离心萃取装置中硝酸羟胺还原反萃钚的研究

用十六级分离式混合—离心澄清萃取装置,在20-24℃,30-34℃,45-50℃等不同温度下进行了3B槽硝酸羟胺还原反萃钚的实验。结果表明,钚的收率均可达99.9%以上。在20-24℃时,有机相出口级附近几级的钚浓度较高,实验条件一旦波动,有可能造成钚的流失,且钚在萃取设备中有明显的积累。温度升高,14级反萃(停留时间约18min)时,钚的收率基本得到保证。     

硝酸羟胺对Pu(Ⅳ)的单级还原反萃数学模型研究

硝酸羟胺是Purex流程钚纯化过程的还原剂。本文建立了30%TBP/正十二烷体系中硝酸羟胺还原反萃Pu(Ⅳ)的单级迭代计算数学模型,并提出了相应的数学算法,编写了模拟连续逆流萃取器中的一级的计算机模拟程序,使用文献数据对模型和程序进行了验证。结果表明:模型计算值与文献实验值符合良好;本文模型计算结果的准确度高于文献模型。最后分析了计算时间单元长度对准确度的影响。     

硝酸羟胺在动力堆乏燃料后处理流程钚线第三循环中的应用

为动力堆乏燃料后处理流程的设计之用，通过还原实验，研究温度、溶液酸度、硝酸羟胺（ＨＡＮ）与钚的初始浓度比值对ＨＡＮ还原Ｐｕ（Ⅳ）的还原百分数的影响。结果表明，升温、低酸和合适的ＨＡＮ用量有利于Ｐｕ（Ⅳ）的还原。用模拟料液进行３Ａ槽和３Ｂ槽串级实验的结果表明：３Ａ槽的钚回收率达９９．９％以上，３Ｂ槽的达９９．９８％；钚中去铀分离系数达５０左右。通过单级和串级实验，研究了含钚３０％（Ｖ／Ｖ）ＴＢＰ－煤     

硝酸肼还原反萃取分离镎/钚的研究

镎的提取和分离是国际后处理领域重点关注的研究课题之一。在Purex流程中,硝酸肼常被用来作为亚硝酸的清扫剂,此外,由于硝酸肼对Np(VI)和Pu(IV)的氧化还原反应具有选择性,理论上可以利用其反应速率上的差异来实现镎与铀钚的分离。为探索硝酸肼分离镎/钚工艺提供可行性,本文采用单级萃取设备研究了硝酸肼还原反萃Np和Pu的过程。通过研究硝酸浓度、硝酸肼浓度和反应温度对还原反萃过程的影响,确定了Np(VI)和Pu(IV)反萃动力学方程和表现活化能。进一步通过动力学方程得出硝酸肼还原反萃Np(VI)和Pu(IV)的半反应时间,并对Np(VI)/Pu(IV)分离过程的工艺进行了初步探索。     

硝酸羟胺用于钚纯化循环的工艺条件优化

采用可控温的单级萃取装置,对羟胺还原反萃取钚的工艺条件进行了优化。实验表明,硝酸肼能够将少量Pu(Ⅳ)还原反萃取到水相,但是当硝酸肼浓度较高时,硝酸肼则表现出盐析效应,抑制钚的还原反萃取;对于钚还原反萃取工艺来说,当保持进料中羟胺与钚的摩尔数之比为定值时（在50℃时n (HAN)/ n (Pu)=2～3较为适宜）,增大还原剂流量能够提高钚的收率,但同时会降低钚的浓缩倍数;温度升高时,硝酸氧化Pu(Ⅲ)的反应速率加快,使得钚在有机相中的浓度有所升高;当溶液中离子强度较高时,在盐析效应的作用下,Pu(Ⅲ)的分配比随离子强度的提高而升高,导致钚在有机相中的浓度上升。     

N,N—二甲基羟胺对Pu（Ⅳ）的还原反萃和相应计算机模型

研究了N,N-二甲基羟胺（DMHAN）的HNO3溶液对30％TBP／煤油中Pu(Ⅳ）的还原反萃行为,考察了N,N-二甲基羟胺浓度、HNO3浓度、温度以及两相接触时间对Pu(Ⅳ）反萃率的影响。结果表明：延长相接触时间能显著提高钚的反萃率;增加HNO3浓度、加大DMHAN的用量、升高温度均能加快钚的反萃速率,但当相接触时间超出一定范围时,这些因素都不能显著增加钚的反萃率。编写了DMHAN单级反萃Pu(Ⅳ）的计算机模拟程序,程序计算值与实验值在一定范围内符合良好。     

