[en] Fossil fuel energy as well as hydropower sources in Vietnam and in the world are being exhausted. And nuclear power offers energy more effectively, safely and economically, while simultaneously combating greenhouse gases. In Vietnam, nuclear power would contribute to ensuring the energy security of the nation and provide power for development, industrialization and modernization. So Vietnam has been considering nuclear power as an option of energy supply since the 1980s. In 2002, the Prime Minister established the Governmental Steering Committee for the Development of Nuclear Power in Vietnam, and in 2006 this Committee developed “the Long-term Strategy for Peaceful Utilization of Atomic Energy in Vietnam up to 2020”, which aims to introduce the first nuclear power plants (NPPs) by 2020. Vietnam has begun to implement this “Long-term Strategy” by establishing a comprehensive Master Plan, enacting the Atomic Energy Law, and approval by the National Assembly on 25 November 2009 for the construction of the first NNPs. The agreed timescales are that the first reactor will start construction in 2014 and operation in 2020, and that four reactors (4000 MW) will be in operation by 2025 under a basic demand scenario. Institute for Technology of Radioactive and Rare Elements (ITRRE), one of institutions of Vietnam Atomic Energy Institute (VINATOM), is responsible for development of nuclear fuel cycle (NFC) in order to guarantee nuclear fuel supply security for the NPPs. On the base of The Decision - No. 906/QD-TTg – “Approving orientations for planning nuclear power development in Vietnam through 2030”, three main articles in the front end of the NFC, namely study on Vietnam’s uranium mining-milling (to product yellow cake), study on nuclear fuel (to fabricate nuclear fuel) and study on radioactive waste treatment (to manage radioactive waste) are developed in Vietnam. (author)

[en] The report “Brandon mathematical model describing the effect of calcination and reduction parameters on specific surface area of UO_2 powders” [14] has built up a mathematical model describing the effect of the fabrication parameters on SSA (Specific Surface Area) of ex-AUC (Ammonium Uranyl Carbonate) UO_2 powders. In the paper, the Brandon mathematical model that describe the relationship between the essential fabrication parameters [reduction temperature (T_R), calcination temperature (T_C), calcination time (t_C) and reduction time (t_R)] and SSA of the obtained ex-ADU (Ammonium Di-Uranate) UO_2 powder product has established. The proposed model was tested with Wilcoxon’s rank sum test, showing a good agreement with the experimental parameters. The proposed model can be used to predict and control the SSA of ex-ADU UO_2 powders. (author)

[en] Studies on modeling uranium dioxide (UO₂) powder and pellet processes from ammonium uranyl carbonate (AUC)- derived uranium dioxide powder (UO₂ ex-AUC powder) were reported in the paper. A mathematical model describing the effect of the fabrication parameters on specific surface area (SSA) of UO₂ powders was built up. To the best of our knowledge, the Brandon model is used for the first time to describe the relationship between the essential fabrication parameters [reduction temperature (T_R), calcination temperature (T_C), calcination time (t_C) and reduction time (t_R)] and SSA of the obtained UO₂ powder product. The Brandon model was tested with Wilcoxon’s rank sum test, showing a good agreement with the experimental parameters; the model can be used to predict and control the SSA of UO₂ powder. Response surface methodology (RSM) based on face centered (CCF), one type of quadratic central composite design (CCD), was used to model the pellet process. The experimental studies on the UO2 pellet process determined region of experimental planning as follows: conversion of AUC into UO₂ powder at various temperatures of 773 K, 823 K and 873 K and sintering of UO₂ pellets at temperatures of 1923 K, 1973 K and 2023 K for times of 4 h, 6 h and 8 h. On the base of the proposed model, the relationship between the technological parameters and density of the UO₂ pellet product was suggested to control the UO₂ ex-ADU pellet process as desired levels. The studies on the modeling were implemented at Nuclear Fuel Technology Center (ITRRE). (author)

