United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 80-38: Cracking in Charging Pump Casing Cladding

                                                       SSINS No.:  6835 
                                                       Accession No.: 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION  
                           WASHINGTON, D.C. 20555 
                              October 31, 1980 


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. 

                                                       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. 

Figure 1 

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