NOVEL RELIABLE HYDROGEN RISK MITIGATION SYSTEM FOR TRANSPORTATION OF RADIOACTIVE MATERIALS

Major issue in the area of radiolysis of radioactive materials during transportation is reliability and safety of transportation casks, especially due to hydrogen build up in the containment vessel. In the past decades, several designing options were identified to ensure that the hydrogen concentration stays below the flammability limit during the whole duration of the transport. The most common option consists in over-dimensioning the volume of the containment vessel so that it can contain all hydrogen that may be released by radiolysis of the transported material, without reaching flammable concentrations. Another option consists in using catalytic hydrogen recombiners in the casks cavity. These recombine hydrogen with the oxygen contained in the gaseous mixture. However, the working duration of these catalysts is limited by the amount of oxygen in the containment vessel. In order to overcome this problem, AREVA TN International together with SNPE and AREVA-ELTA have developed a hydrogen risk mitigation system consisting of hydrogen recombiners, oxygen generators and oxygen release control systems that can be used for long durations to ensure a hydrogen concentration below the flammability limit. The present paper presents this mitigation system, in particular the oxygen generator and the oxygen release control systems. Details are given on the reliability and safety assessment of this system and its conformance with the IAEA-TSR-1 regulation.