[en] 1. Yenphu rare earth ore concentrate treatment by alkali under pressure: On the base of studying mineral and chemical compositions of Yenphu rare earth ore concentrate containing 28% TREO and conditions for digestion of ore concentrate by alkali under pressure such as ore concentrate/ NaOH ratio, alkali concentration, pressure and temperature at bench scale (100 gram and 5 kg per batch), the optimal conditions for decomposition of REE ore concentrate have been determined. The yield of the decomposition stage is about 90%. The studies on alkali washing, REE leaching by HCl, pH for leaching process, and iron and radioactive impurities removing by Na₂S + Na₂PO₄ have been carried out. The obtained results show that mixture of Na₂S 5% + Na2PO₄1% is effective in iron and radioactive impurities removing. The obtained REE oxides get purity of > 99% and meet the need of solvent extraction (SX) individual separation of rare earth elements. The schema for recovery of REEs from Yenphu REE ore concentrate by alkali decomposition under high pressure has been proposed. 2. Fractionation of Yenphu rare earth mixture into subgroups by solvent extraction with PC88A: On the base of simulation program, the parameters for fractional process of rare earths mixture into subgroups by solvent extraction with PC88A have been proposed and determined by experimental verification on mixer-settler set. According to this process, rare earths mixture fractionated into yttrium and light subgroups. In their turn, the light subgroup was separated into light (La, Ce, Pr, Nd) and middle (Sm, Eu, Gd) subgroups. The average yield of the process reached value > 95%. The composition of light subgroup meets the needs for individual separation of Gd, Eu, and Sm. 3. Separation and purification of yttrium: The process for recovery of yttrium consists of two stages: upgrade to get high quality Y concentrate by PC88A and purification by Aliquat 336 in NH₄SCN-NH₄Cl medium. The process parameter for PC88A and Aliquat 336 systems have been optimized using the computer simulation program. The solution containing > 80% pure Y₂O₃ after upgrading by PC88A (18 extraction, 18 scrubbing and 10 stripping stages) is purified further by another cycle of SX (24 extraction, 10 scrubbing and 10 stripping stages) with 25% Aliquat 336 in kerosene in presence of 1.0 M NH₄SCN and 2.0 M NH₄Cl. The impurities of Ho, Er, and another heavy elements are extracted leaving >99.9% pure Y₂O₃ in the aqueous phase. The yield of the process is > 85%. 4. Separation and purification of europium: The isolation and purification of europium consists of following steps: isolation of Eu by reduction on zinc column and precipitation in the form EuSO₄ by H₂SO₄ under CO₂ atmosphere; first purification by conversion of EuSO₄ to EuCl₃, reduction and precipitation in the form EuSO₄; and second purification by reduction on zinc column and precipitation of other rare earth elements in the form RE(OH)₃ by NH₄Cl-NH₄OH buffer of pH = 10 under atmosphere N₂. Eu₂O₃ of 99.9% purity has been recovered with overall yield. 5. Separation and purification of gadolinium: The middle subgroup after Eu removing is subject to Gd recovery by SX with PC88A. The SX parameters for Gd separation had been optimized by computer program. The separation process consists of 12 extraction, 12 scrubbing and 6 stripping stages. The acidity of scrubbing solution is 1.0.M HCl. The purity and yield of the Gd separation process were > 98% and >85% respectively. The obtained Gd₂O₃ was purified by Eu removing using zinc column and H₂SO₄. The final purity of the Gd₂O₃ was reached value 99%. 6. Overall schema for individual separation of some rare earth elements of high purity from Yenphu rare earth ore concentrate: Based on the above obtained results, overall schema for individual separation of some rare earth elements (Y, Gd, Eu and Sm) of high purity from Yenphu rare earth ore concentrate has been proposed. The schema consists of REE ore concentrate decomposition, individual separation by SX (Y, Gd, Eu and Sm) and chemical selective reduction (Eu). (LBT)

[en] The present paper deals with the preparation of UO_2 powder via ammonium uranyl carbonate (AUC) precipitation route from the UO_2F_2-HF solution. The preparation of UO_2 ex-AUC powder includes two steps, namely calcination of AUC into U_3O_8 in environment of H_2O (steam) + N_2 mixture and reduction of the U_3O_8 into the UO_2 powder in environment of H_2 + N_2 mixture. The both were carried out sequentially in a tube rotary furnace and the fluoride in the AUC powder was eliminated by pyro-hydrolysis method in the calcination process. On the base of experimental data, the Bandon multiple regression model that describes the effect of four factors, namely reduction temperature (T_r), calcination temperature (T_c), calcination timing (t_c), and reduction timing (t_r) on the UO_2 ex-AUC powder specific surface area (SSA) is established. The model equation is: y(SSA) = a x f_1(T_r) x f_2(T_c) x f_3(t_c) x f_4(t_r) = 1.016948 x (0.0065T_r - 1.4215) x (2.1769 - 0.0019T_c) x (1.357 - 0.1536 t_c) x (1.6819 - 0.1089 t_r) (author)

