United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 72-03: Southern California Edison Company



                                                                IEB 72-03

                                 UNITED STATES
                           ATOMIC ENERGY COMMISSION
                     DIRECTORATE OF REGULATORY OPERATIONS
                                   REGION V
                               2111 BANCROFT WAY
                          BERKELEY, CALIFORNIA 94704

                                       December 6, 1972


Southern California Edison Company                       Docket No. 050-0206
P. O. Box 800
2244 Walnut Grove Avenue
Rosemead, California 91770

Attention:  Mr. Rollin E. Woodbury
            Vice President and General Counsel

Gentlemen:

We recently received information relating to the malfunction of electric type
valve operators at two reactors.  The valve operators were identified as
Limitorque Models SMB-00 and SMB-000 which are used extensively in safety
related systems at a number of PWR and BWR reactor facilities.  Subsequent
investigation identified a specific production group of these models which
were manufactured between 1969 and mid-1971.  The specific deficiencies are
described as follows:

Plant A

Testing of valves and valve operators used in safety related systems at this
facility disclosed ten valves that failed to close following a "valve fully
open operation" test.  The cause of failure was attributed to malfunction of
the valve operator torque switch due to a lack of proper clearance between the
moving parts of the torque switch unit and the inability of the "torque switch
torsion spring" to return the electrical contacts to a closed position
following operation of the valve.  The weak torsion spring is considered a
common mode of failure.  Approximately 150 valves ranging up to eight inches
in size were equipped with valve operators having the faulty switches.

Plant B

During a reactor startup, the inboard steam supply valve of the reactor core
isolation coolant (RCIC) system failed in the open position.  Several attempts
were made unsuccessfully to close the valve.  The failure was attributed to an
internal torsion spring in the valve operator torque switch which normally
resets the electrical contacts.  The valve operator in question is similar to
the units which failed at Plant A.

Two additional facilities have recently experienced similar failures since
those reported at Plants A and B.
.

Southern California Edison Company-    2 -

It is requested that you determine whether valve operators of the described
make, model and vintage are installed or scheduled to be
installed in your facility.  If your findings show that valves installed or
scheduled to be installed are equipped with the described valve operators,
please inform this office within thirty days, in writing, of the number of
valves equipped with the valve operators, the systems in which the subject
valves are installed or scheduled to be installed, a description of corrective
actions taken or planned, and the scheduled completion date of your corrective
actions.

Should you have any questions concerning this matter, we will be pleased to
discuss them with you. 

                                             Sincerely,


                                             R. W. Smith
                                             Director

cc:  H. L. Ottoson, San Onofre Nuclear
     Steam Generation Station


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