Študija izvedljivosti zasnove in uporabe obsevalne naprave s hladnimi nevtroni na reaktorju TRIGA na IJS

According to some conventions, cold neutrons range from energies of 0.1 meV to 5 meV. Within this energy range, the cross sections for scattering and radiative capture are clearly outside the neutron resonance region. The need for increased accuracy in these cross section values arises from the discrepancies between different evaluated nuclear data libraries (ENDL) and experimental neutron cross section data. In this regard, a design of a cold neutron source using neutrons originating from the JSI TRIGA reactor core is proposed. A parametric study of this irradiation facility is performed using the computer code OpenMC for neutron transport calculations. Neutron beam is sampled and directed through a guide tube with a cold temperature moderator at the beginning, made of graphite or light-water. At first, the simulation is done for a facility in the absence of targets, where energy spectra and cold neutron flux fractions are obtained and evaluated, using moderator thickness and temperature as degrees of freedom. Then, for selected thickness of 70 cm in graphite and 20 cm in H2O, where the cold neutron fluxes were found to be high, the evaluation is made at different temperatures of interest and the highest cold neutron fluxes were found at around 20 K and 58 K respectively for the moderators With the combination of these moderator thicknesses and temperatures, targets of 207Pb and 241Am were added and the scattering and absorption reaction rates were obtained in the simulation, leading to the calculation of their respective cross sections over the cold energy range.Glede na relativno splošno sprejeto definicijo hladni nevtroni obsegajo v energijsko območje od 0,1 meV do 5 meV. V tem energijskem območju so preseki za sipanje in radiativno zajetje nevtrona seveda izven območja nevtronskih resonanc. Potreba po večji natančnosti teh vrednosti presekov izhaja iz razhajanj med različnimi evalviranimi knjižnicami jedrskih podatkov (angl. Evaluated Nuclear Data Libraries – ENDL) in eksperimentalnimi podatki za reakcijske preseke z nevtroni. V tem kontekstu je predlagana zasnova za vir hladnih nevtronov, ki uporablja nevtrone, ki izvirajo iz raziskovalnega jedrskega reaktorja TRIGA na IJS. Izvedena je parametrična študija te obsevalne naprave s pomočjo računalniškega programa OpenMC za izračune Monte Carlo transporta nevtronov. Nevtronski snop je vzorčen in usmerjen skozi vodilo s ohlajenim moderatorjem na začetku, izdelanim iz grafita ali lahke vode. Najprej je simulacija izvedena za napravo brez tarč, kjer se pridobijo in ovrednotijo energijski spektri in deleži hladnih nevtronov, pri čemer sta prostostni stopnji debelina in temperatura moderatorja. Nato je za izbrano debelino 70 cm v grafitu in 20 cm v vodi, kjer so bile gostote hladnih nevtronov visoke, izvedeno ovrednotenje pri različnih temperaturah. Najvišje gostote hladnih nevtronov so bile dosežene pri približno 20 K za grafit in 58 K za vodo. Nato so bile dodane tarče 207Pb in 241Am ter v simulaciji pridobljene hitrosti sipanja in absorpcije reakcij, kar je privedlo do izračuna njihovih presekov za nevtrone v območju hladnih energij