N. K. Chaudhuri

Application of the fission track registration technique in the estimation of fissile materials: 235U-content in natural and depleted uranium samples and total uranium in solutions

Abstract The results of an investigation on the estimation of the 235 U content in natural and depleted uranium samples and total uranium in solutions including highly active fuel reprocessing waste streams using the solid state track registration technique are described. Two different methods were used: the “dry” method in which the detector (Lexan strip) was in contact with the fissile material in a 2 π geometry and the “wet” method in which the Lexan detector strips were kept immersed in the solution of the fissile material. The relative merits and demerits and also the accuracy and precision attainable by the two methods are discussed. The feasibility of using a portable neutron source for the estimation of the 235 U content was demonstrated and some of the practical problems encountered and the way in which they were overcome are discussed.

Fission-track registration in solid-state track detectors immersed in fissile-material solutions

Abstract Fission-track registration characteristics of some solid-state track detectors immersed in aqueous solutions of fissile materials have been studied. The track density registered on the detector is related to the number of fissions occurring per unit volume of the solution of fissile material. In view of the many possible applications of fission-track registration in solution, the factor, K wet , which gives a measure of the track-registration efficiency in solution and which directly relates the measured track density to the total number of fissions occurring per unit volume of a given solution of the fissile material, has been determined for some of the common track detectors. The values of K wet for Lexan, Makrofol-E, Melinex-O and Mica are (8.1±0.2)10 −4 cm, (6.1±0.1)10 −4 cm, (8.9±0.3)10 −4 cm, and (7.8±0.2)10 −4 cm, respectively. Preliminary studies on the effect of neutron irradiation of the detectors on the values of K wet have been carried out, and there is a general decrease in the value of K wet for irradiated plastics compared to non-irradiated plastics. The usefulness of this factor in the development of a versatile neutron-flux monitor and for the determination of absolute fission yields is discussed.

Stabilisation of tetravalent cerium in perchloric acid medium and measurement of the stability constants of its fluoride complexes using ion selective potentiometry

The stability constants of the fluoride complexes of cerium(IV) in 1 M (HClO(4), NaClO(4)) medium have been measured potentiometrically using a fluoride ion-selective electrode. Quantitative oxidation of cerium to its tetravalent state and its stabilisation in the perchlorate medium were accomplished by oxidation with AgO followed by quick addition of a known amount of fluoride ion. This procedure ensures stability of the oxidation state and prevents hydrolysis and polymerisation of Ce(IV). Logarithms of the average values of beta(1), beta(2), beta(3) and beta(4) were estimated to be 7.57+/-0.04, 14.50+/-0.03, 20.13+/-0.37 and 24.14+/-0.10 respectively.

Modified pyrohydrolysis apparatus for the separation of fluorine and chlorine trace impurities from nuclear fuel samples for quality control analysis

A quartz pyrohydrolysis apparatus designed for the safe handling of pyrophoric carbide nuclear fuel samples while separating C1 and F trace impurities for quality control analysis is described. It has several advantages over the commonly used pyrohydrolysis apparatus. Performance of the apparatus during routine analysis of a large number of nuclear fuel samples has been found to be quite satisfactory.

Nuclear track registration from solution media: Alpha track registration in solid state track detectors in solutions of actinides

Abstract The results are reported of a study on various aspects of registration and revelation of alpha tracks in the three most commonly used cellulose nitrate detectors (namely LR 115, Ca 80-15 and Daicel) immersed in solutions of actinide elements. Americium, plutonium and enriched uanium in dilute nitric acid solution were used as alpha sources. Experimentally determined values of Kwet (a measure of the efficiency of track registration from solution) are around 2–5×10−4 cm for the three detectors under various conditions of exposure and etching. These values have been examined in the context of the range of the particle, its energy loss rate in the solution medium and the sensitivity of the detectors. Optimum conditions of track registration and revelation for the analytical applications of the technique have been experimentally established. Linear relationships were obtained between the concentrations of uranium or plutonium in the solution and the number of tracks per cm2 obtained under uniform experimental conditions of exposure and etching.

