Loose Parts In the Steam Generator and Core at Wolf Creek (oops)

This was released today. As a by the way, the outage before the last Palisades found foreign material sitting on top of one of their SG on the secondary side. They plugged a few tubes the the material was siting on, and then left it sitting on top of the SG because it was too big to take out.

Palisades?
What is the difference between foreign object wear and loose parts?
ENO Response
2. During the 2012 refueling outage steam generator inspections, the three tubes
listed in table 6 for steam generator (SG) E-50A as "LP Preventive Stabilization"
were plugged because loose parts could not be retrieved. Even though wear due to
these loose parts was not present, the three tubes were plugged as a preventive
measure should future wear occur.
To further clarify the 2012 refueling outage inspection results, the following
inspection report changes were made:
Two changes were made to Table 2, "Active Damage Mechanisms." The first is that
the location "Historical foreign object (FO) wear" was changed to "Loose Part (LP)
wear." Second, since historical FO wear, now labeled LP wear, is an active damage
mechanism in both E-50A and E-50B, E-50A was added to the LP wear location.
To better categorize the bases for SG tubes plugged in 1 R22, Table 5, "Tube
Plugging Summary by Damage Mechanism," was revised to change the row "Wear
- Loose Part" for SG E-50A from "3" to "0." A row was added to the Tube Plugging
Summary column labeled "Preventive - Loose Part (LP)" with a "3" in the SG E-50A
column.

Wolf Creek Special Report ...got pictures

 

Note: a rounded nut...there is a lot of damage for three days operation.

August 27, 2002

MEMORANDUM TO: Docket File

FROM: Jack N. Donohew, Senior Project Manager, Section 2
Project Directorate IV /RA/
Division of Licensing Project Management
Office of Nuclear Reactor Regulation

SUBJECT: RESPONSE TO REQUEST FOR INFORMATION ON LOOSEPARTS FOUND IN THE STEAM GENERATOR AT WOLF CREEK GENERATING STATION

Wolf Creek Nuclear Operating Corporation (the licensee) conducted a refueling outage at Wolf Creek Generating Station (WCGS) that began on Friday, March 22, 2002. On May 10, 2002, in coming out of the outage, there were indications of an unusual noise followed by an alarm in the plant loose parts monitoring system for Steam Generator D. The plant was shut down on May 13, 2002, and the steam generator was entered to find the loose parts.

Enclosed are three e-mails dated May 17 and 20, and June 20, 2002, from the licensee. The May 17, 2002, e-mail provided (1) a copy of a special report issued by the licensee to the WCGS employees describing the loose parts found in the steam generator, and (2) pictures of the two parts found in the steam generator. The special report and the pictures can be found in ADAMS Accession No. ML022270414.

The May 20, 2002, e-mail provides answers to the six questions sent by me by e-mail to the licensee. The responses to the questions prevented the need for the staff to have a telephone call with the licensee to discuss the loose parts founds in the Steam Generator "D." The licensee’s answers follow the phrase "Answer)" in the e-mail. The Westinghouse letters referenced in the [...]’s in the licensee’s answers were not requested or reviewed by the staff.

The June 20, 2002, e-mail provides the licensee’s agreement to have the information provided in the previous two e-mails docketed. This memorandum dockets the information received from the licensee on the loose parts found in Steam Generator "D." No further action was needed to be taken by the staff.

Docket No. 50-482

Enclosures: 1. E-mail dated May 17, 2002
2. E-mail dated May 20, 2002
3. E-mail dated June 20, 2002

From: Kenneth Karwoski [mailto:KJK1@nrc.gov]

Sent: Friday, May 17, 2002 1:04 PM
To: Jack Donohew
Cc: Louise Lund
Subject: Wolf Creek Loose Part

Jack,

This is to remind you of our conversation.

 I would like to have a discussion with Wolf Creek to discuss their loose part with the intent that a summary of the call would be made publicly available.

Specifically, I would like information related to the following:

What provided the initial indication of the part (e.g., loose part monitor alarm)? When was the initial indication?

