单甲基肼改善铀纯化循环中钌的净化

通过单级条件实验研究单甲基肼或肼浓度、预处理酸度、温度等因素对钌的预处理效果的影响。采用确定的条件进行了模拟铀纯化循环2D槽的串级实验,获得了料液经单甲基肼或肼预处理后钌的净化系数（DF_Ru）。结果表明,单甲基肼作为预处理试剂提高钌净化的效果明显,与料液中未加预处理试剂相比,其净化系数提高近10倍,且在相同预处理条件下,其预处理效果优于肼。通过台架温试验,进一步验证了单甲基肼对钌的预处理效果,钌的净化系数达到10⁴。     

单甲基肼预处理对2D槽中钌的净化研究

通过单级条件实验研究单甲基肼或肼浓度、预处理酸度、温度等因素对钌预处理效果的影响。采用确定的条件进行了模拟铀纯化循环2D槽的串级实验，获得了1CU料液经单甲基肼预处理后钌的净化系数（DF（Ru））。串级结果列于表1。结果表明，单甲基肼作为预处理试剂提高钌净化的效果明显，较料液中未加预处理试剂的净化系数提高近8倍。     

氨基羟基脲反萃TBP中的Np(Ⅳ)

为有效提高铀中除镎的分离效果,对氨基羟基脲反萃30%TBP-煤油中Np(Ⅳ)的性能进行了研究,探讨了反萃剂浓度、酸度、温度、反萃时间、相比、有机相铀浓度对Np(Ⅳ)反萃率的影响。单级研究结果表明,氨基羟基脲能有效反萃TBP中Np(Ⅳ)。使用氨基羟基脲为反萃剂的台架实验结果表明,6级反萃对1BU中Np的净化系数为20。     

微量钌在Pu纯化循环中的行为

为了了解钌在Pu纯化循环中的行为,研究了相接触时间、相比、硝酸浓度对钌(Ru)分配比的影响,并通过台架试验研究了流比、料液酸度、洗涤级数、萃取级数、铀浓度对Ru净化的影响。结果表明：流比(2AF∶2AX)、料液(2AF)HNO₃浓度、洗涤级数、萃取级数、铀饱和度对Ru的净化具有显著的影响。台架热试验结果表明,Ru的净化系数高于1 000,远高于设计指标100。     

羟胺预处理改善铀线二循环钌去污的工艺研究

研究了羟胺浓度，酸度，时间及稳定剂浓度对预处理的处理效果的影响，给出了羟胺预处理改善铀线二循环钌去污的工艺条件。结果表明：单独采用羟胺进行预处理，对钌的去污效果较差，在预处理体系中加入少量肼，可得到满意结果。     

预处理过程对Np(Ⅴ)稳定性的影响

为了提高Purex流程铀纯化循环2D槽中镎的净化效果,研究了Np(Ⅳ)氧化条件,考察了用硝酸肼对钌进行预处理的过程中,预处理试剂浓度、酸度、温度、时间等不同预处理条件对Np(Ⅴ)稳定性的影响.结果表明,在0.2 mol/L酸度、85℃下保温2h,可以将料液中97％的Np(Ⅳ)氧化为Np(Ⅴ)或Np(Ⅵ).预处理时离子强...     

氨基羟基脲还原反萃高浓度Pu(Ⅳ)

采用氨基羟基脲（HSC）的硝酸水溶液研究了从30%（体积分数,下同）TBP/煤油中还原反萃高浓度四价钚（Pu（Ⅳ））的性能,并与羟胺-肼（HAN-HN）、N,N-二甲基羟胺-单甲基肼（DMHAN-MMH）在钚净化浓缩循环中反萃行为进行了对比。结果表明：在一定HSC浓度下,适当延长相接触时间、减小相比（o/a）、降低酸度和提高温度,均有利于Pu（Ⅳ）的还原反萃。HSC作为还原反萃剂,可以有效实现30%TBP/煤油中高浓钚的反萃,反萃效果较其它几种还原剂更好,有望在先进二循环流程的钚净化浓缩工艺中得到应用。     

无盐有机还原剂结构与其氧化产物的定量关系

对羟胺、N,N-二甲基羟胺、甲醛肟、氨基羟基脲和对二氨基脲五种还原剂及其氧化产物进行了分析,并通过分子结构描述符研究了还原剂结构与其相应氧化产物之间的构效关系。结果表明:还原剂氧化产物包含N2、CH3OH、CH4、CH2O和CHOOH等,还原剂分子结构描述符与其相应氧化产物构效关系方程拟合良好,对新还原剂开发具有较强的指导意义;氨基羟基脲的氧化产物简单,在PUREX流程中具有良好的应用前景。     

Purex流程的改进Ⅰ.共去污单元锆、钌净化工艺

通过单级实验,研究了不同铀饱和度、酸度、温度条件下30%TBP对锆、钌的萃取规律,在此基础上确定了提高1A净化锆、钌的工艺,并进行了台架实验验证。研究结果表明：提高铀饱和度、温度和酸度有助于降低钌在30%TBP中的分配比;在30%TBP中,高铀饱和度条件下,锆分配比受铀饱和度的影响远大于水相硝酸浓度的影响;温度对锆的分配比影响不显著。当1A槽采用4mol/L硝酸进料、4mol/L硝酸洗涤时,45℃条件下,铀、钚的回收率达99.98%,钌的去污系数约达到10⁵。     

