Zur Abtrennung des Spaltstrontiums aus Kernbrennstoffen an Ammoniummolybdatophosphat

The separation of fission strontium from solutions of prolonged cooled nuclear fuel has been performed using ammoniummolybdatophosphate (AMP) columns. The sorption mechanism of bivalent ions on AMP has been investigated by column and batch experiments. A pure ion exchange of Sr²⁺ for two H⁺ or NH ₄ ⁺ ions has been established. Conditions for the sorption and elution of fission strontium and other fission products on AMP columns are described.     

Final purification and concentration of americium/curium separated from high-level reprocessing waste

A cation-exchange cycle has been developed for the recovery and concentration of the Am/Cm product from a DTPA/lactic acid solution used in an extraction process for the isolation and separation of the actinides from lanthanide fission products. The optimum pH region for the sorption of Am³⁺ from 0.05M DTPA/1M lactic acid solutions by strongly acidic cation-exchange resins is pH 0.9–1.0. Maximum usable capacities, heights of the exchange zone, and concentration factors for different resins, cross-linkages and temperatures have been determined. Decontamination factors are given for some fission products, as well as U, Np and Pu.     

Volatility of tellurium and various fission products in heated nitric acid solutions

The volatility of tellurium and some other fission products was radiochemically studied in heated nitric acid solutions. As tracers ¹²¹Te produced by bremsstrahlung of an electron LINAC and other fission products produced by neutron irradiation were used. The distribution rate of radionuclides between the mother solution and the condensate, was considered as volatility, and was determined. The volatility of tellurium was found to be small and close to that of cesium. Volatilization tests were also performed in the presence of large amounts of solutes.The authors wish to thank Mr. Roy Jacobus for his help in preparing this paper.     

Volatility of tellurium and various fission products in heated nitric acid solutions

The volatility of tellurium and some other fission products was radiochemically studied in heated nitric acid solutions. As tracers ¹²¹Te produced by bremsstrahlung of an electron LINAC and other fission products produced by neutron irradiation were used. The distribution rate of radionuclides between the mother solution and the condensate, was considered as volatility, and was determined. The volatility of tellurium was found to be small and close to that of cesium. Volatilization tests were also performed in the presence of large amounts of solutes.The authors wish to thank Mr. Roy Jacobus for his help in preparing this paper.     

Separation of gram quantities of uranium from fission products by extraction chromatography

The separation of gram quantities of uranium from fission products has been investigated by extraction chromatography. The separation which is based on the difference in distribution coefficients between uranium and the fission products on a tributyl phosphate (TBP) resin in nitric acid medium, was carried out by means of high acidity feed and stepwise elution on a TBP chromatography column. The results show that this technique is capable to separate 5 g of uranium from a large quantity of fission products. The recovery of uranium is more than 99%. The decontamination factors of g- and b-activities were 2.1^.10³ and 2.3^.10³, respectively.     

Isolation of radiocesium from a fission product mixture

A method of¹³⁷Cs isolation from strongly, acidic solutions of fission products is described, in which vanadyl ferrocyanide is used as a selective ion exchanger for cesium. The effects of the acidity of medium and the carrier concentration on the quantitative yield of separation have been studied and convenient conditions have been found for¹³⁷Cs isolation from the solution of fission products formed after irradiating uranium with neutrons.     

Measurements of fission yield in 8 MeV bremsstrahlung induced fission of 232Th and 238U

