Self-Radiolysis of Tritiated Water Stored in Zeolites 4A: Production and Behavior of H₂ and O₂

Abstract

Radiolysis of confined water and self-radiolysis of tritiated water gives rise to several unanswered questions. To take into account this double specificity, we studied systems of zeolites 4A containing tritiated water at different water loading ratios. Two tritiated water were synthesized at the volumetric activities of 27 TBq.L-1 and 60 TBq.L-1. For each one, five samples were prepared, differentiated by their water loading ratios, expressed in percentage, close to 4, 7, 11, 14 and 19 %. The study of the radiolysis in those systems revealed a double role of zeolites 4A: first, they increase the decomposition of water. Then they enhance the recombination of the major stable radiolytic products detected. We actually evidenced a total recombination between H 2 and O 2 which is catalyzed by the zeolites.

Effect of the water coverage on the interaction of O2and H2with the Na-LTA zeolite by first-principles simulations

“…As the surface catalyses the dissociation of dihydrogen and dioxygen molecules, its coating by water prevents both from interacting with the surface. Acres thus shows the necessity for the molecules to be in contact with the adsorbing surface in order to be activated, in good agreement with the observations from experimental works by L. Frances et al 1 concerning the delay-ing effect of water on the decrease of the amounts of O 2 and H 2 molecules in zeolite. L. Morales 10 , who studied the recombination on a plutonium dioxide surface, emphasizes the important role of catalyst that the surface plays in the reaction and minimizes that of the radicals formed during radiolysis.…”

“…On the one hand because of the competition between the two molecules (O 2 and H 2 O) for the occupation of the cationic sites, on the other hand because of the congestion created by the water molecules forming rings between them via hydrogen bonds and Na + cations. One of the direct consequences of this phenomenon was observed experimentally by L Frances et al 1 on the consumption of the gaseous phase composed, among other elements, of O 2 that has been released following the radiolysis of water in Na-A zeolite (figure 13). The delay between each decrease in the O 2 component is closely related to the amount of water present in the structure, i. e. the water loading rate that is indicated in mass % in the results.…”

“…2) of the O 2 molecule positioned between two Na + cations located on sites I and II (Na(I)/Na(II)) and on sites I and III (Na(I)/Na(III)) in the α cagethe adsorption energy (E ad ) is expressed in eV and the other values are distances expressed in Å where: Na(X)⋯Na(Y) is the distance between two cations, O(O 2 )⋯Na(X) is the distance between the oxygen atom of the molecule and one Na + cation, (X and Y = I, II or III), and diff is the difference between the calculated values in config. 1 The first observation is that, in most configurations, the water molecule remains on its adsorption site (Fig. 9a-c) where its equilibrium position has already been well optimised.…”

Hydrogen Production by γ-Ray Irradiation from Different Types of Zeolites in Aqueous Solution

“…Previous studies dealing with the radiolysis of zeolites with adsorbed water agree to the point that irradiation of the solid matrices of the zeolites induces decomposition of water in the pores resulting in H 2 production. − The energy/charge transfer from the zeolites was confirmed by pulse radiolysis studies of excess electrons in hydrated zeolites. − The pulse radiolysis studies concluded that generation of excess electrons hydrated in the zeolite pores occurred at yields greater than hydrated electron (e – aq ) during the radiolysis of bulk water. The high yields of e – aq would qualitatively explain the H 2 production by the irradiation of hydrated zeolites because e – aq is a main precursor of H 2 in water radiolysis. , However, understanding radiation-induced reactions in zeolites is not sufficient to estimate the yield of H 2 because the reaction scheme of H 2 production is not well-defined .…”

On the hydrogen production of geopolymer wasteforms under irradiation

“…The hydrogen production by water radiolysis in zeolite was also studied, 30,31 and zeolites type A4 (Na) were subject to numerous investigations as they were used to store tritiated water, or for the decontamination of Three Mile Island water. With zeolites, the importance of energy transfer from the matrix to the porous water was clearly observed.…”