铀纯化循环中乙异羟肟酸净化锆的研究

为了考察Purex流程铀纯化循环采用乙异羟肟酸(AHA)纯化铀时锆的净化效果,进行了模拟2D槽萃取段和洗涤段条件下锆的单级分配实验以及模拟2D槽工艺的试管串级实验.单级实验结果表明,增大AHA浓度或降低洗涤酸度都有利于降低锆的分配比;对含铀体系,当磷酸二丁酯(HDBP)的浓度低于0.1 mol/L时,基本不影响锆的净化效果.在以0.2 mol/L AHA-0.5 mol/L HNO3为洗涤液,第8级进料、8级萃取、8级洗涤,流比(2DF/2DX/2DS)为1:0.48 :0.06工艺条件下进行了2次2D槽串级实验,结果表明,铀中锆的净化系数分别为3.2×104,4.3×104.     

氨基羟基脲应用于钚净化浓缩循环

进行了氨基羟基脲(HSC)的硝酸水溶液对30%(体积分数,下同)磷酸三丁酯（TBP）/煤油中高浓度四价钚(Pu(Ⅳ))的还原反萃行为研究,并采用试管串级实验对HSC在钚净化浓缩循环中反萃段工艺进行了验证。结果表明：HSC能有效地实现有机相中高浓Pu(Ⅳ)的反萃;采用13级逆流反萃试管串级实验(还原反萃段10级,补充萃取段3级),对PUREX流程钚净化浓缩反萃段工艺进行了验证,在相比(2BF∶2BX∶2BS)为1∶0.25∶0.15的条件下,Pu的收率为99.99%;钚中去铀的分离因子SF(U/Pu)=3.7×10⁵。HSC作为还原反萃剂,可以实现30%TBP/煤油中高浓度Pu(Ⅳ)的有效反萃,在钚净化浓缩循环工艺中有良好的应用前景。     

Purification of uranium products in crystallization system for nuclear fuel reprocessing

Uranium crystallization system has been developed to establish an advanced aqueous reprocessing for fast breeder reactor (FBR) fuel cycle. In the crystallization system, most part of uranium in dissolved solution of spent FBR-MOX fuels is separated as uranyl nitrate hexahydrate (UNH) crystals by a cooling operation. The targets of U yield and decontamination factor (DF) on the crystallization system are decided from FBR cycle performance and plutonium enrichment management. The DF is lowered by involving liquid and solid impurities on and in the UNH crystals during crystallization. In order to achieve the DF performance (more than 100), we discuss the purification technology of UNH crystals using a Kureha Crystal Purifier (KCP). Results show that more than 90% of uranium in the feed crystals could be recovered as the purified crystals in all test conditions, and the DFs of solid and liquid impurities on the purified UNH crystals are more than 100 under longer residence time of crystals in the column of KCP device. The purification mechanism is mainly due to the repetition of sweating and recrystallization in the column under controlled temperature.     

微量锆在钚纯化循环中的行为

研究了相接触时间、相比、硝酸浓度对锆萃取性能的影响,并通过台架试验研究了流比、料液酸度、洗涤级数、萃取级数、铀浓度对Pu产品中Zr净化效果的影响。结果表明:流比(2AF∶2AX)、料液(2AF)中HNO3浓度、洗涤级数对Zr的净化具有显著的影响,而铀浓度对Zr的净化效果影响有限。台架温试验证明,选择的优化工艺可以满足Pu的收率和Pu产品中Zr的净化因子大于100的要求。     

Potential reprocessing improvements in the Advanced Fuel Recycle System

From the aspects of economical competitiveness, proliferation resistance, and minimizing waste problems, PNC has proposed an improved recycle concept for the FBR fuel cycle, termed Advanced Fuel Recycle System. Reprocessing in this system is based on the well-known PUREX flowsheet and features a “single cycle Pu/U co-extraction flowsheet” with lower decontamination factor (DF) than that in the conventional process. This feature is practical because of the FBR's low neutronic sensitivity to impurities.

Such a simplified extraction process without purification cycles should substantially reduce not only the number of process components but also the quantities of liquid to be treated in other related processes, so it will lead to the proportional reduction in waste processing, waste itself, and all other related equipments and facilities. This should improve overall economics. One method being examined to further reduce the liquid throughputs and simplify the process is to apply the crystallization technique to dissolver solution.

Overall, with this proposed concept, proliferation resistance will be significantly improved because plutonium is always recovered as a mixture with the uranium and DF of the plutonium product is low.

Reprocessing and fabrication processes are integrated into one fuel cycle plant in this system further contributing to these improvements.     

Effect of decontamination factor of recycled actinide and FP on the characteristics of SCNES

Effect of the decontamination factor (DF) of nuclides to be confined in the closed fuel cycle was examined in terms of the system characteristics. Two kinds of indices, equilibrium mass and equivalent radiotoxicity, were used to determine the recovery perfectivity of the nuclides. By using the equilibrium mass, extremely high DF had to be attained. The required values of DF were 10⁸ for LLFP and 10¹² for actinides. On the other hand, using the radiotoxicity, inferior perfectivity of recovery, DF=10⁶, could be acceptable for actinides and there is no necessity of LLFP recycling for transmutation because they only have comparable radiotoxicity with the supplied uranium to the system. The required DF which provide ignorable loss of waste to the outside of the system depends on what index we use. Generalization of index to quantify the hazard or nuisance of nuclear waste and setting the criteria remains unsettled questions.