P.A. Di Maio

Experimental tests on Li-ceramic breeders for the helium cooled pebble bed (HCPB) blanket design

The Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) to be tested in ITER (International Thermonuclear Experimental Reactor) Reactor foresees the utilization of Lithiate ceramics as Tritium breeder in form of pebble beds. Since 1998, ENEA has launched many experimental activities for the evaluation of the breeder thermomechanics and the interaction between the pebble beds and the prismatic steel containment walls. Main objectives of these activities are the measurement of the pebble bed effective thermal conductivity, the wall heat transfer coefficient, the pressure loads and deformations on the lateral walls and their dependency from the mechanical constraints. The paper presents the progress of the second test campaign performed at ENEA Brasimone HE-FUS3 facility on Li4SiO4 pebbles.

Modelling of the thermal-mechanical behaviour of a single size beryllium pebble bed

The Helium Cooled Pebble Bed (HCPB) Blanket for fusion power reactors and the ITER breeding blanket are based on the use of pebble beds of lithium ceramics as breeder and beryllium as neutron multiplier. Experimental activities were performed at Forschungszentrum Karlsruhe concerning the measurement of pebble bed heat transfer parameters. At the Department of Nuclear Engineering of the University of Palermo, the experimental results have been reproduced by means of the ABAQUS finite element code. Moreover, a thermal-mechanical theoretical model has been developed for single size beryllium pebble beds. In the paper the results from the numerical and theoretical analyses and the comparison with experimental data are presented and critically discussed.

On the nuclear response of the water-cooled Pb–17Li test blanket module for ITER-FEAT

Abstract Within the European Fusion Technology Programme, the Water-Cooled Lithium Lead (WCLL) DEMO breeding blanket line was selected in 1995 as one of the two EU lines to be developed in the next decades, in particular with the aim of manufacturing a Test Blanket Module (TBM) to be tested in ITER-FEAT. The present paper is focused on the study of the WCLL-TBM nuclear response in ITER-FEAT, being specifically oriented to the investigation of the local effects due to the typical C-shaped tubes of the breeder zone, since they could play a pivotal role in the module-relevant thermo–mechanical design. A 3D heterogeneous model of the WCLL-TBM, realistically simulating its new lay out and taking into account 9% Cr martensitic steel as reference structural material, has been set-up. A particular attention has been paid to the simulation of the characteristic ‘C’ shape of the breeder zone double walled tubes, which have been realistically reproduced. The WCLL-TBM model has been inserted into an existing ITER-FEAT 3D semi-heterogeneous model accounting for a proper D–T neutron source. Analyses have been performed by means of MCNP-4C code running on a cluster of four workstations through the implementation of a parallel virtual machine. For each analysis a large number of histories (>10.000.000) have been simulated, obtaining statistical uncertainties on the results lower than 3%. The main features of the WCLL-TBM nuclear response have been determined focusing the attention on power deposition density, material damage through DPA and He and H production rate, daily tritium production and tritium production rate radial distribution in the module. The obtained results are herewith presented and critically discussed.

Neutronic and photonic analysis of the water-cooled Pb17Li test blanket module for ITER-FEAT

Abstract Within the European Fusion Technology Program, the Water-Cooled Lithium Lead (WCLL) DEMO breeding blanket line was selected in 1995 as one of the two EU lines to be developed in the next decade, in particular with the aim of manufacturing a Test Blanket Module (TBM) to be implemented in ITER. This specific goal has been maintained also in ITER-FEAT program even if the general design parameters of the TBMs have reported some changes. This paper is focused on the investigation of the WCLL-TBM nuclear response in ITER-FEAT through detailed 3D-Monte Carlo neutronic and photonic analyses. A 3D heterogeneous model of the most recent design of the WCLL-TBM has been set-up simulating realistically its new lay out and taking into account 9% Cr martensitic steel as structural material. It has been inserted into an existing 3D semi-heterogeneous ITER-FEAT model accounting for a proper D–T neutron source. The analyses have been performed by means of MCNP-4C code running on a cluster of four workstations through the implementation of a parallel virtual machine. The main WCLL-TBM nuclear responses have been determined focusing the attention on power deposition density, material damage through displacement per atom (DPA) and He and H production rate, daily tritium production and tritium production rate radial distribution in the module. Moreover, the impact of using lithium at various Li6 enrichment on the TBM nuclear response has been investigated. The results obtained are herewith presented and critically discussed.

