结合硝化反应和超临界流体萃取的高温气冷堆燃料元件中UO2芯球的处理

项目名称： 结合硝化反应和超临界流体萃取的高温气冷堆燃料元件中UO2芯球的处理

项目编号： No.21071089

项目类型： 面上项目

立项/批准年度： 2011

项目学科： 化学工业

项目作者： 段五华

作者单位： 清华大学

项目金额： 15万元

中文摘要： 对高温气冷堆乏燃料进行后处理可回收核资源，减少其对环境的危害，是实现高温气冷堆可持续性发展的重要措施之一。本研究项目进行了结合硝化反应和超临界流体萃取的新型方法处理高温气冷堆燃料元件中UO2芯球的实验研究。首先采用镧系氧化物Nd2O3进行了实验研究。在一定实验条件下，Nd2O3与N2O4反应转化为其硝酸盐的转化率可达99%以上，含TBP的超临界CO2萃取反应产物的萃取率可达99.57%。高温气冷堆燃料元件中的UO2芯球较难直接与N2O4反应，而当在通氧气下经600 ℃热处理自发转化成粒径为20-70 μ#30340;U3O8粉末后，很容易与N2O4反应，转化率达99%以上，同时研究了温度、反应时间、N2O4用量和水用量对转化率的影响。反应产物易被含TBP的超临界CO2萃取，萃取率达到99%以上。通过这些研究，建立新型的高温气冷堆燃料元件中UO2芯球的处理方法，获得了重要基础数据，为将来进一步研究新型的、具有自主知识产权的、产生二次放射性废物少的高温气冷堆乏燃料后处理流程打下基础，也为我国研究新型的轻水堆和快堆的乏燃料后处理流程提供一条思路。

中文关键词： 高温气冷堆；UO2；N2O4；超临界流体萃取

英文摘要： Reprocessing of spent nuclear fuels from high temperature gas-cooled reactor (HTGR) can recover nuclear resources and reduce their hazard to environment, which is one of important measures to ensure HTGR sustainable development. In this work, studies on treatment of UO2 kernels from the HTGR fuel elements by nitration reaction followed by supercritical fluid extraction have been carried out. Firstly,studies were carried out with lanthanide oxide Nd2O3. Nd2O3 was easily converted into nitrate with N2O4, and above 99% of conversion efficiency was obtained under optimized experimental conditions. The nitrate obtained was extracted by SC-CO2 containing TBP, and the extraction efficiency could reach 99.57%.UO2 kernels from HTGR fuel elements are difficult to be converted completely into nitrate with N2O4. When UO2 kernels broke spontaneously into U3O8 powders with most particle size from 20 to 70 μunder O2 flow and 600 ℃ U3O8 powders obtained were easy to be converted into nitrate with N2O4, and above 99% of conversion efficiency can be reached. The effects of temperature, reaction time, N2O4 amount and H2O amount on the conversion efficiency have also been investigated. The extraction efficiency of the nitrate product with TBP in SC-CO2 can reach more than 99%. Based on these studies, the new method to treat UO2 kernels from the HTGR fuel elements was developed. Moreover, the research foundation was set up for further research new reprocessing process of HTGR spent nuclear fuel with independent intelligent property rights, in which the generation of second waste was minimization.A new research idea can be provided for our coumtry's reprocessing of spent nuclear fuels from light water reactor and fast breeder reactor.

英文关键词： high temperature gas-cooled reactor;UO2 kernels; N2O4; supercritical fluid extraction