[en] The paper describes studies that have been undertaken to analyse the mass inventory of the thorium-uranium mixed oxide fuel removed from the standard CANDU 6 reactor. The analysed T37 fuel bundle configuration is based on thorium and low enriched uranium (LEU) oxide, considering the ThO₂ ratio of 100% in the central pin, 60% in the inner and intermediate rings and 80% in the outer ring. The ²³⁵U enrichment has been varied in the radial direction from 6% to 10%. The study focuses on identifying optimal thorium - uranium combination from the viewpoint of reducing the content of plutonium and highly radiotoxic minor actinides content the spent fuel accumulated in 30 years operating reactor. The lattice simulations have been performed using the Continuous-energy Monte Carlo Reactor Physics Burn-up Calculation Code - SERPENT 2, version 2.1.30. In order to perform the depletion calculations, the ACE format cross section library JEFF-3.1.1 have been used. (author).

[en] A numerical study of the vibrational relaxation at 500 K of a mixture of ortho-H₂ and para-H₂ is described. The required state-to-state rate constants were calculated and missing pieces of data were estimated by interpolation. It is concluded that only one relaxation time will be observed in any mixture of orth-H₂ and para-H₂ and that (except at very high dilutions in a third inert gas) the relaxation rate constant will be close to the mean of the individual rate constants for relaxation, weighted according to the respective mole fractions of ortho-H₂ and para-H₂ present in the mixture. The relaxation process can be modelled as an electrical RC network, whose time constants can be written down as sums of the appropriate microscopic rate constants. By using this model the conditions required for a mixture of two gases to exhibit two distinct vibrational relaxation times can be explored

[en] The paper describes studies that have been undertaken to analyze the mass inventory of the thorium-uranium mixed oxide fuel removed from the standard CANDU 6 reactor. The analyzed T37 fuel bundle configuration is based on thorium and low enriched uranium (LEU) oxide, considering the ThO₂ ratio of 100% in the central pin, 60% in the inner and intermediate rings and 80% in the outer ring. The ²³⁵U enrichment has been varied in the radial direction from 6% to 10%. The study focuses on identifying optimal thorium – uranium combination from the viewpoint of reducing the content of plutonium and highly radiotoxic minor actinides content the spent fuel accumulated in 30 years operating reactor. The lattice simulations have been performed using the Continuous-energy Monte Carlo Reactor Physics Burn-up Calculation Code - SERPENT 2, version 2.1.30. In order to perform the depletion calculations, the ACE format cross section library JEFF-3.1.1 have been used. (author).

[en] The present study represents a brief analysis of the neutronic parameters (infinite multiplication factor and power distribution) in the CANDU 6 reactor estimated by both Monte Carlo and Collision Probability methods. The simulations were performed using the Continuous-energy Monte Carlo Reactor Physics Burn-up Calculation Code SERPENT 2 along with JEFF-3.1.1 library and the Open-Source Deterministic Transport Code DRAGON 5 with the IAEA 69 energy groups library. The fuel composition chosen for this study has different fissile concentration placed in the bundle rings. The central element contains only ThO₂, while the inner and intermediate rings contain 60% ThO₂, and the outer ring 80% ThO2. Different bundle fuel charges were investigated by varying the ²³⁵U enrichment in radial direction and keeping constant the Th/U ratio. The results highlight that using of (Th,U)O₂ in CANDU 6 reactors is both technically feasible and economically useful. (author).

[en] The present study represents a brief analysis of the neutronic parameters (infinite multiplication factor and power distribution) in the CANDU 6 reactor estimated by both Monte Carlo and Collision Probability methods. The simulations were performed using the Continuous-energy Monte Carlo Reactor Physics Burn-up Calculation Code SERPENT 2 along with JEFF-3.1.1 library and the Open-Source Deterministic Transport Code DRAGON 5 with the IAEA 69 energy group library. The fuel composition chosen for this study has different fissile concentration placed in the bundle rings. The central element contains only ThO₂, while the inner and intermediate rings contain 60% ThO₂, and the outer ring 80% ThO₂. Different bundle fuel charges were investigated by varying the ²³⁵U enrichment in radial direction and keeping constant the Th/U ratio. The results highlight that using of (Th,U)O₂ in CANDU 6 reactors is both technically feasible and economically useful. (author).

