Experimental and Analytical Investigations to Loss of Vacuum Accidents for Fusion Reactors

Loss of vacuum accidents (LOVA) in fusion reactors will
lead to an air ingress into the vacuum vessel, oxidation
of the hot armour material and a partial mobilization of
the sorbed tritium. Also burnable carbon monoxide will
be formed during these accidents. In continuation to the
testing of carbon candidate materials for the First Wall
under oxidizing conditions in oxygen and steam in
collaboration with NET the carbon compound Aerolor AO5
of Carbone Lorraine has been examined in detail in the
experiments INDEX2 and SPALEX of the Institute of Safety
Research and Reactor Technology of Forschungszentrum
Jülich. The chosen parameters for these oxidation
experiments with oxygen in the inpore diffusion
controlled regime are temperatures between 973 K and
1173 K and partial pressures of oxygen between 1140 Pa
and 21000 Pa at system pressures between and; that means
reaction gas con centrations between 1 vol.-% and 20
vol.% oxygen in argon. From these results a semi-
empirical kinetic equation for the heterogeneous primary
reaction was developed. The equation considers the
dependence of the reaction rate on temperature, partial
pressure and burn-off of the material.
For calculations of LOVA the code RALOC Mod 4.0 AD -
developed by the Gesellschaft für Anlagen- und
Reaktorsicherheit (GRS) mbH has been extended by the
model COX (Carbon Oxidation) to consider carbon
oxidation kinetics. This kinetic model is based on the
above mentioned experimental results. First calculations
have been done for leak areas of 0.01 m², 0.1 m² and 1.0
m² and for different numbers of nodes in the reaction
chamber. The comparison of these results with earlier
calculations of JRC Ispra, GRS and Technicatome showed
that the new model COX and the nodalisation scheme lead
to more reliable statements concerning the spatial
dependencies especially for the burn-off of the armour
material and for the masses of the formed gases CO and
CO2.