Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 85-54
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
July 15, 1985
Information Notice No. 85-54: TELETHERAPY UNIT MALFUNCTION
Addressees:
All NRC licensees authorized to use teletherapy units.
Purpose:
This information notice is intended to alert users of teletherapy units of a
recent incident involving an Atomic Energy of Canada Limited (AECL)
Theratron 60 unit. It is expected that licensees will review the information
for applicability to their facilities and consider actions, if appropriate,
to preclude a similar problem occurring at their facilities. However,
suggestions contained in this information notice do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
A pressure regulator switch (Sl5) on the pneumatic system to an AECL
Theratron 60 teletherapy unit failed. As a result, the compressor in the
unit continued to run causing an overpressure condition in the holding tank.
This condition prevented the source drawer from immediately closing on
command.
After treating a patient, the operator noticed that the compressor kept
running and that there was an unusual odor at the back of the machine. The
machine was then turned off. The operator notified management, but no
maintenance was ordered at the time. When more patients arrived, the machine
was turned back on and the treatments continued. After several patients had
been treated, the teletherapy unit failed to automatically return its
cobalt-60 sealed source to the shielded position. The operator observed that
the indicator light on the radiation monitor in the treatment room remained
on after the unit timer reached its zero setting. Attempts to turn off the
Unit by using the console controls failed. The operator immediately removed
the patient from the treatment room. The pneumatically operated source
drawer independently returned to the closed position approximately an hour
later.
Discussion:
An AECL representative has evaluated the incident and has concluded that
this is an isolated incident resulting from a failure to follow prescribed
maintenance
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IN 85-54
July 15, 1985
Page 2 of 2
procedures on the unit. In this case, prompt emergency response by licensee
personnel to remove the patient from the treatment room after the failure
rather than continue efforts to return the source to the "off" position
avoided unnecessary radiation exposure.
No specific action or written response is required by this information
notice. If you have any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
office.
James G. Partlow, Director
Division of Inspection Programs
Office of Inspection and Enforcement
Technical Contact: H. Karagiannis, IE
(301) 492-9655
Attachment: List of Recently Issued IE Information Notices