Application of track registration technique in the estimation of fissile materials: Analysis of uranium in rock samples

Abstract The track registration technique has been employed in the estimation of trace quantities of uranium in rock or ore samples either from their solution or directly from the powdered materials themselves by registering nuclear tracks on dielectric plastic detectors. In the first case, the method of standard addition was adopted to eliminate the matrix effect. By this method, uranium in the ng/ml range could be estimated with a precision of 2%. Based on the experience gained from this work some of the precautions necessary for getting precise data are recommended. Various aspects concerning the estimation of uranium directly by registering spontaneous alpha and induced fission tracks from the powdered matrix itself without taking recourse to the dissolution step are discussed. By a comparative study of fission track registration from a solution of fissile material (uranium) and a powdered rock sample, a factor, K p , which gives a measure of the track registration efficiency in powdered rock was evaluated. For a typical rock powder the value is (6.67±0.46)×10 −4 g/cm 2 for Lexan detector. The applications and significance of this factor are also discussed.

Studies on fluoride complexing of hexavalent actinides using a fluoride ion selective electrode

Complex formation between actinide(VI) and fluoride ions in aqueous solutions has been investigated using a fluoride ion selective electrode (F-ISE). As fairly high acidity was used to suppress hydrolysis of the actinide(VI) ions, significant liquid junction potentials (Ej) existed in the systems. An iterative procedure was developed for computing free hydrogen ion concentration [H+], as it could not be measured directly, using data obtained with F-ISE. Ej values were estimated from known [H+] and the stability constants of fluoride complexes of actinide(VI) ions were calculated following KING and GALLAGHERs method using a computer program. The stability constants were found to follow the order U(VI)>Np(VI)>Pu(VI).

Determination of sulphur species in the presence of common anions with indirect measurement of sulphide by ion chromatography (IC)

ABSTRACT A two-step ion chromatographic method for the determination of sulphur containing anions with indirect measurement of sulphide in the presence of common anions in tannery wastewater has been developed. In the first step, species like , , and SCN− are separated isocratically on an anion exchange separator column using the mobile phase mixture solution and quantified by conductivity detection. The total sulphate equivalent of all these species is then calculated. In the second step, in another aliquot of the sample, all the sulphur species are converted into sulphate using ammoniacal hydrogen peroxide and quantified as sulphate. The amount of sulphide is then arrived at by subtracting the total sulphate equivalent obtained in the first stage from the total sulphate obtained in the second step. The detection limits for all the ions are less than 0.5 ppm with reproducibility of better than 10%.

Application of fission track registration technique in the estimation of fissile materials

Analysis of fissile materials in solution by fission track registration technique has been extended to plutonium in solution of its alloys. In these estimations, the results agreed within 1–4% with the average of those obtained by other chemical and instrumental methods like potentiometry, mass-spectrometry and X-ray fluorescence. Some special practical problems encountered in the analysis of plutonium solutions are noted. Various factors affecting the results have been investigated and the necessary precautions for reducing these errors have been indicated. The advantages of the method over some other conventional methods have also been discussed. It is suggested that a source of about 10 μg of252Cf corresponding to a neutron flux of about 107 n·cm−2·sec−1 is ideal for these experiments.

A critical review on the stability constants of the fluoride complexes of actinides in aqueous solution and their correlation with fundamental properties of the ions

Literature data on the stability constants of the fluoride complexes of the actinides in different oxidation states have been compiled. In order to have a reasonable inter-comparison, the stability constant (β1) values obtained in diverse ionic strength media are converted to so called thermodynamic stability constants, β10 using the DAVIES equation (a modification of Debye-Huckel equation). A correlation of the β10 values with the fundamental properties of the actinide ions using various models available in the literature has been attempted. Using the values of inonic radii and best available values of the stability constants of a large number of metal ions from recent compilations a comparative study of the various models or relations available in the literature has been tried. For metal ions in general, the semi-empirical relation recently developed by BROWN, SYLVA and ELLIS (BSE equation)_gives the best correlation. In an attempt to accommodate the unusual trend in the stability constants of the tetravalent actinides a modification in a parameter of the BSE equation has been proposed. Good agreement between the theoretically calculated and experimentally determined values for actinides in different oxidation states is obtained in most of the cases. Further improvements in theoretical relation as well as experimental data are required for better correlation.