New reprocessing system for spent nuclear reactor fuel using fluoride volatility method

Our proposed spent nuclear fuel reprocessing technology named FLUOREX, which is a hybrid system using fluoride volatility and solvent extraction, meets the requirements of the future thermal/fast breeder reactors (coexistence) cycle. We have been done semi-engineering and engineering scale experiments on the fluorination of uranium, purification of UF₆, pyrohydrolysis of fluorination residues, and dissolution of pyrohydrolysis samples in order to examine technical and engineering feasibilities for implementing FLUOREX. We found that uranium in spent fuels can be selectively volatilized by fluorination in the flame type reactor, and the amount of uranium volatilized is adjusted from 90% to 98% by changing the amount of F₂ supplied to the reactor. The volatilized uranium is purified using UO₂F₂ adsorber for plutonium and purification methods such as condensation and chemical traps for fission products provide a decontamination factor of over 10⁷. Most of the fluorination residues that consist of non-volatile fluorides of uranium, plutonium, and fission products are converted to oxides by pyrohydrolysis at 600-800 °C. Although some fluorides of fission products such as alkaline earth metals and lanthanides are not converted completely and fluorine is discharged into the solution, oxides of U and Pu obtained by pyrohydrolysis are dissolved into nitric acid solution because of the low solubility of lanthanide fluorides. These results support our opinion that FLUOREX has great possibilities for being a part of the future spent nuclear fuel cycle system.     

Determination of Organic Group Parameters: (AOCI,AOBr, AOS) in Water by Means of Ion-Chromatographic Detection. Pyrohydrolysis and Absorption

Abstract

In recent years methods have been developed to determine organic halogen at the μg/1 level in water samples by adsorbing these compounds on active carbon and by detecting the inorganic halides formed after conversion of the adsorbates by pyrohydrolysis. Applying these techniques the analysis of the so-called group parameter “Adsorbable Organic Halogen (AOX)” is performed.

The distinction of each of the halogens in the group parameter AOX and the determination of the parameter “adsorbable organic sulfur compounds (AOS)” can be realized using ion-chromatography for the detection of the anions, obtained after pyrohydrolysis of the adsorbed organic compounds.

Further investigations have shown good adsorption capacity of a newly developed nearly chlorine- and sulfur-free active carbon for organic model substances. This report presents the examinations concerning pyrohydrolysis of the organic solutes and absorption of the formed inorganic species.

The conditions for complete conversion of the model substances and high recovery rates in inorganic anions have been proved successfully. The optimization of the pyrohydrolysis apparatus and of the combustion conditions have been performed and proved with good results.     

Pyrohydrolysis of carbon nanotubes for Br and I determination by ICP-MS

Bromine and iodine determination was performed in carbon nanotubes (CNTs) by inductively coupled plasma mass spectrometry (ICP-MS) after sample preparation using pyrohydrolysis. Samples of CNTs (up to 500 mg) were mixed with 750 mg of V₂O₅ and heated at 950 °C during 12.5 min in a quartz tube under water vapor and air. The main operational conditions of pyrohydrolysis (carrier gas, absorbing solution, heating time, sample mass and use of V₂O₅) were evaluated. Accuracy was evaluated using certified reference materials (CRM) with similar matrix and also by comparison of results obtained after digestion of samples by microwave-induced combustion (MIC) and determination by ICP-MS. Agreement with CRM values was higher than 97% for Br and better than 96% in comparison with reference values (MIC/ICP-MS) of Br and I in CNTs samples. The limit of detection of the method for Br and I determination by ICP-MS was 0.05 and 0.004 μg g^? 1, respectively. Using a relatively simple and low cost pyrohydrolysis apparatus up to four samples can be processed per hour. The pyrohydrolysis sample preparation procedure is easy to be performed and provide a clean solution for analysis by ICP-MS, which is very attractive for Br and I control in CNTs.     

