Experimental assessment of interaction between boric acid enriched in boron-10 and cementitious matrix

After some decades in applying boric acid with natural isotopic abundance (natural boric acid, NBA) solution as a neutron absorber, some nuclear facilities have started to use boric acid enriched in B-10 (enriched boric acid, EBA) to increase the control ability and parallelly, decrease the amount of liquid waste. Meanwhile, the stabilization condition of EBA in the cementitious matrix and durability of the waste form in disposal facilities have not been assessed or at least have not been reported yet. However, high relative mass difference between the two stable isotopes of boron (B-10 and B-11) implies a different leachability index for cementitious matrix prepared with NBA and EBA wastes.

In this study, the leachability (ASTM C1308-08 standard, 2017) of boron isotopes from cementitious matrix and its geochemical background will be assessed using ICP-OES, XRD, SEM-EDX and Raman-spectroscopy. The effects of parameters such as temperature, water to cement ratio (w/c), boric acid concentration and shape of the waste form will be studied. Geochemical modeling of the experiments will be done via PHREEQC software, which should support our understanding of the different geochemical behavior of NBA and EBA.

Based on the theoretical knowledge, a significant increase in leachability of boron from the cementitious matrix is expected when EBA is used instead of NBA because of the geochemical behavior of the two stable isotopes. Increase in leachability is expected when temperature and w/c increased, whereas the leachability will decrease when the normal cylindrical shape of samples are changed to spherical shape.

References:

• M. Saleh and H. A. Shatta; 2013; Immobilization of Simulated Borate Radioactive Waste Solution in Cement-Poly(methylmethacrylate) Composite:Mechanical and Chemical Characterizations; Journal of Nuclear Chemistry; Article ID 749505.
• Lucile Dezerald, Jorge J. Kohanoff, Alfredo A. Correa, Alfredo Caro, Roland J.-M. Pellenq, Franz J. Ulm and Andrés Saúl; 2015; Cement as a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters; Journal of Environmental science and technology; 49; 13676−13683.
• ASTM C1308 - 08(2017); Standard Test Method for Accelerated Leach Test for Diffusive Releases from Solidified Waste and a Computer Program to Model Diffusive, Fractional Leaching from Cylindrical Waste Forms; west conshohocken, PA 19428, United state
• IAEA; 1996; Processing of nuclear power plant waste streams containing boric acid; IAEA-TECDOC-911, ISSN 1011-4289; Vienna, Austria.