United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9504050223

     Commonwealth Edison
     1400 Opus Place
     Downers Grove, Illinois 60515

March 31, 1995

U.S. Nuclear Regulatory Commission
Attn.: Document Control Desk
Washington, D. C.  20555

Subject:  ComEd 10 CFR Part 21 Interim Report (File 94-12)
          Limitorque Actuator Potential Motor Pinion Key Failure

Reference:     I. Johnson (ComEd) letter to U.S. NRC (Document Control
               Desk), dated November 11, 1994.

The purpose of this letter is to update the NRC staff regarding the
information contained in the referenced 10 CFR Part 21 interim report. 
The interim report notified the NRC Staff of concerns by ComEd toward the
Limitorque motor operator valve actuator AISI type 1018 motor pinion
keys.  The action plan listed in the referenced letter contained the
following steps:

     1)   Complete additional review of the KALSI testing to identify the
          failure mechanism and applicability to installed actuators by
          the end of the fourth quarter, 1994.

     2)   Establish a model via bench testing to validate this failure
          mechanism and identify susceptible actuators during the first
          quarter, 1995.

ComEd's review of the KALSI SMB-0 key failures identified impact loads as
the probable failure mechanism.  Inspection of the KALSI motor shaft and
pinion gear found the keyway to be enlarged, allowing significant side-
to-side movement of the key.  KALSI had not spot drilled the shaft for
proper seating of the set screw per Limitorque recommendations.  Motor
pinion key movement will increase impact loads.

ComEd has completed two bench tests of a SMB-0 Limitorque actuator.  Each
test utilized a 40 ft-lb motor, but with a different overall actuator
ratio (OAR).  A 39:1 OAR (worst case) was used in the first test, and a
61:7 OAR (KALSI configuration) was used in the second test.  No visible
signs of key deformation were found after either test was completed.

(illegible print)

U. S. NRC                        - 2 -                     March 31, 1995

The test results are summarized below.

                              Maximum Actuator
     Motor     OAR                 Torque         Cycles    Results 3_/

40 ft-lb 1_/   39:1      500 ft-lb (100% of the   2300      Visible
                         motor actuator torque              inspection
                         rating, MATR)                      found no 
                                                            signs of

40 ft-lb       61:7      600 ft-lb (120% of MATR  2600      Visible
               (KALSI                                       inspection
          configuration)2_/                                 found no
                                                            signs of

1_/  ComEd used the 40 ft-lb motor from the KALSI test.

2_/  KALSI experienced three consecutive motor pinion key failures at
     approximately 200 cycles at and actuator output torque of 525 ft-lb.

3_/  ComEd drilled the motor shaft per Limitorque guidance from
     Limitorque Maintenance Update 89-1 to ensure proper seating of the
     set screw.

ComEd is conducting additional testing of the KALSI configuration with
the set screw removed to determine the criticality of this step in the
motor pinion key installation process.  This configuration is expected to
duplicate the KALSI results.  If key failure occurs, additional testing
as well as review of the KALSI testing will be conducted to determine the
impacted actuator configurations.  If key failure does not occur, KALSI
Engineering will be contacted and an appropriate test plan will be
developed to resolve the apparent discrepancy in test results between
KALSI and ComEd.

ComEd will update this 10 CFR Part 21 interim report no later than July
31, 1995

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U.S. NRC                         - 3 -                     March 31, 1995

If there are any questions regarding this notification, please direct
them to Eric Steckhan at (708) 663-7437.


Irene M. Johnson
Licensing Operations Director

Attachment: Test Methods and Results

cc:  J. B. Martin, Regional Administrator - RIII
     R. Capra, Directorate III-2 Director - NRR
     R. Assn, Braidwood Project Manager, NRR
     G. Dick, Byron Project Manager, NRR
     R. Pulsifer, Quad Cities Project Manager, NRR
     W. Reckley, LaSalle County Project Manager, NRR
     C. Shiraki, Zion Project Manager, NRR
     J. Stang, Dresden Project Manager, NRR
     S. DuPont, Senior Resident Inspector - Braidwood
     H. Peterson, Senior Resident Inspector - Byron
     J. Roton, Senior Resident Inspector - Zion
     M. Leach, Senior Resident Inspector - Dresden
     C. Miller, Senior Resident Inspector - Quad Cities
     P. Brochman, Senior Resident Inspector - LaSalle
     Office of Nuclear Facility Safety - IDNS

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                      10 CFR Part 21 File No. 9412
         Limitorque Actuator Potential Motor Pinion Key Failure
                        Test Methods and Results

1.0       PURPOSE

The purpose of this test program is to perform torque testing of SMB-0
Limitorque actuators to validate the capability of AISI Type 1018 keys
for 2000 cycles. Specifically this testing will:

     1.   Verify motor pinion key capability under worst case conditions
          for SMB, SB, and SBD actuators.  Failure has been attributed to
          impact loads at the actuator worm clutch.

     2.   If motor pinion key failure occurs, establish criteria to
          extrapolate failures to other actuator configurations.

2.0       RESULTS

Testing of the predicted worst case SMB-0 and the KALSI configuration
were completed without any visible signs of key deformation.  Inspection
of the KALSI motor found that the motor shaft was not spot drilled in
accordance with the Limitorque guidance.  Additional testing without the
set screw will be performed to determine the criticality of the set

3.0       SCOPE

Failure of AISI Type 1018 keys has been attributed to insufficient
material strength for certain Limitorque actuators.  In 1983 Limitorque
notified the industry that 4140 keys are required in size 3 and 4
actuators.  Industry failures and the failure of a SMB-0 during the KALSI
Limitorque Actuator Testing Program, indicate that size 0 and 2 actuators
may also require 4140 key material.