Catalytic spectrophotometric determination of iodine in coal by pyrohydrolysis decomposition

A method for the determination of iodine in coal using pyrohydrolysis for sample decomposition was proposed. A pyrohydrolysis apparatus system was constructed, and the procedure was designed to burn and hydrolyse coal steadily and completely. The parameters of pyrohydrolysis were optimized through the orthogonal experimental design. Iodine in the absorption solution was evaluated by the catalytic spectrophotometric method, and the absorbance at 420 nm was measured by a double-beam UV-visible spectrophotometer. The limit of detection and quantification of the proposed method were 0.09 μg g⁻¹ and 0.29 μg g⁻¹, respectively. After analysing some Chinese soil reference materials (SRMs), a reasonable agreement was found between the measured values and the certified values. The accuracy of this approach was confirmed by the analysis of eight coals spiked with SRMs with an indexed recovery from 94.97 to 109.56%, whose mean value was 102.58%. Six repeated tests were conducted for eight coal samples, including high sulfur coal and high fluorine coal. A good repeatability was obtained with a relative standard deviation value from 2.88 to 9.52%, averaging 5.87%. With such benefits as simplicity, precision, accuracy and economy, this approach can meet the requirements of the limits of detection and quantification for analysing iodine in coal, and hence it is highly suitable for routine analysis.     

Determination of 36Cl in biological shield concrete using pyrohydrolysis and liquid scintillation counting

A method for the determination of 36Cl in biological shield concrete of nuclear reactors was developed. Cl in the concrete sample was extracted quantitatively by pyrohydrolysis at 900 degrees C and recovered in Na2CO3 solution for subsequent measurement of 36Cl by liquid scintillation counting. WO3 was used as an accelerator in the pyrohydrolysis. The Cl extraction procedure was optimized by investigating experimental conditions with the use of ion chromatography and its recovery was evaluated by the analysis of the geochemical reference samples. The detection limit of 36Cl was 0.02 Bq g(-1) for a sample weight of 2 g. The relative standard deviation was 3-7% for the samples containing 0.5 Bq g(-1) levels of 36Cl. The method was applied to determine 36Cl in biological shield concrete of the Japan Power Demonstration Reactor.     

Use of indigenous microwave system for dissolution and treatment of waste from nuclear materials

Microwave heating technique has the unique advantages of low processing time, less consumption of reagents, homogeneous heating and maintenance-free adaptability to glove box. Dissolution of thorium and plutonium containing fuel viz sintered thorium oxide, thorium-uranium oxide and thorium-plutonium oxide pellets is one of the most difficult step for their analysis and characterization. Complete dissolution of the fuel samples is a pre-requisite for the analysis of fuel material in the solution form. Even a trace level of un-dissolved particle may interfere with the accurate and precise determination in the analysis. Large volumes of liquid and solid wastes are generated during the processing and analysis of samples. These wastes being radioactive can’t be disposed directly to sea or soil. They have to be segregated and categorised and all possibilities are explored to see the feasibility of retrieving the precious nuclear material. The present paper describes an overview of all the efforts made at AFFF for rapid dissolution of nuclear materials using an indigenous microwave digestion system as well as its use for the treatment of waste being generated.     

高温热水解离子色谱法快速同时测定粘土中的卤素

建立高温热水解分解粘土样品,离子色谱快速同时测定其中的氟、氯、溴和碘含量的方法。优化了影响粘土高温热水解的主要参数,得到以下最佳测定条件:2.0 g粘土,反应温度1000℃,停留时间10 min,样品与催化剂V2O5质量比为1∶1,空气流量90 mL/min,15 mL 5.4 mmol/L Na2CO3和5.1 mmol/L NaHCO3混合溶液为粘土释放卤素的吸收液;考察了粘土高温热水解后卤素的赋存形态。结果表明,这些卤素在吸收液中以F!、Cl!、Br!和I!形式存在,且能被离子色谱很好地分离。粘土样品较好的卤素加标回收率和较小的相对标准偏差及土壤标准物质中卤素的评估说明本方法的准确度和精密度良好。分析了4个粘土样品,氟、氯、溴和碘的检出限分别为0.030,0.043,0.09和0.13#g/g,本方法简单、可靠、低消耗和快速,每小时可分析5个样品,可同时分析粘土和其它无机基质中的氟、氯、溴和碘的含量。     

The high-temperature analytical uses of vanadium(V) oxide

The review surveys the available representative information from several fields, on high-temperature analytical uses of vanadium(V) oxide during the last half-century. A brief historical background is included. The three main fields of use are organic microchemical analysis, macrocombustion determinations, and pyrohydrolysis, and the review covers apparatus and equipment, reagents, chemical considerations, characteristics of vanadium(V) oxide, procedural details, and evaluation of the results.     

