A graded approach for safety assessments for decommissioning of facilities usingradioactive material: lessons learned from international experience (Desa Project)

摘要

It is an important task to assess the safety of the measures which are planned fordecommissioning of facilities using radioactive material and to have a comprehensive and reliable framework forsafety assessments. This is one of the reasons why the international project on Evaluation and Demonstration ofSafety during Decommissioning (DeSa) has been launched by the IAEA in 2004. One of the working groupswithin the DeSa Project is the working group on the Application of the Graded Approach in safety assessments.Grading in safety assessments can relate to many aspects, such as: the complexity and level of detail ofmodelling and calculation methods, the way in which radiological characterisation and screening measurementsare performed, the number and level of details of scenarios, the complexity of dose assessments, the way inwhich safety assessments are reviewed internally and by the competent authorities, as well as to many otherfeatures. Grading may depend on the risk potential of the facility or the activity inventory, which is still present,as well as on other features. The aim is to identify those areas where a detailed approach is most relevant andwhere the effort should be directed to. Application of a graded approach ensures that methods are used which arecommensurate to the hazards, helps to direct efforts to those areas where they achieve the highest benefit andavoids spending costs for irrelevant analyses. During the course of its work, the Graded Approach WorkingGroup has discussed a variety of areas and aspects where the use of a graded approach might be beneficial. Someaspects are presented in this paper. The following points have emerged from the work of this working group:? A number of countries use a graded approach in various aspects of safety assessments. Examples for sucha use may be:Radiological characterisation in accordance with the remaining hazard potential of the facility;Adjustment of dose assessments for effluents to the activity release of the facility;Initiating events and scenarios in accordance to realistic pathways, cancellation of events and scenarioswhich are no longer possible in the facility under decommissioning.? Other countries need guidance on how to implement graded approaches for various aspects of safetyassessments.? A comprehensive list of areas of safety assessments where a graded approach is beneficial would be mostwelcome.? This paper draws conclusions from the work and the results of the Graded Approach Working Group ofthe DeSa Project. It identifies areas where grading has already been used successfully and where the useof the graded approach would be effective without compromising safety or the significance of the safetyassessment.