United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-03, Supplement 1: Separation of Primary Reactor Coolant Pump Shaft and Impeller

                                                     SSINS No.: 6835       
                                                     IN 85-03, Supplement 1 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                April 9, 1985

Information Notice No. 85-03, SUPPLEMENT 1:    SEPARATION OF PRIMARY REACTOR COOLANT PUMP SHAFT AND IMPELLER 

Addressees: 

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

Purpose: 

This notice provides additional information regarding the primary reactor 
coolant pump impeller separation from the pump shaft, discussed in IE 
Information Notice 85-03. New information as well as additional background 
information is provided herein. Specifically, the description of the event 
circumstances is modified, an additional pump shaft failure is described, 
and the probable cause of the failure at Palisades is discussed. 

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

Discussion: 

Information Notice No. 85-03 described an event at the Palisades Nuclear 
Plant involving the separation of the primary reactor coolant pump impeller 
from the pump shaft during operation. That notice stated that electric 
current to the pump increased by approximately 10 to 15 percent in the 
3-hour period prior to securing the pump. Subsequent information received 
from the licensee indicates this current increase did not occur. 

An event potentially leading to pump impeller stoppage occurred at Prairie 
Island on June 11, 1981. In that event, the reactor coolant pump shaft 
vibration and seal leakoff increased. Subsequent pump inspection found a 
crack extending 270 to 300 degrees of arc around the shaft. The Palisades 
event (September 16, 1984); the Prairie Island event (June 2, 1981), and the
Surry 1 event (November, 1973), mentioned in IE Notice 85-03, were all 
accompanied by (1) indication of reactor coolant pump seal failure and (2) 
higher than normal pump shaft vibration. 



8504050042
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                                                    IN 85-03, Supplement 1 
                                                    April 9, 1985         
                                                    Page 2 of 2           

The postulated cause of the Palisades' cap screw failure was fatigue brought
about by preload on the bolts insufficient to resist cyclic loading. This is
believed to have been caused by the poor surface condition of the capscrew 
threads. This condition resulted in the specified torque values not being 
sufficient to properly preload the cap screws that join the impeller to the 
shaft in 1971. This situation suggests two points that should be stressed. 
First, the failure described in IN 85-03 was not caused by improper 
disassembly and reassembly of the reactor coolant pump; rather, the problem 
apparently occurred during initial assembly. Second, the cause of under 
tightening of the cap screws was the poor (rough) surface condition of the 
screw threads themselves. Thus, use of the torque to measure axial bolt 
loading was, in this case, misleading. 

No specific action or written response to this information notice is 
required. If you need additional information about this matter, please 
contact the Regional Administrator of the appropriate NRC regional office or
this office. 


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

Technical Contact:  Bill Jones, IE
                    (301) 492-7613

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