Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9705300009
Donald C. Cook Plant, Units 1 and 2
Docket Numbers 50-315 and 50-316
Operating Licenses DPR-58 and DPR-74
This fax serves as a report of a 10 CFR Part 21 defect, reported under 10
CFR 21.21.d.3.i.
Description of Event
On January 8, 1997, while installing a new torque switch assembly for
motor operated valve 2-MMO-421, it was noted that a spacer appeared to be
missing from the torque switch. An inspection of all the standard SMB-00
torque switches assemblies remaining in stock determined that they were
all missing a spacer. These torque switch assemblies were part of a
group of 7 received from Limitorque for general use at DC Cook under ASP
18787. A condition report was written to investigate if this was a new
design.
On January 12, 1997, 2-WMO-728, West Essential Service Water (ESW) Supply
to the 2CD Emergency Diesel Generator (EDG) Heat Exchanger Shutoff Valve,
failed to fully close during performance of routine surveillance **2 OHP
4030.STP-027CD, "CD Diesel Generator Operability Test". Investigation of
the failure on January 14, 1997 discovered that the torque switch
assembly installed on the valve was also missing a spacer, The valve was
declared inoperable, however the valve was still capable of performing
its design basis function of opening, therefore, the operability of the
2CD Diesel Generator was not affected.
On January 14,1997, in evaluating the failure of 2-WMO-728 and the
effects of the missing spacer on the torque switch assembly, it was
determined that the lack of the spacer allows the torque switch shaft to
rotate slightly along the shaft length. This shaft rotation allowed the
torque switch contacts to open. With the closed torque switch contacts
open, the actuator control circuit will not allow the actuator to run in
the closed direction and therefore will not allow the valve to fully
close. The actuator control circuit uses only the closed set of contacts
and therefore the open operation is not affected.
In the investigation, it was determined that 2-CMO-415, the Component
Cooling Water (CCW) to Miscellaneous Header Shutoff Valve for Train A,
had received one of the torque switch assemblies from the lot of 7 which
Part 21 Report
DC Cook Plant
Page 2
were missing the spacer. Because the operability of the valve could not
be assured, it was declared inoperable. As the defective assembly had
been installed in September of 1996, it was determined that a
10CFR50.72(b)(1)(ii)(B) ENS call for a condition outside the design basis
was appropriate. The ENS call was made on January 14, 1997 at 1650
hours.
The fourth defective torque switch assembly was found to have been
installed in 1-WMO-754. With the exception of the 2-CMO-415, all the
valves in which the defective assemblies had been installed had either an
"open" safety function (2-WMO-728 and 1-WMO-724) or were a BOP valve (2-
MMO-421), and thus their operability was not in question.
During the investigation of this event, an operability evaluation was
performed for 2-CMO-415. The valve was found to have been successfully
tested under dynamic conditions during the September 1996 to January 1997
interval and that the defective torque switch assembly would not have
kept the valve from performing its design basis function of closing.
Therefore, the valve had never been inoperable. The ENS notification was
retracted on February 22, 1997.
Cause of Event
The defective lot of 7 received from Limitorque apparently resulted from
a manufacturing/assembly error at the Limitorque facility.
Effect of Failure on Plant Operations
The double pole torque switch is a standard configuration for American
Electric power and is used extensively at the DC Cook Plant in SMB-00
actuators. The 7 assemblies supplied under ASP 18787 were placed in open
stock for use in the next valve requiring one. Therefore, the 3 torque
Part 21 Report
DC Cook Plant
Page 3
switch assemblies in open stock could have been used in any number of
safety related applications with unknown results. The failures in the 4
valves in which they were installed did not result in any safety impact,
however, this could not be guaranteed for all other SMB-00 valve
actuators in the plant due to the large variety of applications for the
assembly. Because it is not possible to definitively evaluate all
possible applications for significant safety hazard, it was
conservatively decided to submit this event as a Part 21.
Corrective Action
All 4 of the defective assemblies which were installed have been either
replaced, or repaired by addition of a spacer. All 7 assemblies were
returned to Limitorque for evaluation on March 10, 1997. Limitorque has
not been able to predict when their evaluation might be complete.
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