二甲基羟胺存在下四价钚的反萃动力学

用恒界面池法实验考察了DMHAN／H_N03／TBP-煤油-Pu（Ⅳ）体系中Pu（Ⅳ）的反萃动力学。实验结果表明：在选定实验条件（转速295r／min,温度18．8℃,钚浓度1．30×10^-6～1．30×10^-4mol／L）下,DMHAN／HN03／TBP-煤油-Pu（Ⅳ）体系q~Pu（IV）的反萃属于扩散控制。     

PUREX流程钚还原反萃过程的计算机模拟研究进展

PUREX流程为当前后处理工业的主流流程,其计算机模拟研究为研究热点。国外一些国家已进行全流程模拟计算,能够开展工艺条件分析和工艺优化工作,具有重要的应用价值。铀钚分离工艺单元(1B)和钚反萃单元(2B)是PUREX流程的重要环节,二者计算机模拟的基础为钚的还原反萃单元模型。本文总结了国外PUREX流程计算模拟程序中的钚还原反萃模型的研究进展,重点对模型的建立和算法做了介绍。     

铀钚萃取洗涤-共反萃工艺的离心萃取器台架实验研究

由于快堆MOX乏燃料放射性强,需要缩短停留时间以降低溶剂辐解,本工作以离心萃取器为萃取设备,在短停留时间下进行了快堆MOX乏燃料后处理铀钚萃取洗涤-共反萃工艺研究。研究结果显示,该工艺在单级停留时间约20s时具有良好的铀钚收率,萃取洗涤过程中铀和钚收率均大于99.99%,共反萃过程中铀和钚收率分别为99.99%和99.94%;同时能有效防止第三相的形成,避免钚的聚合沉淀。     

HNO3介质中羟胺还原微量Pu（Ⅳ）的动力学研究

研究了ＨＮＯ３介质中羟胺还原微量Ｐｕ（Ⅳ）（ｃＰｕ（Ⅳ）≤１０＾－５ｍｏｌ／Ｌ）的动力学。测定了酸度、羟胺、Ｐｕ（Ⅳ）、Ｐｕ（Ⅲ）和ＮＯ＾－３浓度对微量Ｐｕ（Ⅳ）还原速率的影响。     

亚硝酸与肼或羟胺的反应热测量及工艺验证

采用C80微量热仪分别测定了亚硝酸与肼或羟胺的反应热，得到了亚硝酸与肼以不同摩尔比反应时的摩尔反应热：亚硝酸与肼的摩尔比大于2时，消耗单位摩尔肼的反应放热量ΔE₁=284.4 kJ/mol；亚硝酸与肼的摩尔比小于1时，消耗单位摩尔亚硝酸时的反应放热量ΔE₂=166.7 kJ/mol；亚硝酸与肼的摩尔比介于1和2之间时，消耗单位摩尔肼的反应放热量介于ΔE₁和ΔE₂之间。得到了亚硝酸与羟胺以不同浓度比进行反应时的反应热：亚硝酸过量时，消耗单位羟胺的反应放热量为ΔE₄=200.0 kJ/mol；羟胺过量时，消耗单位亚硝酸时的反应放热量为ΔE₅=194.9 kJ/mol。基于获得的亚硝酸与肼或羟胺的反应热数据，对核燃料后处理工艺流程中1BP调料过程中的温度升高情况进行了计算分析，并通过工艺实验进行了验证。     

亚硝酸与肼或羟胺的反应热测量及工艺验证

采用C80微量热仪分别测定了亚硝酸与肼或羟胺的反应热,得到了亚硝酸与肼以不同摩尔比反应时的摩尔反应热：亚硝酸与肼的摩尔比大于2时,消耗单位摩尔肼的反应放热量ΔE₁=284.4 kJ/mol;亚硝酸与肼的摩尔比小于1时,消耗单位摩尔亚硝酸时的反应放热量ΔE₂=166.7 kJ/mol;亚硝酸与肼的摩尔比介于1和2之间时,消耗单位摩尔肼的反应放热量介于ΔE₁和ΔE₂之间。得到了亚硝酸与羟胺以不同浓度比进行反应时的反应热：亚硝酸过量时,消耗单位羟胺的反应放热量为ΔE₄=200.0 kJ/mol;羟胺过量时,消耗单位亚硝酸时的反应放热量为ΔE₅=194.9 kJ/mol。基于获得的亚硝酸与肼或羟胺的反应热数据,对核燃料后处理工艺流程中1BP调料过程中的温度升高情况进行了计算分析,并通过工艺实验进行了验证。     

溶液中钚α活度的直接测量研究

选取YAP∶Ce闪烁体作为仪器核心部件,建立了接触式测量溶液中微量、痕量钚α活度的分析方法。结果表明:水相钚溶液浓度在5.20×10-5~1.30×10-3 g/L范围内线性良好(R2=0.987 7),定量检测下限为5.20×10-5 g/L;有机相钚溶液浓度在2.27×10-5~1.13×10-3 g/L范围内线性良好(R2=0.992 3),定量检测下限为2.27×10-5 g/L。本分析方法有别于传统的α计数法,过程无需制源,操作简单、方便,有望为后处理工艺过程中微量和痕量钚的在线或实验室分析提供一种新的途径。     