Pyrohydrolytic separation technique for fluoride and chloride from radioactive liquid wastes

A rapid method for simultaneous determination of fluorine and chlorine in radioactive liquid wastes with ion chromatography after pyrohydrolysis separation was proposed for routine analysis. The elements were separated from radioactive liquid wastes by pyrohydrolysis and were subsequently determined with ion chromatograpy. Total time taken to determine these elements is about 45 min including 30 min for the pyrohydrolysis and 15 min for ion chromatography. The results of recovery tests ranged 95% or above. The limits of detection for F and Cl are 0.5 and 0.8 mg kg⁻¹, respectively.     

Installation of a Shielded SIMS for the Analysis of Irradiated Nuclear Fuels

A CAMECA IMS 6F secondary ion mass spectrometer (SIMS) for the analysis of irradiated nuclear fuel has been installed in the Microbeam Analysis Laboratory of the Institute for Transuranium Elements (ITU). This device is specially equipped with heavy metal shielding to enable the safe examination of irradiated nuclear fuel samples with activities up to 75 GBq. At ITU the shielded SIMS will be used in conjunction with EPMA taking advantage of the complementary nature of the two techniques and will make important contributions to ongoing research programmes such as the safety of nuclear fuels, the partitioning and transmutation programme and the characterisation of spent fuels. The paper describes the shielded SIMS installation and presents a selection of results from the commissioning tests.     

Potentiometric determination of fluoride in geological and biological samples following pyrohydrolytic decomposition

A method for the determination of fluoride in coal, coal fly ash, phosphate rock, limestone, mineral clay, fossilised materials, oyster tissue and vegetation using pyrohydrolysis for sample decomposition is proposed. A specific apparatus was constructed and the influence of vanadium pentoxide (V₂O₅) as a catalyst for the pyrohydrolysis reaction was investigated. It was verified that V₂O₅ does not influence the release of fluoride from the vegetation, oyster tissue, coal and coal fly ash matrices analysed. However, the catalyst was necessary for the phosphate rock, fossil bone, mineral clay and limestone samples. Certified and noncertified samples were analysed using an ion selective electrode (ISE) for the analyte detection. Precise (relative standard deviation—R.S.D.<7%) and accurate (recovery in accordance to certified values) results were obtained. The limit of quantification (LOQ) of the method was 5.0 μg g⁻¹ of fluoride using 20 mg of sample and a final dilution to 10 ml. The sample frequency was five samples per hour.     

Determination of uranium, thorium and plutonium isotopes by ICP-MS

Quantitative and isotopic measurement of actinide elements is required in many circumstances in the nuclear industry. For example, determination of very low levels of these alpha emitters in human urine samples is used to assess the internal committed dose for nuclear workers. Quantifying actinide isotopes in radioactive waste from nuclear processing and nuclear facility decommissioning provides important information for waste management. Accurate determination of the uranium isotopic ratios in reactor fuels provides fuel burnup information. Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of Th, U, and Pu in various samples including urine, nuclear waste, and nuclear fuel in our laboratory. In order to maximize the capability of the technique and ensure quality analyses, ICP-MS was used to analyze samples directly, or after pre-treatment to separate complicated matrices or to concentrate the analyte(s). High-efficiency sample introduction techniques were investigated. Spectral interferences to minor isotopes caused by peak tails and hydride ions of major actinide isotopes were studied in detail using solutions prepared with light and heavy waters. The quality of the isotopic ratio measurement was monitored using standard reference materials.     

Modern Russian mass spectrometers for the atomic industry

Product quality control within the nuclear fuel cycle is a subject of special concern in Russia nowadays. Earlier, mass spectrometers of foreign production were commonly used for elemental and isotope analysis of samples. Currently, a series of domestic mass spectrometers MTI-350 has been developed and their production has been organized in Russia. The series comprises an automated MTI-350G mass spectrometer for the isotope analysis of uranium hexafluoride; thermal ionization MTI-350T mass spectrometer for the isotope analysis of uranium, plutonium, and mixed oxide (MOX) fuels; an MTI-350GS mass spectrometer for controlling the production of uranium hexafluoride; and an MTI-350GP mass spectrometer for the determination of the impurity concentration in uranium hexafluoride. The article considers operation principles, analytical characteristics, and the advantages of the above mass spectrometers.     

