Information Notice 1993-79, Core Shroud Cracking at Beltline Region Welds in Boiling-Water Reactors

Core Shroud Cracking at Beltline Region Welds in Boiling-Water Reactors

ML031070090
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, Three Mile Island, 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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/30/1993
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-93-079, NUDOCS 9309290050
Download: ML031070090 (11)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 30, 1993 NRC INFORMATION NOTICE 93-79: CORE SHROUD CRACKING AT BELTLINE REGION WELDS

IN BOILING-WATER REACTORS

Addressees

All holders of operating licenses or construction permits for boiling-water

reactors (BWRs).

Purpose

The U.S. Nuclear Regulatory Commi'ssion (NRC) is issuing this information

notice to alert addressees that cracks have been observed in the weld regions

of the core support shroud in boiling water reactors. It is expected that

recipients will review the information for applicability to their facilities

and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

During the current refueling outage at Brunswick Unit 1 (a BWR-4 reactor),

in-vessel visual inspection revealed cracks at weld regions of the core

support shroud. The shroud is a stainless steel cylinder that serves to

direct the flow of water inside the reactor vessel. The shroud is completely

contained inside the 15.2 centimeter [6 inch] thick reactor vessel. The

structural integrity of the reactor-vessel is not impacted by the cracks in

the shroud.

Carolina Power and Light Company (CP&L), the licensee for Brunswick, found

both circumferential and axial cracks in the shroud. The circumferential

cracks were located in the inside shroud surface in the heat-affected zone

(HAZ) of weld H-3 and extended 3600 around the circumference of the shroud'

(see Figures 1 and 2). Weld H-3 is a horizontal weld which fuses the top

guide support ring to the lower shroud. The first axial crack discovered was

located on the outside shroud surface of weld H-4 in the lower shroud. CP&L

performed additional visual testing (VT) and ultrasonic testing (UT) of the

shroud and removed boat samples to evaluate the length and size of the cracks.

Discussion

In 1990, crack indications were reported at core shroud welds located in the

beltline region of an overseas reactor (BWR4). This reactor had completed

approximately 190 months of power operation before the cracks were discovered.

As a result of this discovery, General Electric (GE) issued Rapid Information

Communication Services Information Letter (RICSIL) 054, "Core Support Shroud

9309290050 ab e'0

I-V\i

IN 93-79 September 30, 1993 Crack Indications," on October 3, 1990, to all owners of GE BWRs. The RICSIL

summarized the cracking found in the overseas reactor and recommended that at

the next refueling outage plants with high-carbon-type 304 stainless steel

shrouds perform a visual examination of the accessible areas of the seam welds

and associated HAZ on the inside and outside surfaces of the shroud.

Since early July, CP&L has performed VT inspections of the Unit 1 inside and

outside shroud surface in the vicinity of welds. These inspections were

performed in accordance with GE RICSIL 054 and discovered cracks in the weld

regions. CP&L determined that in order to perform an adequate VT it was

necessary to remove the outer blade guides, pre-clean inspection areas, and

obtain an improved resolution of "1-millimeter wire" (in lieu of the

Code-prescribed resolution). Camera and lighting positions were also found to

be crucial-in performing adequate VTs. Also, CP&L has worked with GE to

develop more sophisticated UT equipment to identify how deeply into the shroud

metal the crack extends.

Additional VT inspections revealed more axial cracks at the inside surface of

weld H-4 as well as cracks at welds H-1, H-2, and H-5 of the shroud. One of

the additional cracks, a circumferential crack at weld H-5, appears to be

approximately 76.2 centimeters [30 inches] in length. The majority of the

cracks are located in the HAZ of the welds, although one crack was discovered

in the central region of shroud plate P-6. The crack in P-6, however, may be

associated with a possible weld repair of a surface defect in the plate after

its fabrication at the mill.

The results from the boat samples indicated intergranular stress-corrosion

cracking (IGSCC) as the mechanism. Preliminary results suggest that the crack

in the HAZ of weld H-3 may be 3.8 centimeters [1.5 inches] or more in depth.

The location of this crack is shown in Figure 2.

As a result of the shroud cracks being discovered on Unit 1, CP&L re-examined

the results of the inspection performed during the 1991 refueling outage of

Unit 2. The re-examination revealed three minor crack indications in the HAZ

of weld H-2. The licensee concluded that the cracks do not pose a concern to

normal operation of the reactor.

