| Summary: | Within the project TECNO_FUS on CONSOLIDER- INGENIO 2010 program, a dual
coolant blanket design is developing (DCLL = Dual Coolant Lithium Lead) for
DEMO with Pb-15.7Li and He as coolant. It is a ferritic-martensitic steel with low
activation as structural metrial cooled by He. The Pb-15.7Li acts as tritium breeder,
neutron multiplier and coolant. The Pb-15.7Li outlet temperature has been as high
as possible to achieve the highest possible efficiency, without exceeding the
maximum temperature of steel. Due to the high magnetic fields produced in the
region of the blanket, the Pb-15.7Li needs to be electrically insulated from the steel
to reduce the magnetohydrodynamic pressure drop (MHD). Also, it should be
thermially insulated from stell to avoid heat loss. This is one of the main functions of
the Flow Channel Iserts (FCI), which also act as thermal insulator to maximize the
Pb-15.7Li temperature, and thus, the efficiency.
Silicon carbide is the main candidate material for FCI in the DLL blanket, due to its
excellent thermal, mechanical and chemical stability at high temperatures, low
thermal expansion, good thermal shock resistance, low corrosion by Pb-15.7Li, low
activation and good resistance to neutron irradiation, low activation and good
resistance to neutron irradiation. Porous SiC is one of the most attractive types of
SiC under consideration, since it is expected to achieve the required properties
following a simple and inexpensive manufacturing route compared to SiCf/SiC
materials. To avoid tritium permeation and corrosion by Pb-15.7Li, a dense coating
must be applied on the porous SiC surface.
In this work the results obtained in the production of porous SiC powder
metallurgical route by pressureless sintering are presented. For the manufacture of
porous SiC different particle size starting SiC and carbonaceous powders, with and
without additives, have been used. A study on liquid phase sintering by varying
sintering temperature and time is performed. Carbonaceus powders are used as poreformers
by their burnout during oxidation after sintering. A study on the effect of
different processing parameters on final relevant properties of porous SiC has been
carried out and the two most promising porous SiC materials were selected on the
basis of lowest thermal conductivity (11-13 W/mK a 700 °C) and highest flexural
strength (100-140 MPa). The two selected materials are coated with a 30 μm thick
CVD SiC layer. Electrical conductivity was measured at CIEMAT before and after
irradiation in a Van de Graaff accelerator with 1.8 MeV electrons up to 130 MGy,
and values < 20 S/m at 400°C are obtained. Corrosion tests under static Pb-15.7Li are
conducted at 700C during 1032 houers under 99% Ar + 1% H2 atmosphere at IQS;
even though the used Pb-17.5Li has very high O content, the 30 μm CVD SiC layer
provide partial protection against corrosion.
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