A Semi-Theoretical Approach to a Correlation for the Thermal Conductivity of a Beryllium Pebble Bed

In the framework of the European Fusion Technology Programme, Lithium ceramics and Beryllium packed pebble beds are foreseen to be used as Tritium breeders and neutron multipliers, respectively, for the Helium Cooled Pebble Bed breeding blanket of a fusion power reactor operating with a D-T plasma. The present work is focused on the semi-theoretical investigation of the thermal conductivity of single size Beryllium pebble beds, starting from the main hypothesis that this conductivity depends linearly on pebble bed local temperature and mechanical volumetric strain and introducing a method to determine the coefficients of such dependence on the basis of the results obtained by the SUPER-PEHTRA experiments. It has been mainly assumed that the SUPER-PEHTRA Beryllium pebble bed can be considered as a homogeneous, isotropic, and linear elastic medium, and the analytical solution of the direct static problem of the thermo-elasticity for such a system has been used to fit the experimental thermal distributions, uncovering the best values for the thermal conductivity function coefficients. This thermal conductivity has been used together with a constitutive model, realistically taking into account the pebble bed mechanical behavior to reproduce the experimental tests. The results of the analyses agree quite well with the experimental ones, thus encouraging the use of the derived thermal conductivity correlation for Beryllium pebble beds undergoing low plastic volumetric strain.

Assessment of the importance of neutron multiplication for tritium production

One of the major requirements for a fusion power plant in the future is tritium self-sufficiency. For this reason the scientific community has dedicated a lot of effort to research activity on reactor tritium breeding blankets. In the framework of the international project DEMO, many concepts of breeding blanket have been taken into account and some of them will be tested in the experimental reactor ITER by means of appropriate test blanket modules (TBMs). All the breeding blanket concepts rely on the adoption of binary systems composed of a material acting as neutronic multiplier and another as a breeder. This paper addresses a neutronic feature of these kinds of systems. In particular, attention has been focused on the assessment of the importance of neutrons coming from multiplication reactions for the production of tritium. A theoretical framework has been set up and a procedure to evaluate the performance of the multiplier-breeder systems, under the aforementioned point of view, has been developed. Moreover, the model set up has been applied to helium cooled lithium lead and helium cooled pebble bad TBMs under irradiation in ITER and the results have been critically discussed.

First Flight Escape Probability and Uncollided Flux of Nuclear Particles in Convex Bodies with Spherical Symmetry

Abstract This paper deals with the evaluation of the first flight escape probability of nuclear particles from convex bodies with spherical symmetry by means of some geometrical arguments and very simple probability considerations. The cases of a full sphere, a one-region spherical shell with an empty central zone, a spherical shell region containing a black central zone, and a full sphere with a sourceless shell have been considered. In all the aforementioned cases, a homogeneous medium and uniform isotropic source have been taken into account. Moreover, a simple and general formula has been derived for the calculation of the uncollided flux that is presupposed to be valid for arbitrary geometries. The results obtained have been validated by Monte Carlo analyses performed by the Monte Carlo N-Particle (MCNP5) code and critically discussed.

Electrical aging tests on enameled wire exposed to gamma irradiation

Stator windings of low voltage electrical motors are usually insulated by means of organic enamels. If motors are used in particular industrial plants or in nuclear applications, the enamel adopted to insulate the motor stator windings may be exposed to very intense gamma photonic irradiation fields. In this research activity, attention has been focused on the potential influence of gamma irradiation dose on the performances of an electrical insulation system based on enameled wires having a thermosetting matrix. The aim of this research activity is to assess the prospects of exploitation of such insulating materials inside electromechanical devices intended to operate in presence of gamma photonic fields as in the frame of nuclear plant dismantling or, in general, of the manipulation of radioactive products. Suitable specimens, insulated by the considered enamel, have been set-up using enameled wire exposed to gamma photonic irradiation within a panoramic irradiator endowed with Co60 gamma sources. These pre-aged specimens have been subjected to electrical aging tests up to the enamel breakdown condition, chosen as end-point criterion, in order to study the electrical performances of the considered wires. The peak to peak voltage amplitude of the considered waveform has been set higher than the partial discharges inception voltage level in order to work in presence of surface partial discharges activity. Enamel life curve has been plotted in order to point out gamma irradiation dose influence on the performances of the considered insulating material. The obtained results show the significant effects of the exposure to a gamma irradiation field on the performances of the considered insulating enameled wire.

Study of a water-cooled convective divertor prototype for the DEMO fusion reactor

The plasma facing components of a fusion power reactor have a large impact on the overall plant design, its performance and availability and on the cost of electricity. The present work concerns a study of feasibility for a water-cooled prototype of the convective divertor component of the DEMO fusion reactor. The study has been carried out in two steps. In the first one thermal-hydraulic and neutronic parametric analyses have been performed to find out the prototype optimized configuration. In the second step thermo-mechanical analyses have been carried out on the obtained configuration to investigate the potential and limits of the proposed prototype, with a particular reference to the maximum heat flux it can undergo without incoming both in critical heat flux and in mechanical stress limits. The results show that the proposed divertor prototype is able to safely withstand peak heat fluxes of 9 MW/m2.