Oxidation of Ruthenium Oxide Deposits by Ozone

Titre de la revue : Radiochimica Acta Volume : 96 N° : 6 Pagination : 375-384 Date de publication : 01/08/2008

During an hypothetical severe accident on a Pressurized Water Reactor (PWR), it may occur the formation of highly radiotoxic RuO4(g) in the reactor containment building, resulting from the interactions of ruthenium oxide deposits with the oxidising medium induced by air radiolysis. Consequently, the gaseous ruthenium tetroxide could be dispersed into the environment; therefore data concerning the ruthenium oxide deposits behaviour is of primary importance for nuclear safety studies and Ru source term assessment. An experiment was designed to model the interactions of ruthenium oxide deposits with ozone, formed by air radiolysis. Experimental results have shown that the oxidation reaction leading to the formation of RuO4(g) occurred in a large extent. An oxidation kinetic rate law has been determined, in dry and moist air, for ruthenium deposited onto painted substrates, representatives of the inner surfaces of PWR's. This law combined with tetroxide stability data, will allow making a first evaluation of ruthenium revolatilisation phenomenon occurring in the containment, during a severe accident.