The cumulative yields (i.e. the sum of isobaric independent yield up to the isobar of interest) for various fission products have been determined in the 8 MeV bremsstrahlung induced fission of ²³²Th and ²³⁸U by using off-line gamma ray spectrometric technique. From the cumulative yields of the fission products, their mass-chain yields (i.e. the sum of independent yields of all the isobars) were obtained by using charge distribution correction. The mass-chain yields in the ²³²Th(γ, f) and ²³⁸U(γ, f) reactions were compared with the data of similar excitation energy in the ²³²Th(n, f) and ²³⁸U(n, f) reactions to examine the effect of nuclear structure. From these data, it was found that the yields of fission products for the mass numbers 133–134, 138–140 and 143–144 as well as their corresponding complementary products are significantly higher than other fission products. Higher yields of the fission products around the mass numbers 133–134 and 143–144 were explained from the standard I and standard II asymmetric mode of fission, which indicates the role of shell closure proximity. However, the amplitude of yields for the mass numbers 133–134 and 143–144 are reverse in the ²³²Th(γ, f) and ²³²Th(n, f) reactions than in the ²³⁸U(γ, f) and ²³⁸U(n, f) reactions, which has been explained from the point of shell combinations of the complementary fragments.     

Separation of95Zr and95Nb from each other and from other fission products by adsorption and desorption on silica gel using hydrochloric acid solutions

The silica gel adsorption behaviour of zirconium, niobium, ruthenium and cerium in hydrochloric acid has been investigated by batch and column techniques. A satisfactory radiochemical separation of zirconium and niobium from each other and from other fission products has been achieved by a two column technique. The recommended procedure consists of sorption of all the nuclides on a primary silica gel column. Fifteen per cent of⁹⁵Nb, all of the zirconium and all of the other fission products are eluted first by washing with 5.5 M HCl. A second elution with concentrated hydrochloric acid then recovers the⁹⁵Nb (free from other products). The solution from the first elution after evaporation to 1 ml is then passed through another silica gel column and successively washed with 0.5M HCl, 5.5M HCl and concentrated HCl to obtain three fractions—other fission products—⁹⁵Zr free from other products—⁹⁵Nb free from other products, respectively.     

The determination of fission products in irradiated uranium by electrophoretic focussing of ions

Electrophoretic focussing of ions was applied to the separation of fission products present in solutions of nuclear uranium fuel irradiated in various European reactors. By combining two separation methods, all the long-lived fission products could be determined individually and quantitatively by counting with a NaI(T1) and a GM detector of known detection efficiency. Radiography and autoradiography were used for semi-quantitative purposes. The concentrations of²³⁵U and²³⁸U were determined from a short post-irradiation of the fuel solution and counting of¹⁴⁰Ba−¹⁴⁰La and²³⁹Np, respectively. An iterative calculus method is presented which allows calculation of the irradiation history of the fuel solution from the above analyses. without any a priori knowledge.     

New approaches to processing and fabrication of oxide nuclear fuels

It was shown that, in contrast to the Purex process using aggressive and environmentally hazardous 8M HNO₃ solutions for dissolving spent oxide nuclear fuel (SNF), this fuel can be easily dissolved in aqueous subacid ([H⁺] ∼0.1 M) solutions of Fe(III) nitrate (chloride) with partial separation of uranium and plutonium from fission products (FP). The low acidity of the solutions obtained (pH ∼1) allows direct application of modern technologies of finishing processing of nuclear fuel by fluoride, carbonate, oxalate, or peroxide precipitation of uranium and plutonium. It was established that U(VI) is isolated from nearly neutral nitric acid solutions as a poorly soluble uranyl hydroxylaminate complex after adding hydroxylamine. It was shown that on thermal decomposition at 200–300°C under ambient atmosphere this compound converts into uranium dioxide. A similar approach was applied to obtain mixed oxide uranium-plutonium fuel (MOX fuel).     

Extraction of U(VI), Th(IV) and some fission products from nitric acid medium by sulfoxides and effect of γ-irradiation on the extraction

The extracting abilities for thorium, uranium and some fission products by five sulfoxides are given. The results show that di(2-ethylhexyl) sulfoxide (DEHSO) is not only completely miscible with kerosene, but also superior to tri-n-butyl phosphate in some properties. The extraction behavior of uranium, thorium and some fission products such as zirconium, niobium and ruthenium from aqueous nitric acid with DEHSO in kerosene has been studied over a wide range of conditions. DEHSO extracted uranium and fission products better than TBP under all conditions and is similar to TBP in extraction of thorium. A study of extraction mechanism indicates that U and Th are extracted as disolvates, whereas HNO₃ is extracted as monosolvate. Extraction of the two actinides decreases with increasing temperature, indicating the extraction to be exothermic. Preliminary studies show that -ray irradiated DEHSO extracts Zr and Nb to a smaller extent than irradiated TBP in the range of 10⁴–10⁷ rad.     

