outage in December 2003 (D2F40), ultrasonic testing indicated

that the probe installed in 2001 was missing. Based on a GE evaluation, the licensee

determined that the probes apparently failed from mechanical, high-cycle fatigue induced by

flow vibrations during their respective service periods. The licensee evaluation determined that

the potential for lost parts in the reactor vessel did not compromise reactor safety.

Also during pre-outage work to support D2R18, the licensee found the condensate

demineralizer effluent sample probe in a condensate booster pump casing. The licensee

evaluation determined that pieces missing from this probe presented a moderate risk of fuel

fretting but no fuel or control rod drive safety concerns.

A new condensate demineralizer effluent probe, modified in accordance with GE SIL 257, was

installed in Unit 2 during the D2R18 outage.

Dresden Unit 3:

During the refueling outage in 2002 (D3R17), the licensee likewise found the feedwater sample

probe missing. The licensee evaluation determined that the missing probe was most likely in a

feedwater sparger and did not present a safety concern. Another probe was installed to replace

the missing probe in accordance with GE SIL 257. 

In response to the experience at Unit 2, the licensee planned internal and external inspections

of all Unit 3 spargers to locate the missing probe. During the Unit 3 outage for steam dryer

maintenance in 2003 (D3M10), the licensee conducted the planned inspections and found no

sparger damage but did find two probes resting in the N4B 150 sparger. Based on a GE

evaluation, the licensee determined that the probes failed from mechanical, high-cycle fatigue
IN 2004-06

Page 3 of 3

induced by flow vibrations during their respective service periods. The licensee evaluation

determined that the potential for lost parts in the reactor vessel did not compromise reactor

safety.

During maintenance outage D3M10, a new condensate demineralizer effluent probe, modified

in accordance with GE SIL 257, was installed in Unit 3 to replace the previous probe that was

found intact.

Discussion:

In reviewing related operating experience and conferring with GE, the Dresden licensee found

that similar probe failures had occurred at the Perry, Braidwood, Browns Ferry, and Grand Gulf

nuclear power plants during the years 1990-2001. In 1996 and 1997, the licensee for Quad

Cities Units 1 and 2 replaced the similarly located isokinetic feedwater sampling probes in

accordance with GE SIL 257. 

The GE evaluation, performed for the Dresden licensee, indicated that the natural frequency of

the initial unmodified feedwater sample probe was within the range to lock into the vortex

shedding frequency of the pre-EPU flow rate. The natural frequency of the SIL 257-modified

feedwater sample probe was within the range to lock into the vortex shedding frequency of the

post-EPU flow rate. The licensee found no indication of pre-installation design analysis for flowinduced vibration in the initial installation of the sample probes and the licensee reported that

the SIL 257-modified probe was not analyzed for the increased flow rates associated with EPU

prior to installation. The GE analysis indicated that the SIL 257-modified feedwater sample 

probe natural frequency would not have locked into the pre-EPU flow rate vortex shedding 

frequency had it been installed pre-EPU. 

The BWR Owners Group is coordinating the overall industry response to potentially adverse

flow effects from power uprate operation, including sample probe performance.

This information notice requires no specific action or written response. If you have any

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

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

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Maitri Banerjee, NRR Dr. C. Vernon Hodge, NRR

(301) 415- 2277 (301) 415-1861

E-mail: mxb@nrc.gov E-mail: cvh@nrc.gov

Attachment: List of Recently Issued NRC Information Notices
____________________________________________________________________________________O

L = Operating License

CP = Construction Permit

Attachment 1

IN 2004-06

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

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.

2004-02 Strontium-90 Eye Applicators

New Calibration Values and

Use

02/05/2004 All U.S. Nuclear Regulatory

Commission (NRC) medical-use

licensees and NRC master

materials license medical-use

Permittees.

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

issued by subscribing to the NRC listserver as follows:

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command in the message portion:

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