Research On Cement Solidification Of Radioactive Spent Resins

Spent radioactive resins is waste useless material produced in nuclear power plant,nuclear fuel cycle,decontamination and retirement of nuclear facilities and radioactive waste liquid treatment,the handling method of spent radioactive resins includes cement solidification,glass curing,compaction and oxidation decomposition,etc.At present,cement solidification is most commonly used,while the huge enlargement ration and strength degradation under the influence of water make a difficult on the use of cement solidification.Aiming at the problems above,the solidification formula and curing technology were studied,which make an assistance on the engineering application of cement solidification of radioactive waste resins.The performance of solidification matrix was discussed under the influence of silica fume,fly ash and zeolite,the measure indicators were strength,resistance to soak,hydration heat and leaching rate.The results showed that the increase of dosage of fly ash and silica fume leaded to the matrix strength increased at first and then decreased,and with the increase of dosage of zeolite the strength of matrix decreased rapidly.The hydration heat of matrix was depressed mixed with fly ash,and a subtle amount of zeolite could reduce the leaching rate of Cs+.According to the orthogonal experimental results the optimum formula was determined for cement:silica fume:fly ash:zeolite=80:5:10:5(mass ration),by this time the 28d strength of solidification matrix was 19.41MPa,9.45%of strength loss after soaking and 7.15%strength loss after freezing and thawing,the wet resins loadings volume capacity is about 30%.When the wet resins loadings volume capacity exceeded 40%,solidified matrix invalidated in the process of swelling cracking.On the basis of the optimization formula,the performance of solidification matrix was.researched under the influence of varieties and dosage of fibrous materials,while the measure indicators were water resistance and resin loadings of matrix.The results showed that the matrix mixed with polypropylene fiber had a higher strength than that mixed with basalt fiber,alkali resistant glass fiber and steel fiber,and the stabilization was favorable.The performance was optimal when the volume content of polypropylene fiber reached 0.2%.at this time the 28d strength of solidification matrix was 20.53MPa,1.06%of strength loss after soaking and 2.27%strength loss after freezing and thawing.The maximum wet resins loadings volume capacity was increased from 40%to 55%,while the 28d strength of matrix was 13.28MPa,20.7%of strength loss after soaking and 10.0%strength loss after freezing and thawing.The performance of solidification matrix was researched under the influence of curing process,while the measure indicators were strength and condensation rate of slurry of matrix.The results showed that pretreatment(using calcium hydroxide and sodium silicate)of radioactive waste resins could improve the strength of matrix,according to the strength results of matrix the optimum formula was determined for cement:silica fume:fly ash:zeolite:calcium hydroxide=67:4.2:8.4:4.2:16.2(mass ration),the module of sodium silicate was 1.5,polypropylene fiber volume content was 0.2%,water cement ratio was 0.35.In the moment,the 28d strength of solidification matrix was 23.74MPa,0.85%of strength loss after soaking and 1.93%strength loss after freezing and thawing.SEM analysis was obtained from the cross section of matrix which was non-pretreated and pretreated,the results showed that the resins surface which was non-pretreated was smooth,and the other was coated a layer of flocculating substance,the flocculating substance was determined as calcium silicate by EDS analysis.The pretreatment method could improve the maximum wet resins loadings volume capacity from 55%to 60%,while the 28d strength of solidification matrix was 12.95MPa,23.6%of strength loss after soaking and 18.3%strength loss after freezing and thawing.The performance of fly ash based geopolymer was researched under the influence of dosage of sodium silicate,metakaolin,lime and mineral powder,while the measure indicators were strength and setting time.The results in simple variable method showed that the increase of dosage of odium silicate,metakaolin,lime and mineral powder leaded to the matrix strength increased at first and then decreased,and with the increase of dosage of metakaolin,lime and mineral powder the setting time was shortened greatly.The optimum strength of matrix was obtained under the condition of the dosage of sodium silicate was 40%(which was ratio content of sodium silicate to the quality of activated powder),the dosage of metakaolin,lime and mineral-powder was 25%,4%,20%respectively in a single,while the 7d compressive strength of fly ash based geopolymer was 66.35MPa,50.49MPa,47.52MPa.The possibility of employ of fly ash based geopolymer in solidification ofradioactive waste resin,while the measure indicators were strength and resistance to soak.The results showed that the slurry under the high temperature curing system was easily to overflow,which was even more serious with the increase of curing temperature.The setting time under the room temperature curing system was so long,and the development of strength was slowly,which was difficult to meet the requirement of national standard.