Effect of gamma irradiation on the mechanical behavior, thermal properties and structure of epoxy/glass-fiber composite

Nuclear fusion devices based on the magnetic confinement principle heavily rely on the existence and performance of superconducting magnets and have always significantly contributed to advancing superconductor and magnet technology to their limits. In view of the presently ongoing construction of the tokamak device ITER and the stellerator device Wendelstein 7X and their record breaking parameters concerning size, complexity of design, stored energy, amperage, mechanical and magnetic forces, critical current densities and stability requirements, it is deemed timely to review another critical parameter that is practically unique to these devices, namely the radiation response of all magnet components to the lifetime fluence of fast neutrons and gamma rays produced by the fusion reactions of deuterium and tritium. I will review these radiation effects in turn for the currently employed standard "technical" low temperature superconductors NbTi and Nb3Sn, the stabilizing material (Cu) as well as the magnet insulation materials and conclude by discussing the potential of high temperature superconducting materials for future generations of fusion devices, such as DEMO.

Radiation effects on superconducting fusion magnet components

Magnets built for fusion devices such as the newly proposed Fusion Ignition Research Experiment (FIRE) need to be highly reliable, especially in a high radiation environment. Insulation materials are often the weak link in the design of superconducting magnets due to their sensitivity to high radiation doses, embrittlement at cryogenic temperatures, and the limitations on their fabricability. An insulation system capable of being vacuum impregnated with desirable properties such as a long pot-life, high strength, and excellent electrical integrity and which also provides high resistance to radiation would greatly improve magnet performance and reduce the manufacturing costs. A new class of insulation materials has been developed utilizing cyanate ester chemistries combined with other known radiation-resistant resins, such as bismaleimides and polyimides. These materials have been shown to meet the demanding requirements of the next generation of devices, such as FIRE. Post-irradiation testing to levels that exceed those required for FIRE showed no degradation in mechanical properties. In addition, the cyanate ester-based systems showed excellent performance at cryogenic temperatures and possess a wide range of processing variables, which will enable cost-effective fabrication of new magnets. This paper details the processing parameters, mechanical properties at 76 K and 4 K, as well as post-irradiation testing to dose levels surpassing 10 8 Gy.

Highly radiation-resistant vacuum impregnation resin systems for fusion magnet insulation

In the present work, mechanical p roperties of laminates fabricated by Hand lay-up technique using fibre glass (woven-mat) of density 3.6 N/ m 2 and general purpose polyester resin was investigated. Fibre glass polyester composite samples were fabricated with d ifferent fibre glass volume fractions (A-0.05, B-0.10, C-0.15, C-0.20, D-0.25 and E-0.30). The materials properties; ultimate tensile strength, Young's modulus of elasticity, elastic strain, and impact strength of the materials were determined through standard tests on standard test samples. It was observed that the various mechanical properties (exclud ing the impact strength) were improved with increase in fibre g lass volume and that the fibre glass - polyester co mposite is characterized by h igh toughness. It was concluded that the optimu m fibre g lass volume fraction for the composite is 0.25.

/pdf/mechanical-properties-of-a-polyester-fibre-glass-composite-5dn1th0pxd.pdf

Mechanical Properties of a Polyester Fibre Glass Composite

https://publik.tuwien.ac.at/files/PubDat_185552.pdf

Characterization of advanced cyanate ester/epoxy insulation systems before and after reactor irradiation

Novel radiation-resistant insulation systems for fusion magnets

Because of their excellent electrical and mechanical material performance, organic and organic/inorganic hybrid materials are candidate insulation systems for fusion magnets. Wrappable inorganic insulation systems combine the high strength and modulus of a ceramic composite with the simple processing of an organic insulation system. Various types of organic as well as organic/inorganic hybrid material compositions containing a ceramic fiber fabric as well as a ceramic and an epoxy matrix were irradiated at ambient temperature in the TRIGA reactor (Vienna) up to neutron fluences of 1021, 1022 and 5×1022 m−2 (E>0.1 MeV). Tensile, short-beam-shear and double-lap-shear tests were performed at 77 K. The influence of reactor irradiation on the mechanical material performance will be presented for different compositions of these materials.

Characterization of reactor irradiated organic and inorganic hybrid insulation systems for fusion magnets

Improved performance and reduced manufacturing costs for high field accelerator and fusion magnets can only be achieved with a high strength, high temperature insulation system A new wrappable inorganic insulation system has been developed that combines the high strength and modulus of a ceramic composite with the ease of processing of an organic pre-preg insulation The attraction of a ceramic pre-preg that could be fired at the same time that the superconducting wire is being reacted could save much time and expense by reducing processing steps and costs By wrapping the ceramic onto the conduit, as opposed to spraying or dipping, the same equipment used today for organic pre-preg insulation can be re-used Secondly, with the high temperature stability of the ceramic, more design flexibility would be afforded allowing higher performance magnet coils to be fabricated Many magnet systems can also take advantage of the increased radiation resistance of the ceramic This paper will compare several different inorganic insulation systems The processing of the wrappable insulation will be described as well as typical material performance test results

Wrappable ceramic insulation for superconducting magnets

Mechanical properties of the ITER central solenoid model coil insulation under static and dynamic load after reactor irradiation

Superconducting fusion magnets require a high electrical and mechanical material performance of their insulation. A newly developed wrappable inorganic insulation system combines the high strength and modulus of a ceramic composite with the simple processing of an organic insulation system. This paper reports on tests performed to assess their mechanical properties and to obtain information on the damage mechanisms, swelling and weight loss after irradiation. Different material compositions containing a ceramic fiber reinforcement as well as a ceramic and an epoxy matrix system were irradiated at ambient temperature in the TRIGA reactor (Vienna, Austria) up to neutron fluences of 1021, 1022 and 5x1022 m−2 (E>0.1 MeV). After irradiation, swelling and weight loss of the samples were measured prior to tensile and short-beam-shear testing at 77 K. The influence of reactor irradiation on swelling and weight loss as well as on the mechanical properties will be discussed for the different material compositions.

J. A. Rice

Papers

Novel radiation-resistant insulation systems for fusion magnets

Characterization of reactor irradiated organic and inorganic hybrid insulation systems for fusion magnets

Wrappable ceramic insulation for superconducting magnets

Mechanical properties of the ITER central solenoid model coil insulation under static and dynamic load after reactor irradiation

Mechanical Strength, Swelling and Weight Loss of Inorganic Fusion Magnet Insulation Systems Following Reactor Irradiation