Solubility of Tributylphosphate in Plutonium Nitrate Solution and Highly Radioactive Liquid Waste Solution

Abstract

The solubility of tri-n-butylphosphate (TBP) in aqueous solutions of plutonium nitrate (PuN) and in highly radioactive liquid waste (HRLW) of PUREX nuclear fuel reprocessing was investigated. By an empirical formula the solubility of TBP in PuN solutions was described in the range of 0–0. 1 M Pu and 1–8M HNO₃ concentrations. The following items were elucidated:

(1) The logarithm of TBP solubility (S) in the solution of interest varies inversely in proportion to the concentration of Pu(IV) in the range of 0–0.1M PU(IV) at a constant concentration of HNO₃, indicating that Pu(IV) simply behaves as an electrolyte for the salting-out of TBP. Log S subsequently levels off with increasing Pu concentration, which would be due to a change in the principal dissolution form of TBP having an interaction with Pu (IV).

(2) The variation in S in PuN solutions (0–0.1M PU) with nitric acid concentration shows almost the same tendency as that in HNO₃ solution.

(3) A dependency of S on fission product metal ions in HNO₃ for HRLW similar to that for PuN was observed.

(4) The logarithm of the ratio of TBP solubility in water to that in solution of interest was nearly proportional to l/T for HRLW solution or for low concentration of PuN solution. That deviates from the linear relation at high temperature when the concentration of PuN is increased, which can be explained by the change in ionic form of Pu.     

Accurate Volume Measurement System for Plutonium Nitrate Solution

Abstract

An accurate volume measurement system for a large amount of plutonium nitrate solution stored in a reprocessing or a conversion plant has been developed at the Plutonium Conversion Development Facility (PCDF) in the Power Reactor and Nuclear Fuel Development Corp. (PNC) Tokai Works. A pair of differential digital quartz pressure transducers is utilized in the volume measurement system. To obtain high accuracy, it is important that the non-linearity of the transducer is minimized within the measurement range, the zero point is stabilized, and the damping property of the pneumatic line is designed to minimize pressure oscillation. The accuracy of the pressure measurement can always be within 2 Pa with re-calibration once a year. In the PCDF, the overall uncertainty of the volume measurement has been evaluated to be within 0.2%. This system has been successfully applied to the Japanese government's and IAEA's routine inspection since 1984.     

Long Term Change in Level-Volume Relation of an Accountability Tank for Plutonium Nitrate Solution

A slight change in the level-volume relation for an accountability tank for a large amount of plutonium nitrate solution (PuN) was observed at the Plutonium Conversion Development Facility (PCDF) in the Power Reactor and Nuclear Fuel Development Corp. (PNC), Tokai Works. From the results of annual tank re-calibrations for the plutonium receiving tank from 1985 to 1992 using the incremental feed of nitric acid as the density standard, it became clear that the relation between the level and the volume changed slightly, and the rate of the change was a linear function of operating time. Also it became clear that the change was linear in relation to the level. In the PCDF, the cumulative change in the volume at the nominal level was evaluated to be 0.1% during 8 years' operation. It was also evaluated that the repeatability of the re-calibration is much better than 0.1%. A reasonable frequency of tank re-calibration is once every 5 years.     

脉冲阳极溶出伏安法测定钚中痕量银

本工作以Nafion树脂修饰玻碳电极为工作电极、铂片电极为对电极、饱和甘汞电极(SCE)为参比电极,进行电极修饰技术研究,建立了脉冲阳极溶出伏安法测定钚中痕量银的分析方法。实验结果表明,银的阳极溶出峰的峰电流与银离子浓度在10~100μg/L范围内呈线性关系,银离子的定量检测下限为5ng/mL,回收率为90%~109%,该方法取样量小、抗干扰能力强、重现性好。     

超临界二氧化碳中TBP络合萃取硝酸钕

将超临界流体萃取技术应用于乏燃料后处理中,可简化后处理流程、减少二次废液的产生。本工作进行了含磷酸三丁酯(TBP)的超临界二氧化碳(SC-CO2)络合萃取硝酸钕的实验研究,考察了硝酸钕粒径、TBP流量、系统温度和压力对络合萃取过程的影响。实验结果表明,含TBP的SC-CO2可高效萃取硝酸钕,萃取率达97%以上,增大TBP流量可加快萃取过程,而粒径、温度和压力对萃取速率的影响则较小。由实验结果可推断,该络合萃取过程的动力学受络合反应控制,并用一动力学模型计算出表观反应速率常数。