Browsing by Author "Tkaczyk, Alan H."

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Assessment of NORM in bauxite residue to facilitate valorization
(2nd Bauxite Residue Valorisation and Best Practices Conference, 2018) Goronovski, Andrei; Tkaczyk, Alan H.
In the new Euratom Basic Safety Standard (BSS), materials with elevated concentrations of natural radionuclides can be considered as a potential source of radiological exposure. Such materials are often found in mining and metal extractive industries, where natural radionuclides are likely to end up and accumulate in the residue streams. Radiological assessment of the produced residues is a first and often sufficient step to demonstrate worker safety against radiological exposure. Bauxite Residue (BR) is an example of a material which has an elevated natural radionuclide concentration. BR used in this work is coming from Greece and was assessed to be below the BSS reference levels and therefore does not pose a significant risk of elevated radiological exposure. The processing of BR might result in further radionuclide accumulation in secondary residues, which also should be characterized to demonstrate the radiological safety of workers. In this work, the radiological properties of the residues produced after applying different extractive techniques for the recovery of iron, alumina and Rare Earth Elements (REE) were examined. All the analyzed samples were produced at the laboratory scale. The results suggest that for these residues, there is no significant radionuclide accumulation which would cause potentially elevated radiological exposure.
Development and computational fluid dynamics (CFD) simulation of cryostat thermal shielding for a portable high purity germanium (HPGe) gamma spectrometer
(Taylor&Francis, 2020) Malgin, Vladislav; Tkaczyk, Alan H.; Yakovlev, Oleg; Jeltsov, Marti; Priimägi, Priit
The effect of vacuum degradation in cryostat of a gamma spectrometer on the steady-state temperature of thermal shield and its efficiency are analyzed in this study. Considering the thermal load due to radiation, the thermal conductivity of residual gases and shield supports, the steady-state temperature of the shield is determined based on the differential energy balance equation for a simplified thermal model of the cryostat. A more complex model corresponding to the design of a real cryostat is simulated using computational fluid dynamics. The obtained temperature distribution is presented. The simulated results are compared with experimental data measured on an operating cryostat with a cryocooler in the temperature stabilization mode. The same measurements were carried out for a cryostat with and without a thermal shield, as well as with multilayer insulation. The obtained results confirm that the thermal shield provides decreasing heat transfer even for a vacuum degradation in a cryostat
Development and validation of a CFD-enabled digital twin of a portable HPGe gamma spectrometer
(IOP Publishing, 2020-01-22) Jeltsov, Marti; Priimägi, Priit; Malgin, Vladislav; Takovlev, Oleg; Tkaczyk, Alan H.
This paper presents the design of an easily portable spectrometer using high purity germanium (HPGe) detector – HandSpec. The key challenge in the design of a lightweight spectrometer is to minimize its heat losses so that efficient electric cooling could be used instead of bulky dewars. The design process has been largely based on experimental investigations. In this study, a digital twin of the HandSpec cryostat using computational fluid dynamics (CFD) method is developed to support the design and optimization of the physical prototype.