Purex流程中锝的走向

裂变产物锝的裂变产额高（6.13％）,化学行为极其复杂,在Purex流程诸多物流中都有锝的分布。生产堆中由于燃耗低,锝的产生量小,其影响可以忽略。随着动力堆中燃耗的加深,锝的产生量增多,流程中锝的走向与控制日益引起人们关注。在Purxe流程中,锝的化学行为奇特:在1A槽中,锝与锆、铀、钚等共萃;在1B槽中,会影响铀钚分离,消耗大量还原剂;锝还会进入铀产品中,给铀的开放操作带来很多困难。要解决这些问题,就需要在对锝的行为深入认识的基础上选择合适的工艺条件,有效地控制锝的走向,以使锝对流程的     

Purex流程1A工艺单元锝萃取行为研究

通过计算机模拟研究了不同燃耗和不同工艺条件下,硝酸、锆、铀、钚和锝在Purex流程1A中的萃取行为,获得了相应萃取行为数据,测定了不同硝酸浓度下锝锆共存时锝的分配比D₍Tc(Zr))、锆的分配比D_Zr以及锝的分配比D_Tc,再结合1A中硝酸、锆、铀和钚萃取行为数据,解析锝的萃取行为。结果表明,萃取段锝因锆锝共萃进入有机相,洗涤段锝因铀锝共萃和钚锝共萃留在有机相,相比于硝酸浓度变化对锝萃取的影响,洗涤段铀锝共萃和钚锝共萃的作用更重要。     

Purex流程1A工艺条件下锝的萃取动力学研究

锝是乏燃料后处理工艺中广泛关注的元素,锝的裂变产额高,行为复杂,对铀钚分离工艺过程的影响较大。锝的萃取行为是影响锝在Purex流程中走向的关键因素,而萃取动力学则是研究其萃取行为的一个重要方面,不仅可为认识过程机制提供参考,而且能够提供有实用价值的数据。关于锝萃取动力学的研究目前鲜见报道,因此,有必要开展这方面的研究工作。     

APOR后处理流程1B槽中锝的走向

在以甲基肼-二甲基羟胺为还原剂的APOR乏燃料后处理流程1B工艺中,锝主要走向1BP,但其走向的原因尚不清楚。本工作综合锝与还原剂的反应动力学、串级实验、台架实验结果,解释了锝在1B槽走向的原因。结果表明:锝在1B槽中被甲基肼还原为不被TBP萃取的低价锝形态,该反应在铀存在条件下会被大大加速,这是影响锝在1B槽走向的主要因素;还解释了串级萃取实验与混合澄清槽台架实验中锝走向差异的原因。     

Purex流程共去污工艺计算机稳态模拟

在萃取串级理论基础上,建立了模拟“分液漏斗法”串级萃取实验操作的数学模型,编写了HNO₃、U和Pu体系的稳态模拟程序。利用文献报道的实验数据和计算数据,对该程序进行了验证。结果表明,该程序模拟萃取器逐渐达到稳态的过程中,各组分的浓度剖面与实验结果符合良好。在此基础上,利用该程序对1A工艺进行了安全分析和工艺寻优计算。结果表明,1AS流量变化对U、Pu收率的影响不大,1AX和1AF流量变化对U、Pu收率影响大。提高洗涤液酸度有利于扩展工艺操作弹性范围,但不利于U对稀土的去污。     

PUREX流程1A槽中锝的走向分析

结合基础研究数据和工艺实验数据,对核燃料后处理PUREX流程共去污槽（1A槽）中锝的走向进行了分析。工艺实验数据表明：1A槽萃取段中TBP对锝与锆的共萃取行为是影响锝走向的主要因素。硝酸浓度会显著影响TBP对锝与锆的共萃取性能,当c(HNO₃)＜3 mol/L时,提高硝酸浓度可以促进水解的锆解离生成Zr⁴⁺,从而促进锆锝共萃取;当c(HNO₃)≥3 mol/L时,硝酸可能会参与锆与锝的萃取。在0.5~5 mol/L的范围内,提高硝酸浓度有利于锝的萃取。在1A槽洗涤段硝酸浓度分布相近的条件下,1A槽中锝的走向取决于萃取段硝酸浓度的分布。萃取段硝酸浓度分布不同,将导致进入1A槽有机产品液（1AP）的锝含量比例不同,萃取段硝酸浓度越高,越有利于锝进入1AP。     

