ML20057E028

Forwards Draft in Discussing Core Shroud Cracking at Plant & GE RICSIL 054.Requests Review of Draft in to Ensure Ref to RICSIL Accurately Described

ML20057E028
Person / Time
Site:	Brunswick
Issue date:	09/30/1993
From:	Chaffee A Office of Nuclear Reactor Regulation
To:	Gifford L GENERAL ELECTRIC CO.
References
GE-RICSIL-054, GE-RICSIL-54, NUDOCS 9310070133
Download: ML20057E028 (6)

Text

SEP 3 01993 1

-i Mr.. Larry Gifford, Manager Regulatory Operations Technical Services General Electric Nuclear Energy i

12300 Twinbrook Parkway Suite 315 i

Rockville, MD 20852

SUBJECT:

INFORMATION NOTICE REGARDING BRUNSWICK'S SHROUD CRACKS The U.S. Nuclear Regulatory Commission is planning to issue an information notice (IN) discussing the core shroud cracking at the Brunswick Steam Electric Plant.

The proposed IN discusses GE RICSIL 0S4.

Please look at the draft IN to ensure that the references to your RICSIL are accurately described.

Sincerely,

[ original signed by]

Alfred E. Chaffee, Chief Events Assessment Branch Division of Operating Reactor Support Office of Nuclear Reactor Regulation

Enclosure:

Draft Information Notice cc w/ enclosure:

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DRAFT UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C.

20555 September xx, 1993 NRC INFORMATION NOTICE 93-XX: CORE SHROUD CRACKING AT BELTLINE REGIONS WELDS IN BOILING WATER REACTORS Addressees All holdt.rs of operating licenses or construction permits for boiling water reactors (BWRs).

Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees that cracks have been observed in the weld regions of the core support shroud.

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 I, in-vessel visual inspection revealed cracks at two 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. The shroud is completely contained inside the 15.2 centimeters (6 inches) 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.

The circumferential cracks were located in the inside shroud surface in the heat-affected zone (HAZ) of weld H-3 and extended 360 around the circumference of the shroud (see Figures I 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 BWR.

This reactor had completed approximately 190 months of power operation before the cracks were discovered.

As of result of this discovery, General Electric (GE) issued Rapid Information Communication Services Information Letter (RICSIL) 054, " Core Support Shroud 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 plants with high-carbon-type 304 stainless steel perform visual examination of the shroud surfaces.

IN 93-XX-September xx, 1993 Page 2 of 2 In early July, CP&L performed initial VT inspection of the inside and outside shroud 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 a 1-millimeter wire resolution (in lieu of the prescribed 1/32-inch wire reference for VT-1).

Camera and lighting position were found to be crucial. Also, CP&L has worked with GE to develop more sophisticated UT l

equipment to identify how deeply into the shroud metal the crack extends. The licensee's additional VT and UT revealed more axial cracks at the H-4 weld, as well as cracks in 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 30 inches in length. The majority of the cracks are located in i

the HAZ of the welds, although one crack was discovered in the central region i

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 weld H-3 may be 3.8 centimeters (1.5 inches) or more in depth.

The crack in weld H-3 isshown in Figure 2.

The IGSCC mechanism may be assisted by the neutron flux emanating from the core.

CP&L plans to repair the core shroud before the plant is brought back into service.

It 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.

GE issued Revision 1 to RICSIL 054 on July 21, 1993 to update the information on the core support shroud cracks.

The NRC has been informed by GE that they are evaluating Brunswick's results and will provide updated information to owners i

of GE BWRs.

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 rr the appropriate Office of Nuclear Reactor Regulation '(NRR) project r 'r ager.

Brian K. Grimes, Director Division of Operating Reactor Support Office of Nuclear Reactor Regulation Technical contacts:

R. A. Hermann, NRR-(301) 504-2768 P. Byron, Region II (919) 457-9531 J. Medoff, NRR l

(301) 504-2715 T. Greene, NRR (301) 504-1175 c-

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Attachments:

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-1. ~ Figure 1: Welds in the Beltline Region of the Brunswick Unit 1 Core Shroud 2.

Figure 2:

Details of Welds and Cracks at Weld Locations H-2 and H-3 in the Brunswick Unit 1 Core Shroud 3.

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