A new method for the radiochemical separation of copper from fission products

A new method for obtaining radiochemically pure⁶⁷Cu from highly active fission product solutions is described. The method is based on the solvent extraction of the Cu(II)-diethyldithiocarbamate complex in n-butyl acetate in the presence of hold-back carriers for Ni, Co, Mn, Mo, rare earths, Cd, Te and Sb, and subsequent purification steps involving scavengings for Ag, Ba, Sr and Fe followed by an anion-exchange purification step for decontamination from Te. Copper is finally extracted as the α-benzoin oxime complex in which form it is mounted and counted. The method has several advantages over other methods in that decontamination is very high and it is sufficiently fast considering the stringent radiochemical purity achieved. The⁶⁷Cu separated by this procedure from a one-day-old mixture of fission products arising from 10¹⁰ fissions was found to be completely free of any contamination.     

The extraction of chromium(VI) from sulphuric acid solutions by 4-(5-nonyl)pyridine and its separation from fission products

4-(5-Nonyl)pyridine, a new liquid anion exchanger, has been studied for the extraction of chromium(VI) from sulphuric acid solutions. The optimal acidity is 0.1–1 M, depending on the concentration of chromium. Common anions have little effect on extraction in concentrations up to 0.1 M. Reducing agents such as ascorbic acid and thiosulphate prevent extraction at concentrations above 0.1 M. Separation of chromium(VI) from fission products was achieved.     

A procedure for concentrating americium and curium combined with their separation from plutonium and fission products using a chelating resin

The effect of agitation time and resin quantity on the sorption of americium, curium and europium from mineral acid solutions, using a chelating resin based on aminopolystyrene and Arsenazo I was determined, and the behaviour of plutonium and fission products was investigated under optimum conditions with respect to the sorption of americium and curium. A procedure is proposed for concentrating americium and curium from dilute solutions, combined with their separation from iron, plutonium and fission products. The procedure consists of sorption on the chelating resin from 0.1–1N mineral acid solutions, washing of the resin with 0.5M oxalic acid and 11N sulfuric acid, and elution of americium and curium with 2M triammonium citrate.     

Fission product yields in the fast-neutron fission of238U

The fission yields of 38 fission products in the fast-neutron induced fission of²³⁸U have been determined using a rapid, multiscaling gamma-ray spectroscopic method. To obtain absolute yields for fission products having half-lives ranging from 32 s to 40 d, a total of 56 multi-scaling gamma-ray spectra were collected using various irradiation and cooling periods. Gamma-rays and photopeak areas of interest were assigned to the fission products by their energies and half-lives. Fission product activities were evaluated from spectral data using growth and decay calculations and fission yields were determined by normalizing the¹⁴⁰Ba yield to the average value from reported data. The depleted uranium target, covered with a boron-cadmium thermal neutron shield, was used to keep interference from the fission of²³⁵U minimal. Results for the cumulative fission yields, including 17 mostly short-lived fission products measured for the first time, are compared with previous measurements and with the recommended yields in recent evaluations. The agreement, and some discrepancies, in the comparisons are discussed. No explicit even-odd pairing effects are observed in the fission yield data for fast-neutron induced fission of²³⁸U.     

Measurement of absolute intensity of 1001 keV gamma-ray of 234mPa

The sorption behavior of ²³⁵U fission fission products ⁹⁹Mo and ¹³²Te was studied through batch and dynamic experiments when they were dissolved in 1 to 7M HNO₃ solutions. It was found that ⁹⁹Mo is always totally adsorbed on hydrated SnO₂, while ¹³²Te is rather weakly adsorbed, therefore they can be separated from each other although ¹³²Te in the solution still remains contaminated with other radionuclides as well as ⁹⁹Mo does in the solid.     

