Study On The Mechanism And Properties Of Phosphorus Borosilicate Glass Immobilizationed MoO₃

The extracts from the spent nuclear fuel reprocessing process contain chemicals(e.g.,HNO₃,TBP,Na NO₃,and SO₄^2-)added during reprocessing,unrecovered U,Pu,and small amounts of actinides,which are highly radioactive and are therefore referred to as highly radioactive waste（HLW）or highly discharged waste.Due to its high loading capacity,easy synthesis（melting+casting）,and very good self-irradiation resistance and chemical durability,glass is recognized as a better HLW treatment method.Nuclear borosilicate glasses curing HLW rich in molybdenum and other insoluble elements may produce a yellow phase,which affects the reliability of the glass curing body.Phosphate glass can absorb large amounts of molybdenum without phase separation,but due to the curing body performance security is not high.If small amounts of phosphate doping do not unduly impair the chemical durability,thermal durability,or cause phase separation of borosilicate glasses,then this mode may prove to be the key to improving molybdenum solubility in borosilicate glasses.A soda borosilicate glass（NBS）matrix was selected and different levels of Mo O₃ were doped into the NBS glass to prepare the glass curing body and test its properties.The solubility of NBS molybdate was about 2 mol%,and by doping phosphate into the molybdenum-rich NBS glass,an increase in the inclusion capacity of the borosilicate glass for molybdenum to4 mol%was achieved.The NBS,NBS-1Mo,and NBS-2Mo samples The glass transition temperatures of the NBS,NBS-1Mo and NBS-2Mo samples are 630°C,623°C and 619°C,respectively.the highest LRSi of the NBS-x Mo series is about 1.37×10^-5 g.m^-2.d^-1,the highest LRNa is 0.62×10^-5 g.m^-2.d^-1 and the highest LRMo is 8.5×10^-6 g.m^-2.d^-1,which meets the requirements of the nuclear industry.the Raman test the results show that a part of the molybdenum is transferred to the form of P-O-Mo in the glass matrix,which may be the main reason why phosphate can promote the solubility of molybdate in borosilicate glasses.Phosphate in borosilicate glasses can act as a network formers or as isolated phosphate species in a proportion that is dependent on the Na content in the glass composition,so the Na content was varied under the condition of controlling the constant boron content in order to investigate the effect and mechanism of phosphate for molybdenum-rich borosilicate glasses with different Na contents.As the z value increases,i.e.,Si O₂ is gradually replaced by Na₂O,the content of P⁰ and P¹ in the glass structure gradually increases,the content of P-O-B/P-O-Al gradually decreases,and the content of P-O-Mo also gradually decreases,and the samples re-precipitate Na₂Mo O₄,and sample M34 needs to be doped with 8 mol P to get the glass amorphous samples.The normalized leaching rates of samples M19 and M24 show similar trends,while M34-1 is more anomalous,which may indicate that low levels of phosphate doping do not unduly impair the chemical durability of M19 and M24.Conversely,the chemical durability of the glass-cured bodies would be compromised.For HLW generally rich in Mo,Na,the effect of increasing molybdenum solubility in borosilicate glasses can be achieved by varying the Al content of the formulation with a small amount of phosphate doping under high Na conditions.Under the high Na component,element Al can improve the solubility of molybdenum in phosphor borosilicate glass by influencing the formation of P-O-Mo,and the effect is more significant,and the amorphous state of glass can be achieved by doping 2 mol Al₂O₃ on the basis of M34,and the corresponding thermal and chemical stability meets the requirements of nuclear industry.The density of MAl series samples is as low as 2.685 g/cm³ and as high as 2.701 g/cm³.