Information Notice 2004-17, Loose Part Detection and Computerized Eddy Current Data Analysis in Steam Generators

Loose Part Detection and Computerized Eddy Current Data Analysis in Steam Generators

ML042180094
Person / Time
Issue date:	08/25/2004
From:	Costello F NRC/NRR/DIPM/IROB
To:
Klein P, EMCB/DE 301-415-4030
References
IN-04-017
Download: ML042180094 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

August 25, 2004 NRC INFORMATION NOTICE 2004-17:

LOOSE PART DETECTION AND

COMPUTERIZED EDDY CURRENT DATA

ANALYSIS IN STEAM GENERATORS

Addressees

All holders of operating licenses for pressurized-water reactors (PWRs), except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor.

Purpose

The U.S. Nuclear Regulatory Commission is issuing this information notice to inform

addressees about recent operating experience with (1) challenges associated with detection of

loose parts and related tube damage in steam generators and (2) computerized data screening

algorithms used in the evaluation of steam generator tube eddy current data. The NRC

anticipates that recipients will review the information for applicability to their facilities and

consider taking actions, as appropriate, to avoid similar issues. However, no specific action or

written response is required.

Description of Circumstances

In 2001, at the Shearon Harris nuclear power plant, the licensee, Progress Energy, installed

replacement recirculating steam generators containing thermally treated Alloy 690 tubing. The

licensee conducted a pre-service eddy current inspection before the steam generators were

placed in service and, in 2003, conducted the first inservice eddy current inspection of all active

tubes. No tube degradation was detected. In late April 2004, however, the licensee detected

minor primary-to-secondary leakage in the C steam generator. In May 2004, following a unit

trip for an unrelated reason, the licensee investigated the source of the primary-to-secondary

leak. In the days preceding the unit trip, leak rates varied between approximately 20 to 40 liters

per day (5 to 10 gallons per day). A secondary side pressure test, an eddy current inspection

and a visual foreign object search were performed to identify the source of the leakage. This

investigation identified the leaking tube and damage in two adjacent tubes above the cold leg

tubesheet. A foreign object search and retrieval (FOSAR) examination identified a loose part in

the C steam generator at the damage location. This part was removed during the FOSAR

examination. The metallic object was magnetic and approximately 57 mm (2.25 inches) long

and had an irregular shape with some sharp edges.

Bobbin coil eddy current inspection performed during the May 2004 outage resulted in the

identification of loose part wear in two of the three affected tubes, neither of which was the

leaky tube. Even with the information from the secondary side pressure test, standard bobbin

coil analysis techniques did not readily detect the damage in the tube with the primary-to- secondary leak. This indication, however, was apparent when a 3-frequency (turbo) mix

bobbin coil channel was used. Damage was also readily detected with the +PointTM coil. This

damage was located about 4 mm (0.16 inch) above the tubesheet and was masked, when

using standard bobbin coil analysis techniques, by signals from the nearby expansion transition

located at the top of the cold leg tubesheet. The loose part wear that was detected in the other

two tubes was located at about 12 mm (0.48 inch) and 20 mm (0.77 inch) above the cold leg

tubesheet. A +PointTM coil measurement indicated the depth of loose part wear damage in the

three tubes at 77 percent through-wall (the leaking tube), 80 percent through-wall, and 45 percent through-wall. This examination did not detect a loose part since the part had been

removed prior to the +PointTM examination. Subsequent in situ pressure testing of the leaking

tube and the tube with 80 percent through-wall wear (as measured by +PointTM) demonstrated

adequate structural integrity and indicated adequate leakage integrity.

After evaluating the 2004 inspection test results, the licensee reviewed the 2003 steam

generator bobbin coil eddy current inspection results in the vicinity of the loose part location.

Two of the three tubes with loose part wear, including the tube that leaked, had no detectable

degradation and no signals indicative of a loose part in the 2003 data. However, a bobbin coil

indication, estimated at 37 percent through-wall, was present in the third tube but was missed

by both primary (manual) and secondary (computer) analysis. Since this tube was not

inspected with a rotating probe in 2003, this depth estimate was obtained using bobbin coil

phase angle analysis. This indication was estimated as 66 percent through-wall in 2004, using

the same bobbin coil technique analysis.

Investigation into why the computerized data screening (CDS) algorithm used for secondary

analysis did not detect this indication in 2003 revealed that some improper values were used in

the CDS settings. Automated data analysis was facilitated by dividing the tube lengths into five

regions. When the inspection parameters were entered into the CDS system for these regions, a 13-mm (0.5-inch) gap in the tube analysis (from 13 mm [0.5 inch] above the tubesheet to 25 mm [1 inch] above the tubesheet) was inadvertently created above the tubesheet. These input

values caused the computerized tube analysis process to skip the portion of the tube containing

the 37-percent through-wall bobbin indication in the 2003 analysis. The licensee properly

adjusted the CDS settings and re-analyzed the portion skipped during the 2003 analysis. Other

than the one wear indication discussed above, the licensee detected no other indications during

the reanalysis of the 2003 data.

