Development Of Lanthanide Titanate Neutron Absorber Materials And Their Iradiation Behavior Investigation

The advantages of using gray control rods to control nuclear reactivity are that they greatly reduce the daily dealing with reactor coolant,distinctly simplify the chemical and tolerant control system and its operation,significantly decrease high expense for short time change,and also make the nuclear reactor safer.Based on the excellent characteristics of lanthanide titanates,they will act as important candidates for neutron absorbers.Lanthanide titanates used as neutron absorbers in nuclear power reactor were synthesized by the process of high energy ball milling,cold isostatic pressing and then sintering.The microstructure and properties of sintered samples were discussed and analyzed by using grazing incidence X-ray diffraction(GIXRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Also,the evolution behaviors of Ln2TiO5 and Ln2Ti2O7 under ion irradiation were systematically investigated.When Ln2Ti2O7 and Ln2Ti05 milled powders were sintered at 1500? and 1300? for 24h,respectively,the reactions would prepared single phase samples.Simultaneously,these sintered bulks had good mechanical properties.When the GIXRD method was used to analyz the phases of sintered bulks,the X-ray penetration depths would change with grazing angles of incidence.In the Tb2TiO5-Dy2Ti05 and Tb2Ti2O7 samples irradiated by 400keV Kr+,the tested amorphous fraction was first increased with the increasing penetration depth of X-ray from 0.1° to 0.5° and then reached maximum value around 79.24%and 89.11%at 0.5°,respectively.For Ln2TiO5 samples,the formed amorphization was increased with increasing irradiation damage.The GIXRD results demonstrated that Tm2TiO5 had the best amorphization resistance among the prepared Ln2TiO5 samples.Pyrochlores samples Ln2Ti2O7 had similar irradiation results with Ln2TiO5.The light ions could not induce lanthanide titanates to product amorphization.Although Tm2TiO5 was irradiated at 400?,the samples still kept crystallization due to high temperature irradiation.After Tb2TiO5-Dy2TiO5 samples irradiated by 100keV Fe+ and 400keV Fe+,the results showed that lower energic ions were difficult to make material amorphization.Under heavy ion irradiation,the crystal structures of the Tb2TiO5-Dy2TiO5 were transformed from orthorhombic to cubic due to the rearrangement of both cation ions and oxygen vacancies.The samples were also producted part of amorphization.At the same time,the irradiated Tb2Ti2O7 was transformed completely from pyrochlore to cubic fluorite structure.In the irradiation experiments with light ions,the irradiated Tb2Ti05-Dy2TiO5 would be transformed completely from orthorhombic to cubic fluorite structure.However,there were non amorphization in these samples.The crystal structure of the irradiated Tm2Ti05 always kept cubic structure,which was obvious different with other titanate materials.Meanwhile,the pyrochlore Tm2Ti2O7 samples were irradiated by 400keV He+ ions with a fluence of 1×1017 ion/cm2 at room temperature,the polymorphic transformation was achieved and 51.39%fluorite structure was obtained in our experiment.When the ion irradiation fluence was reached to 1.5×1017 ion/cm2,the pyrochlore structure was transformed completely cubic fluorite structure.The heavy ion and light ion irradiation would induce information of vacancy defects,interstitials,defect clusters and antisite defects which caused the swelling of titanate samples in all experiments.The volume of the irradiated layer was increased with increasing irradiation ion fluence under 400keV.However,when Tm2TiO5 samples were irradiated by 400keV Kr+ ions with a fluence of 1.15×1016 ion/cm2 at room temperature,the volume of the irradiated layer shrinked slightly and the volume growth rate decreased from 2.03%to 1.85%.In addition,pyrochlore samples had similar swelling under high irradiation fluence.However,it had quite different swelling under low irradiation fluence.Simultaneous,for Tm2Ti2O7 samples irradiated by 400keV He+,the irradiated layer was increased with increasing irradiation fluence for both of the pyrochlore and fluorite structure.When irradiation fluence was reached 1×1017 ion/cm2,the volume change rate of pyrochlore structure was 1.2%,which was higher than that of fluorite structure(about 1.01%).Meantime,the surface of the samples irradiated with 400keV Kr+ were fractured and then exfoliated.The order of severitywas increased with increasing displacement damage.When the displacement damage was reached 24dpa,there were more spallings and cracks appearing on the surface of Tb2Ti05-Dy2TiO5 samples compared with Tm2Ti05 samples.It coud be conclued that Tm2TiO5 samples had the better radiation damage resistance than that of Tb2Ti05-Dy2TiO5 samples under the same irradiation conditions.Similarly,Tm2Ti2O7 samples had the better radiation damage resistance than that of Tb2Ti2O7 samples.