United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-42: Cracking in the Lower Region of the Core Shroud in Boiling-Water Reactors

UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.  20555-0001

June 7, 1994


NRC INFORMATION NOTICE 94-42:  CRACKING IN THE LOWER REGION OF THE CORE SHROUD
                               IN BOILING-WATER REACTORS


Addressees 

All holders 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 a 360-degree crack has been observed at a weld
in the lower region of the core shroud in two 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 April 1994 refueling outage at Dresden Unit 3, Commonwealth Edison
Company, the licensee, found a 360-degree crack that extended around the
outside circumference of the core plate support ring weldment.  The shroud is
a 5.1 centimeter [2 inch]-thick stainless steel cylinder that directs the flow
of water inside the reactor pressure vessel.  The shroud is completely
contained inside the reactor pressure vessel.  The structural integrity of the
reactor pressure vessel is not affected by cracks in the shroud.

The cracking was found during a visual inspection and was located in the lower
section of the shroud in the heat-affected zone (HAZ) of weld H-5.  (See
Figures 1 and 2.)  Weld H-5 is a horizontal weld that joins the core plate
support ring to the core shroud.  Subsequent ultrasonic testing, utilizing
automated equipment from General Electric, determined that the maximum crack
depth was 2.13 cm [0.84 inches].

Commonwealth Edison Company also performed a visual inspection of the      
Quad Cities Unit 1 core shroud.  That inspection revealed a similar 360-degree
circumferential crack located at the same place as the crack found at Dresden
Unit 3.  Both Dresden and Quad Cities units are BWR-3s and have similar core
shroud geometries.  Core shroud designs for other BWRs may exhibit some
differences, and weld identification numbers are not necessarily congruent
between the designs.



9406060138.                                                            IN 94-42
                                                            June 7, 1994
                                                            Page 2 of 3


Discussion

At Dresden Unit 3, in addition to the 360-degree circumferential crack in the
HAZ of weld H-5, numerous crack indications were also found in the HAZ of weld
H-3.  The licensee plans to perform UTs and take boat samples at both Dresden
Unit 3 and Quad Cities Unit 1 to help determine the root cause of the
cracking.

Commonwealth Edison Company inspected the Dresden shroud using a criterion
that required the resolution of a 25 micron [1 mil] wire with a 25-mm camera
lens positioned to within 2.5 to 7.6 cm [1 to 3 inches] of the shroud surface. 
The same 25 micron [1 mil] wire resolution criterion had been used previously
at Quad Cities, but with a 9 mm camera lens positioned approximately 15.2 to
30.5 cm [6 to 12 inches] from the shroud surface.  Using this technique, no
crack indications were initially detected at Quad Cities. However, after
Commonwealth Edison Company detected the crack at Dresden, the H-5 weld at
Quad Cities was inspected again, this time using the Dresden technique, and
the 360-degree crack was detected.

Related Generic Communications

In Information Notice (IN) 93-79, "Core Shroud Cracking at Beltline Region
Welds in Boiling-Water Reactors," (issued September 30, 1993) which discusses
cracks detected at Brunswick Unit 1, the staff pointed out that camera and
lighting positions were crucial in performing adequate visual inspections.  It
is imperative to position the camera or video probe as near to the examination
surface as possible and to use an appropriate camera lens.  The lighting
direction and intensity are important factors and should be adjustable to
enhance the detection of these tight surface crack indications.

Crack indications have been previously reported at shroud welds in domestic
and overseas reactors at the beltline region and higher in the shroud. 
However, the severely cracked H-5 shroud welds at Dresden Unit 3 and       
Quad Cites Unit 1 are located 45.7 centimeters [18 inches] below the bottom of
the fuel, suggesting that horizontal welds in all regions of the shroud may be
susceptible to stress corrosion cracking 

The IN 93-79 also referred to GE Rapid Information Communication Service
Information Letter (RICSIL) No. 054, Revision 1, "Core Support Shroud Crack
Indication."  Since IN 93-79 was issued, GE issued additional information on
core shroud cracks in October 1993, April 1994, and May 1994.

The BWR Owner's Group (BWROG) submitted an evaluation of core shroud cracking
to the staff on April 5, 1994.  After reviewing the evaluation, and in light
of the Dresden and Quad Cities findings, the staff issued a list of questions
to the Chairman of the BWROG Executive Oversight Committee on May 12, 1994.

The NRC staff is evaluating the safety implications of the shroud cracks for 
normal plant operating and accident conditions and will consider the need for
additional generic communication.



                                                            IN 94-42
                                                            June 7, 1994
                                                            Page 3 of 3


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.

                                    /s/'d by BKGrimes


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

Technical contacts:  R. Hermann, NRR
                     (301) 504-2768

                     J. Schapker, RIII
                     (708) 829-9715

                     T. Greene, NRR
                     (301) 504-1175

Attachments: (see figure IN94042.WP1 for figures)
1.  Figure 1:  Shroud Weld Locations for Dresden Unit 3
2.  Figure 2:  Details of Weld Locations H-5 and H-6 in the 
               Dresden Unit 3 Core Shroud
Page Last Reviewed/Updated Friday, November 15, 2013