Nuclear reactor descriptions for space power systems analysis

For the small, high performance reactors required for space electric applications, adequate neutronic analysis is of crucial importance, but in terms of computational time consumed, nuclear calculations probably yield the least amount of detail for mission analysis study. It has been found possible, after generation of only a few designs of a reactor family in elaborate thermomechanical and nuclear detail to use simple curve fitting techniques to assure desired neutronic performance while still performing the thermomechanical analysis in explicit detail. The resulting speed-up in computation time permits a broad detailed examination of constraints by the mission analyst

A neutron diode for subcritical multistage multipliers with special reference in tritium breeding

This is a copy of the author 's final draft version of an article published in the Journal of fusion energy. The final publication is available at Springer via http://dx.doi.org/10.1007/s10894-015-0049-7In this paper the interaction between a magnetic field and the neutron spin magnetic moment is explored for use in the design of a neutron diode or valve that allows a neutron flux to pass in one direction, while preventing a neutron flux in the opposite direction. A neutron diode that ensures the unidirectional movement of neutrons could be used in the design of a subcritical multistage neutron multiplier, a device that has thus far not been realised. With a subcritical multistage neutron multiplier, an initial source of neutrons could be multiplied substantially in a very small area. Such a device could have potential applications in tritium breeding in a fusion reactor, in medicine, in space exploration, etc. Utilizing a simplified geometrical model, a first preliminary study is performed to assess the feasibility of this concept.Peer ReviewedPostprint (author's final draft

Meson-exchange contributions to the nuclear charge operator

The role of the meson-exchange current correction to the nuclear charge operator is studied in electron scattering processes involving the excitation of medium and heavy nuclei to energies up to the quasi-elastic peak. The effect of these contributions in the quasi-free electron scattering process is a reduction of at most a 3% in the longitudinal response at the energy of the peak, a value which is below the experimental error and must not be taken into account in calculations in this energy region. On the other hand, the excitation of low-lying nuclear levels of neutronic character shows, with respect to the protonic ones, a considerable effect due to the inclusion of the two-body term in the charge operator. More realistic calculations, such as those performed in the random-phase approximation framework, give rise to a mixing of one particle-one hole configurations of both kinds which reduce these effects. However, it has been found that the excitation of some of these levels is sizeably affected by the meson-exchange contribution. More precise experimental data concerning some of these states, such as e.g. the high-spin states in 208Pb, could throw some light in the problem of a more feasible determination of these effects and, as a consequence, could provide an alternative procedure to obtain the charge neutron form factor.Comment: 26 pages, 10 figures, LateX file and Postscript figure

Specifications for a coupled neutronics thermal-hydraulics SFR test case

Coupling neutronics/thermal-hydraulics calculations for the design of nuclear reactors is a growing trend in the scientific community. This approach allows to properly represent the mutual feedbacks between the neutronic distribution and the thermal-hydraulics properties of the materials composing the reactor, details which are often lost when separate analysis are performed. In this work, a test case for a generation IV sodium-cooled fast reactor (SFR), based on the ASTRID concept developed by CEA, is proposed. Two sub-assemblies (SA) characterized by different fuel enrichment and layout are considered. Specifications for the test case are provided including geometrical data, material compositions, thermo-physical properties and coupling scheme details. Serpent and ANSYS-CFX are used as reference in the description of suitable inputs for the performing of the benchmark, but the use of other code combinations for the purpose of validation of the results is encouraged. The expected outcome of the test case are the axial distribution of volumetric power generation term (q'''), density and temperature for the fuel, the cladding and the coolant

Robustness of nuclear core activity reconstruction by data assimilation

We apply a data assimilation techniques, inspired from meteorological applications, to perform an optimal reconstruction of the neutronic activity field in a nuclear core. Both measurements, and information coming from a numerical model, are used. We first study the robustness of the method when the amount of measured information decreases. We then study the influence of the nature of the instruments and their spatial repartition on the efficiency of the field reconstruction