Relevant Radionuclides Research Articles

Optimal shielding conditions for low level Ge detectors

We have determined the production yields for radionuclides in Al2O3, SiO2, S, Ar, K2SO4, CaCO3, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides 10Be, 14C and 26Al produced in quartz targets, 26Al in Al2O3 and S targets, 36Cl in K2SO4 and CaCO3 targets, and 53Mn in Fe2O3 targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ− capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ− capture, by fast muons and by neutron capture.

Colloid Properties in Granitic Groundwater Systems, with Emphasis on the Impact on Safety Assessment of a Radioactive Waste Repository

ABSTRACTSince colloids are present in all groundwaters, they are studied because of their potential role in the migration of relevant radionuclides in the geosphere. Colloid sampling and characterization campaigns have been carried out in the Grimsel area, Switzerland (Transitgas tunnel, Grimsel Test Site) and in the North Switzerland/Black Forest area (Menzenschwand, Bad Sickingen, Zurzach, Leuggem). On the basis of results obtained for 25 groundwaters a consistent picture is emerging. Colloids in granitic systems are basically composed of components of the aquifer materials (clay, silica). Under the hydrogeochemical conditions existing at depth in crystalline rock systems, colloid concentrations are not expected to exceed 100 ppb. However, under transient conditions when physical and/or chemical changes are occuring (e.g., hydrothermal activity), colloid generation may be enhanced. Colloid concentration of 10 ppm may be observed when the calcium concentration is low enough (<5 ppm).Whereas reversible sorption on the host rock leads to conservative predictions for radionuclide migration rates, the reverse is true for sorption onto colloids. The most conservative assumptions are therefore reversible nuclide sorption and colloid attachment on the rock and irreversible sorption on colloids.For calcium concentrations larger than 5 ppm, and sorption capacities at the nM level, their presence in granitic aquifer can be neglected in safety analyses when reversible sorption onto colloids is considered. This situation could change when sorption is followed by aggregation or incrustation processes. This study shows that for the colloid conservative size distributions found and for the granitic water conducting fissures considered, sorption-agglomeration reactions are unlikely to take place. Therefore, irreversible sorption by this mecanism is improbable.

Migration of Radionuclides: Experiments Within the Site Investigation Program at Gorleben

ABSTRACTExperiments concerning the sorption of radionuclides carried out on the site-specific unconsolidated sediments have been in progress in 6 laboratories since 1981 as part of the Gorleben site investigation program for the most relevant radionuclides. Sorption data are being determined for the site-specific conditions, and the influence of parameters, such as e.g. pH, Eh, complexing agents and NaCl concentrations is investicated. The data are necessary for the safety assessment of the repository. As the investigations have not yet been terminated, the results represent a preliminary state.