Review of the key sizes for all actuators reveals that the size 0
actuator uses the same size key as the size 00 actuators, whereas the key
size increases with increasing actuator size for all other actuators. 
This results in higher relative stress for the size 0 actuator key. 
Furthermore, the size 0 and larger actuators

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                      10 CFR Part 21 File No. 9412
         Limitorque Actuator Potential Motor Pinion Key Failure
                        Test Methods and Results

have a worm shaft clutch resulting in higher impact loads.

Shear and bending stresses at the motor pinion key generated during the
KALSI testing were well below the stresses needed to fail 1018 keys. 
Yet, the key failed three consecutive times.  Subsequently, KALSI and
ComEd have reviewed motor torque data gathered during recent KALSI tests
and identified significant impact loads at the worm clutch just after

The following actuator attributes will affect impact loads:

     Attributes                         Worst Case

Motor speed              High speed

Motor size               Larger motors, increased mass

Worm set                 Lower ratio, higher speed drive sleeve and
                         higher torque at key for the same thrust

Motor set ratio          Lower ratio, higher worm shaft speed and higher
                         torque at key

Spring pack stiffness    Heavier pack, higher impact loads

Soft clutch vs. hard     Hard clutch, higher impact loads

Release torque           Locking gear sets may impose higher impact
                         torques due to higher release torques.  However,
                         motor torque data from KALSI indicates that the
                         release torque may not affect impact loads.

3.1       ComEd POPULATION

The worst case conditions for impact loads are identified in the table
above.  Table 1, on page 5 of this Attachment, summarizes the GL 89-10
MOV actuator configurations installed at ComEd facilities.  The shaded
configurations in Table 1 should bound all SMB-O applications at ComEd

                               Page 2 of 5

                      10 CFR Part 21 File No. 9412
         Limitorque Actuator Potential Motor Pinion Key Failure
                        Test Methods and Results


Table 2, on page 5 of this Attachment, provides a list of the actuator
configurations identified for testing.  Testing started with the worst
case configuration, utilizing a 40 ft-lb motor and a 39:1 OAR.  Testing
of SMB actuators is believed to be bounding for SB and SBD actuators
(except SB/SBD actuators with hammer blow devices) since these actuators
are supplied with compensators that dampen impact loads and typically
have lower seating/unseating loads.

4.0       TEST PLAN


1.   Simulate the worst case conditions for motor pinion key stresses.
2.   Perform 2000 cycles at these conditions.
3.   Test several representative configurations for SMB-0 actuators.


One test bench was built for the SMB-0 MOV.  The tested configuration has
a SMB-0 actuator mounted on a 6" Velan gate valve

The 1018 keys were obtained and tested to identify specific material
properties.  The specified motors, gears, worm clutches, and spring packs
were obtained as specified in Table 2 of this Attachment.  VOTES torque
cartridge (VTC) and motor power monitor (MPM) equipment for torque,
thrust, and motor power monitoring were obtained.

4.3       TEST METHODS

4.3.1     Facilities

The Quad Cities training facility was used for the testing.

4.3.2     Procedure   Prerequisites

                               Page 3 of 5

                      10 CFR Part 21 File No. 9412
         Limitorque Actuator Potential Motor Pinion Key Failure
                        Test Methods and Results

MOV thermal overloads were set as low as possible to prevent motor damage
without causing spurious tripping.   Methods

Table 2 of this Attachment provides a list of the actuator test
configurations.  The first test configuration is considered the worst
case.  If key failure occurred during this test, this test configuration
should bound all other actuator configurations.  Each test consisted of
approximately 2500 cycles at approximately 110% of the Limitorque
actuator torque rating.

The test program would have been considered to be complete if the first
configuration completes a successful 2000 cycle test (i.e., key
deformation occurred within 2000 cycles).
A new motor pinion key was installed after each test.

Each 2500 cycle test sequence was conducted as follows:

1.   The actuator configuration was verified that it is as specified for
     the configuration to be tested.

2.   The new motor pinion key was installed in accordance with Limitorque

3.   The appropriate torque output was established, two strokes were
     performed to acquire VTC and MPM data, and the 2500 cycle test was

4.   At approximately 500, 1500, 2000, and 2500 cycles, the test was
     stopped and:

     a)   The torque output was verified.

     b)   The valve was stroked two to three times to acquire VTC and MPM
          data.  The results were documented.

     c)   The MOV cycling was continued.

5.   The MOV cycling was stopped at approximately 2500 cycles.  At this
     time, three valve strokes were performed to acquire VTC and MPM
     data.  The results were documented.  The motor, motor pinion, motor
     pinion key and the worm shaft gear were removed and inspected.  The
     results were documented.

                               Page 4 of 5

                      10 CFR Part 21 File No. 9412
         Limitorque Actuator Potential Motor Pinion Key Failure
                        Test Methods and Results

If failure occurs prior to 2000 cycles for any configuration, the next
configuration will be immediately tested to establish extrapolation
criteria.  In addition, the first actuator configuration to fail will be
reassembled and retested at consecutively lower output torques (e.g.,
80%, 50%, 20% of MATR) to determine the effect of release torque.

Table 1 "ComEd Valves" omitted

Table 2 "Test Sequence/Configurations" omitted.

                               Page 5 of 5


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