Review of the safety concept of the LSA-II and LSA-III material requirements of the IAEA Transport Regulations SSR-6

The LSA-II and LSA-III material requirements were introduced into the IAEA Transport Regulations in the early 70s and revised in the 80s of last century. Proposals to change these requirements were also part of the revision processes of the IAEA Transport Regulations in the 90s and in the first years after 2000, but there has never been available enough information to justify and to approve any change. Meanwhile much progress has been achieved internationally regarding the knowledge of material characteristics of LSA-II and LSA-III and their release behaviour under accident conditions of transport. This progress now allows a comprehensive review of these requirements, based on which justified changes to simplify and clarify the appropriate provisions can be derived.Comprehensive experimental and theoretical research work was performed in recent years to investigate the release behaviour of various LSA-II and LSA-III materials under different mechanical impact conditions and to use the results to assess the potential radiation exposure caused by such materials under severe handling and transport accident conditions. Based on this research work a comprehensive review of LSA-II and LSA-III requirements was performed. It was mainly focusing on the safety concept these requirements are based on, in particular the need and the justification of the LSA-III leaching test, which has often been questioned in the past, and on improved guidance on how to demonstrate compliance with homogeneity requirements for the activity distribution throughout the LSA-II and LSA-III material.The review leads to the conclusion that the whole LSA safety concept based on limitations of the average specific activities for LSA-II and LSA-III and the exclusion of powder from LSA-III material can be confirmed as being a well-founded and conservative system providing a high level of safety without the need to perform the leaching test for LSA-III material. Sensitivity studies based on empiric equations found in experiments confirmed this conclusion for different package volumes, drop heights and exposure times. In particular, it was demonstrated that for the most critical scenario of an indoor accident the amount of inhalable material remains always below 10 mg, which is a very basic assumption of the original safety concept. The paper summarizes the main research results, the main conclusions of the review of the safety concept including the sensitivity studies and the proposed changes to the IAEA Transport Regulations SSR-6 as well as to the Advisory Material SSG-26 and describes the status of these changes within the current IAEA Revision Process of SSR-6 and SSG-26.