Purex过程锝的走向研究

本文报道了用串级萃取方法研究Purex过程中鍀的走向,讨论了在萃取过程中影响鍀萃取的因素及萃取机理。实验证明了进入铀产品中鍀的含量将取决于1A槽和2D槽进料液水相的酸度,这与Siddall的结果是一致的。我们对Purex过程的进料液采用两种不同的酸度,当进料液水相的酸度为2.0MHNO_3时,经过1 A槽后有60%的鍀留在1 AW废液中,当进料液水相的酸度为1.4 MHNO_3时,有20%左右的鍀被留在1 AW废液中,在此酸度下,经1 A槽直至2 D槽,仍有50%左右的鍀随着铀一起被回收。1 AW废液中鍀的含量只取决于1 A槽进料液水相的酸度,而不取决于进料液中鍀的浓度,铀的浓度在此影响较小。     

Purex流程共去污工艺稳态趋近过程计算机模拟

乏燃料后处理Purex流程中的铀钚共去污工艺（1A）是整个化学分离过程的关键环节之一，该工艺计算机模拟计算对1A进行流程优化和安全分析具有重要意义。     

Purex流程中所氚的行为研究

研究了氚在Ｐｕｒｅｘ流程中的行为，测量了氚和ＨＮＯ３在３０％ＴＢＰ－煤油和水相之间的分配比，研究了γ辐照和铀浓度对氚分配的影响及辐照对氚在有机相中保留的影响，萃取有有机相中氚的洗涤实验表明，洗涤是一种氚在两相间重新分配的简单过程，对氚在一循环中的行为进行了台架实验，结果表明１Ａ混合－澄清槽（６级萃取，９级洗涤）中对氚的去污系数在１０＾４以上，并且氚主要集中１Ａ的萃取段，残留在１ＡＰ中的氚易在附加的     

Purex流程1A槽中Pu(Ⅵ)行为的计算机模拟

在乏燃料后处理Purex流程中,共去污循环的安全稳定运行是整个生产过程的关键之一。Pu(Ⅵ)在TBP中的分配系数比Pu(Ⅳ)的低而易导致钚流失。文章采用计算机模拟1A萃取槽中UO²⁺₂、HNO₃、Pu⁴⁺、PuO²⁺₂的运行。计算结果表明,Pu(Ⅵ)的流失是造成钚收率降低的主要因素之一,提高Pu(Ⅵ)的收率能够有效提高钚产品的收率。当1AF中ρ(U)＝225g/L、c(HNO₃)＝3.0mol/L、ρ(Pu)＝2.20g/L,1AS中c(HNO₃)＝3.0mol/L,1AX为30％TBP/煤油,流比1AF∶1AS∶1AX＝1.25∶0.75∶3.00时,为使1A萃取槽中钚的收率不低于99.9%,应控制1AF料液中Pu(Ⅵ)量（占总Pu百分数）不超过7%。     

The Distribution of Tc in Purex

Tc is an important fission product (fission yield of 99Tc is 6.13%) and has complex chemical behavior. It distributes in many flows of Purex. The influence of Tc can be ignored in military plutonium production reactor because the burning up of it is very low and the production of Tc is little. The burning up of PWR is much deeper and the production of Tc is much higher than the former so the tendency and controlling of Tc in Purex causes popular consideration. The main reason for that is the peculiar chemical property of Tc. Tc co-extracts with Zr, U and Pu in 1A cell and effect the separation of U or Pu in 1B cell by consuming large amount of reductants and     

乏燃料后处理洗涤槽中锝的走向控制研究

研究了乏燃料后处理工艺流程中锝的去除方法。实验结果表明在TcSF∶TcSS1∶TcSS2=（8～10）∶1∶1的流比下,采用双酸（高酸,7mol/LHNO3;低酸,2mol/LHNO3）洗涤,锝的去污系数可达到10以上。     

