Information Notice 1988-03, Cracks in Shroud Support Access Hole Cover Welds

Cracks in Shroud Support Access Hole Cover Welds

ML031150673
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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	02/02/1988
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-88-003, NUDOCS 8802010084
Download: ML031150673 (4)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 February 2, 1988 NRC INFORMATION NOTICE NO. 88-03: CRACKS IN SHROUD SUPPORT ACCESS HOLE

COVER WELDS

Addressees

All holders of operating licenses or construction permits for boiling water

reactors (BWRs).

Purpose

This notice alerts addressees to the potential for cracks in the welds of the

covers of the shroud support access holes within the reactor vessel. The cracks

could result in weld failure with resulting formation of loose parts and core

by-pass flow. The event described highlights the importance of inspecting the

access cover welds. It is expected that recipients will review the information

for applicability to their facilities and consider actions, as appropriate, to

preclude similar problems from occurring at their facilities. However, sug-

-gestions contained in this information notice-do not constitute NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

Jet pump BWRs are designed with access holes in the shroud support plate which

is located at the bottom of the annulus between the core shroud and the reactor

vessel wall. Each reactor vessel has two such holes which are located 180

degrees apart. These holes are used for access during construction and are

subsequently closed by welding a plate over the hole. The covers and shroud is

support ledge are Inconel Alloy 600 material. The connecting weld material

also Inconel 600 (Alloy 182 or 82).

The high residual stresses resulting from welding, along with a possible crevice

geometry of the weld, when combined with less than ideal water quality, present

a condition conducive to intergranular stress corrosion cracking (ISGCC). This

has been recognized by General Electric and, as a result, they have developed a

remotely operated ultrasonic testing capability for detecting cracks in the

cover plate welds. The first use of this custom ultrasonic testing fixture

was at Peach Bottom Unit 3.

On January 21, 1988, intermittent short cracks were found in the weld heat- affected zone around the entire circumference of the covers at Peach Bottom

Unit 3. It is estimated that cracking exists over 50% to 60% of the circum- ference with cusps as deep as 70% through the wall. It is believed that cover

plate welds have not been inspected previously on any other BWR. It is possible

that the cracking is generic and may, therefore, affect all BWRs with Jet pumps.

880

IN 88-03 February 2, 1988 Discussion:

General Electric has identified three concerns if

cover plates is postulated due to weld cracking: failure of the access hole

1. Loose parts - In the event of complete failure of

during normal reactor operation, the slightly higher the access cover weld'

pressure would lift the cover out of its recess. bottom head area

It would most likely

fall to one side, but there is a potential for it

circulation pump suction line causing severe pump to be swept into the re- damage.

2. Core flow bypass (normal operation) - Loss of one

• would allow some recirculation system flow to bypass or both cover plates

Jet pump discharge through the open access hole the core, from the

to the

suction. This flow transient would be readily detectable recirculation pump

reactor shutdown. and would require

3. Core flow bypass (Loss of Coolant Accident) - If

plate welds were to fail as a direct consequence the access hole cover

of: a recirculation suction

line break, the bypass path would prevent the emergency

from reflooding the core to the 2/3 level. The core core cooling system, capable of maintaining adequate core cooling provided spray system would be

degradation in the core spray piping. there has been no

No specific action or written response is required

by this information notice.

If you have any questions about this matter, please

contact listed below or the Regional Administrator contact the technical

office. of the appropriate regional

harl s E. Rossis Di~rec or

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Warren Hazelton, NRR

(301) 492-0911 Attachment: List of Recently Issued NRC Information Notices

. Attachnent

IN 88-03 February 2, 1988

- LIST OF RECENTLY ISSUED -

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

88-02 Lost or Stolen Gauges 2/2/88 All NRC licensees

authorized to possess

gauges under a

specific or general

license.

88-01 Safety Injection Pipe 1/27/88 All holders of OLs

Failure or CPs for nuclear

power reactors.

86-81, Broken External Closure 1/11/88 All holders of OLs

Supp. 1 Springs on Atwood & Morrill or CPs for nuclear

Main Steam Isolation Valves power reactors.

87-67 Lessons Learned from 12/31/87 All holders of OLs

Regional Inspections of or CPs for nuclear

Licensee Actions in Response power reactors.

to IE Bulletin 80-11

87-66 Inappropriate Application 12/31/87 All holders of OLs

of Commercial-Grade or CPs for nuclear

Components power reactors.

87-28, Air Systems Problems at 12/28/87 All holders of OLs

Supp. 1 U.S. Light Water Reactors or CPs for nuclear

power reactors.

87-65 Plant Operation Beyond 12/23/87 All holders of OLs

Analyzed Conditions or CPs for nuclear

power reactors.

87-64 Conviction for Falsification 12/22/87 All nuclear power

-of Security Training Records reactor facilities

holding an OL or CP

and all major fuel

facility licensees.

OL = Operating License

CP = Construction Permit

I

IN 88-03 February 2, 1988 Discussion:

General Electric has identified three concerns if failure of the access hole

cover plates is postulated due to weld cracking:

1. Loose parts - In the event of complete failure of the access cover weld

during normal reactor operation, the slightly higher bottom head area

pressure would lift the cover out of its recess. It would most likely

fall to one side, but there is a potential for it to be swept into the re- circulation pump suction line causing severe pump damage.

2. Core flow bypass (normal operation) - Loss of one or both cover plates

would allow some recirculation system flow to bypass the core, from the

jet pump discharge through the open access hole to the recirculation pump

suction. This flow transient would be readily detectable and would require

reactor shutdown.

3. Core flow bypass (Loss of Coolant Accident) - If the access hole cover

plate welds were to fail as a direct consequence of a recirculation suction

line break, the bypass path would prevent the emergency core cooling system

from reflooding the core to the 2/3 level. The core spray system would be

capable of maintaining adequate core cooling provided there has been no

degradation in the core spray piping.

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

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

contact listed below or the Regional Administrator of the appropriate regional

office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Warren Hazelton, NRR

(301) 492-0911 Attachment: List of Recently Issued NRC Information Notices

Titt4 NRRg C - EA NR

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