Microdetermination of fluoride by spectrophotometry of arsenazo(III)-complex of Zr back-extracted from htta in benzene

A spectrophotometric method for the determination of trace amounts of fluoride in aqueous solution is developed. It is based on the back extraction of Zr(IV) from its thenoyltrifluoroacetonate complex in benzene by aqueous F^– followed by the development of Zr-arsenazo(III) coloured complex and the measurement of the absorbance at 665 nm. Optimum conditions and effect of interfering ions are studied. The coefficients of variation obtained are 1.5% and 2.2% in 11 determination at the F^– concentration level of 10.0 g/ml and 1.6 g/ml. An excess of Al(III) is used for decomplexing Zr-fluoride prior to the colour formation if the fluoride amount is high. The method is useful for the determination of trace impurities of fluoride in nuclear fuel after separating fluoride from fuel matrix by pyrohydrolysis.     

A comprehensive two-dimensional gas chromatography method for analyzing extractable petroleum hydrocarbons in water and soil

A flow-switching two-dimensional gas chromatography (GCxGC) apparatus has been constructed that can operate at temperatures as high as 340 degrees C. This system is employed to analyze complex hydrocarbon mixtures such as diesel fuel, gas-oil, motor oil, and petroleum contaminated environmental samples. The GCxGC system generates two-dimensional chromatograms with minimal overlap between the aliphatic and aromatic regions This allows these compound classes to be independently quantitated without prior fractionation. The GCxGC system is used to analyze extracts of spiked water samples, wastewater, and soil. The accuracy of the method is compared to that of the Massachusetts Extractable Petroleum Hydrocarbons (MA EPH) method. The GCxGC system generates a quantitative accuracy similar to the MA EPH method for the analysis of spiked water samples. The GCxGC method and the MA EPH method generate comparable levels of total hydrocarbons when wastewater is analyzed, but the GCxGC method detects a significantly higher aromatic content and lower aliphatic content. Both the GCxGC method and MA EPH method measure comparable levels of aromatics in the soil samples.     

Nuclear activation methods for the characterization of fossil fuels

A review is presented on the use of neutron activation analysis (NAA) for the analyses of coal, oil shale, tar sands and petroleum. Fast NAA has been widely used for the determination of oxygen, and to a limited extent, of other elements such as nitrogen and silicon. Reactor NAA followed by instrumental counting, and in specific cases, after radiochemical separations is discussed. Thermal and epithermal neutrons are both used. Limited use of the²⁵²Cf source has been made in fuel analysis. A complementary technique to NAA is the photon-activation analysis with linear accelerator. It can determine over thirty elements, many of them not possible to do by NAA. Round-robin analyses of standard coal, fly ash, or oil shale samples indicate nuclear activation methods are comparable in accuracy and precision to X-ray fluorescence or atomic spectrometric methods for most elements.     

Integrated analysis of video and radiation data for nuclear material monitoring system

The analysis algorithm, which simultaneously interprets the transfer route and types of nuclear materials and the types of transfer container, has been developed for the radioactive material transfers in the nuclear facility. This method can be accomplished by integration of video images based on pixel differences and radiation data imported by NDA radiation sensors in real time. This technology, based on pattem recognition by neural networks, is well suited for surveillance systems of large automated facilities, spent fuel storage facilities and new conceptual hot cell facilities such as DUPIC(Direct Use of spent PWR fuel in CANDU reactors) facility.     

Fluorine standards for activation analysis

Stoichiometric, stable fluorides for comparison standards in neutron activation analysis were prepared by horizontal zone-refining or sublimation in HF atmospheres. The fluorides of Na, Mg and Al were shown by thermogravimetry to be anhydrous and to remain water-free after exposure to room air. Fluorine in the purified samples was separated by the pyrohydrolysis method and subsequently measured by acid-base titrimetry or selective ion electrodes. Deviations from theoretical values were ±0.1, ±0.9 and ±2.8% respectively for fluorides of Na, Mg and Al.     

Application of EPMA data for the development of the code systems TRANSURANUS and ALEPH.

In the present article, electron probe microanalysis data for Pu and Nd is being used for validating the predictions of the radial power profile in a nuclear fuel rod at an ultrahigh burn-up of 95 and 102 MWd/kgHM. As such the validation of both the new Monte Carlo burn-up code ALEPH and the simpler TUBRNP model of the fuel rod performance code TRANSURANUS has been extended. The analysis of the absolute concentrations and individual isotopes also indicates potential improvements in the predictive capabilities of the simple TUBRNP model, based on the one-group cross sections inferred from the neutron transport calculations in the ALEPH code. This is a first important step toward extending the application range of the fuel rod performance code to burn-up values projected in nuclear power rods based on current trends.