M. Sumini

A well-balanced coarse-mesh flux expansion method

Abstract An efficient low-order coarse-mesh method for LWR criticality problems, which allows for fast routine computations as well as for more accurate, but still unexpensive, reference solutions, is presented. The efficiency of the method rests upon a very simple nodal flux expansion formula and an improved scheme for outer iterations, coupled with a fast ADI technique.

Feasibility analysis of a Plasma Focus neutron source for BNCT treatment of transplanted human liver

Abstract Boron Neutron Capture Therapy preliminary treatments on transplanted human liver have been recently conducted at Pavia University. The need of high fluences of thermal neutrons imposed the use of the available thermal channel of a TRIGA reactor properly modified for this application. We analyse the possibility of using the Plasma Focus (PF) machine as a pulsed neutron source for this medical application instead of a nuclear reactor. Thermalization of the fast (2.45 MeV for D–D reactions) neutrons produced by the PF is gained with a paraffin or polyethylene moderator which contains both the neutron source and the irradiation chamber. The design parameters of a PF optimized for such an application are discussed, as well as other considerations on the advantages that this machine can bring to this kind of cancer therapy.

The heating of plasma focus electrodes

Plasma focus (PF) technology development today is strictly related to the possibility of a high frequency repetitive working regime. One of the more relevant obstacles to this goal is the heating of structural components due to direct interaction with plasma. In this paper, temperature decay measurements of the inner electrode of a 7 kJ Mather type PF are presented. Data from several series of shots at different bank energies are analysed and compared with theoretical and numerical models. Two possible scale laws are derived from the experimental data to correlate thermal deposition with bank energy. It is found that a fraction of about 10% of total energy is released to the inner electrode. Finally, after some considerations about the cooling and heating mechanisms, an analysis on maximum temperature sustained by materials is presented.

A 3D coarse-mesh time dependent code for nuclear reactor kinetic calculations

Abstract A coarse-mesh code for time-dependent multigroup neutron diffusion calculation based on a direct integration scheme for the time dependence and a low order nodal flux expansion approximation for the space variables has been implemented as a fast tool for transient analysis.

Approximate averaged Gaunt factors for free-free Bremsstrahlung emission from a weakly degenerate plasma{

The aim of the paper is the analysis of some aspects of the theoretical models used for the description of the Bremsstrahlung emission from non-Maxwellian plasmas, more precisely when quantum weak degeneracy effects come into play. Referring to the standard Sommerfeld Parameter ρ as a measure of the degree of degeneracy, we considered some reference physical environments, as Inertial Confinement Fusion experiments or the first stage of LIBS, characterized by high densities (even higher than solid state values) and relatively low temperatures (tens of eV). We investigated the relevance of the first order in ρ analytical corrections into the Born and Kramers approximations for the Gaunt factors calculations due to the evaluated non-Maxwellian electron distribution function for the weakly degenerate plasma. The shown results suggest that the degeneracy effects produce up to a 20% correction to the classical values for the Gaunt factors that should be taken into account to properly validate Bremsstrahlung spectra resulting from experiments.

Application of a numerical Laplace transform inversion technique to a problem in reactor dynamics

Abstract A newly developed numerical technique for the Laplace transform inversion is applied to a classical time-dependent problem of reactor physics. The dynamic behaviour of a multiplying system has been analyzed through a continuous slowing down model, taking into account a finite slowing down time, the presence of several groups of neutron precursors and simplifying the spatial analysis using the space asymptotic approximation. The results presented, show complete agreement with analytical ones previously obtained and allow a deeper understanding of the model features.

Some dynamic A-n, S-2n analytic calculations

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.