Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
Accession No.:
8008220180
IN-80-38
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
October 31, 1980
Information Notice No. 80-38: CRACKING IN CHARGING PUMP CASING CLADDING
Description of Circumstances:
In January 1980 Commonwealth Edison Company (CECo) reported to the NRC that
a radiographic examination had revealed crack indications in the cladding on
the suction end plate of the 1A charging pump at Zion Unit 1. This
centrifugal charging pump 1A is one of two pumps installed in Zion Unit 1
for high head safety injection of borated water to the reactor loops. These
pumps are additionally utilized as charging pumps during normal operation.
ASME Section XI inservice inspection rules referenced in the plant technical
specification requires pump examination only once during the 10 year service
interval and this pump had been in service about 7 years.
The pumps are 2-1/2 inch, 11 stage, Type IJ manufactured by the Pacific
Pumps Division of Dresser Industries. The pump casing end assembly in the
area of interest, Figure 1, consists of a suction end plate of A515 grade 60
carbon steel plate welded to the casing barrel forging of A266 class 1
carbon steel using an Inconel weldment. The entire inner surface is clad
with type 308 stainless steel applied by submerged arc welding.
An in-situ ultrasonic examination conducted in late April confirmed clad
cracking indications at the barrel case to end plate inner radius for
approximately 330 degrees around the circumference and that the cracking
possibly extended into the pump base material in the bottom 180 degrees of
the assembly. A review of the original radiographs revealed crack like
indications in the clad overlay, however, not to the extent observed during
this examination.
Subsequently, the entire suction end of the pump was removed and cross
sections metallographically examined to further evaluate the nature and
extent of the cracking. It was determined that initiation and propagation of
the clad cracks probably resulted from stress concentration and dilution
effects in the initial corner bead pass due to the difficult access and bead
sequencing required by the fairly sharp corner geometry. Extension of the
cracks at the base metalclad interface ranged to a depth of 1/16 inch
maximum in the 1-1/2 inch thick base material. These crack tip areas were
well blunted and slightly cavitated from corrosion effects due lengthy
exposure to the localized boric acid attack. Examination of the crack
morphology revealed that the clad cracking essentially arrested at the base
metal-clad interface and that base metal corrosion progressed at a
relatively slow rate.
The 1A charging pump was replaced with a new pump provided with a casing
constructed entirely of stainless steel. The licensee is currently
developing improved NDE procedures for examination of the three remaining
pumps at the next refueling outage. Further, the licensee and pump
manufacturer are developing repair procedures in the event cracks are
discovered in the remaining pumps.
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IN-80-38
October , 1980
Page 2 of 2
A corrosion evaluation provided CECo by Westinghouse indicates the corrosion
rate of carbon steel subject to environmental conditions typical of the
installed pumps is on the order of 2-1/2 to 4 mils per month. Additionally,
a stress analysis of the pump casing by the manufacturer using ASME Section
III, Subsection NC rules, indicates that at design conditions a flaw with
depth of 0.763 inches could be tolerated.
Based on the available information no immediate safety concern is indicated.
However, the observed conditions reveal a potential source of pump
degradation over long term operations. Therefore, to assure maximum
availability, it appears prudent to perform a nondestructive examination of
this pump type at the earliest practical time during the first code required
in-service inspection interval and if cracking is confirmed, take
appropriate corrective actions per the rules of ASME Section XI BP&V Code.
This Information Notice is provided as a notificaton of a potential source
of degradation of a safety related component that is still under review by
the NRC staff. It is expected that recipients will review the information
for possible applicability to their facility. No specific action or response
is requested at this time. If you have any questions regarding this matter,
please contract the director of the appropriate NRC Regional Office.
Enclosure:
Figure 1