[en] Studies on modeling uranium dioxide (UO₂) powder and pellet processes from ammonium diuranate (ADU)- derived uranium dioxide powder (UO₂ ex-ADU powder) were reported in the paper. A mathematical model describing the effect of the fabrication parameters on specific surface area (SSA) of UO₂ powders was built up. The Brandon model is used to describe the relationship between the essential fabrication parameters [reduction temperature (T_R), calcination temperature (T_C), calcination time (t_C) and reduction time (t_R)] and SSA of the obtained UO₂ powder product. Response surface methodology (RSM) based on face centered (CCF), one type of quadratic central composite design (CCD), was used to model the pellet process. The experimental studies on the UO₂ pellet process determined region of experimental planning as follows: conversion of ADU into UO₂ powder at various temperatures of 973 K, 1023 K and 1073 K and sintering of UO₂ pellets at temperatures of 1923 K, 1973 K and 2023 K for times of 4h, 6h and 8h. On the base of the proposed model, the relationship between the technological parameters and density of the UO₂ pellet product was suggested to control the UO₂ ex-ADU pellet process as desired levels. (author)

[en] Solvent extraction experiments have been performed to investigate an optimum condition to separate Nd and Pr from chloride solutions using PC88A and IP2082 solvent applying for the pilot scale extraction system of 120 stages. The extraction process bases on the distribution coefficients of Nd were higher than those of Pr and other reasonable conditions. The effect of various parameters, such as equilibrium time, aqueous pH, extractant concentration, chloride ion concentration, organic solvent, and others on the extraction has been discussed. Results indicated that the conditions including the speed of feed solution with 150 g/L concentration of di-dim is 150 mL/min; rate of 20% PC88A 20% is 2L/min; 0.1 mL/min of NaOH 4.5 N and 0.2 L/min of HCl 3 N and the balance of extraction process is obtained in 80 hours. In this study, about 50 Kg product of neodymium 99% concentrate is obtained by the solvent extraction system including 100 stages of extracted separation and scrubbing; and 20 stages of tripping. (author)

[en] The studies on technology for preparation of metallic dysprosium from the oxide by metallothermic reduction method were reported in this work. The fluorination of dysprosium oxide (Dy₂O₃) by ammonium bifluoride (NH₄HF₂) to prepare anhydrous dysprosium fluoride was implemented. The temperatures of the fluorination determined by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) ranged from 350℃ to 450℃. Energy-dispersive X-ray spectroscopy (EDS) method was used to analyze the elemental composition in the as-prepared products; the fluorine (F₂) and dysprosium (Dy) elemental composition calculated from the [DyF₃] formula are in good agreement with those calculated from the EDS pattern. The anhydrous oxygen-free dysprosium fluoride was used to study the preparation of metallic dysprosium by the calcinothermic reduction method. The parameters of the calcinothermic process were temperature, time and ratio of calcium to anhydrous DyF₃. The metallic dysprosium of > 96% was obtained from the processes. (author)

[en] The AUC was precipitated using NH₃ and CO₂ gases, starting from a pure uranyl fluoride solution, with addition of amount NH₄OH solution. The effects of the precipitation conditions on the powder properties are determined. The crystal morphology of AUC powders was characterized by using SEM and X-ray. The results obtained were compare with those of a reference AUC produced from the reaction of (NH₄)₂CO₃ with uranyl fluoride solution. (author)

[en] In this paper, Ammonium Uranyl Carbonate (AUC) powders were prepared by precipitation method in solution. UO₂F₂/HF, ammonium carbonate (AC), and ammonium hydroxide solution were used as precursors for precipitation. The influence of C/U ratio (mol/mol), AC concentration (g/L), reaction temperature (^oC), on characteristics of AUC powders was also investigated. Then, the synthesized AUC powders were analyzed (to define) phase composition (X-ray), fluorine content, morphology (by SEM), and specific surface area (BET). (author)