Study Of Preparation And Durability Of Monazite-(Ce) Ceramic Waste-forms

Lanthanide praseodymium(Eu³⁺) was used to simulate trivalent minor actinide americium( Am³⁺) in this paper. The Eu-doped monazite-?Ce? ceramics(Ce_0.5Eu_0.5PO₄) have been fabricated by hot-pressing sintering?HPS? and presureless sintering?PLS? using Eu₂O₃, Ce₂?C₂O₄?₃·10H₂O,and NH₄H₂PO₄ as the starting materials. The density of the samples have been measured by Archimedes law. The phase composition and microstructure of the samples were investigated by means of XRD, FESEM, EDS and so on. The results show that the optimal preparation parameter of Ce_0.5Eu_0.5PO₄ ceramic waste-form prepared by PLS is 1450 ? for 4 h, which the relative theoretical density could reach 95.11%. The denser monazite ceramic waste-form has been fabricated by HPS at 1150? for 2 h, which is 300? lower than that of PLS.The chemical durability and leaching behaviour of Ce_0.5Eu_0.5PO₄ monazite ceramic waste-forms under the coupling effect of Thermodynamics-Hydrodynamics- Mechanics- Chemistry?p H=3-11,T=90-200?,P=0.070-1.554 MPa? were researched by MCC-1 static leaching using the hydrothermal reaction still as the leaching device for simulating the environment of geologic disposal, and the leaching elements and sample phases were investigated by the ICP-MS, XRD, FESEM, EDS, IR and so on. The results show that both the Eu and Ce elements have low normalized leaching rates?10-6-10-5g·m-2·d-1? after 42 days in p H=5-11 leachates,showing the high chemical durability. Howover, the samples have the low leach resistance in p H=3 leachates, which the normalized leaching rates of Eu and Ce elements were between 10-4-10-3g·m-2·d-1. The sintering methods?HPS and PLS? have no significant effect on the chemical stability. The decrease of the sample chemical durability with an increase of temperature. The effect of temperature is a little less p H. An decrease of p H?p H?7? will quickly reduce the leach resistance, the formation of newborn(Ca_xLn_1-2x/3PO₄,n H₂O) leads to a slowing down of the element release in the p H>7 leachate.The results of calculations for basic radiation defect modellings were discussed in Ce PO₄ crystal, along with the examination of their defect formation energies as well as the effect of defect concentrations. The study is based on building a fully relaxed Ce PO₄ model by step iterative optimization in DFT-GGA calculations using VASP and CASTEP database, and the cell parameter calaulation is similar to that of experiment, which shows effective way to solve the f shells of Ce by VASP and CASTEP step optimization. Ce PO₄ structure of its structural defects in a strong self-healing capabilities. The formation of Cerium and Oxygen of vacancies and Frenkel defects are large, showing such defects could be formed only in high-energy particle collision.