Information Notice No. 86-39: Failures of RHR Pump Motors and Pump Internals

                                                           SSINS No: 6835 
                                                           IN 86-39        

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                            Washington, DC 20555

                                May 20, 1986

Information Notice No. NO 86-39:   FAILURES OF RHR PUMP MOTORS AND PUMP 
                                   INTERNALS 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 

Purpose: 

This notice is provided to alert licensees to serious damage which has 
occurred at a licensed nuclear power plant to residual heat removal (RHR) 
pumps manufactured by Bingham-Willamette with motors supplied by General 
Electric The damage identified at the Philadelphia Electric Co (PECO), 
Peach Bottom facility involved failure of motor bearings and/or failure of 
pump impeller wear rings 

It is expected that recipients will review this notice for applicability to 
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities However, suggestions contained in 
this notice do not constitute requirements; therefore, no specific action or
written response is required 

Description of Circumstances: 

On November 2, 1985, during core reload of PECO's Peach Bottom Unit 3, a 
fire occurred in the 3C RHR pump motor which totally engulfed the motor and 
rendered the pump inoperable A lower guide bearing high temperature alarm 
had been received for 3 days prior to the pump failure, but this warning of 
potential pump failure went unnoticed by personnel because of the large 
number of other alarms that were received during the shutdown The motor, a 
2000 HP GE vertical induction model 5K6348XC29, and pump, a 
Bingham-Willamette single stage centrifugal model 18x24x28 CVIC (Figure 1), 
were uncoupled, disassembled and inspected for damage Results of the 
inspection identified that the motor lower guide bearing was destroyed, the 
rotor bars were gouged and scorched, and the stator windings were burned and
gouged The pump internals were found to have sustained internal damage 
Specifically, the lower impeller wear ring (Figure 1) was separated from the
impeller and fused to the casing wear ring No other wear surfaces indicated
wear or damage On November 16, 1985, while replacing the lower pump casing 
gasket on the 3A RHR pump, PECO personnel discovered that the lower pump 
impeller wear ring was separated from the impeller and cracked in three 
places Subsequent inspections of the remaining two unit 3 RHR pumps and two
unit 2 pumps (2A and 2C) revealed similar wear ring failures in three of the
pumps inspected 



                                                             IN 86-39    
                                                             May 20, 1986 
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On December 22, 1985, after several overcurrent alarms with pump 2D from 
Unit 2, PECO inspected this pump and discovered the lower pump impeller wear 
ring separated and cracked, a 6-inch piece of wear ring missing, and the 
impeller vanes damaged Not all failures noted above were as severe as the 
ones identified on pumps 3C and 2D However, the similarity was evident 

The RHR pump impeller wear rings are press fit to the impeller and attached 
with eight dowel pins The wear rings provide a wearing surface on the pump 
impeller The wear rings are 410 stainless steel, A 182 grade F6 with a 
Rockwell C hardness of 33 to 39 Metallurgical examinations of the wear ring
fracture surfaces indicate the presence of intergranular stress corrosion 
cracking (IGSCC) PECO has classified the wear ring failures as IGSCC On 
November 26, 1985, PECO made an INPO Network notification regarding these 
RHR pump failures PECO has repaired all affected pumps by replacement of 
damaged motors and pump internals Tennessee Valley Authority's Browns Ferry 
Units 1, 2, and 3 utilize the identical pumps for RHR service Similar motor 
and pump impeller wear ring failures have occurred at these facilities, but 
not to the extent identified at Peach Bottom Pumps of similar design, but 
different size, are utilized for core spray service both at Peach Bottom and
Browns Ferry However, these pumps use the "integral" impeller wear ring 
design, ie , extended impeller part replaces separate wear ring and forms 
a single unit, and therefore are not susceptible to the type of wear ring 
failure previously described 

Discussion: 

These multiple events are of concern because of the potential for commonmode
failures of all pumps in the same system At Peach Bottom, six of eight 
pumps inspected exhibited degraded pump impeller wear rings and internals 
These flaws could lead to pump hydraulic degradation and, under the worst 
conditions, complete pump failure The motor guide bearing failures are 
significant because they could cause failure of the pump motors and pump 
internal damage 

The full extent to which this type of pump may be used in safety-related 
services at other facilities is not known with complete certainty According
to information ascertained from Bingham-Williamette records and confirmed by
contact with affected sites, other plants utilizing this type of pump in the
RHR system include the following: Cooper, Pilgrim 1, and Vermont Yankee 

The exact cause of the pump internal failures has not been fully determined,
except that there is evidence that IGSCC has contributed to the impeller 
wear ring failures Operating pumps with inadequate flow and lubrication, 
whereby high internal temperatures develop, is also a likely contributor, 
eg, pump cavitation  PECO is continuing to pursue root causes and wear 
ring redesigns to prevent such occurrences in the future 



                                                             IN 86-39      
                                                             May 20, 1986  
                                                             Page 3 of 3   

No specific action or written response is required by this information 
notice If you have any questions regarding this matter, please contact the 
Regional Administrator of the appropriate NRC regional office or the 
technical contact listed below 


                                   Edward L Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Ronald M Young 
                    (301) 492-8985 

Attachments: 
1   Figure 1 - Typical CVIC RHR Pump 
       Sectional Assembly 
2   List of Recently Issued IE Information Notices