Online measurement of the atmosphere around geopolymers under gamma irradiation

ABSTRACT

The gas production of wasteforms is a major safety concern for encapsulating active nuclear wastes. For geopolymers and cements, the H₂ produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the gas composition evolution around geopolymers was monitored online under ⁶⁰Co gamma irradiation. The transient evolution of the hydrogen release yield was measured for samples with different formulations. Its evolution and the final values are consistent with the presence of a pseudo-first-order chemical reaction consuming hydrogen in the samples. The results show that this phenomenon can significantly reduce the hydrogen source term of geopolymer wasteform provided their diffusion coefficient remains low. Lower hydrogen production rates and faster kinetics were observed with geopolymer formulations in which pore water pH was higher. Besides hydrogen release, a steady oxygen consumption was observed for all geopolymer samples. The oxygen consumption rates are proportional to the diffusion coefficients estimated in the modelization of hydrogen recombination by a pseudo-first-order reaction.

KEYWORDS:

• Geopolymer
• irradiation
• hydrogen
• safety
• diffusion
• radioactive wastes

Acknowledgments

Our appreciation goes to Maryline Charlot, Karine Ressayre, and the team of Steris company for their experimental support during irradiation and gas measurements in the Gammatec facility.

This work was done in the framework of a collaboration between the Commissariat à l’Energie Atomique et aux Energies Alternatives and the Japan Atomic Energy Agency.

Data availability

The data that support the findings of this study and the code used for finite element computations are available from the corresponding author, VC, upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the authors.