In addition to the eddy current data review from the 2003 outage, the licensee also reviewed

secondary side steam generator FOSAR tapes from that outage. Though evident on the tape, the loose part was not identified in 2003. Comparison of the tapes from the 2003 and 2004 outages at the loose part location indicates that the loose part moved further into the tube

bundle after the 2003 outage. Discussion:

The staff recently issued Information Notice (IN) 2004-10, Loose Parts In Steam Generators, to discuss the potential for loose part degradation to affect steam generator tube integrity.

IN 2004-10 discussed the importance of supplementing the steam generator tube eddy current

examinations with secondary side visual inspections. A secondary side visual inspection was

performed at Shearon Harris during the 2003 refueling but the presence of the loose part was

not detected. If the part had been detected and removed, it would have prevented continued

tube wear and the subsequent leak. In addition, the visual detection of the part would have

given the licensee an opportunity to detect the associated tube degradation and possibly notice

the inappropriate settings for the CDS software.

IN 2004-10 also discussed the possibility that tube damage from loose parts may not always be

identified due to the presence of interfering signals. The recent operating experience at

Shearon Harris confirms this statement. Interfering signals from the nearby tube expansion

transition posed an inspection challenge for the bobbin coil (i.e., the interfering signals masked

the flaw signal associated with the leaking tube). Although this particular indication was

detected in hindsight analysis by the application of a 3-frequency bobbin coil mix, it is not

known if this analysis technique would detect loose part damage in different circumstances.

Inspection with the +PointTM coil clearly identified damage in all three affected tubes.

In addition to reinforcing some of the information communicated in IN 2004-10, the recent

experience at Shearon Harris shows the importance of properly setting automated data

screening parameters. Improper settings caused a small portion of tubing not to receive the

secondary analysis of eddy current data. This analysis would have detected loose part wear in

one tube during the previous outage inspection before the primary-to-secondary leak occurred.

This shows the importance of verifying proper automated data screening parameters used for

either primary or secondary analysis. Improper setting of these parameters may not be readily

apparent during data analysis. In this particular instance, the eddy current computer screening

system completed the site-specific performance demonstration, but the demonstration data did

not contain indications in the 0.5-inch length of tube that was not analyzed by the computer.

Also, proper setting of the computerized screening system parameters is necessary to ensure

the analysis of eddy current data by two independent analysis teams.

Recent steam generator tube leaks at a number of plants with thermally treated Alloy 600 or

Alloy 690 tubing (i.e., H.B. Robinson, Palo Verde, Shearon Harris) illustrate the need for

thorough inspections and robust inservice inspection programs alert to the potential for tube

degradation regardless of tube material, location, or steam generator history. Overall, experience with corrosion-related degradation mechanisms in these plants has been favorable.

Nevertheless, this experience indicates that damage by loose parts or damage incurred during

manufacture of steam generator tubes can result in primary-to-secondary system leakage.

These experiences also show the importance of being alert to all potential tube degradation

mechanisms and to aggressively interrogate eddy current inspection signals that may be

associated with tube degradation. 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

listed below or the appropriate project manager in the NRCs Office of Nuclear Reactor

Regulation (NRR).

/RA/

Francis M. Costello, Acting Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Paul Klein, NRR

Jerome Blake, RGN II

301-415-4030

404-562-4607 E-mail: pak@nrc.gov

E-mail: jjb1@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

• See previous concurrence

DOCUMENT NAME: G:\\DIPM\\OES\\Staff Folders\\Hodge\\harr_sg_fme m40715.wpd

OFFICE OES:IROB:DIPM

TECH EDITOR

EMCB

EMCB

C:EMCB:DE

NAME

CVHodge*

PKleene*

PAKlein*

ALLund*

WHBateman*

DATE

07/27/2004

07/28/2004

07/27/2004

07/31/2004

08/04/2004 OFFICE A:SC:IROB:DIPM

A:C:IROB:DIPM

NAME

ACMcMurtry*

FMCostello

DATE

08/23/2004

08/25/2004

______________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

_____________________________________________________________________________________

Information

Date of

Notice No.

Subject

Issuance

Issued to

_____________________________________________________________________________________

2004-16

Tube Leakage Due to a

Fabrication Flaw in a

Replacement Steam Generator

08/03/2004

All holders of operating licenses

for pressurized-water reactors

(PWRs), except those who have

permanently ceased operations

and have certified that fuel has

been permanently removed from

the reactor.

2004-15 Dual-Unit Scram at Peach

Bottom Units 2 and 3

07/22/2004

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.

2004-14

Use of less than Optimal

Bounding Assumptions in

Criticality Safety Analysis at

Fuel Cycle Facilities

07/19/2004

All licensees authorized to

possess a critical mass of special

nuclear material.

2004-13

Registration, Use, and Quality

Assurance Requirements for

NRC-Certified Transportation

Packages

06/30/2004

All materials and

decommissioning reactor

licensees.

2004-12

Spent Fuel Rod Accountability

06/25/2004

All holders of operating licenses

for nuclear power reactors, research and test reactors, decommissioned sites storing

spent fuel in a pool, and wet

spent fuel storage sites.

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:

subscribe gc-nrr firstname lastname