Assessment of POFA -Cementitious material as backfill barrier in DSRS borehole disposal: 226Ra confinement

Disused Sealed Radioactive Sources (DSRS) borehole disposal is an innovative concept recommended by international atomic energy agency (IAEA) to improve the safety and security of the management end point for these sources. A green application of Palm Oil Fuel Ash (POFA) as a supplementary material for cementitious backfill barrier in DSRS borehole disposal facility is proposed. Samples with up to 50% POFA replacement complied with the mechanical and hydraulic performance requirements for backfill barriers in retrievable radioactive waste disposal facilities. The structures of one year old OPC and optimum OPC-POFA cement backfills were evaluated using FESEM, XRD, EDXRF, BET, and TGA and their Ra-226 confinement performances were assessed. 30% POFA replacement improved the geochemical conditions by reducing competitive Ca2+ release into the disposal environment. It enhanced Ra-226 confinement performance independently on the amount of water intrusion or releases below 2% of 1 Ci source. The improved performance is attributed to the higher fraction of active sites of OPC-POFA backfill compared to that of OPC backfill. Ra-226 sorption onto C-S-H is irreversible, spontaneous, endothermic, and independent on the degree of the surface filling. The provided experimental data and theoretical analysis proved the feasibility of this green use of POFA in reducing the radiological hazard of Ra-226.

Automated summary

The study introduced the green application of POFA in the backfill barrier of DSRS borehole disposal facility. Experimental results showed that 30% POFA replacement improved geochemical conditions and enhanced Ra-226 confinement performance.