Comparative radiological assessment of SiC/SiC composites as structural materials in nuclear fusion technology

The fusion technological consequences of the radioactive decay behaviour of SiC-based structural material were analysed based on a complete chemical analysis of an industrial SiCf/SiC composite. Radioactivation simulation was performed with the FISPACT-2 code and EAF-2 cross-section library, taking n-spectra from the SEAFP reactor study for first wall and blanket. The decay of radioactivity in SiCf/SiC after shut down and derived radiological quantities are presented and compared with those of SEAFP structural materials. The effective dose equivalent (EDE) to the population from accidental release of activated material was computed with the GENII code. SiCf/SiC performs favourably. Contact dose rates and γ-dose rates inside the plasma chamber are given. Assuming an upper limit of 104 Gy h−1 for robotized maintenance, SiCf/SiC renders the first wall a zone where immediate repair would be possible. For this short-term activation limit, an elemental “critical list” is presented. Long-term decay heat generation and contact dose rates show which material fulfils waste limits. Although Al-26 is generated in the first wall, SiCfSiC is a safely disposable material, owing to other characteristics such as inertness against corrosion

Silicon carbide and the new low activation requirements for a fusion reactor first wall

The radioactive behaviour of silicon carbide is compared to that of other structural materials proposed for fusion applications. This analysis takes into account short- and long-term issues like accident safety, maintenance and waste management. Low activation criteria based on the compliance with radioactivity limits are proposed. According to these criteria, steels can hardly be considered as possible low-activation materials. Even the elementally-tailored reduced activation steels can never fulfil completely all criteria. Vanadium alloys and SiC in the form of a new ceramic matrix/ceramic fibre composite ("SiC/SiC") must be regarded as the most promising low-activation materials, as far as radiological/activation behaviour is concerned. Some of the problems associated with the activation of vanadium alloys are examined. SiC/SiC turns out to be an ideal low-activation material as all criteria are fulfilled. Attention is given to the activation of SiC impurities

Purity and radioactive decay behaviour of industrial 2D-reinforced SiCf/SiC composites

Ceramic matrix composites based on SiC with continuous fibres (SiCf/SiC) are considered promising structural materials for future fusion devices. It was still to clarify, whether impurities in industrial SiCf/SiC could jeopardise radiological advantages. Experimental impurity analyses revealed a two-dimensionally reinforced SiCf/SiC with the matrix produced by \CVI\ as very pure. Chemo-spectrometric methods were combined with radioactivation methods (CPAA, NAA). A quantification of the main constituents Si, C and O was added. Calculations with the FISPACT-2.4 code and EAF-2 library identified elements detrimental for different low-activation criteria. For the neutron exposure, \EEF\ reactor-study first wall and blanket conditions were simulated. The calculated SiCf/ SiC included 48 trace elements. Even under conservative assumptions, all low-activation limits of European interest are fulfilled. Exclusively the hands-on recycling limit for the First Wall can intrinsically not be satisfied with SiC. The theoretical goal of a SiCf/SiC depleted of 28Si (isotopic tailoring) is critically discussed

Equal division kernel and reference coalitions in three-person games: results of an experiment

SIGLETIB Hannover: RN 5363 (111) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Magnetic resonance imaging of dissolved hyperpolarized 129Xe using a membrane-based continuous flow system

A technique for continuous production of solutions containing hyperpolarized (129)Xe is explored for MRI applications. The method is based on hollow fiber membranes which inhibit the formation of foams and bubbles. A systematic analysis of various carrier agents for hyperpolarized (129)Xe has been carried out, which are applicable as contrast agents for in vivo MRI. The image quality of different hyperpolarized Xe solutions is compared and MRI results obtained in a clinical as well as in a nonclinical MRI setting are provided. Moreover, we demonstrate the application of (129)Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized (129)Xe that has been both dissolved in and outgassed from a carrier liquid in a lung phantom, illustrating its potential for the measurement of lung perfusion and ventilation