Part 21 Report - 1995-068
PRIORITY ATTENTION REQUIRED MORNING REPORT - REGION I MARCH 17, 1995
Consolidated Edison Co. Of N.Y. MR Number: 1-95-0038
New York Power Authority Date: 03/17/95
Indian Point 2 3 SRI/PC
Subject: Potential Failure of Dresser Pacific Safety Injection Pumps
Reportable Event Number: N/A
Indian Point 2 (Con Edison) and Indian Point 3 (NYPA), each recently
identified loose safety injection pump shaft lock nuts on Dresser Pacific
ten stage centrifugal pumps. The lock nuts, one located at each end of
the pump shaft, hold the rotating impellers in position. Without the
lock nuts, the impellers are free to move axially on the shaft. Movement
of the impellers can cause them to contact the stationary diffusers or
the pump casing, which could lead to pump failure. The shaft lock nuts
are designed to be self locking with right hand threads on one end of the
shaft and left hand threads on the other. The lock nuts are not torqued,
but require only hand tightening. Some applications of these pumps have
set screws installed in the lock nuts to further guard against loosening.
The use of set screws was recommended by the manufacturer for
applications that are subject to back flow when idle. The configuration
at both sites, i.e., the use of a discharge check valve to prevent back
flow, was considered by the licensee to be adequate to not require
On February 19, 1995, the #33 safety injection pump at Indian Point 3
seized. The failure occurred during pump coast down after replacing a
leaking seal. Maintenance personnel noted the seized shaft while
attempting to rotate the shaft for seal adjustments. Inspection of the
pump internals revealed that the outboard shaft lock nut had backed off
about a quarter of an inch. This resulted in the tenth stage impeller
contacting the pump casing. NYPA also discovered that the sixth stage
impeller was damaged due to axial movement caused by the loose lock nut.
Preliminary review of previous vibration data indicates that the sixth
stage problem occurred between March and August of 1993.
As a result of the problems identified at Indian Point 3, Con Edison
inspected the Dresser Pacific safety injection pumps at Indian Point 2.
Inspection of the #23 pump indicated that the lock nut was finger tight,
not hand tight, potentially allowing movement of the impellers upon
further loosening. Previous routine testing had not identified problems
with this pump. During the inspection with the pump vendor
representative onsite, indications of overheating (not currently thought
to be related to the lock nut) caused Con Edison to replace this pump.
Con Edison is continuing with inspections of the other pumps. NYPA and
Con Edison are still investigating the cause of the loosening shaft lock
nuts. The Dresser Pacific vendor representative was not aware of any
other customers reporting loose lock nuts. Dresser Pacific is currently
investigating whether this problem had been reported in the past.
REGION I MORNING REPORT PAGE 2 MARCH 17, 1995
MR Number: 1-95-0038 (cont.)
Reverse rotation is suspected as the cause, but both licensees have not
been able to determine when or why the reverse rotation occurred. Both
utilities monitor idle pumps for reverse rotation during pump runs and
none has been previously identified. NYPA has modified the shaft lock
nuts to install set screws to positively lock the nuts in place.
The resident inspectors at both sites are following licensee actions.
Contact: Richard Rasmussen (914)739-8565
Barry Westreich (914)739-9360
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