| With the increasing development of nuclear energy all over the world, thecontradiction between resource utilization and environmental security becomes moreand more serious. It has been proved that material solidification technique will be aneffective approach to deal with the radioactive waste of nuclear industry. For low andintermediate level radioactive waste, cement solidification is a hot researchpiont. Thiswork focus on cement solidification technology based on simulations of low andintermediate level radioactive waste including solid waste (radioactive ion exchangeresins) and liquid waste (radioactive steam residue). These researches will help us todevelop a new way to design binding material with double efficacy and the cementsolidification formula to meet the requirements of state standard GB14569.1-93, andto improve the process of cement solidification.The experiments with7factors and28levels were performed using uniformdesign method derived from pseudo-Monte Carlo theory. By using Portland cement,the nuclear waste resin, containing boron, was solidified with accelerator anddual-doped inorganic additives such as zeolite and silica fume. The optimizedformulas have been developed, by which the waste resin volume is greater than50%in capacity and meet the requirements of state standard GB14569.1-93. In the three compositions, the volume capacities of formulas are55%(S1),60%(S2) and52%(S3), and the compressive strength at28d are7.04MPa,7.62MPaand9.65MPa, respectively. The solidification product shows good impulse strength,freezing thawing resistance and anti-penetration property. The leaching rates of Sr2+at42d, for standard formula samples of S1and S3, are8.89×10-4cm/d and9.92×10-5cm/d, but rarely be detected for S3at21d. The leaching rates of Cr2+at42dfor all standard formula samples are3.81×10-4cm/d,4.95×10-4cm/d and1.33×10-4cm/d, respectively. According to the comparison and analysis, S2isrecommended as the optimized formula of boron containing waster resin cementsolidification. Meantime, using the same component design, it solidifies the simulated boron containing liquid waste successfully, with a w/c value of0.6. The formulas of L2and L3are listed as below:The compressive strength of the solidification products for L2and L3at28d was measured to be16.53MPa and19.13MPa, respectively. It meets the requirements of state standard GB14569.1-93for condensation performance, impulse strength, freezing-thawing resistance and radiation. The leaching rates of Sr2+at42d for standard formula samples of L2and L3are5.18×10-4cm/d and7.75×10-4cm/d. The leaching rate of Cr2+at42d for all standard formula samples are7.39x10-6cm/d and5.28x10-6cm/d respectively. Thus L2is strongly suggested as the optimized formula for boron containing radioactive waste solution cement solidification.The relationships between the microstructure and macroscopic performances of solidification form for each formula have been investigated by means of XRD, SEM/EDS, IR and other advanced techniques. The hydration process, products of cement and hydration mechanism has been also discussed.Boron ion adsorbed on the surface of waste resin, which forms CaO·B2O3·6H2O and B-AFt by reacting with cement hydration products, infiltrates the cement paste deep during solidification. It also slows down the hydration process of cement particle. The resultant structure of boron is3-fold BO33-and4-fold BO45-. With the increase of boric acid concentration, the degree of inhibition increases gradually. With W/C ratio increases, it performs in a similar way.When boric acid concentration exceeds3%and the W/C ratio is between0.3-0.5, the main phase in cement harden paste is determined to be un-hydrated cement particles and large number of CaO·B2O3·6H2O. Due to dramatically decrease of CSH and AFt and the existence of the framework structure and plate shape calcium borate appear in the solidification products, the compressive strength and harder process are strongly influenced.The results indicate that, when the resin volume capacity exceeds65%, cracks are easily formed in the cement solidification form during soaking in water. Zeolite and silica fume doped are valid to improve the pore structure and the density of hardened paste. Accelerator eliminates retarding cement setting effect by boron ion, and it accelerates the hydration process and improves the strength of the cementsolidification form.
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