[en] In an attempt to better understand the influence of prompt and delayed neutrons on nuclear reactor dynamics, a continuous slowing down model based on Fermi age theory was developed several years ago. This model was easily incorporated into the one-group diffusion equation and provided a realistic physical picture of how delayed and prompt neutrons slow down and simultaneously diffuse throughout a medium. The model allows for different slowing down times for each delayed neutron group as well as for prompt neutrons and for spectral differences between the two typed of neutrons. Because of its generality, this model serves not only a a useful predictive tool to anticipate reactor transients, but also as an excellent educational tool to demonstrate the effect of delayed neutrons in reactor kinetics. However, because of numerical complications, the slowing down model could not be developed to its full potential. In particular, the major limitation was the inversion of the Laplace transform, which relied on a knowledge of the poles associated with the resulting transformed flux. For this reason, only one group of delayed neutrons and times longer than the slowing down times could be considered. As is shown, the new inversion procedure removes the short time limitation as well as allows for any number of delayed neutron groups. The inversion technique is versatile and is useful in teaching numerical methods in nuclear science

[en] Calculations of the diffusion of unpolarized photons in thin thickness targets have been performed with recourse to a vector transport model taking rigorously into account the polarization introduced by the scattering interactions. An order-of-interactions solution of the Boltzmann transport equation for photons was used to describe the multiple scattering terms due to the prevailing effects in the X-ray regime. An analytical expression for the correction factor to the attenuation coefficient is given in term of the solid angle subtended by the detector and the energy interval characterizing the detection response. Although the main corrections are due to the influence of the pure Rayleigh effect, first- and second-order chains involving the Rayleigh and Compton effects have been considered as possible sources of overlapping contributions to the transmitted intensity. The extent of the corrections is estimated and some examples are given for pure element targets

[en] A-n, S-2n dynamic equations in neutron transport theory are given an analytic solution, suitable for numerical safety code validation. Some numerical results are presented for plane geometry with periodic boundary conditions, within the monokinetic isotropic scattering case. They turn out to be very interesting and physically well interpretable and seem to give a deep insight into the transport effects connected with the finite velocity space migration of localized neutron signals. Balance equations are solved by means of a space Helmholtz series expansion connected to a time-variable Laplace transformation technique. The equations that are to be solved for the considered slab geometry, although perfectly equivalent to S-2n equations, are actually the ones corresponding to the typical second-order A-n model. The given fully analytic solution can be used to yield standard reference results for peculiar space transients, against which any numerical safety code exploiting the same discrete ordinate model can be validated

[en] A method to obtain an approximate solution to the transport equation, when both sources and collisions show a linearly anisotropic behavior, is outlined and the possible implications for numerical calculations in applied neutronics as well as shielding evaluations are investigated. The form of the differential system of equations taken by the method is quite handy and looks simpler and more manageable than any other today available technique. To go deeper into the efficiency of the method, some typical calculations concerning critical dimension of multiplying systems are then performed and the results are compared with the ones coming from the classical Ssub(N) approximations. The outcome of such calculations leads us to think of interesting developments of the method which could be quite useful in alternative to other today widespread approximate procedures, for any geometry, but especially for curved ones. (author)

[en] The effect of quantum degeneracy on the electron collisional excitation is investigated, and its effects on line emission evaluated for applications to spectroscopy of dense, cold plasmas. A correction to Saha equation for weakly-degenerate plasmas is also presented

[en] GENII-LIN is an open source radiation protection environmental code with capabilities for calculating radiation dose and risk to individuals or populations from radionuclides released to the environment and from pre-existing environmental contamination. The code can be used for purposes such as siting facilities, environmental impact statements, and safety analysis reports. The code can handle exposure pathways that include: external exposure from finite or infinite atmospheric plumes; inhalation; external exposure from contaminated soil, sediments, and water; external exposure from special geometries; and internal exposures from consumption of terrestrial foods, aquatic foods, drinking water, animal products, and inadvertent intake of soil. The flexible modular structure and the strictly object oriented software design simplify code improvement and patching: other modules can be added and the present ones updated, with minimal effort. - Author-Highlights: • Development an Open Source Multipurpose Health Physics Code. • Code usage: facility siting, environmental impact statements and safety analysis. • Radiation doses from routine and accidental radionuclide releases to the environment. • Radiation dose from long or short term exposure to environment contamination. • Nuclides transport through air, deep and surface water, deep and surface soil

[en] The present paper is devoted to deriving an analytical solution to a simple but physically significant and paradigmatic problem in local reactor kinetics, i.e. the one where the effects of the neutron migration during the slowing-down process, from fission to thermal energies, are taken into account by means of a dynamic generalization of the stationary Fermi continuous slowing-down approach. The attention is focused essentially on the influence of the space displacement and time delay undergone simultaneously by prompt and delayed fission neutrons and the analysis is restricted to the situation where the space asymptotic reactor theory may be applied. The Laplace transform technique is used throughout all the work. The solution is written down initially as a power series of the delayed-neutron fraction β, which is easy to handle and rapidly convergent within a time interval as long as a few slowing-down times after the perturbation event. Later on the adoption of a quite simple asymptotic form of the inverse Laplace transform may be fully justified. Therefore, by means of these two fully analytical forms of the solution to the local dynamics of a bare multiplying structure, within the frame of the quasi-continuous slowing-down model, it is possible to describe the neutron population evolution over the whole time axis. (author)

[en] The paper proposes a physically consistent technique to obtain average broad energy group cross sections from fine group data, in place of currently used neutron spectra averaging. The method is based upon the principle that in energy averaging procedures the 'total importance content' has to be preserved and it can be inserted within the framework of the so-called 'bilinear weighting' procedures, that have already been introduced and used in neutronic calculations. (author)

[en] The work presented in this paper completes the theoretical analysis that concerns the use of the Asub(n) approximate method in solving the monokinetic neutron transport equation. The method has been devised from the integral form of the transport equation and is connected to a proper approximation of the transport kernel which may be accomplished by means of a general integration formula. It is proved that under a suitable choice of the Asub(n) approximation parameters, namely referring to the classical Gauss-Legendre integration technique, the system of space second-order differential equations which constitute the discrete ordinate one. (author)

[en] Analytical solutions of nonstationary equations of neutron transport theory in A-n, S-2n approximations applicable for testing computer programs used to study safety problems are presented. For plane geometry with periodical boundary conditions certain numerical results obtained by one-velocity theory in the assumption of isotropic neutron scattering are given. The results explain visually transport effects related to the finite velocity of neutron propagation in space from a local pulsed sources. Balance equations are solved by the expansion into a series over eigen functions of the Helmholtz equation in combination with use of the Laplace transformation for time variable. The analytical solution under consideration can be used as a model one to study specificity of spatial transient processes