 Answer) The initial indication of the presence of loose part(s) was an "unusual noise" heard on Channels 11 and 12 on the plant Loose Part Monitoring System (LPMS), relating to steam generator D. This "unusual noise", followed closely by the LPMS alarm, occurred on 5/10/2002 at 0115 hours during a return to power after a reactor trip.

When was the plant shut down?

 Answer) The plant shutdown commenced at 1710 hours on 5/13/2002 directly subsequent to a Westinghouse presentation of the results of their just concluded evaluation of the LPMS tapes transmitted to them.

 Were the parts on the primary or secondary side or both?

 Answer) Two loose parts were retrieved from the primary side of steam generator D, consistent with the Westinghouse conclusions from their evaluation of the LPMS tapes.

 What was the extent of the damage?

 Answer) The known guide tube support pin damage is based upon the retrieval of the support pin nut and locking device (disc) from steam generator D. Although one possible failure mode is that the guide tube support pin shank did not fracture but that the nut, locking disc, and dowel pin came loose leaving an intact support pin in place in the guide tube, the evaluation for continuing operation assumed, more conservatively, that the assumed unrecovered loose parts included: 1) The guide tube support pin shank, 2) the guide tube support pin dowel pin, and 3) Fragments from the guide tube support pin nut.

There were no indications within the S/G of serious damage to the tubes, tubesheet, welds, or the divider plate caused by the loose parts.

Generalized peening to various degrees of the entire bowl region/bottom face of the tubesheet and divider plate was observed. All tube plugs were found in the proper tube hole location. The skirts of the tube plugs were peened to various degrees. Most of the entire inner surface of the channel head bowl was peened to various degrees. There was no indication of a foreign object present in any of the tubes. There appeared to be indications of scratching and displaced metal on the ID’s of various tubes. Whether this was caused by the objects found in the channel head, or from tooling associated with tubing NDE and other channel head maintenance operations was not determinable. It must be noted that the objects removed were larger than the tubing ID. The level of damage was considered not as severe as that of a comparison plant.

What was the acceptance criteria? What is the basis for the acceptance criteria?

Answer) The acceptance criteria for continuing operation with guide tube support pin damage and the assumed unrecovered loose parts, including the associated bases, through the end of the planned operating cycle, is documented in the Westinghouse evaluation [Westinghouse Letter LTR-MSI-02-62, Wolf Creek - Guide Tube Support Pin Loose Part JCO – Reactor Internals Evaluation]. This evaluation considered the safety concerns regarding the structural integrity of guide tubes with potentially fractured support pin shanks during operation and the potential effects on the nuclear fuel, the control rod drive mechanisms and drive line, and the applied impact and wedging loads upon the reactor pressure vessel and internals during operation from the assumed missing pieces.

The acceptance criteria and basis for the steam generator damage was documented in a bounding evaluation performed by Westinghouse [Westinhouse Letter LTR-SGDA-02-156]. The inspection and evaluation used industry experience from plants with damaged channel head components caused by loose parts. For the analysis, it was assumed that all of the tube welds were damaged and may be unable to perform their intended structural and leak prevention function. Resistance to tube pullout and resistance to primary-to-secondary side leakage was evaluated. Visual inspection of the mechanical plugs was adequate to establish confidence that the plugs will perform their intended plugging function through the end of the planned operating cycle. For the cladding, it was assumed that loose part impacts resulted in the cladding being breached in at least one location on the tube sheet and one location on the curved portion of the channel head and that the low-alloy steel is exposed to the primary liquid during the entire cycle.

What was the source of the part (if known)?

Answer) The two parts retrieved have been identified as the support pin nut and locking device (disc) from a guide tube support pin.

I have a phone call with Diablo at 12:30 p.m. on Monday. I will be leaving at 1:45 on Monday. I can support a call up to about 1:00 on Tuesday and I will be traveling the rest of the week.

Thanks,

Ken

415-2752