Feasibility and Mechanism of Solidifying Simulated Radioactive Waste Resin Using Ordinary Portland Cement

To systematically evaluate the feasibility of solidifying radioactive waste resin using ordinary Portland cement and to compare the performance commonalities and differences among various cement brands, three ordinary Portland cements (B-brand PII42.5R and PO42.5R, and C-brand PO42.5R) were selected together with a dedicated cement (A-brand PII-A) as a comparison. Under a fixed mix proportion, laboratory-scale tests were carried out for all four cements, and two optimally performing cements were further subjected to a 400 L engineering-scale cold test. Microstructural characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FT-IR) were performed. Mechanical and durability tests such as compressive strength measurement, freeze-thaw cycling, gamma irradiation, impact resistance, and simulated nuclide leaching experiments were conducted to systematically assess the physical and mechanical properties, chemical stability, and engineering adaptability of the solidified waste forms. The results show that the 28 d compressive strengths of all ordinary Portland cement waste forms range from 21.92 MPa to 31.54 MPa, and the strength loss rates after durability tests meet the requirements of the Chinese national standard GB 41930-2022. Notably, the 28 d strengths of cement C-brand in laboratory specimens and engineering cored samples reach 31.54 MPa and 35.18 MPa, respectively, both well above the minimum requirement of 7 MPa. Microstructural analysis reveals that each cement system forms a dense structural framework dominated by calcium silicate hydrate (C-S-H) gel. Regarding the immobilization of simulated nuclides, Co²⁺ is mainly incorporated into the C-S-H lattice via isomorphous substitution to form a solid solution, Cs⁺ is primarily immobilized by adsorption, and Sr²⁺ predominantly forms SrSO₄ precipitates. Simulated nuclide concentrations in the leachate are kept below the safety limits by the synergy between chemical fixation and matrix densification. Engineering-scale tests further confirm that the two selected cements (B-brand PII42.5R and C-brand PO42.5R) exhibit good durability. Their 28 d compressive strengths are 25.54 MPa and 22.66 MPa, respectively. No severe damage is observed after durability tests and impact loading, and the drilled cores validated the consistency of performance. Ordinary Portland cement, under appropriate mix design and processing conditions, can effectively solidify radioactive waste resin. Its hydration products share similar phase compositions and structural evolution patterns with those of the dedicated cement, thus offering both long-term safety and engineering economic value.