Design of Cement-curing Formulations for Radioactive Heavy Metal Concentrated Solution and Evaluation of Performance Stability

As one of the most potential reactors in the fourth generation nuclear power system, the lead-bismuth fast reactor inevitably produces a large amount of radioactive waste liquid containing heavy metal during its operation, maintenance and decommissioning due to equipment decontamination and laboratory testing activities. The radioactive heavy metal concentrated solution formed after the waste liquid is subjected to evaporation and volume reduction treatment, which not only contains fission products Sr, Cs, Co, Ce and Nd, but also contains harmful heavy metal elements such as Pb, Bi, Po and the like at a certain concentration. Therefore, realizing the safe and stable disposal of this kind of waste liquid is one of the key problems which should be solved immediately in the waste management system of lead-bismuth fast reactor. Cement solidification technology has become an effective method for treating low and medium radioactive waste liquid by virtue of its advantages of low cost, high compressive strength and mature technology. However, the research on solidification treatment of radioactive concentrated liquid containing Pb, Bi and Po heavy metals produced by lead-bismuth fast reactor has not been reported in public literature at present, and the relevant technical scheme is still blank. This work is intended to carry out the cement-curing formula design and performance stability evaluation for the radioactive heavy metal concentrated solution produced during the operation of lead-bismuth fast reactor. 15 groups of cement-solidified bodies were designed and prepared by changing the types of cement and cement additives. By comparing and analyzing the compressive strength, leaching resistance and gamma radiation resistance of various solidified forms, the optimal formula of cement solidified form is finally selected. The results of preliminary screening test show that the compressive strength and leaching performance of PⅡ-S (PⅡ+slag), PSA-S (PSA+slag) and PSA-F (PSA+fly ash) are better than that of other three formula. The comprehensive performance evaluation data show that PⅡ-S is screened out because the loss rate of γ-irradiation resistance is more than 25% and the cumulative leaching fraction P_t of Sr is more than 0.17 cm. Under the same conditions, the leaching resistance of PSA-S is better than that of PSA-F. Therefore, the best cement formula recommended in this experiment is PSA-S, namely P.S.A42.5 cement+slag additive, the mass ratio of hydrated lime∶slag ash∶cement is 1∶2∶20. The experimental results are expected to provide formula reference and performance reference for cement solidification of radioactive heavy metal concentrated solution produced by lead-bismuth fast reactor.