乏燃料電冶金廢熔鹽中放射性核素的脫除與固化
發(fā)布時(shí)間：2018-08-06 16:42
【摘要】：隨著核電工業(yè)的快速發(fā)展,勢(shì)必產(chǎn)生大量的乏燃料,其中含有較多放射性元素,對(duì)人類(lèi)的生態(tài)環(huán)境構(gòu)成嚴(yán)重威脅。因此,乏燃料后處理是核能工業(yè)可持續(xù)發(fā)展的重要保障。在乏燃料后處理方法中,以高溫熔鹽(LiCl-KCl)為介質(zhì)的電冶金后處理是研究最廣泛、發(fā)展較成熟的一種工藝,但電解后的熔鹽(后簡(jiǎn)稱(chēng)廢熔鹽)中仍含有少量有毒雜質(zhì)及放射性元素,如La、Ce、Pr、Nd、Sm、Gd、Cr、Ni、Sr、U、Pu等。本文擬采用水熱法和高溫固相法對(duì)廢熔鹽中放射性核素進(jìn)行脫除與固化,實(shí)現(xiàn)熔鹽的循環(huán)利用及高放廢物的減量化和無(wú)害化。采用XRD、ICP、XRF等手段對(duì)沉淀產(chǎn)物、固化體、凈化后熔鹽進(jìn)行物相及組成表征。水熱法：采用La3+、Ce3+、Nd3+、Cr3+和Ni2+等離子模擬廢熔鹽中的裂變產(chǎn)物、腐蝕產(chǎn)物及錒系元素。用KOH調(diào)節(jié)廢熔鹽水溶液的pH值并置于水熱條件下進(jìn)行沉淀反應(yīng),以去除上述離子。結(jié)果表明,pH為9時(shí),即可將脫除上述絕大部分離子。高溫固相法：(1)以氧化鋯為基質(zhì),脫除并固化廢熔鹽中稀土元素La3+、Ce3+、Pr3+、Nd3+、Sm3+、Gd3+,即在熔鹽介質(zhì)LiCl-KCl中加入鋯及稀土的硝酸鹽合成稀土鋯酸鹽(Ln2Zr2O7),使稀土離子固化在鋯酸鹽的晶格中,達(dá)到凈化熔鹽的目的。結(jié)果表明,在1000℃以上,La3+、Pr3+、Nd3+及Sm3+均可與Zr4+形成結(jié)晶良好的燒綠石結(jié)構(gòu),Gd3+則與Z4+形成結(jié)晶良好的缺陷螢石結(jié)構(gòu),從而被完全固化。而Ce3+則形成CeO2及Ce2Zr2O7的混合物,固化不完全。(2)以鋯酸釓(Gd2Zr207)為基質(zhì)脫除并固化廢熔鹽中的La3+、Ce3+、Nd3+、Cr3+和Ni2+。將上述某一種元素或多種元素取代Gd2Zr2O7中部分Gd進(jìn)行摻雜合成,即以上述元素的氯化物、硝酸釓、硝酸鋯為原料,在熔鹽介質(zhì)中進(jìn)行反應(yīng),達(dá)到固化的目的。結(jié)果表明,當(dāng)合成溫度為800℃時(shí),10%單一元素?fù)诫s固化時(shí), Cr的固化率幾乎為0，，其它離子的固化率均在99.9%以上；多種元素(取代率10%)同時(shí)進(jìn)行固化時(shí),Cr的固化率明顯提高,達(dá)80%。(3)以鋯酸釓為基質(zhì),研究Sr在其中的固化條件。結(jié)果表明,在LiCl-KCl熔鹽中,在800℃下, Sr在Gd2Zr207中的固溶度可達(dá)10%。本論文的研究結(jié)果對(duì)乏燃料電冶金過(guò)程產(chǎn)生的廢熔鹽的凈化及循環(huán)利用研究提供了實(shí)驗(yàn)和理論數(shù)據(jù)。
[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.
【學(xué)位授予單位】：廣西大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：X756;X591
本文編號(hào)：2168332
[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.
【學(xué)位授予單位】：廣西大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：X756;X591
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