Volume 89, Issue 3 -

The luminescence lifetimes of An(III) and Ln(III) ions [An=Am and Cm; Ln=Nd, Sm, Eu, Tb and Dy] were measured in dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF), methanol(MeOH), water and their perdeuterated solvents. Nonradiative decay rates of the ions were in the order of H 2 O > MeOH > DMF > DMSO, indicating that O-H vibration is more effective quencher than C-H, C=O, and S=O vibrations in the solvent molecules. Maximal lifetime ratios τ D /τ H were observed for Eu(III) in H 2 O, for Sm(III) in MeOH and DMF, and for Sm(III) and Dy(III) in DMSO. The solvent composition in the first coordination sphere of Cm(III) and Ln(III) in binary mixed solvents was also studied by measuring the luminescence lifetime. Cm(III) and Ln(III) were preferentially solvated by DMSO in DMSO-H 2 O, by DMF in DMF-H 2 O, and by H 2 O in MeOH-H 2 O over the whole range of the solvent composition. The order of the preferential solvation, i.e., DMSO > DMF > H 2 O > MeOH, correlates with the relative basicity of these solvents. The Gibbs free energy of transfer of ions from water to nonaqueous solvents was further estimated from the degree of the preferential solvation.

Improved correlations using the 238 Pu/( 239 Pu + 240 Pu) alpha activity ratios determined alpha spectrometrically and the different atom ratios viz. 240 Pu/ 239 Pu, 241 Pu/ 239 Pu and 242 Pu/ 239 Pu determined mass spectrometrically are presented for Pu produced in Pressurised Heavy Water Reactors (PHWRs). These correlations are useful to obtain the different atom ratios, with reasonable accuracy (1 to 10% depending upon the atom ratio), using only the 238 Pu/( 239 Pu+ 240 Pu) alpha activity ratio determined alpha spectrometrically from a plutonium sample purified from 241 Am. Since the correlations involve the relative values and not the absolute values of the atom% abundance of any specific isotope, the accuracy of the data obtained using these correlations is much better. In addition, the change in the atom% abundance of 241 Pu due to the relatively short half-life of 241 Pu (14.4 yr) does not create any ambiguity in the ratio 242 Pu/ 239 Pu and hence the accuracy of data for 242 Pu is not affected by the uncertainty in the data for 241 Pu.

Atom numbers of 239 Np and 239 Pu, which had been produced by the neutron capture reaction of 238 U in the uranium solution of the JCO criticality accident at Tokai-mura, Japan, were determined precisely by a radiochemical method. It was found that the measured atom ratio of 239 Np/ 239 Pu at termination of the criticality depends sensitively on the history of the neutron capture reaction during the accident (about 20-hours continuance). The history was evaluated by comparing the measured value and those calculated by a burnup calculation code. The percentage of the number of the neutron capture reaction at the initial stage of the criticality during 25 min against the total events was determined to be 24±6%.

Differential pulse voltammetric (DPV) technique has been developed for the simultaneous determination of the elements in Tc(VII)-U(VI) and U(VI)-Cr(VI) mixtures in alkaline solutions. The method gave a precision of about 14% to 2% in the range of 1×10 -7 --1×10 -4 for Cr(VI) and Tc(VII) and 1×10 -6 --1×10 -4 for U(VI). The detection limits are 8×10 -8 mol l -1 for Tc(VII) and 3× -7 mol l -1 for Cr(VI), and 8×10 -7 for U(VI). It has been established that Tc(VII) could be determined in the presence of about 350 excess fold U(VI). The reduction of Tc(VII) with hydrazine has been suggested to eliminate the effect of Tc(VII) ions on the U(VI) determination. U(VI) has been determined in the presence of Cr(VI) up to molar concentration ratio U(VI)/Cr(VI)=1:1, while Cr(VI) could be determined in the presence of U(VI) in the solutions with up to molar concentration ratio Cr(VI)/U(VI)=1:15. The reliability of the determination of the elements of Tc(VII)-U(VI) and U(VI)-Cr(VI) mixtures in alkaline solution has been tested by a standard addition method.