Studies on Behavior and Trend Controlling of Technetium in 1A and Scrubbing Extractor

The effect of the concentration of HNO3 on distribution ratio of Tc (Ⅶ) between 30% TBP-kerosene and HNO3 solution at various ratio of U, Zr, Tc is determined. The trend and extraction behavior of Tc in 1A extractor with mixer-settler is studied. The results show that 14.4% and 27.0% of Tc is in 1AP, respectively while the concentrations of HNO3 in 1AF solution are 2 mol/L and 3 mol/L which prepared by chemicals. However after heating pretreatment of 1AF solution , 99.8% of Tc is in 1Ap while concentration of HNO3 in 1AF is 3 mol/L.Meanwhile, The HNO3 driving out method of U-Tc-Zr in efflux 1AP is studied. The aim is     

Determination of Optimal Process Variables for Two-Cycle Purex Process

The large and complicated system that is the Purex process is decomposed into units possessing common functions. Then, using the concentration plofile determined by linear search, the inputs, the outputs and the concentration profiles of all the individual units can be determined systematically. Using this approach, Powell's method and multilevel control theory is applied to the Purex process design problem, which is thereby reduced to a problem of optimization. Numerical calculations are carried out, resulting in optimal process variables well within the range of practicability. These process variables are calculated without taking into consideration such relevant but difficult factors as criticality and the instability of Pu solutions. These factors could, however be accounted for by adding appropriate penalty terms to the performance index. The computer program devised for the present calculations is given the code name POSER (Program for Optimization of Solvent Extraction Process).     

在普雷克斯流程中亚硝酸的行为

主要论述了在核燃料后处理中亚硝酸的生成和它的行为 ,亚硝酸和还原剂中的肼反应生成叠氮化物的危害 ,以及预防叠氮化物危害的措施     

Mass Transfer Model of Purex Process in Mixer-Settlers

The formation rate of ruthenium tetroxide (RuO₄) from nitrosyl ruthenium trinitrate (RuNO(NO₃)₃) was measured at temperatures of 70–115°C in 3–9 mol·dm^?3 nitric acid solutions. The gas-liquid equilibrium ratio was measured at temperatures of 40–80°C in 0.1–9 mol·dm^?3 nitric acid solutions. The gas-liquid equilibrium ratio of RuO₄ ranged about 60–260 under the experimental conditions. The reaction rate increased greatly with acid concentrations above 6 mol·dm^?3. The activation energy of the reaction was about 130 kJ·mol^?1 in 9 mol·dm^?3 nitric acid solution. It was concluded that the rate of RuO₄ formation dominated the distill-out phenomena of Ru in an evaporator as used in nuclear fuel reprocessing plants.     

Precipitation Formation of Zirconium-Dibutyl Phosphate Complex in Purex Process

Dibutyl phosphate (DBP) was added to 30% TBP-70% dodecane solvent (DBP concentration, 30–1,150mg/l). These samples were used to investigate distribution behavior of Zr from a 3 M nitric acid solution (Zr concentration, 60–4,000 mg/l). The experimental results show that the Zr distribution depended mainly on the total DBP/Zr mole ratio. Below DBP/Zr=2, the Zr distribution to the organic phase became larger as the DBP/Zr mole ratio increased. Above DBP/Zr=2, the Zr distribution factor was saturated. Moreover, colloidal precipitation at the interface between organic and aqueous phases was observed above DBP/Zr=2.

Then in order to characterize the precipitation, 3 M nitric acid solution containing Zr ion was directly reacted with DBP and the obtained products were analyzed by ¹³C, ³¹P and ¹⁴N NMR spectroscopy. The measured NMR spectra indicated that the products were polymers having four kinds of bonding structures. One was a hydrogen bonded structure and the others were Zr bridged structures with two to four DBP molecules coordinated per Zr atom. The Zr bridged structure with four DBP molecules was thought to make the biggest contribution to precipitate formation.