Performance assessment of a 3-D steady-state and spatial kinetics model for the CROCUS reactor
This dissertation covers both experimental and numerical neutronics studies to evaluate
the adequacy of the Serpent/PARCS code sequence for modeling the steady-state and
kinetics behavior of the CROCUS reactor. The reactor presents design characteristics
that raise questions about the acceptability of diffusion theory for its modeling. The
PARCS model of CROCUS has been developed considering several potential sources of
biases. More precisely, albedo boundary conditions were used to limit the axial geometry
to the grid plates where diffusion theory may lead to inaccuracies due to the presence of
Cadmium layers. Proper treatment of scattering anisotropies through in-scatter correction
of diffusion coefficients were also fundamental for producing accurate eigenvalues in the
CROCUS reactor. A parametric study has been conducted to evaluate transport effects
and the impact of energy discretization on eigenvalue and pin power distribution.
Steady-state and time-dependent experimental data has been obtained from CROCUS
with the purpose of validating the computational scheme. A comprehensive evaluation of
experimental uncertainties provided support for the generation of reliable experimental
data. Particular focus was placed upon the development of transient experiments that
involve local perturbations of the flux. Delayed neutron effects were not captured in these
transients because of the tightly coupled nature of the reactor.
The comparison of PARCS simulations against experimental data indicated that control
rod reactivity worth is predicted within (43)%. PARCS radial fission rate distributions
are in considerable disagreement with experimental data for the outer core region, where
differences are as large as 15%. This was attributed to the fact that PARCS does not
allow using adaptable mesh sizes in the radial plane, which results in a mismatch between
the mesh and explicit pins of the outer core region. However, from a safety viewpoint,
these biases are conservative and are located in the outer core region where the power is
low. PARCS axial fission rate profiles agree within 1% with experimental data for the
bottom and mid regions for the core. On the other hand, larger deviations of about 20%
were encountered for the top region, which are attributed to transport effects near the
water/air interface. Finally, the investigation on neutron kinetic effects verified that the
PARCS code is capable of modeling the transient experiments with spatial effects in the
CROCUS reactor, where maximum differences are in the order of 5%.
Overall, the Serpent/PARCS scheme shows satisfactory performance for modeling the
CROCUS reactor, except for the estimation of radial reaction rate profiles, where biases
were attributed to the impossibility of adapting the mesh size to match the fuel pitch of
both fuel zones.
EPFL_TH8248.pdf
openaccess
8.6 MB
Adobe PDF
2a99d4b7bf601a6324479a30e8b187f2