Information Notice 1987-44, Thimble Tube Thinning in Westinghouse Reactors

Thimble Tube Thinning in Westinghouse Reactors

ML031130612
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill, Crane
Issue date:	09/16/1987
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-87-044, NUDOCS 8709100056
Download: ML031130612 (8)

SSINS No.:

6835 IN 87-44

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

September 16, 1987

NRC INFORMATION NOTICE NO. 87-44: THIMBLE TUBE THINNING IN WESTINGHOUSE

REACTORS

Addressees

All pressurized water reactor facilities employing a Westinghouse nuclear

steam supply system (NSSS) holding an operating license or a construction

permit.

Purpose

This information notice is being provided to alert addressees to potential

problems resulting from thimble tube thinning in Westinghouse reactors. It

is expected that recipients will review the information for applicability

to their facilities and consider actions, if appropriate, to avoid similar

problems.

However, suggestions contained in this information notice do not

constitute NRC requirements; therefore no specific action or written response

is required.

Description of Circumstances

During the recent refueling outage at North Anna Unit 1, eddy current (EC)

testing identified wall thinning on approximately 23 out of 50 thimble tubes.

The wall degradation occurred on the thimble tubes just above the lower core

plate, between the lower core plate and the fuel assembly guide tubes.. 'Several

thimble tubes with greater than 35% wall thinning were identified, with one

thimble tube thinned as much as 49%.

Discussion:

The movable incore neutron detectors travel within retractable thimble tubes.

The thimble tubes normally extend (as indicated in Attachment 1) from a 10-path

transfer device, through the seal table, through the bottom of the reactor

vessel, and into selected fuel assemblies. The thimble tubes are supported

by guide tubes within the lower vessel region and the fuel assemblies, and

by high-pressure conduits between the reactor vessel and the seal table.

The thimble tubes are sealed at the leading (reactor) end, but are open at the

10-path transfer device to allow insertion of an incore neutron detector.

91000

K>1_

IN 87-44 September 16, 1987 Mechanical high-pressure seals, located at the sail table, are used to seal

the area between the thimble tube and'th6 high-pressure conduit.

This seal

serves as a reactor coolant system (RCS) pressure boundary since the area

between the thimble tube and the high pressure conduit is at RCS pressure.

Consequently, a leak in a thimble tube results in degradation of the RCS

pressure boundary by creating a path for reactor coolant to bypass the

mechanical seal.

In order-to halt'the flow of-leaking react6r coolant, the manual isolation valve must be'closed.

As indicated, the thimble tubes are supported over most of their length.

However, a small portion of the thimble tube is directly exposed t&-RCS'

flow.

This exposed portion is between the top of the lower core plate

and the bottom of the fuel- assembly.;

This region is approximately 1.8.4

to 34.8 mm in length, depending on the reactor type.

Itis believed that

flow-induced vibration on this exposed portion causes fretting at the'

adjacent guide tubes.

Undetected thinning of a thimble tube could lead to the development ofb'a

non-isolable leak-and a corresponding loss of reactor-coolant. Asdiscussed

previously, the manual isolation valve would have to be closed'to'halt thd

flow of leaking reactor coolant.

The leaking coolant-'may create an environ- ment in the vicinity of the isolation-valves too hazardous- for personnel to

enter.

-

Leaking thimble tubes could result in degradation of the incore neutron moni- toring system.

If not isolated, reactor coolant from leaking thimble tubes

can flow into the 10-path transfer device, allowing coolant to fTood'the other

thimble tubes originating from that device.

This could result in rendering

inoperable more than just the leaking tube.

In addition to North Anna-Unit 1, incore thimble'tube'thinning and leakage

has been detected at facilities in France and Belgium; In this country, leaks in thimble tubes -are-known to have occurred at Salem-Unit-1. In

Licensee Event Report (LER)81-028, Publie.-ServiceiElectric`& Gas Co (PSE&G)

reported that three incore thimble tubes were known to have developed leaks

because of fretting.

One of these leaks resulted in the flooding o6f alli'six

10-path transfer devices, partially or completely flooding all the thimble

tubes in the reactor.

In addition, thinning has been detected on the Farley

thimble tubes.

-

At North Anna Unit 1, the proposed corrective action was to retract selected

thimble tubes approximately 2 inches.

This- would move the thinned area out

of the region of high turbulence. :In addition, -the thimble tube'that expeti- enced the most degradation will be taken out of service by closing the corre- sponding isolation valve.

