Studies On Crystal Growth And Doping Of Uranium Dioxide

Uranium dioxide is an important nuclear material as well as an excellent semiconductor material and thermoelectric materials.UO₂has excellent semiconductor performance and anti-irradiation ability,and has potential applications in the fields of semiconductor,solar energy,thermoelectricity.But UO₂is prone to change in oxidation state at high temperature,thereby forming hyperstoichemetric UO_2+x.The non-stoichiometric UO₂nuclear fuel shows a decrease in thermal conductivity and an increase in thermal expansion,which can cause radiation swelling and fission gas release,leading to serious nuclear safety issues.Single crystal uranium oxide can fix the oxidation state and show long-term stability in the air,indicating that single crystal fuel rods are extremely helpful for nuclear safety.UO₂crystal has ultrahigh melting point of 2878℃.It is difficult to grow UO₂crystals and only small grains were obtained by the hypdrothermal and skull melting methods up to now.Crystal growth is a key issue for applications of UO₂crystal as a multifunction material.In the present work,crystal growth and luminesence properties of UO₂were investigated based on the research progress on UO₂crystals.The thesis is composed of 5 cheapters and mainly includes the recent progress of UO₂crystals,the flux growth of UO₂with Al₂O₃flux and UO₂-doping in Bi₄Si₃O₁₂scintillation crystals.According to phase diagram,it is possible to obtain UO₂crystal from Al₂O₃-UO₂high temperature solution and 42mol%,45mol%,48mol%Al₂O₃fluxes were used in the experiment.UO₂crystal has been grown from W crucible in a home-made furnace.Some UO₂particles were obtained from the as-grown ingots.Only pure UO₂and Al₂O₃phases were detected by XRD,which means the flux is suitable for UO₂growth.The transmittance and luminescent spectra were measured and only the peaks related to U⁶⁺were found.That means the UO₂has been oxided from U⁴⁺to U⁶⁺during the crystal growth in air.The doping of UO₂affects the crystallization behavior of BSO.As the doping concentration of UO₂increases,the crystallinity of BSO decreases,and the BSO crystal exhibits a glass transition tendency.