May 25, 1999
The purpose of this information bulletin is to alert licensees to the possibility of source disconnects as a result of radiography drive cable failures and to describe recommended action to prevent such occurrences.
This information bulletin will be of interest to all radiography licensees and to manufacturers and distributors of exposure devices and associated equipment.
In Canada and the United States over the last two years there have been 10 reported incidents (nine in US, one in Canada) of source disconnects. Some of the incidents resulted in personal exposures to the operators. The incidents were attributed to the failure of the drive cable immediately behind the male connector on the teleflex cable.
The U. S. Nuclear Regulatory Commission (USNRC), because of the generic nature of the failures and the potential for substantial radiation exposure, investigated the failures and published the findings, conclusions, and recommendations in the USNRC NUREG 1631 document, entitled Source Disconnects Resulting from Radiography Drive Cable Failures (June 1998). This document may be found in the Reference Library within NRC's web site at www.nrc.gov.
AECB staff concur with the findings, conclusions, and recommendations in NUREG 1631. They are discussed below.
Currently one manufacturer supplies the TCI 5222 cable used in the drive cable assemblies for all cable driven radiography systems used in Canada. The recent incidents involving drive cable failures were not limited to any one type of radiography system and therefore it was concluded that the failures were not the result of a manufacturing defect of any of the radiography systems.
The investigation conducted by the USNRC was very exhaustive and NUREG 1631 concludes that the following were root causes for the radiography drive cable failures:
"The cable is not designed for use in Industrial Radiography
The cable is designed for use in the aerospace, marine, and other industries, as a component in cable control systems. These systems are specifically designed for their intended operating environment and use conditions, which are markedly different from the industrial radiography industry. These control systems are generally sealed and as a result protect the cable from harsh environmental conditions.
The importance of radiography drive cables is not sufficiently emphasized.
Manufacturers and the radiography industry have not adequately emphasized the importance of observing and evaluating the condition of radiography drive cables. As a result, opportunities to detect precursor events may have been missed because of incomplete or ineffective visual examinations during daily equipment checks. Failure to maintain radiography control cables and/or poor maintenance practices may also have resulted in the degradation and eventual failure of the control cables."
NUREG 1631 concluded that the existing drive cable is not designed for use in industrial radiography exposure device systems. Nevertheless it is adequate with careful and regular maintenance and monitoring for safe use.
The immediate cause for the drive cable failures has been corrosion and fatique of the inner cable core. Every exposure device operator should check the drive cable each day before use by visually inspecting the male connector and the directly adjacent length of drive cable.
Observance of any of the following conditions could indicate a potential failure. Drive cables that exhibit any of these conditions should be removed from service and further evaluated to determine suitability for use.
The following materials have been determined to be deleterious to the TCI 5222 cable used in industrial radiography exposure devices and should not be used for cleaning purposes.
The following materials should not be used for lubrication of drive cables:
All licensees and exposure device operators should conduct daily checks of the exposure device drive cable assemblies and specifically the drive cable. Any cable should be removed from service if it does not meet manufacturers' specifications or is suspected to be prone to failure. Further, users of exposure devices should perform all manufacturers' recommended maintenance procedures and should use only manufacturers' recommended lubricants.
Questions or comments related to this information bulletin should be addressed to:
Licence Assessment Officer
Materials Regulation Division
Tel: (613)995-1571 Fax: (613)995-5086
Atomic Energy Control Board
P.O. Box 1046, Station B
280 Slater Street
Ottawa, Ontario K1P 5S9
R. Thomas Director, Materials Regulation Division