In a LWR severe accident, carbon monoxide (CO) may be
generated inside the containment due to molten corium concrete
interaction (MCCI). As a component of the accident atmosphere, CO will
interact with passive auto-catalytic recombiners (PARs) which are
installed inside LWR containments for hydrogen (H2) removal. Depending on the boundary conditions, CO may either react with oxygen to carbon dioxide (CO2)
or act as catalyst poison, reducing the catalyst activity and hence the
hydrogen conversion efficiency. A new experimental test programme
performed in co-operation between JÜLICH and RWTH investigates these
aspects aiming at providing data for model development for advanced
severe accident analyses.
In the first test series presented here, the parallel catalytic reaction of H2
and CO on the catalyst surface has been studied, i.e. the hydrogen
recombination reaction was started before CO was injected. In total, 33
steady state measurements have been performed. The test series was
jointly evaluated by JÜLICH, RWTH and IRSN.
The test results show that under the given conditions the conversion of CO into CO2
has no negative impact on the parallel hydrogen conversion. The
efficiency of the CO recombination in terms of molar rates is
significantly smaller (by a factor of ∼2) than the corresponding H2
conversion efficiency. Due to the exothermal reaction, the parallel CO
conversion may also have an impact on the possible ignition of the
flammable gases at hot PAR surfaces.
The authors have used three different numerical codes for the simulation of the parallel CO/H2
recombination. The codes REKO-DIREKT (JÜLICH/RWTH), SPARK (IRSN), and
CFX (ANSYS) were able to capture the effects observed in the
experiments, providing a versatile basis for further investigations in
this important safety issue. The different model approaches and
additional enhancements in order to simulate the CO test series are
described in the paper.