[en] In this paper we address stereodynamical issues in the inelastic encounters between OH (Χ²Π) radicals and HCl (Χ¹Σ⁺). The experiments were performed in a crossed molecular-beam machine at the nominal collision energy of 920 cm^-1. Prior to the collisions, the OH molecules were selected using a hexapole in a well-defined rotational state v=0, Ω=3/2, J=3/2, M_J=3/2, f, and subsequently oriented in a homogeneous electrical field. We have measured rotationally resolved relative cross sections for collisions in which OH is oriented with either the O side or the H side towards HCl, from which we have calculated the corresponding steric asymmetry factors S. The results are presented in comparison with data previously obtained by our group for the inelastic scattering of OH by CO (E_coll=985 cm^-1) and N₂ (E_coll=985 cm^-1) studied under similar experimental conditions. The dissimilarity in the behavior of the OH+HCl system revealed by this comparison is explained on the basis of the difference in the anisotropy of the interaction potential governing the collisions. The interpretation of the data takes into account the specific features of both nonreactive and reactive parts of the potential-energy surface. The results indicate that the scattering dynamics at this collision energy may be influenced by the HO-HCl van der Waals well and by reorientation effects determined by the long-range electrostatic forces and, furthermore, may involve reactive collisions

No abstract available

[en] Previous studies of photometric time sequences from pulsating aurora have established that the O(¹S) metastable leading to the emission of the auroral green line is excited by two processes, one direct, the other indirect, with the indirect precursor having a lifetime of about 0.1s. In this paper the authors report on new high time-resolution measurements which extend the observations of precursor lifetime down to about 0.01s. Simultaneous observations of pulsations in the Begard-Kaplan band system were also made in order to obtain direct measurements of the lifetimes of the N₂(A³Σ_u⁺) metastable; there were found to be essentially equal to those of the precursor over the lifetime range from 0.01s to 0.1s, and less well-correlated for longer lifetimes. This result identifies the O(¹S) precursor as N₂(A³Σ_u⁺), at least over the altitude range 97 to 125 km

[en] In this paper, a numerical model has been developed in order to simulate thermal-hydraulic phenomena for the lead-cooled fast reactor demonstrator, ALFRED (Advanced Lead Fast Reactor European Demonstrator). This model has been applied in case of normal operating conditions which show satisfactory results that seem to be in good agreement with ALFRED parameters. These results were used in order to validate the numerical model. Also, the model has been used to simulate an air ingress accident which can cause lead oxide depositions on the steam generator. The simulation has been performed for a lead oxide deposition of 3mm on the bayonet tubes of the steam generator which shows a decrease of the steam generator performance from 36.2 MW to 14 MW. (author).

[en] Cross-section libraries, for 556 isotopes at 11 temperatures (300K, 400K, 500K, 600K, 700K, 800K, 900K, 1000K, 1200K, 1500K and 1800K) have been produced applying the NJOY21 processing code at the ENDF/B-VIII.0 evaluated data files. The aim of this study is the ″validation″ of the above cross-section libraries by benchmarking them (criticality studies) on ″by design″ critical assemblies, as well as on more complex fast systems, and ″point-wise″ comparing the outcome with equivalent results obtained using LANL cross-section libraries produced by the NJOY16 processing code. While the computations have been performed for a larger set of temperatures, a ″point-wise″ comparison is feasible among the sets of cross-section libraries at (300K, 600K, 900K and 1200K), showing a very good agreement on integral and differential neutron parameters. (author).