Volume 93, Issue 6 -

We measured activation cross sections via γ-ray spectroscopy using high-purity germanium detectors for 16 reactions induced by (14.4 ± 0.2) MeV neutrons on isotopes of tin. The cross sections are: Two 112 Sn targets enriched to 62.5% and 84%, respectively, were used for these measurements in addition to the natural tin. The cross sections were compared with experimental data found in the literature, with published empirical formulae and with model calculations including also the pre-equilibrium contribution. For reactions which do not involve protons from below the closed Z = 50 shell, the agreement to the data is reasonable, it is somewhat weaker for the ( n , p ) reactions and still worse in the case of ( n , α), where, however, the pre-equilibrium component is not described properly by the models included so far. The possibility of production of 111 Sn → 111 In generator system is considered.

The extraction equilibrium and kinetics of uranium(VI) from aqueous nitric acid with bis(octylsulfinyl)methane (BOSM) in 1,1,2,2-tetrachloroethane extraction has been studied. The extracted species was established to be UO 2 (NO 3 ) 2 ·2BOSM. The extraction process rate is controlled by the following reaction: The change in enthalpy associated with the extraction reaction was established to be −22 ± 3 kJ/mol.

The sorption of uranium(VI) ions onto PAN loaded PUF has been investigated. Quantitative sorption of uranium(VI) onto PAN loaded PUF was achieved after 30 minutes equilibration time from pH 7 buffer solution. The sorption data followed Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. Langmuir parameters Q = 45.3 ± 0.2 μmol g −1 and b = (76.2 ± 0.2) × 10 3 dm 3 mol −1 , Freundlich constants 1/ n = 0.21 ± 0.01 and K F = 229 ± 21 μmol g −1 and D–R parameters β = −0.0015 ± 0.00005 kJ 2 mol −2 , X m = 72.23 ± 3.11 μmol g −1 and E = 18.3 ± 0.3 kJ mol -1 have been evaluated. The variation of sorption data with temperature gives Δ H = 176 ± 5 kJ mol −1 , Δ S = 626 ± 17 J mol −1 K −1 and Δ G = −10.6 ± 0.7 kJ mol −1 at 298 K. The positive value of enthalpy (Δ H ) and negative value of free energy (Δ G ) show endothermic and spontaneous nature of sorption respectively. A number of solvents were tested to elute the uranium-PAN complex from the PAN loaded PUF, only amine solvents and cyclohexanone have the capability to desorb the complex. The sorption mechanism has been discussed.

A problem with plutonium in sorption studies is its tendency to occur in a mix of oxidation states. This work was a study of the sorption of plutonium on the solid phase UO 2 — in a perchlorate medium as a function of pH — where plutonium is kept in its trivalent oxidation state. Experiments also showed that uranium(IV) oxide can reduce Pu(IV) to Pu(III) in an acidic solution and maintain it in that state. It was observed at the same time that the chemically inert solid phases TiO 2 and ThO 2 possibly increase the rate of disproportionation of Pu(IV) at a pH of about 0.5. In accordance with previous studies MnO 2 was found to have an oxidizing effect, converting Pu(IV) into Pu(VI). A comparison is made between the sorption of Th(IV), Pu(III) and Co(II) on UO 2 and TiO 2 , and Pu(VI) on TiO 2 .

The solubility of uranium(IV) hydrous oxide was measured at 25 °C in NaClO 4 solution containing Na 2 S 2 O 4 as a reducing agent in the pH range from 12 to 14. The experiment was carried out from oversaturation at I = 0.5, 1.0 and 2.0 mol/dm 3 (M). The solubility data were analyzed to obtain the hydrolysis constants (β m ) of U(OH) m (4-m) . By taking the specific ion interaction theory (SIT) for ionic strength corrections and by using the solubility product log K sp ° = −53.93 ± 0.20, the hydrolysis constants at I = 0, log β 5 °<48.10 and log β 6 ° = 48.95 ± 1.01, were determined together with the ion interaction coefficients of U(OH) 5 − and U(OH) 6 2− .

