PUREX流程中镎的萃取及非平衡态还原反萃取行为研究

Neptunium is a Minor actinides (MAs) element (primarily Np, Am, and Cm). The α emitting nuclide of 237-Np with a half-life of 2.14×106 years is a major contributor to long-time radiotoxicity of the radioactivity waste. The consideration of environmental and radiobiological issues of neptunium has increasingly arised. If MAs and Long-lived fission products (LLFPs, such as 99-Tc and 129-I) in spent nuclear fuel are separated and recycled by using advanced reprocessing separation technology and then transmuted in fast reactors, the long-time radiotoxicity and hazard of the waste would be reduced obviously. It helps to minimize the radioactivity waste. .According to the requirements of nuclear fuel proliferation and transmutation in the advanced nuclear fission energy system, and considering the separation of neptunium of MAs in spent nuclear fuel (SNF) reprocessing, in this project, we will study on the Np chemical behaviors and mechanisms in the neptunium extraction and nonequilibrium reduction-stripping. Then we try to search a new route to entirely separate neptunium from spent nuclear fuel, that is to say, neptunium is co-extracted with uranium and plutonium from solution of SNF by TBP, then is quickly separated from U and Pu depending on the differentia of reaction kinetic with reductants by nonequilibrium reduction-stripping. We hope to offer a new efficient neptunium separation method in reprocessing for separation and transmutation of Np in the advanced nuclear fission energy system.

镎是次锕系元素。237-Np是α放射体，其半衰期长达2.14×106 年，在放射性废物中，237-Np是产生长期放射毒性的主要核素之一，因此，镎对环境和生态的影响日益受到关注。通过先进的后处理分离技术，将乏燃料中的次锕系元素（Np，Am，Cm）和长寿命裂变产物（例如99-Tc和129-I）分离回收、最终通过快堆嬗变，将能够大大降低核废物的长期放射毒性和危害，实现核废物的最少化。本项目基于先进核裂变能体系中对核燃料增殖与嬗变的要求，针对乏燃料后处理中次锕系元素镎的分离,研究镎在萃取和还原反萃取分离过程中的化学形态变化和萃取分离机理，探索从乏燃料中完全分离镎的新方法：首先从乏燃料溶解液中将Np与铀钚共同萃取到TBP有机相中，然后通过非平衡还原反萃取技术，利用反应动力学的差异将Np快速还原反萃取到水相，而铀钚保留在有机相中，从而实现镎与铀钚的分离。

镎是次锕系元素，237Np的半衰期长达2.14×106 年，是产生长期放射毒性的主要核素之一。通过先进的后处理分离技术，将乏燃料中的次锕系元素和长寿命裂变产物分离回收，并最终通过快堆嬗变，能够大大降低核废物的长期放射性毒性和危害，实现核废物的最少化。.本课题组系统研究了镎的氧化还原可逆反应动力学和肼类还原剂还原反萃取Np(VI)和Pu(IV)的动力学，采用数值模拟方法对分离工艺进行了模拟计算，并进行了铀钚与镎共萃取和镎/钚分离的台架实验。本项目提出了基于核燃料增殖与嬗变要求的分离回收镎的工艺流程：首先通过提高进料酸度、温度等工艺参数，在PUREX流程的共去污循环铀钚共萃取工艺段将乏燃料溶解液中的Np与铀钚共同萃取到有机相，然后，通过非平衡还原反萃取，利用反应动力学的速率差异将乏燃料中98%的Np快速还原反萃取到水相，而将乏燃料中95%的钚保留在有机相中，从而实现镎与铀钚的分离，钚中除镎的分离系数SF(Np/Pu)=87，镎中除钚的SF(Pu/Np)=20。分离出的镎可以与铀和钚按照一定比例混合后制造成快堆MOX燃料，也可以经过浓缩和纯化后作为生产238Pu的原材料。研究成果在先进乏燃料后处理、镎的分离提取、快堆MOX燃料生产等方面具有应用价值。

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