The neutron imaging instrument TRIXIE is located at one of the horizontal beamlines of the research reactor LVR-15 in the Czech Republic. Before the construction of the TRIXIE instrument, the beamline was not equipped with a collimator; therefore, a new collimator had to be designed and implemented. The beamline was initially equipped with a meter-long single-crystal silicon filter. But, because of the lack of space in the beam (the size of the original filter limited the space for the collimator) and because the beamline needs to be filtered (the spectrum of an empty beamline roughly copies the reactor spectrum, with a high ratio of fast neutrons and gamma rays), a new filter had to be designed as well. The optimisation process of calculations of the collimator and filters of different materials and thicknesses was performed using the Monte Carlo calculation code MCNP. After the installation of the collimator and filters into the beamline, a series of measurements was performed to confirm the calculated results and to characterise the neutron beam.
The Research Centre Řež operates the LVR-15 reactor, where storage pool B is used for long-term storage of irradiated materials, mainly aluminium and steel. Corrosion of these materials leads to elevated concentrations of iron and aluminium in the pool water. This work investigates the use of pressure-driven membrane filtration (3.0–0.22 µm), employing two types of membranes—MCE (mixed cellulose ester) and nylon membranes—to reduce these concentrations under different pH conditions and with increased iron levels in order to evaluate colloid formation and separation efficiency.
Uranium dihydride UH2 is a metastable phase unknown in bulk form but accessible through thin-film synthesis. We prepared UH2 films by reactive dc sputtering on CaF2 (001) or Si(001) substrates, the latter equipped with a Mo buffer layer to suppress a U-Si interdiffusion. On CaF2, UH2 adopts the fluorite-type structure with a near[1 11] out-of-plane texture, four rotational domains, and a lattice parameter a = 539 +/- 3 pm without measurable strain, whereas the Mo-buffered film is polycrystalline. X-ray photoelectron spectroscopy confirmed complete hydrogenation and minimal oxidation. Magnetization and XMCD measurements show ferromagnetic ordering with Curie temperatures of 120-130 K and a uranium 5f moment of approximate to 0.9 mu B/U, dominated by the orbital contribution (mu L approximate to 1.4 mu B, mu S approximate to -0.5 mu B), in a good agreement with GGA + U computations, which otherwise overestimate absolute values of the spin and orbital components. The slightly reduced moment in thinner CaF2-supported films is attributed to surface U(IV) species. These results demonstrate that thin-film synthesis enables stabilization of UH2 and direct probing of 5f magnetism, opening pathways toward higher uranium hydrides and interface-engineered actinide systems.
Within the framework of extending the lifetime of nuclear facilities, an experiment of accelerated radiation ageing of one of the key components of the nuclear power plant, biological shielding concrete, was performed. Short-term irradiation of nine little concrete samples was executed at the LVR-15 research reactor in Řež near Prague. After the irradiation; the gamma emissions were measured using HPGe detector, samples activities were determined by Genie−2000 software and compared with estimates calculated by MCNP and FISPACT-II software packages. Input data originated from SEM–EDS analysis of the concrete specimen. Measured and calculated gamma spectra differed considerably in most of the experiments. Discrepancy between measured and predicted values of gamma activity or equivalent dose was caused probably due to insufficiently described material. For radionuclides Fe-59 and Sc-47 the measured-to-calculated activity ratio yielded to 0.6 and 2.1. Long-term experiments discovered that the highest activity belongs to Ca-45 and Fe-55.
Pile noise experiments in current mode were successfully conducted on the 37-fuel-assemblies core configuration of the LR–0 reactor operated by the CV Rez (Czech Republic). The experimental prompt decay constant (αp) was found equal to 244.0 ± 8.3 s−1, the effective delayed neutron fraction (βeff) equal 712 ± 15 pcm, and the generation time (Λ) was derived at 29.17 ± 1.2 µs. All uncertainties are equal to one standard deviation. The effective delayed neutron fraction was derived using a Diven factor computed at 0.875 with TRIPOLI-4.12. A bootstrap method was extensively applied on data to derive the kinetic parameters. Namely to compute the uncertainties on the power spectral density spectra, and throughout the data fitting procedure. The differences with MCNP6.1 and ENDF/B-VIII.0 nuclear data library are equal to −1.6 ± 3.4 % and +0.23 % ± 2.19 % on αp and βeff, respectively. These results are analysed in the light of several other pile noise experiments.