Determination of243Am in244Cm by gamma spectroscopy

Gamma spectroscopy with a high resolution Ge(Li) detector is used to determine²⁴³Am by its 74.7-keV gamma transition in solutions containing much higher specific activities of other actinides and fission products. As little as 100 ppm of²⁴³Am relative to²⁴⁴Cm can be determined. A relative standard deviation of 1.4% was obtained for routine samples. The method is well suited for analytical control of curium process steps because of its simplicity, speed, and reliability.     

Separation of fission produced 106Ru and 137Cs from aged uranium targets by sequential distillation and precipitation in nitrate media

Summary Ruthenium-106 and ¹³⁷Cs have been separated from thermal-neutron irradiated UO₃ targets aged for ~2.5 years by distillation and surface interactions in nitrate media of controlled chemical composition. After digestion of the aged targets with their aluminum wrapper in 2M NaOH solution, nitric acid was added to complete dissolution of the formed residue. The prepared fission product solution was separated from ¹²⁹I and 91.8% ¹⁰⁶Ru by sequential distillation from 20% and 40% HNO₃ solutions containing H₂O₂ and KMnO₄, as oxidants, and by boiling for 4 and 2.5 hours, respectively. The recovery yield of ¹⁰⁶Ru collected in 0.1M NaOH solution was ~68.2% with a radionuclidic purity of 399.99%. Thereafter, the fission product solution was brought to pH 9.5 by addition of NaOH solution to precipitate Al(OH)₃, MnO₂, and Na₂U₂O₇ which selectively retained the remaining fission products leaving, mainly, ¹³⁷Cs in the supernatant solution. The recovery yield of ¹³⁷Cs was ≥97.3% with ~99.75% radionuclidic purity. The gamma-ray emitter contaminants which could be detected and identified in the recovered ¹³⁷Cs solution, were ~0.25% ¹³⁴Cs and ~1.4 ^. 10^-3% ^152,155Eu.     

Separation of heavier rare earths from neutron irradiated uranium targets

A radiochemical method is described for the separation of heavier rare earths from the fission of uranium. The method is particularly suitable for the separation of low yield (10⁻⁵%–10⁻⁷%), highly asymmetric rare earth fission products viz.^179,177Lu,¹⁷⁵Yb,¹⁷³Tm,^172,171Er,¹⁶⁷Ho and^161,160Tb in the neutron induced fission of natural and depleted uranium targets. Additional separation steps have been incorporated for decontamination from²³⁹Np (an activation product) and^93-90Y (a high fission-yield product) which show similar chemical behaviour to rare earths. Separation of individual rare earths is achieved by a cation exchange method performed at 80°C by elution with α-hydroxyisobutyric acid (α-HIBA).     

Determination of americium-243 through its daughter product neptunium-239

The extraction of Np(IV), Zr, Nb, Cs, Ce(III) and Am(III) from nitric acid solutions containing oxalate and phosphate ions by solutions of 1-phenyl-3-methyl-4-benzoylpyrazolon-5 (PMBP) and tri-n-butyl phosphate (TBP) in benzene has been investigated. A solution 0.1M in respect to PMBP and 0.25M in respect to TBP was found to extract 99% of neptunium from aqueous solutions 1M in respect to H₃PO₄ and 0.5M in respect to HNO₃. Under these conditions, the extraction of the other investigated elements does not exceed 0.1%. Based on this finding, a procedure was developed to determine²⁴³Am through its daughter product²³⁹Np in solutions containing large quantities of curium and its fission products. The sensitivity of the procedure is 1·10⁻⁷ mg of²⁴³Am in the sample. The²⁴³Am content is obtained by calculation from measurements of the γ-activity of the extracted²³⁹Np. The purification ratio of²³⁹Np is∼10⁵ from Zr, Nb and Ru, ∼10⁸ from Ce and Cm and >10¹² from Cs.