CP&L plans to. repair the Brunswick Unit 1 core shroud before the plant is

brought back into service. CP&L intends to restore the strength of the shroud

by adding stiffening braces around the top portion of the shroud. However, the licensee will continue to examine and evaluate the cracks in the core

shroud.

General Electric issued Revision 1 to RICSIL 054 on July 21, 1993, to update

the information on the core support shroud cracks and to provide revised

interim recommendations to perform visual examination of accessible areas of

the shroud at all GE BWRs during the next scheduled outage. The NRC has been

informed by GE that they are evaluating the Brunswick results and will provide

-K

IN 93-79 September 30, 1993 updated information to owners of GE BWRs. The NRC staff is evaluating the

implications of the shroud cracks for reactor core configuration and emergency

core cooling system performance under accident conditions at operating plants

and will consider the need for additional generic communications.

This information notice requires no 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 Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: R. A. Hermann, NRR J. Medoff, NRR

(301) 504-2768 (301) 504-2715 P. Byron, Region II T. Greene, NRR

(919) 457-9531 (301) 504-1175 Attachments:

1. Figure 1: Weld and Plate Locations in the Beltline

Region of the Brunswick Unit 1 Core Shroud

2. Figure 2: Details of Weld Locations H-2 and H-3 in the

Brunswick Unit 1 Core Shroud

3. List of Recently Issued NRC Information Notices

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Figure 2. Details of Weld Locations H-2 and H-3 in the

Brunswick Unit 1 Core Shroud (From CP&L)

At,.dhment 3 IN 93-79 September 30, 1993 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

93-78 Inoperable Safety Systems 10/04/93 All holders of OLs or CPs

At A Non-Power Reactor for test and research

reactors.

93-77 Human Errors that Result 10/04/93 All nuclear fuel cycle

in Inadvertent Transfers licensees.

of Special Nuclear

Material at Fuel Cycle

Facilities

93-76 Inadequate Control of 09/21/93 All holders of OLs or CPs

Paint and Cleaners for for nuclear power reactors.

Safety-Related Equipment

93-75 Spurious Tripping of 09/17/93 All holders of OLs or CPs

Low-Voltage Power Circuit for nuclear power reactors.

Breakers with GE RMS-9 Digital Trip Units

93-74- High Temperatures Reduce 09/16/93 All holders of OLs or CPs

Limitorque AC Motor for nuclear power reactors.

Operator Torque

93-73 Criminal Prosecution of 09/15/93 All NRC licensees.

Nuclear Suppliers for

Wrongdoing

93-72 Observations from Recent 09/14/93 All1 holders of OLs or CPs

Shutdown Risk and Outage for nuclear power reactors.

Management Pilot Team

Inspections

93-71 Fire at Chernobyl Unit 2 09/13/93 All holders of OLs or CPs

for nuclear power reactors.

93-70 Degradation of Boraflex 09/10/93 All holders of OLs or CPs

Neutron Absorber-Coupons for nuclear power reactors.

OL = Operating License

CP = Construction Permit

UNITED STATES

NUCLEAR REGULATORY COMMISSION

FIRST CLASS MAIL

WASHINGTON, D.C. 20555-0001 POSTAGE AND FEES PAID

USNRC

PERMIT NO. G-67 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, S300

)

PIftTED ON RECYCIED PAPER

IN 93-79

'.-' September 30, 1993 updated information to owners of GE BWRs. The NRC staff is evaluating the

implications of the shroud cracks for reactor core configuration and emergency

core cooling system performance under accident conditions at operating plants

and will consider the need for additional generic communications.

This information notice requires no 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 Office of

Nuclear Reactor Regulation (NRR) project manager.

orig /s/'d by BKGrimes

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: R. A. Hermann, NRR J. Medoff, NRR

(301) 504-2768 (301) 504-2715 P. Byron, Region II T. Greene, NRR

(919) 457-9531 (301) 504-1175 Attachments:

1. Figure 1: Weld and Plate Locations in the Beltline

Region of the Brunswick Unit 1 Core Shroud

2. Figure 2: Details of Weld Locations H-2 and H-3 in the

Brunswick Unit 1 Core Shroud

3. List of Recently Issued NRC Information Notices

• See previous concurrences

OFC OEAB:DORS SC/OEAB:DORS PUB:ADM C/OEAB:DORS

NAME TAGreene* RDennig* Tech Ed* AChaffee*

DATE 09/30/93 09/30/93 09/30/93 09/30/93 OFC EMCB:DE SC/EMCB:DE C/EMCB:DE PDII-1:DRP D

NAME JMedoff* RAHermann* JRStrosnider* PDMilano*

DATE 09/28/93 09/28/93 09/28/93 09/28/93 OFC PDII-1:ADR2 RII /DE OGCB:DORS

NAME SBajwa* PByron* JWiggins NCampbell*

DATE 09/30/93 09/30/93 / /93 09/30/93 l OFC C/OGCB:DORS

NAME GMarcus* _____________

DATE 09/30/93 09/3c/59 3

[OFFICIAL RECORD COPY]

