Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
.
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
Attachment: List of Recently Issued IE Information Notices
