[en] A simplified method to evaluate the neutron balance for organic-cooled, heavy-water-moderated lattices was established at the Reactor Physics Department of EURATOM-C.C.R., Ispra (Italy). The method used to calculate the cold unirradiated lattice parameters (Caroline I code for IBM 7090) is based on the French correlation for heavy-water-cooled and moderated lattices; the replacement of heavy water by organic as coolant is properly taken into account. A test of this calculation method, based on the results of recent Canadian and EURATOM critical experiments on natural-uranium, organic, heavy water lattices proved to be satisfactory. 18 refs, 11 figs

[en] The method used today at EURATOM for reactivity evaluations of ORGEL-type reactors is described in the paper: ''A simplified method for organic, heavy water lattice calculations''. Following the requirements fixed by the general activity programme of EURATOM regarding this reactor type, a development of the method used is needed. The method necessary for the engineering work is not a recipe such as it could be used for industrial design purposes, but a method which must make possible a satisfactory evaluation of the incidence on the kilowatt-hour price of very important design variations. Due to this fact, the right way seems not to be that of a further development in the direction of an empirical correlation recipe, but that of the development of a more ''physical'' method by which the elements entering in the reactivity determination are, as far as possible, physically analysed and carefully taken into account. Our work is now going in two directions: (1) The of analysing the interest of extensive numerical computations based on fundamental data. The presence at Ispra of important computation facilities may make this way interesting; (2) That of trying to develop simplified methods which do not need high computation times but treat the essential points in a correct physical way. An analysis of the interest of the two lines considered should be possible. In this paper some particular problems studied in the framework of the second line of approach are analysed. The main ones are an improvement in the determination of the p factor and a correct description of the space-dependent neutron spectrum in the lattice. Both points are of particular importance for lattices with fuel-element bundles of great dimensions and containing moderating coolant. (author). 13 refs

[en] A molecular model previously proposed by one of us (V. A.) to describe the slow neutron scattering by polyphenyls has been applied to the evaluation of spectral indices and thermal reactivity parameters in organic-cooled heavy-water lattices. To predict the interaction between slow neutrons and bound nuclei in polyphenyls the single benzene molecule was regarded as the basic dynamic unit. The idea in this molecular model was to replace the very complicated and anisotropic vibrational spectrum of the average proton bound in the benzene molecule by a highly simplified isotropic one: two vibrational oscillators at 0.12 eV and 0.38 eV. Free molecular translations and hindered rotations are also included. The hindered rotations are formally replaced by a torsional isotropic oscillation with a single frequency at 0.02 eV and with a rotational mass M_r = 21.3. The model was able to predict successfully experimental results on integral scattering quantities for benzene and diphenyl at room temperature, showing in this way that such quantities are not excessively dependent on the structure of the molecule or on the vibrational details of various polyphenyls. Hence we assume that this model can be applied for a quantitative understanding of thermal reactor parameters. To investigate the sensitivity of the mentioned reactor quantities to the description of the neutron interaction the calculations have also been performed with the free-gas model. We have employed two completely independent numerical methods for solving the Boltzmann transport equation (THERMOS, WDSN). The aim was to compare the sensitivity to the scattering law with the differences in the results connected with the adopted numerical method, by using the same nuclear data library. The calculations concern such quantities as spectral indices (²³⁹Pu-²³5 U and ¹⁷⁶Lu-Mn reaction rate ratios), coolant temperature coefficients, thermal fission and thermal utilization factors and are referred to a typical ORGEL lattice, with clustered uranium carbide fuel element. (author)

[en] The paper summarises imaging of orbital diseases by CT and MRI. As localisation is an important clue to differential diagnosis in orbital tumours, the different pathologies are described according to sites of prevalent occurrence. Morphological criteria of orbital pathology are described, and the more frequent entities are illustrated. (orig.)