DOCUMENT NAME: 93-79.IN

IN 93-79 September 30, 1993 This information notice requires no 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 Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: R. A. Hermann, NRR J. Medoff, NRR

(301) 504-2768 (301) 504-2715 P. Byron, Region II T. Greene, NRR

(919) 457-9531 (301) 504-1175 Attachments:

1. Figure 1: Weld and Plate Locations in the Beltline

Region of the Brunswick Unit 1 Core Shroud

2. Figure 2: Details of Weld Locations H-2 and H-3 in the

Brunswick Unit 1 Core Shroud

3. List of Recently Issued NRC Information Notices

• gp nruvinhi cnnricrrenfces

OFC OEAB:DORS S fE DpRS PUB:ADM C/OEAB:DORS

NAME TAGreene R Tech Ed* A_

DATE 7 130/93 1"I/3 793 09/30/93 1 /3/93 OFC EMCB:DE SC/EMCB:DE C/EMCB:DE l PDII-1:DRP l

NAME JMedoff* RAHermann* JRStrosnider* PDMilano*

DATE 09/28/93 09/28/93 09/28/93 09/28/93 OFC PDII-1:ADR2 RII (t5.-O,_ D/DJ OGCB:DORS

NAME SBajwa 1W PByron ins NCampbel 7 DATE /30/93 7/3o/93 I /93 / /93 llOFC l C/OGCB:DORS D/DORS I

NAME GMarcus pc BGrimes

DATE '7/3od93 / /93

[OFFICIAL'RECORD COPY]

DOCUMENT NAME: 93-79.IN (S:\DORSSEC)

J V- IN 93-XX

August XX, 1993 discovered in the central region of shroud plate P-6. The crack in P-6, however, may be associated with a possible weld repair of a surface defect in

the plate after its fabrication at the mill.

The results from the boat samples revealed that the cracking mechanism is by

intergranular attack (IGSCC). Preliminary results suggest that the cracks in

weld H-3 may be 1.5 inches or more in depth. The intergranular cracking

mechanism may be assisted by the high degree of neutron fluence emanating in from

the core. The licensee is continuing to examine and evaluate the cracks

the core shroud. Figures 1. and 2. are provided to show the weld locations.

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

you have any questions about the information in this notice, please contact

(one of) the technical contact(s) listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact(s): T. Greene, NRR J. Medoff, NRR R. A. Hermann

(301) 504-1175 (301) 504-2715 (301) 504-2768 Attachments: 1) Figure Showing Locations of Welds in the Brunswick Unit 1 Core Shroud

2) Figure Showing Details of Welds in the Top Guide Support

Ring Region

3) List of Recently Issued NRC Information Notices

OFC OEAB:DORS SC/OEAB:DORS PUB:ADM C/OEAB:DORS

NAME TAGreene Tech Ed AChaffee

DATE / /93 I /93 / /93 / /93 OFC EMCB:DE SC/EMC C/EMCB:DE PDII-1:DRP

NAME JMedoff RAHermm-in X RStrosnider PDMiIan

DATE L

9.!f/9 9 AO /93 93 I/z/93 OFC C/OGCB:DORS D:DORS

NAME GHMarcus BKGrimes

DATE I /93 / /93 / /93 /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\MEDOFF\INBRUN.1

b

• See previous concurrences_

OFC lOEAB:DORS SC/OEAB:DORS PUB:ADM C/OEAB:DORS

NAME TAGreene RDennig Tech Ed AChaffee I

DATE l / /93 J / /93 1? /g.O93 / /93 OFC lEMCB:DE SC/EMCB:DE lC/EMCB:DE PDII-1:DRP

NAME JMedoff* RAHermann* lJRStrosnider* PDMilano* l

DATE 1 09/28/93 1 09/28/93 109/28/93 T09/28/93 l

OFC RII - oRII DiDE C OGCB:DORS

NAME PByron JJohnson Siggins GHMarcus

DATE / /93 / /93 / /93 / /93 OFC } D:DORS

NAME BKGrimes

DATE / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\ATB1\INBRUN2