Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 19, 1990
Information Notice No. 90-32, SUPPLEMENT 1: SURFACE CRACK AND
SUBSURFACE INDICATIONS IN
THE WELD OF A REACTOR
VESSEL HEAD
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice supplement is intended to update the information
previously provided in Information Notice No. 90-32. It is expected
that recipients will review this information for applicability to their
facilities and consider actions, as 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:
In April 1990, during the refueling outage at the James A. FitzPatrick
Nuclear Power Plant, the licensee found a group of four subsurface
indications in the reactor vessel head as a result of performing an
ultrasonic inservice inspection from the outside of the vessel head. The
preliminary sizing indicated that the subsurface indications have a total
length of 12 inches, and a maximum depth of 2 inches (50 percent through
wall). The licensee also observed a surface indication measuring 1 inch in
length on the inside surface of the head in the general area of the
subsurface indications and confirmed this observation by liquid penetrant
examination (PT). The licensee reported the surface indication and
subsurface indications to be located in the circular dollar plate weld at
the top of the vessel head. NRC issued Information Notice No. 90-32 on May
3, 1990, to report this event. Subsequently, the licensee performed the
following additional examinations to further characterize the indications:
1. Ultrasonic examination (UT) from the outside surface using automatic
mode,
2. Ultrasonic sizing of the indications from both inside and outside
surfaces including the use of refracted longitudinal waves,
3. Radiographic examinations from the inside of the head,
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IN 90-32, Supplement 1
June 19, 1990
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4. Examination of radiographic films with an enhanced technique, and
5. Magnetic particle examination (MT) on the inside head surface.
The results of these additional examinations indicate that the subsurface
indications are not cracks, but original fabrication flaws such as slag or
inclusions, and are not connected to the surface. The previously reported
surface indication appears to be a very shallow surface scar that was
removed during surface preparation for MT.
Discussion:
When performing nondestructive examinations and determining the real
significance of reflector indications from within any metal, experience and
knowledge in the various advanced inspection techniques used in performing
surface and volumetric examinations and in flaw discrimination are
important. In performing its initial assessment, the licensee interpreted
the combination of the surface indication and the multiple subsurface
reflections as a very large flaw. Subsequent additional examinations to
better characterize the surface and subsurface indications have concluded
that the multiple reflections were caused by a combination of inclusions in
the material, a proximate surface scar and subsurface slag. The licensee's
reactor vessel vendor, the General Electric Company (GE), has confirmed this
current assessment. GE, using a test sample of equivalent material to the
FitzPatrick reactor vessel head, duplicated ultrasonically the multiple
reflections from inclusions in the material. The licensee has concluded
that the surface indication was not a crack, but a very shallow surface
scar, and that the subsurface indications are not cracks, but original
fabrication flaws, such as slag and inclusions, that are not connected to
the surface.
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 NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: William H. Koo, NRR
(301) 492-0706
Robert H. Hermann, NRR
(301) 492-0768
Attachment: List of Recently Issued NRC Information Notices
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