G. H. Rizvi

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.

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).

Extraction of actinides with tropolone

The partition coefficient of tropolone in xylene, dichloroethane and chloroform was determined from 0.05M HCl medium. The values obtained were 5.6, 25.5 and 43, respectively. In the extraction of UO22+ using tropolone (HT) in xylene from an aqueous medium of ionic strength 0.05, the species UO2T2·HT was established. The species extracted in presence of a neutral donor was found to be UO2T2·S[S+dioctyl sulfide (DOS), dibutylhexanamide (DBHA), tri-n-butyl phosphate (TBP), dioctyl sulfoxide (DOSO), and tri-n-octylphosphine oxide (TOPO)]. The equilibrium constant of complex formation between the self-adduct and the neutral donor was calculated and was found to follow the basicity order (DOS«DBHA<TBP<DOSO»TOPO). The thermodynamic parameters of the adduct UO2T2·DOSO were also calculated by the temperature coefficient method. The values of free energy, enthalpy and entropy changes obtained were −1.26 kJ·mol−1, −1.98 kJ/mol and −2.5 J·mol−1·deg−1, respectively.

Potassium ferrocyanide as a spectrophotometric reagent for the determination of uranium

Potassium ferrocyanide gives a colour reaction with U(VI), which is suitable for its determination. The complex absorbs in the wavelength range of 390–397 nm. The optimum pH range for colour development was 1.5–3.5. The molar absorptivity was found to be 4.65·103 1·mol−1·cm−1. Most of the anions up to 1000 μg did not interfere. The method was made selective by extracting U(VI) first with DOSO from the mixture of interfering cations from 1–2M HNO3 medium and then determining uranium in the back-extracted solution by developing the colour with ferrocyanide. 20 μg/10 ml of U(VI) in the final solution could be satisfactorily determined within an RSD of ±2%.

Determination of nitrogen in UO2 by Kjeldahl spectrophotometry

A method for the dissolution of sintered UO2 samples and the determination of ammonium ions in the solution by spectrophotometry for the chemical quality control of UO2 fuel for nitrogen is described. The acid mixture used simplifies the problem of recovery of uranium from the waste generated during the analysis of nitrogen. Nitrogen content in ppm in the sintered UO2 samples is determined within an RSD of 10%.

Determination of the stability constant of Np(V) fluoride complex using a fluoride ion selective electrode

Fluoride complexing of Np(V) has been studied using fluoride ion selective electrode (F-ISE). Free fluoride ion concentrations in the presence of Np(V) were measured at 0.1 and 1.0M ionic strength. The data were used to calculate the stability constant of the fluoride complex of Np(V) and the values obtained are reported here.

EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF URANIUM/VI/ WITH TROPOLONE

Tropolone reacts with uranium/VI/ and forms orange yellow precipitate extractable in chloroform. The maximum absorption occurs at 405 nm and the absorbance is found to remain constant in the pH range of 5.5 to 7.0. Beers law is obeyed upto 37.6 ppm of U/VI/. The sensitivity of the colour reaction is 0.034 μg cm−2. Most of the common ions do not interfere. The method becomes more selective by masking some of the interfering cations with EDTA. The method was applied to determine uranium in monazite sand.

Anion exchange separation and determination of yttrium in uranium oxide — Yttrium oxide mixture

A procedure has been developed for quantitative separation of yttrium from uranium by anion exchange from nearly saturated NH4Cl solution in 0–2N HCl medium. Apparently no organic matter is leached out during the separation as yttrium could be determined by EDTA titration without resorting to fuming with perchloric acid before titration. The precision obtained in the analysis of yttrium in a mixture containing about 12 mg of yttrium and about 300 mg of uranium was ±0.3% (27 determinations).

A CONDUCTIVITY METHOD FOR COMBINED CARBON AND FREE CARBON DETERMINATION IN URANIUM CARBIDE

A conductivity method based on differential temperature oxidation of combined carbon and free carbon has been worked out for their determination in uranium carbide employing purified air for oxidation. The combined carbon determined at 550°C and free carbon at 900°C were found to be 4.58% and 0.27% with a precision of 2% and 11%, respectively. The free carbon determined by the present method and that by dissolution followed by conductivity method agreed within ±5%. Effect of temperature and time on the oxidation of free carbon /taken as graphite/ in air atmosphere was also studied.

ON THE USE OF HYDROGEN PEROXIDE AS A MASKING AGENT FOR THE DETERMINATION OF YTTRIUM IN URANIUM OXIDE - YTTRIUM OXIDE MIXTURE

Use of hydrogen peroxide as a masking agent for uranium during the EDTA titration of yttrium in an yttrium-uranium mixture containing large amounts of uranium has been investigated. High acetate ion concentration was necessary to keep the peroxy complex of uranium in solution during the titration. It has been observed that upto 500 mg of uranium could be tolerated in the determination of yttrium with 0.5 ml of 30% hydrogen peroxide in {lM acetate medium. The precision and accuracy of the method based on 16 determinations of yttrium at 6–16 mg level in presence of 300 mg uranium has been found to be ±0.2%.