Hydrogen radiolytic release from zeolite 4A/water systems under γ irradiations

Abstract

International audienceWe irradiated samples of zeolites 4A which contained different quantities of water. We measured the quantity of hydrogen released. Hydrogen radiolytic yields, present two maxima, for two water loading ratios. Hydrogen release is enhanced by the strength of the zeolite/water interaction. Hydrogen release is enhanced by the quantity of water interacting with the zeolite. a b s t r a c t Although the radiolysis of bulk water is well known, some questions remain in the case of adsorbed or confined water, especially in the case of zeolites 4A, which are used to store tritiated water. An en-hancement of the production of hydrogen is described in the literature for higher porous structures, but the phenomenon stays unexplained. We have studied the radiolysis of zeolites 4A containing different quantities of water under 137 Cs gamma radiation. We focused on the influence of the water loading ratio. The enhancement of hydrogen production compared with bulk water radiolysis has been attributed to the energy transfer from the zeolite to the water, and to the influence of the water structure organization in the zeolite. Both were observed separately, with a maximum efficiency for energy transfer at a loading ratio of about 13%, and a maximum impact of structuration of water at a loading ratio of about 4%

Production of H2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study

“…It is worth noting that in irradiated zeolites [66] the H2 radiolytic yield is lower than 10 -8 mol J -1 at the lowest water content whereas here, the yield we determine in dry S3 is significantly higher than this value. At this low water content, water is immobilized in the cages of zeolites while it is confined, but mobile in the 2D interlayer space of cement paste.…”

On the hydrogen production of geopolymer wasteforms under irradiation

“…The slope of the associated linear regression is the hydrogen apparent radiolytic yield (in mol/J). For zeolite A the obtained values of 2.1 × 10 −8 and 1.8 × 10 −8 mol/J respectively for zeolites beads and powder are very close to the yield measured in the literature by L. Frances 30 and by Nakashima 43 for zeolite 4A saturated with water.…”

“…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.…”

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 .…”