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The ITER pre-compression ring system is based on two sets of 3 rings made in fibreglass-epoxy composite and is located on top and bottom of the inner straight leg region. These rings will provide a radial force of about 70 MN/coil (35 MN at the top and 35 MN at the bottom) under cryogenic conditions, pulling the TF coils into contact, reducing the gap between the poloidal shear keys and their keyways during operation and also reducing the toroidal tension in the four outer intercoil structures bands. The paper describes the stress relaxation test performed in ENEA Frascati laboratories on a reduced scale glass fibre-epoxy composite ring. The ring was manufactured with a diameter of 1 m (1/5 of the real scale one) by winding S2 glass fibres then impregnated with epoxy. The volumetric glass content was of 69% and no significant presence of defects was verified by an X-ray survey. The test has been carried out following as close as possible the ASTM standard E 328-86. The ring has been inserted into a dedicated hydraulic testing machine consisting of 18 radial pulling actuators and then loaded up to a ring membrane hoop stress of 800 MPa. The deformation has been maintained constant during the test by inserting a solid steel disk in the machine centre restraining the machine radial motion. Average hoop stress has been daily monitored measuring the force required to lift the ring just free of the constraints during the test period. The ring performed 125 testing days showing no significant stress relaxation and a small reduction of the ring stiffness that appeared mainly in the first days of the test.

The PERMCAT is a membrane reactor proposed for processing fusion reactor plasma exhaust gas: tritium removal is obtained by isotopic swamping operating in counter-current mode. In this work, a membrane reactor using a permeator tube of length about 500 mm produced via diffusion welding of Pd–Ag thin foils is described. An appropriate mechanical design of the membrane module has been developed in order to avoid any significant compressive and bending stresses on the very long and thin wall permeator tube: two expanded bellows have been applied to the Pd–Ag tube, so that it has been pre-tensioned before operating. The elongation of the metal permeator under hydrogenation has been theoretically estimated and experimentally verified for properly designing the membrane reactor.

Cold-rolled and annealed Pd-Ag 25% at. foils of thickness 50 μm have been joined by diffusion bonding in order to obtain permeator tubes used in laboratory applications for hydrogen separation and purification. The tubes produced present a sound and effective joint along the generatrix line: particularly, this procedure has shown better performance than arc welding, responsible for formation of thermally stressed zones and embrittlement of permeators.

Three techniques were used to produce palladium–ceramic (Pd–ceramic) composite membranes for hydrogen separation and production. They are sputtering, electroless deposition and rolling of thin Pd alloy films over ceramic porous tubes. After studying and developing the three coating techniques, an extensive testing and characterizing work was carried out on these thin film composite membranes. The results show that in the sputtered (0.5–5 μm) and electroless (2.5–20 μm) composite membranes, the thermal cycling of the hydrogenated metallic layer produces membrane failures. Such failures are characterized by crack formation and metal film peeling. This fact has been explained by an evaluation of the shear stresses at the metal–ceramic interface due to the differential elongation between the palladium (Pd) coating and the ceramic support under thermal cycling and hydrogen loading. The rolled membranes (50–70 μm), however, because of the particular coating solution, have shown a complete hydrogen selectivity and good chemical and physical stability in long-term tests.

The JET Toroidal Field (TF) coils were originally designed for operation at 3.4 tesla. In order to upgrade the field to 4 tesla and thus improve the performance of the JET machine, new mechanical tests and analysis were carried out on the insulation of TF coil samples. They are aimed at investigating the mechanical properties and the status of the insulation in order to set allowable stresses and force limits. In particular since the shear stress in the insulation is strongly affected by the shear modulus of elasticity G, it is important to measure this parameter. A method for the measurement of G in glass-resin fibres, the V-notched beam method (Iosipescu method) , was applied. The particular shape of the rectangular Iosipescu V- notched sample and the particular modality of force application produce pure shear stress for a reliable measurement of the G value and of the shear strength of the insulation. The effect of temperature on these mechanical properties was also investigated. Results show higher average shear strength with lower scatter compared with previous tests on conventional rectangular samples, thus confirming the reliability of the method. Micrographic analysis of the insulation and comparison between the straight and curved regions of the magnet, where the highest stress occurs, confirm the good quality of the impregnation of the coil. Glass-resin content, void content, micros and TG measurements have been performed on different samples and correlation between the different properties of the insulation investigated. Moreover fatigue tests at different temperatures were performed and data analyzed with the cumulative damage technique, which allows for an extrapolation of the fatigue curve with less samples than the standard method. (6 refs).

Fasteners are generally considered a matter of a mature technology with a variety of solutions ready to meet a wide range of applications, but their use in remote handling needs accurate considerations. The fastening system has a substantial effect on the total time to perform maintenance operations, and therefore care should be taken from the beginning of the project to its standardization. The set of requirements to be satisfied by a qualification activity on fasteners to be remotely handled within the environmental conditions relevant to the NET—ITER machine (high temperature, radiation, vacuum, cryogenic temperature) deals with shape and dimensions, materials properties, surface finish of mating parts, lubricant compatibility, precautions against galling and seizure, provisions of remedial actions from an emergency situation, fabrication process specification, methods of preload application and control of its persistence under machine operation. The qualification of high strength bolts at cryogenic temperature (4 K) and relevant fracture mechanics tests, and the qualification of suitable coatings and lubricants has been extensively investigated on both specimens and full size components. In this paper we report final results of a three-year development programme on fastener technology.

This paper deals with the work done to define, construct and test a detailed critical part, spatially limited at about 10 cm3, reproducing the essential configuration of the FT-U magnet coil. The tests were performed at room and LN 2 temperatures in order to study the degradation of the insulating materials after repeated mechanical stresses. We describe criteria required to design a practical model with the possibility to simulate the thermo- -mechanical behaviour of the coil and allowing the measurement of the electrical insulation properties. The experimental set-up is described, as well as the operations for test analysis, optical observations and measurements on the components. Finally some results and typical microphotographs are reported.