Targeted alpha therapy (TαT) represents an emerging and cutting-edge treatment option for patients dealing with highly challenging metastatic cancer diseases. Critically, the limited supply of alpha-particle-emitting radionuclides, so-called alpha in vivo nanogenerators, hampers wider utilization of TαT in clinical settings. This could effectively be circumvented by alternative production routes, including straightforward purification and reformulation strategies. Radionuclide generators offering great potential in simple and robust elution strategies can be provided that still adhere to high radioisotopic, radionuclidic, and radiochemical purity criteria. This study takes a first step towards novel separation strategies by providing additional sources of alpha in vivo nanogenerators for TαT through experiments with various metal surrogates. With different systems, 232Th/natBa was used as a radionuclide generator analogue to 227Th/223Ra, and 232Th/natBa/natLa was used as a triplet analogue to 229Th/225Ra/225Ac. Three selective resins (UTEVA, TEVA, DGA-N) were evaluated for the 232Th/natBa system. Two perturbations of the best-performing resin were further evaluated using a larger diameter column and 1 week of equilibration. For the 232Th/natBa/natLa separation system, a combined column with two selective resins (TK200, TK101) was employed and evaluated. The results thus obtained pave the way for alternative separation strategies in radioactive proof-of-concept validation in the near future.

In this study, Np(V) retention on Illite du Puy (IdP) was investigated since it is essential for understanding the migration behavior of Np in argillaceous environments. The presence of structural Fe(III) and Fe(II) in IdP was confirmed by Fe K-edge X-ray absorption near-edge structure (XANES) and 57Fe Mössbauer spectroscopy. In batch sorption experiments, a higher Np sorption affinity to IdP was found than to Wyoming smectite or iron-free synthetic montmorillonite. An increase of the relative Np(IV) ratio sorbed onto IdP with decreasing pH was observed by solvent extraction (up to (24 ± 2)% at pH 5, c0(Np) = 10-6 mol/L). Furthermore, up to (33 ± 5)% Np(IV) could be detected in IdP diffusion samples at pH 5. Respective Np M5-edge high-energy resolution (HR-) XANES spectra suggested the presence of Np(IV/V) mixtures and weakened axial bond covalency of the NpO2+ species sorbed onto IdP. Np L3-edge extended X-ray absorption fine structure (EXAFS) analysis showed that significant fractions of Np were coordinated to Fe─O entities at pH 9. This highlights the potential role of Fe(II/III) clay edge sites as a strong Np(V) surface complex partner and points to the partial reduction of sorbed Np(V) to Np(IV) via structural Fe(II).

Bentonite is planned to be used as a backfill material in deep geological repositories (DGR) notably for those to be established in crystalline rock. Potential erosion processes have to be clearly understood in order to properly assess its long-term barrier function. A likely scenario over the lifetime of a DGR in certain geographical locations is the intrusion of low mineralized glacial melt water through low transmissivity bedrock fractures that could interact with bentonite and favor release of clay colloids. The objective of this work was to determine the dynamic of erosion under a glaciation scenario for Na-exchanged, Na-Ca-exchanged, Ca-exchanged and raw bentonite. The different bentonite types cover different potential materials used for backfill and different stages of cation loading via cation exchange processes upon contact with groundwater of different composition. To this end, erosion experiments were carried out with highly compacted bentonite confined by a porous filter (20 mu m) under dynamic conditions simulating the presence of a hydraulically active fracture filled with fault gauge and fracture filling minerals. The < 500 mu m size fractions of untreated MX80 bentonite and after Naor Ca-homoionization, were used. Two compacted clay pellets (1.6 +/- 0.1 g/cm(3)) of identical composition were placed in separate compartments of double-side reactors. Post-mortem visual inspection and the observed washout of water soluble MX80 components indicated full equilibration of the bentonite with simulated groundwater taking place during the experiment. The erosion was investigated by circulating a low ionic strength (1.6 10(-3) M) water at pH 8.4. Bentonite swelling was confined by stainless steel filter plates. The erosion (clay colloid detachment) via a low mineralized groundwater flow was quantified by determining an average eluted mass loss rate (AMLR). AMLR values integrated over 1466 days (4 years) erosion time for the raw MX80 bentonite, the Na-MX80 and the Na-Ca-MX80 are at 0.019 +/- 0.003 kg/y/m(2), 0.245 +/- 0.007 kg/y/ m(2) and 0.10 +/- 0.02 kg/y/m(2), respectively. Only by the sensitive ICP-MS analysis of clay-bound Th and U a tiny detachment of particles from Ca-MX80 could be identified, which shows the highest resistivity against erosion (0.004 +/- 0.002 kg/y/m(2)). The experiments pointed to the swelling pressure as main driving force for colloid generation. A possible inhibiting effect of accessory minerals on erosion can also be deduced from this study. Assuming erosion via a groundwater flow from a single fracture intersecting a deposition hole filled with raw MX80 bentonite at an angle of 90o and with a fracture aperture of up to 200 mu m, the present estimations indicated that under the given scenario the mass loss limit of 1200 kg bentonite will not be reached during the first 106 years.

The multiactinide analysis with accelerator mass spectrometry (AMS) was applied to samples collected from the run 13-05 of the Colloid Formation and Migration (CFM) experiment at the Grimsel Test Site (GTS). In this in situ radionuclide tracer test, the environmental behavior of 233U, 237Np, 242Pu, and 243Am was investigated in a water conductive shear zone under conditions relevant for a nuclear waste repository in crystalline rock. The concentration of the actinides in the GTS groundwater was determined with AMS over 6 orders of magnitude from ∼15 pg/g down to ∼25 ag/g. Levels above 10 fg/g were investigated with both sector field inductively coupled plasma mass spectrometry (SF-ICPMS) and AMS. Agreement within a relative uncertainty of 50% was found for 237Np, 242Pu, and 243Am concentrations determined with the two analytical methods. With the extreme sensitivity of AMS, the long-term release and retention of the actinides was investigated over 8 months in the tailing of the breakthrough curve of run 13-05 as well as in samples collected up to 22 months after. Furthermore, the evidence of masses 241 and 244 u in the CFM samples most probably representing 241Am and 244Pu employed in a previous tracer test demonstrated the analytical capability of AMS for in situ studies lasting more than a decade.