Deformed Core Reactivity Evaluation with Mesh Projection–Based Method
Résumé
Fast reactor designs are currently being revisited
aiming at having a consolidated safety dossier. In that
frame, studying any perturbation of nominal operating
condition is mandatory.
Among different initiators, particular attention is
being paid to reactivity insertion due to core assembly
bowing and deformation and induced lattice readjustments
as a consequence of events such as earthquakes.
In this study, a deterministic calculation scheme
based on the mesh projection method has been used in
order to evaluate the reactivity changes occurring in a
deformed sodium fast reactor core.
With the microscopic cross sections calculated by
ECCO, full three-dimensional core calculations are
being conducted with ERANOS (DIF3D), VARIANT,
and SNATCH to solve neutron transport equations in
either diffusion, nodal variational, or Sn transport
approximations.
A simple analytical model based on perturbation
theory has been developed to identify the main
phenomena leading to changes in the core reactivity.
Reactivity changes induced by small deformations can
be estimated as a summation of reactivity perturbations
of individual subassemblies.
The results obtained with this method have been
checked by comparing them to those obtained
with Monte Carlo simulations. A good agreement is
being found allowing the use of this method in
realistic problems with significant computer resource
reduction.
The different contributions to the reactivity changes
confirm the results of the analytical model.