Abstract

For the clearance of accelerators or parts of it, the radiologically relevant radionuclides must always be taken into account and the nuclide-specific clearance values of the Radiation Protection Ordinance must be applied. This requires knowledge of the history of the accelerator parts (time of operation, mode of operation, type of the accelerated particles), the material composition and the presumed activation reactions. The data serve to determine the radionuclides to be taken into account. They are the condition for sorting according to different material groups for which, if necessary, different nuclide vectors must be determined. Different clearance paths may also require sorting.

Even a simple measurement procedure must always be linked to the nuclide vectors relevant to the specific accelerator. From a known nuclide vector for each part of the accelerator it is possible to derive a maximum admissible gamma local dose rate or fluence rate; in this case it is acceptable to apply a procedure which does not involve nuclide-specific measurements (e.g. gamma local dose rate), as long as the sensitivity of the measuring instruments is sufficient. In the case of medical accelerators which are used in large numbers, it might be possible to determine the nuclide vectors for the “clearance relevant” assembly groups in order to use them for all accelerators of this type.

Apart from the specific activity, the parts need to be checked for surface contamination. If surface contamination is detected, the contamination has to be included in the clearance procedure. It might be necessary to perform appropriated decontamination procedures.

In order to harmonize these procedures it would be helpful to develop a guideline or checklist containing the fundamental requirements for the clearance of accelerators and to make them available to both public authorities and operators.

Since there are no rules concerning the removal of exclusively activated parts from radiation protection zones, the Commission on Radiological Protection recommends considering this aspect in the next revision of the Radiation Protection Ordinance.

The Commission on Radiological Protection passed the Statement “Clearance of accelerators and the removal of accelerator parts from radiation protection areas” in its 233rd meeting on 19/20 March 2009.