Catalytic mitigation of hydrogen risk during wet transportation of radioactive materials

Abstract

Major challenges in the area of wet transportation of radioactive materials are reliability and safety of transportation casks. In most cases, the bottom part of the cask is filled with water whereas a gaseous mixture is contained in the upper part. In such a configuration, water radiolysis leads to the formation of hydrogen and oxygen, which continuously enriches the gaseous mixture. Among the functions to be satisfied, wet transportation systems shall thus allow the control of the hydrogen content below its flammability limit. This is currently achieved by limiting the transportation duration so as to reopen the cask before the critical hydrogen concentration is reached. Development of new technologies that would mitigate the hydrogen risk is all the more motivated because it would allow an extension of the transportation duration. AREVA-TN International and the Institut de recherches sur la catalyse et l'environnement de Lyon have developed a catalytic system which aims at buffering the hydrogen concentration far below the flammability limit. The principle of this catalyst is to recombine the hydrogen with the oxygen formed by water radiolysis. The present paper gives an overview of the development of this catalytic recombining system. It describes the laboratory qualification tests undertaken for the evaluation of the recombining efficiency. Particular attention is placed on the recombining efficiency after immersion of the catalyst in borated water, which would occur in a nuclear reactor pool during loading of used fuel. Laboratory investigations, carried out in an autoclave simulating a transportation cask, showed that, after immersion in borated water, the catalytic system allows the recombination of 3% hydrogen in less than 24 h at temperatures as low as 35°C.

Keywords:

• CATALYTIC MITIGATION
• HYDROGEN RISK
• TRANSPORTATION