36 Applying PSA to Radiation Source Facilities and Practices — Results and Recommendations from an IAEA Coordinated Research Project (PSAM-0385)

Radiation sources are used worldwide in many industrial and medical applications. In general, the safety record associated with their use has been very good. However, accidents involving these sources have occasionally resulted in unplanned exposures to individuals. When assessed prospectively, this type of exposure is termed a “potential exposure”. This paper presents the results of an IAEA Coordinated Research Project (CRP) on the application of Probabilistic Safety Assessment (PSA) techniques to assess the risk of potential exposures from radiation source facilities and practices. These results include safety insights, the potential risk reduction measures associated with these, as well as recommendations for the performance of future PSAs for these types of facilities.

Five studies, with participants from six countries, were carried out within the frame of the project. One study dealt with an industrial irradiator while the remaining concerned medical applications of radiation sources. Three studies addressed cobalt teletherapy (external beam) practices and one study covered the international experience in brachytherapy (internal radiation therapy). It is worth noting that significant differences among the facilities were found, even among practices of the same type. At the same time, generic safety and PSA issues were identified, which applied to all practices.

The application of PSA techniques resulted in useful safety insights for each of the practices. An overview of the safety insights obtained in the studies is presented. With the exception of the brachytherapy study, which dealt with a sample of international experience, the facility-specific character of these safety insights should be emphasized. Other facilities may benefit from reviewing whether the general and facility-specific issues that are raised are applicable to them.

In the studies in which an overall quantification was performed, probability values estimated with large uncertainties were used. In spite of these uncertainties, a quantitative approach is highly recommended because it supports a prioritization of the risk contributors and consequently of the recommendations for risk reduction. In addition, during the performance of the studies, the results of intermediate quantifications of the PSA model provided valuable insights for determining an appropriate level of detail for the different parts of the PSA model. For instance, the quantitative information was essential in prioritizing the scenarios to examine, the personnel tasks to analyze, and the data to be sought.

The recommendations for the performance of future PSA studies of radiation source practices are based on the experiences obtained in the exploratory studies. The strongly positive experience of the study teams can be used to recommend the performance of a PSA, or at least an application of PSA techniques, as an element of safety management in radiation source facilities.