[en] An Abelian symmetry already considered by Einstein with respect to his asymmetrical field theories is related to the gravitational and gauge field copy phenomenon. It is shown that gauge field copies arise out of a straightforward generalization of the λ - map. The connection between Einstein's work on the λ-transformation and the copy phenomenon is obtained with the help of the Frobenius Theorem on the existence of foliations on a differentiable manifold. A problem like the one above is usually treated within the language of (intrinsic) Differential Geometry; General Relativity and classical unified field theories are traditionally developed in a classical style, that gap, a long introduction is prepared where the same structures are studied from the traditional and from the more recent point of view. (author)

No abstract available

[en] Solid breeder blankets with lithium ceramics as breeder and reduced activation ferritic martensitic (RAFM) steel as structural material require beryllium (Be) to increase the tritium breeding ratio (TBR) performance. In the event of plasma disruptions the values and distribution of induced currents in the breeding blanket will depend on the electrical resistivity of the adopted materials. The electrical conductivity of the insulating Be oxide layer on the pebbles surface could be significantly altered in the presence of a γ field as well as the electrical conductivity of the purging gas present inside the Be pebble bed assembly. In this paper we report the electrical properties of Be pebble beds under an irradiation environment with a γ radiation field ranging from 5x10⁴ to 1.3x10⁶ Gy/h at the Portuguese Research Reactor. Some Be pebbles were accommodated in a container where a typical purging gas of He+0.1% H₂, as foreseen in the blanket design, was introduced. The results show a decrease of the electrical resistivity values from 0.061 to 0.055 Ωm during the exposure in a γ field of 1.3x10⁶ Gy/h for the beds containing the purging gas mixture. The conductivity of the pebble bed without purging gas was not affected by the radiation. The results suggest that the radiation induced conductivity (RIC) was due to the ionization of the gas present in the bed

[en] Copper rich compounds with YBaCu₁₂O₁₅ stoichiometry were synthesized at 900 deg. C under oxygen rich atmosphere and annealed at 350 deg. C in oxygen flow during 1, 3 and 60 days. Results of AC magnetic susceptibility, thermomagnetic analysis and electron paramagnetic resonance spectroscopy indicate multiphase materials containing the phases YBaCu-123 and YBaCu-247. Critical temperatures were determined by AC magnetic susceptibility and confirmed by EPR measurements

[en] A duplex stainless steel was aged at 475 deg. C for different times up to 500 h. The thermal embrittlement was investigated by thermomagnetic analysis using a vibrating sample magnetometer and a thermomagnetic balance. The results obtained with the two equipment were similar and show that the Curie temperature increases with the ageing time. Relationships between T_c and mechanical properties (hardness and toughness) were proposed

[en] In this work the magnetic properties of a Ni-Co-Ti maraging steel grade 350 were measured in many processing conditions. The influence of the aging temperature is analyzed. Thermomagnetic analyses were also carried out to investigate martensite-austenite transformation

[en] The temperature dependence of the electrical resistivity of a 1 mm single-size pebble bed is presented as a function of different applied pressures. The pebble bed was maintained in a He+0.1 vol.% H₂ flowing atmosphere. In agreement with previous studies, the resistivity displays two distinct regimes under the applied load. The first one is characterised by a strong reduction in the resistivity and is likely correlated with the mechanical rearrangement of the pebbles during the first compression phase. The load range of this regime is strongly reduced when the temperature is increased. The second regime is characterised (in a semilogarithmic plot) by a linear decrease of the resistivity with the applied load. The ultimate reached resistivity was 3.0x10^-4 Ωm under a pressure of 53 MPa at all temperatures from 20 to 800 deg. C. The slope of the resistivity curve decreases with temperature, which can be likely correlated with an increase in the plasticity of the pebbles

[en] Information on the chemical compatibility between Li ceramic breeders and reactor structural materials is an important issue for fusion reactor technology. In this work, Eurofer samples were placed inside a Li ceramic pebble bed and kept at 600 deg. C under a reducing atmosphere obtained by the flow of a purging gas (He + 0.1vol.%H₂). Titanate and orthosilicate Li pebble beds were used in the experiments and exposure time ranged from 50 to 2000 h. Surface chemical reactions were investigated with nuclear microprobe techniques. The orthosilicate pebbles present chemical reactions even with the gas mixture, whereas for the samples in close contact with Eurofer there is evidence of Eurofer elemental diffusion into the pebbles and the formation of different types of compounds. Although the titanate pebbles used in the chemical compatibility experiments present surface alterations with increasing surface irregularities along the annealing time, there is no clear indication of Eurofer constituents diffusion

[en] SiC composite reinforced fibres are still considered to be an important material to be used in nuclear fusion reactors due to their high temperature and low neutron activation properties. Two different kinds of SiC/SiC_f composite were manufactured, one of them presenting an extra SiC coating obtained by chemical vapour deposition technique. Several samples of both materials were placed inside a Be pebble bed and the whole set-up annealed at 800 deg. C for 550 h in a reducing atmosphere, simulating fusion reactor conditions. Surface chemical reactions were investigated with nuclear microprobe analyses techniques and complemented with SEM analysis. For the uncoated samples, surface oxidation is accompanied by a strong C depletion and a Be diffusion. Two different behaviours were found for the coated samples. One of those samples showed extended regions where surface was left almost unaltered. The general behaviour, however, was an increase in the number and extension of the cracks already observed at the surface of the coated virgin samples

No abstract available