In this work a hot demonstration of the DIAMEX process using the new reference molecule DMDOHEMA (N,N ′ -DiMethyl-N,N ′ -DiOctylHexylEthoxyMalonAmide) and genuine high-level PUREX raffinate as feed is reported. The continuous counter-current experiment was carried out in a 16-stage centrifugal extractor battery, installed in a hot cell. In order to produce a representative High Level Liquid Waste (HLLW) a PUREX process was applied on dissolved fuel using the same equipment. It was demonstrated that 5 extraction stages were sufficient to achieve feed decontamination factors above 2200 and 320 for Am and Cm, respectively. Co-extraction of molybdenum and zirconium, as well as of palladium, were efficiently prevented using oxalic acid and HEDTA scrubbing, respectively. However, technetium, yttrium, and to some extent ruthenium, were co-extracted. The back-extraction proved to be very efficient, yielding in 4 stages more than 99.9% recovery of Am and Cm. The extraction profiles were modeled with computer code simulations and the results compared with data obtained from an experiment using the former reference molecule DMDBTDMA (DiMethylDiButylTetraDecylMalonAmide).

The efficiency of Minor Actinides (MA) recovery in the DIAMEX process has already been demonstrated using High Active Raffinate (HAR). The next step aims at the demonstration of reprocessing from High Active Concentrate (HAC) as feed, in view of an industrial application. The volume reduction would reduce the size of the installation to be used and thereby the costs of the process. The first step towards the demonstration of a DIAMEX process using HAC is the production of the genuine solutions. In the hot cell facility of ITU (Institute for Transuranium Elements), a HAR solution has been prepared, from small scale PUREX reprocessing of MOX fuel, and successfully subjected to a concentration/denitration process to obtain HAC. A final concentration factor (CF) of about 10 and an acidity of 4 M were reached. In the experiment a precipitate mainly composed of Sr, Zr, Mo, Sn and Ba was formed. MA precipitation was not significant (< 0.001%).

The transport and partitioning of 129 I has been examined for a shallow groundwater flow system at Sturgeon Falls in northeastern Ontario. Recharge into a sandy surficial postglacial deltaic aquifer occurs in the vicinity of a seasonally-wet boreal forest. Concentrations of stable iodine, 129 I, tritium, radiocarbon, stable isotopes and major ions were measured on samples of groundwater and precipitation. The present-day tritium profile delineates the position of the early 1960's above-ground nuclear weapons pulse at a depth of approximately 12 m. The concentrations of stable iodine for groundwaters above, near and below the above-ground nuclear weapons pulse range from 0.07 to 1.7 ppb. Over that same interval 129 I concentrations decreased from 1.9 × 10 6 atoms/L at 9 m, to approximately 1.9 × 10 5 atoms/L in tritium-depleted waters at 35 m, below the present-day depth of the recharging above-ground nuclear weapons peak at approximately 12.7 m. No substantial increases in the levels of 129 I were evident in waters sampled near the location of the above-ground nuclear weapons peak. The 129 I values in the lower aquifer are 1 to 2 orders of magnitude greater than published estimates of pre-bomb 129 I (10 3 to 10 4 atoms/L), and indicate contribution of 129 I from the fissiogenic decay of 238 U in the basal granite bedrock or from leaching of 129 I from the aquifer grains. A precipitation sample collected at Sturgeon Falls had concentrations of stable iodine and 129 I of 0.2 ppb and 8.5 × 10 7 atoms/L, respectively. Concentrations of 129 I in Sturgeon Falls groundwaters are lower than those reported in other studies in central Canada, suggesting that the levels of 129 I in these groundwaters may have been attenuated by complexation or ion exchange with organic materials in the near-surface soil horizons. Such processes have been documented during a previous study on the behavior of 129 I in a shallow aquifer near a low-level, radioactive waste management area. Along a 30 cm soil profile at piezometer nest 28 at the Sturgeon Falls study site, the concentrations of 129 I ranged from approximately 4.3 × 10 8 atoms/g in the uppermost soil litter layer to 5.6 × 10 7 atoms/g in the siltier bottom soil horizons. Over that same profile, stable iodine varied from 4.7 ppm in the upper layers to 3.9 ppm in the lower layers.