The isolation of the fission product cesium from high-level alkaline liquid waste is studied with inorganic ion-exchange materials. High separation and concentration factors can be obtained using sodium silicotitanate (CST). The leaching behaviour of cesium from CST was studied in clay porewater and Quinary brine at 90 °C. It is shown that cesium leaching in Quinary brine can be drastically reduced by thermal treatment of cesium loaded CST above 1000 °C. To this end, neutralisation of the ion exchange material before heating is required in order to reduce cesium volatility. It is concluded that CST is a good candidate material for geological disposal of the fission product cesium.

The crown ether strontium extraction(CESE) process for partitioning strontium from HLLW was studied. A hot test was carried out in a counter current mode with genuine HLLW by using a miniature centrifugal contactor set. 0.1 mol/L DCH18C6 in 1-octanol was used as extractant. The feed solution was the HLLW raffinate of TRPO process after removing TRU elements. Acidity of the feed was 1.45 mol/L HNO 3 . In the hot test 10 extraction stages and 2 scrubbing stages were used in the extraction section. Four stripping stages were used in the backextraction section. The results of the hot test were very attractive. More than 99.96% of strontium were extracted from the feed solution and above 99.84% strontium was stripped out of the organic phase. Non of the TRU elements was extracted with strontium by the extractant. Only about 0.4% of Cs were extracted and found in the Sr stripping stream. The hot test result proved that the CESE process was a promising process to remove strontium from HLLW.

The emission of uranium and ruthenium oxides from overheated nuclear fuel is a complex phenomenon which depends on the fuel matrix, on temperature, on the oxygen potential of the amosphere in contact and on the emission sequence. All these factors influence the properties of particles before their dispersion in the reactor containment building and in the environment: these properties are, among others, surface composition, particle size, and, as a consequence, weathering rates in the environment. Emission in air increases the solubility of U-oxides mainly. This first paper describes the main physico-chemical characteristics of condensation particles released by overheated U and Ru oxides mixtures, in small-scale laboratory simulations.

The ability of Resonance Ionization Mass Spectrometry (RIMS) to reliably determine the ratio of 135 Cs/ 137 Cs in the presence of large backgrounds has been evaluated. Single-resonance excitation of Cs 6s 2 S 1/2 (F=4)→6p 2 P 3/2 (F'=5) with an extended cavity diode laser was followed by photoionization with the 488 nm line of an argon ion laser. While the principal objective was to avoid isobaric interferences, an optical selectivity of 3 orders of magnitude against stable 133 Cs was attained for both 135 Cs and 137 Cs. The overall RIMS efficiency was found to be ∼ 2×10 -6 with a combined (laser and mass spectrometer) selectivity of ∼ 10 10 for both 135 Cs and 137 Cs against 133 Cs. The performance with respect to efficiency, selectivity, and isobar suppression has been compared to conventional thermal ionization mass spectrometry (TIMS). Measurements to determine the chronological age of a burn-up sample have been performed using both methods.

The lack of published data on the extraction kinetics of Tc(VII) in the system U(VI)/HNO 3 //TBP/dodecane prompted us to investigate its transport behaviour in detail. The aim was to improve the U(VI)/Tc(VII) separation in the PUREX process. We choose the method of analytical ultracentrifugation to determine the concentration gradient profile, the initial flux density and the integral mass transport for both sides of the unstirred liquid-liquid interface as well as the overall mass transfer coefficients as a function of Tc(VII)-, U(VI)-concentrations and temperature from time-dependent changes of the refractive index gradients. The results were supplemented by comparing the experimental with calculated concentration profiles, obtained by modeling a diffusion-limited extraction process. In some of the investigated systems, the transport at the interface is reaction-limited after phase contact. The determined values of J max , I, and α are discussed in terms of the extraction conditions.

The monitoring and evaluation of the radioactivity levels around the Egyptian nuclear facilities located at Inshas, near Cairo, namely, two research reactors, an R & D fuel fabrication laboratory and a fuel fabrication pilot plant, were carried out. Soil, water and plant samples were collected from locations near and around the facilities and analyzed by using gamma, laser and alpha spectrometry. A preoperational radiological map for the new reactor site was established. The results of the postoperational monitoring around the first reactor show that the 38year operation of this reactor did not increase the radioactivity level around the facility. The observed man-made 137 Cs was found to be (0.3-9.2 Bq/kg) and 239+240 Pu 0.096-0.158 Bq/kg. The observed tritium was found to be in the range 0.6-1.48 Bq/L. The absorbed dose rate and radium equivalent are calculated and presented.