Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6870
Accession No.:
8002280650
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
April 2, 1980
Information Notice No. 80-13
GENERAL ELECTRIC TYPE SBM CONTROL SWITCHES DEFECTIVE CAM FOLLOWERS
Description of Circumstances:
This Information Notice alerts licensees and holders of construction permits
of a potential defect in the cam followers of General Electric (GE) Type SBM
control switches. Based on preliminary information, it appears that the
defect is limited to switches manufactured prior to 1976 with cam followers
of polycarbonate material, such as Lexan. In brief, the problem is initiated
by exposing such polycarbonate material to hydrocarbons. Such exposure leads
to severe cracking having a rock salt appearance which ultimately could
progress to mechanical failure. It has been determined that such exposure
has occurred during fabrication and could occur while performing maintenance
(e.g. cleaning the contacts).
On February 22 and March 10, 1980 we were informed that SBM switches with
defective cam followers had been found at Diablo Canyon Unit 1 and at the
Cooper Station, respectively. Although the information was preliminary and
sketchy, the problem is a long-standing one for which GE has issued "Service
Information Letters" to its BWR customers. The problems associated with such
switches, however, are not restricted to GE customers as evidenced by the
Diablo Canyon case. Furthermore, these switches have a broad range of
application. For example, the defective switches at the Cooper Station were
used principally as hand control switches, most of which were located in the
control room. In contrast, those at Diablo Canyon Unit 1 were used as
auxiliary contacts on the 4KV and 12KV "Magna Blast" circuit breakers, with
three SBM switches used per breaker: (1) a breaker mounted auxiliary switch,
(2) a cell mounted auxiliary switch, and (3) a cell interlock switch.
This information is provided as notification of a possibly significant
matter that is still under review by the NRC staff. It is expected that
recipients will review the information for possible applicability to their
facilities. No specific action or response is requested at this time. If you
have questions regarding this matter, please contact the Director of the
appropriate NRC Regional Office.
