Review of the A1 and A2 values: final clap?

The A1 and A2 radioactive transport limit values of the Q System described in the advisory material SSG-26 have been developed to provide the maximum allowable contents in packages not designed to withstand accidents, with the objective to limit the accidental exposure of persons below an effective dose of 50 mSv and a skin equivalent dose of 500 mSv. Current values were determined in 1996 according to specific scenarios for five exposure pathways. Since then, the ICRP has published revised radiological data. In addition, progress in computer hardware and software allow the implementation of new Monte Carlo based calculation methods, which are more representative of the physical processes. An international working group involving NRA, PHE, GRS and IRSN was created in 2013 to discuss the improvement of calculation methods described in the Q System. This group later became part of the IAEA TRANSSC Technical Expert Group (TTEG) on Radiation Protection. The first findings and results were presented during the PATRAM 2016 conference, and the progress of the review was described during PATRAM 2019. While most trends on the potential changes in A1 and A2 values were presented, further discussions aimed at consolidating hypotheses and calculation methods were necessary to complete the review and propose to the TRANSSC Member States an update of the Q system consistent with the latest ICRP recommendations and methodologies. This paper describes the work that has been performed since 2019-especially regarding inhalation, contamination, ingestion, alpha and neutron considerations, explains the main changes in the calculation methods as well as the tools that have been developed to evaluate the Q values for any radionuclide, and shows results that could be implemented in the future revision of the IAEA SSR-6 regulations