CAJ | 학술논문

Gd2Zr2O7中Gd具有很大的中子吸收截面,其烧绿石结构-缺陷萤石结构的转变能较低,使其成为理想的核废料固化基材.使用硝酸盐为原料,添加少量NaF作助熔剂,在较低温度下(和传统高温固相反应相比),合成了烧绿石型 Gd2Zr2O7.以 Ce4+模拟 Pu4+,研究了 Gd2Zr2O7对锕系核素的固化,并合成了系列模拟固化体(Gd1-xCex)2Zr2O7+x (0≤x≤0.6).采用粉末 X 射线衍射(XRD)对系列样品进行了表征.结果表明:随着 x 值的增大,样品从烧绿石结构向缺陷萤石结构转变,且晶胞大小基本保持恒定,但当x=0.6时,衍射峰明显宽化,晶格畸变比较严重,晶格稳定性降低.当x=1时,即用Ce4+完全取代Gd3+进行合成,不能得到Ce2Zr2O8,产物发生了相分离,为四方结构的(Zr0.88Ce0.12)O2和萤石结构的(Ce0.75Zr0.25)O2的混合物.模拟固化体的浸出率测试表明:当x≤0.2时,各元素浸出率均很低,但当x≥0.4时,各元素的浸出率明显升高,说明以Gd2Zr2O7作为固化Pu4+的基材, Pu4+掺入量不宜高于40%.
Gd2Zr2O7중Gd구유흔대적중자흡수절면,기소록석결구-결함형석결구적전변능교저,사기성위이상적핵폐료고화기재.사용초산염위원료,첨가소량NaF작조용제,재교저온도하(화전통고온고상반응상비),합성료소록석형 Gd2Zr2O7.이 Ce4+모의 Pu4+,연구료 Gd2Zr2O7대아계핵소적고화,병합성료계렬모의고화체(Gd1-xCex)2Zr2O7+x (0≤x≤0.6).채용분말 X 사선연사(XRD)대계렬양품진행료표정.결과표명:수착 x 치적증대,양품종소록석결구향결함형석결구전변,차정포대소기본보지항정,단당x=0.6시,연사봉명현관화,정격기변비교엄중,정격은정성강저.당x=1시,즉용Ce4+완전취대Gd3+진행합성,불능득도Ce2Zr2O8,산물발생료상분리,위사방결구적(Zr0.88Ce0.12)O2화형석결구적(Ce0.75Zr0.25)O2적혼합물.모의고화체적침출솔측시표명:당x≤0.2시,각원소침출솔균흔저,단당x≥0.4시,각원소적침출솔명현승고,설명이Gd2Zr2O7작위고화Pu4+적기재, Pu4+참입량불의고우40%.
@@@@Gd2Zr2O7 is a wel known host for nuclear waste immobilization because of the high neutron absorption cross section of Gd and low energy transformation between ordered pyrochlore and disordered defect-fluorite structures. Pyrochlore Gd2Zr2O7 was synthesized at relatively low temperature (compared with traditional high temperature solid-state reaction) using Gd(NO3)3·nH2O, Zr(NO3)4·nH2O as a starting material and a smal amount of NaF as fluxing agent. Ce4 + was used as an analogue for Pu4 + and its immobilization behavior in Gd2Zr2O7 was studied in a series of solidified forms comprising (Gd1-xCex)2Zr2O7+x (0≤x≤0.6). Powder X-ray diffraction (XRD) data showed that the sample structure transformed from pyrochlore to defect-fluorite type with increasing x but maintained constant unit cel volumes. As x was increased to 0.6, the diffraction peaks showed broadening, suggesting considerable lattice distortion. When x=1, i.e., al Gd3+ was placed by Ce4+, the product was not Ce2Zr2O8, but a phase separated mixture of tetragonal (Zr0.88Ce0.12)O2 and an ideal fluorite (Ce0.75Zr0.25)O2. Leach rate measurements indicated that the leach rate of Gd3+, Zr4+, Ce4+ was low when x≤0.2, but increased significantly when x≥0.4. This suggests that the substitution rate of Pu4+ for Gd3+ should not be more than 40% when Gd2Zr2O7 is used as the host matrix for Pu4+.