乏燃料电冶金废熔盐中放射性核素的脱除与固化

发布时间：2018-08-06 16:42

【摘要】：随着核电工业的快速发展,势必产生大量的乏燃料,其中含有较多放射性元素,对人类的生态环境构成严重威胁。因此,乏燃料后处理是核能工业可持续发展的重要保障。在乏燃料后处理方法中,以高温熔盐(LiCl-KCl)为介质的电冶金后处理是研究最广泛、发展较成熟的一种工艺,但电解后的熔盐(后简称废熔盐)中仍含有少量有毒杂质及放射性元素,如La、Ce、Pr、Nd、Sm、Gd、Cr、Ni、Sr、U、Pu等。本文拟采用水热法和高温固相法对废熔盐中放射性核素进行脱除与固化,实现熔盐的循环利用及高放废物的减量化和无害化。采用XRD、ICP、XRF等手段对沉淀产物、固化体、净化后熔盐进行物相及组成表征。水热法：采用La3+、Ce3+、Nd3+、Cr3+和Ni2+等离子模拟废熔盐中的裂变产物、腐蚀产物及锕系元素。用KOH调节废熔盐水溶液的pH值并置于水热条件下进行沉淀反应,以去除上述离子。结果表明,pH为9时,即可将脱除上述绝大部分离子。高温固相法：(1)以氧化锆为基质,脱除并固化废熔盐中稀土元素La3+、Ce3+、Pr3+、Nd3+、Sm3+、Gd3+,即在熔盐介质LiCl-KCl中加入锆及稀土的硝酸盐合成稀土锆酸盐(Ln2Zr2O7),使稀土离子固化在锆酸盐的晶格中,达到净化熔盐的目的。结果表明,在1000℃以上,La3+、Pr3+、Nd3+及Sm3+均可与Zr4+形成结晶良好的烧绿石结构,Gd3+则与Z4+形成结晶良好的缺陷萤石结构,从而被完全固化。而Ce3+则形成CeO2及Ce2Zr2O7的混合物,固化不完全。(2)以锆酸钆(Gd2Zr207)为基质脱除并固化废熔盐中的La3+、Ce3+、Nd3+、Cr3+和Ni2+。将上述某一种元素或多种元素取代Gd2Zr2O7中部分Gd进行掺杂合成,即以上述元素的氯化物、硝酸钆、硝酸锆为原料,在熔盐介质中进行反应,达到固化的目的。结果表明,当合成温度为800℃时,10%单一元素掺杂固化时, Cr的固化率几乎为0，，其它离子的固化率均在99.9%以上；多种元素(取代率10%)同时进行固化时,Cr的固化率明显提高,达80%。(3)以锆酸钆为基质,研究Sr在其中的固化条件。结果表明,在LiCl-KCl熔盐中,在800℃下, Sr在Gd2Zr207中的固溶度可达10%。本论文的研究结果对乏燃料电冶金过程产生的废熔盐的净化及循环利用研究提供了实验和理论数据。
[Abstract]:With the rapid development of nuclear power industry, it is bound to produce a large number of spent fuel, which contains more radioactive elements, which poses a serious threat to the ecological environment of human beings. Therefore, spent fuel treatment is an important guarantee for the sustainable development of nuclear energy industry. In the process of spent fuel treatment, the post-processing of electrometallurgy with high temperature molten salt (LiCl-KCl) as medium is used. It is the most widely studied and mature technology, but the molten salt after electrolysis still contains a small amount of toxic impurities and radioactive elements, such as La, Ce, Pr, Nd, Sm, Gd, Cr, Ni, Sr, U, Pu and so on. This paper is to use hydrothermal method and high-temperature solid-phase method to remove and solidify radioactive nuclides in waste molten salt and realize the recycling of molten salt. And the reduction and innocuity of high level radioactive waste. Using XRD, ICP, XRF and other means to characterize the phase and composition of the precipitates, solidified bodies, and purified molten salts. Hydrothermal method: using La3+, Ce3+, Nd3+, Cr3+ and Ni2+ plasma to simulate the fission products, corrosion products and actinides in the waste molten salt by plasma. The pH values of the waste molten salt solution are adjusted by KOH and placed by KOH. The above ions can be removed by the precipitation reaction under the hydrothermal condition. The results show that the most of the above ions can be removed when pH is 9. High temperature solid state method: (1) zirconium oxide as matrix, removing and curing the rare earth elements La3+, Ce3+, Pr3+, Nd3+, Sm3+, Gd3+ in the waste molten salt, that is, the synthesis of zirconium and rare earth nitrate in the molten salt medium LiCl-KCl Ln2Zr2O7, solidified the rare earth ions in the lattice of zirconate to purify the molten salt. The results showed that at above 1000 degrees, La3+, Pr3+, Nd3+ and Sm3+ could form a good chlorite structure with Zr4+, and Gd3+ formed a good crystallized structure of the faulted fluorite with Z4+, which was completely solidified. Ce3+ formed CeO2 and Ce2. The mixture of Zr2O7 is not cured completely. (2) La3+, Ce3+, Nd3+, Cr3+, and Ni2+. in the waste molten salt are removed and solidified with gadolinium zirconate (Gd2Zr207) as the matrix, and some of the above elements or elements are substituted for the doping of some Gd in Gd2Zr2O7, that is, the reaction of the chloride, gadolinium nitrate and zirconium nitrate in the molten salt medium. The result shows that when the synthesis temperature is 800, the curing rate of Cr is almost 0 and the curing rate of other ions is more than 99.9% when the 10% single element is doped and solidified. The curing rate of Cr is obviously improved when a variety of elements (substitution rate 10%) is cured at the same time, and 80%. (3) is based on gadolinium zirconate, and the curing of Sr in it is studied. The results show that in the LiCl-KCl molten salt, the solid solubility of Sr in Gd2Zr207 at 800 C can reach 10%. in this paper, which provides experimental and theoretical data for the study of the purification and recycling of waste molten salt produced by the electrometallurgical process of spent fuel.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X756;X591

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