-

-

4 IN 87-44 September 16, 1987 No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Jack Ramsey, NRR

(301) 492-9081 Attachments:

1. Typical Westinghouse Incore Neutron Monitoring System

2. List of Recently Issued NRC Information Notices

Attachment 1

TYPICAL WESTINGHOUSE INCORE NEUTRON MONITORING SYSTEM

SAFM SWITCHES

DRIVE UNITS

LIMIT SWItCHES

6-PATH TRANSFERS

INCORE NEUTRON

10-PATH TRANSFERS

DETECTOR CABLE

INCORE NEUTRON

DETECTOR INSIDE

{

\\

\\

1THIMBLE TUBE

SEAL TABLE

MECHANICAL

SEALS

HIGH PRESSURE CONE

'-

REACTOR

l

r

J

CORE

THIMBLE TUBE INSIDE

FUEL ASSEMBLY,_

GDIE TUBE

UNGUIDED THIMBLE-TUBE,.-.

MAY EXPERIENCE THINNING

IN THIS REGION

THIM8LE TUBE INSIDE

LOWER VESSEL REGION-

GUIDE TUBE

LOWER

' HIGH PRESSURE -

PLATE

CONDUITS

7*

IC

' >

K)j

Attachment 2

IN 87-44

September 16, 1987

I

nformatirot

Notice No.

LIST OF RECENTLY ISSUED

INFORMATION NOTICES 1987 I

Date of

Sub ject

Issuance

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Issued to

, Issu,, to

87-43 Gaps in Neutron-Absorbing

Material in High-Density

Spent Fuel Storage Racks

9/8/87

All nuclear power

reactor facilities

holding an OL or CP.

87-42

87-41

.

.

-

87-40

87-39 -

87-38

87-37

87-36

Diesel Generator.Fuse

Contacts

Failures of Certain Brown

Boveri Electric Circuit

Breakers

Backseating Valves Routin

to Prevent Packing Leakag

Control of..Hot Particle

Contamination at Nuclear

Power'Plants

ely

9/4/87

8/31/87

8/31/87

All nuclear power

reactor facilities

holding an OL or CP.

All nuclear power

reactor facilities

holding an OL or CP.

All fnuclear power

reactor facilities

holding an OL or CP.

Inadequate or Inadvertent

Blocking of Valve Movemeni

Compliance with the.Genera

License Provisions of

10 CFR Part 31

Si gnificant Unexpected

Erosion of Feedwater Lines

8121/87

All nuqlear power

reactor Facilities

and spent fuel

storage facilities

holding an NRC

..c nse or CP.

8/17/87 All Inuclear'power

reactor facilities

4ho1ing an OL or CP.

al

8/10/87 Al persons speci f

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calty lica'sed t'

'

mahufacture or to'

initially transfer

devicesc'dntaini g'.

.raioacttive Material

to general licensees,

...,i;as{-defined

i'fh1.0 "CFR

Part 31.

8/4/87

All nuclear power

reactor facilities

holding an OL or CP.

OL = Operating License

CP = Construction Permit

'

-

'

40.

IN 87-44

September 16, 1987

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Jack Ramsey, NRR

(301) 492-9081 Attachments:

1. Typical Westinghouse Incore Neutron Monitoring System

2. List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES

• OGCB:DOEA:NRR

• PPMB:ARM

JERamsey

TechEd

08/31/87

08/31/87

• C/OGCB:DOEA:NRR

CHBerlinger

09/02/87

09//aI87

IN 87-XX

September xx, 1987 This information notice requires no specific action or written response. If

you have any questions about this matter, please contact the Regional Adminis- trator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Jack Ramsey, NRR

(301) 492-9081 Attachments:

1. Typical Westinghouse Incore

2. List of Recently Issued NRC

Neutron Monitoring System

Information Notices

0

~

WVf

H.S FM'IPz

dl /7

• SEE PREVIOUS CONCURRENCES

COO

• OGCB:DOEA:NRR

• PPMB:ARM

C/OGCB:DOEA:NRR

JERamsey

TechEd

CHBerlinger

08/31/87

08/31/87

09/.4487 D/DOEA:NRR

CERossi

09/ /87

0

' V,

IN 87-XX

September xx, 1987

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

you have any questions about this matter, please contact the Regional Adminis- trator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Jack Ramsey, NRR

(301) 492-9081 Attachments:

1. Typical Westinghouse Incore Neutron Monitoring System

2. List of Recently Issued NRC Information Notices

OG & a

NRR

JE

sey

09/ /87 e)21IS3 PPMB:ARM

TechEdr

09/ A7 of/s/

C/OGCB:DOEA:NRR

CHBerlinger

09/ /87 D/DOEA:NRR

CERossi

09/ /87