  The reactor baffle is an important component of a nuclear reactor that fixes
the location of the fuel assembly in the reactor core. The main types of
baffles are called light or heavy. The light baffle has mostly the form of
steel plates with outer space filled by water, and the heavy baffle is mostly a
forged steel element. Both concepts have advantages as well as disadvantages.
In the case of the light baffle, one does not need to solve the issue of void
swelling, but the neutron economy is not ideal, while the heavy baffle has a
good neutron economy, but void swelling is an issue. This paper deals with the
effect of the heavy VVER-1000 baffle on criticality. Criticality was measured
using a well-defined core composed of 6 fuel assemblies moved to a simulator of
the VVER-1000 internals, which is located at the LR-0 reactor. The experiments
confirm the fact that the water filling the cooling channels in the baffle has
a strong neutron absorbing effect. The keff calculated using the ENDF/B-VIII.0
library significantly underpredicts the experiment, whereas calculations using
a new evaluation of 56Fe by the IAEA (INDEN collaboration) give a better
agreement. Generally, the presented results are suitable for validation of iron
cross sections.
