Control rod calculation in axially-heterogeneous fast reactors. Part II: Impact of 3D homogenization on core parameters
Artikel i vetenskaplig tidskrift, 2017
Advanced sodium-cooled fast reactors with improved safety features, such as
the French ASTRID CFV-core concept, is characterized by an axial heteroge-
neous core, which will present a challenge on the homogenization procedures
used today, taking into account all the different axial material transitions.
Reliable modeling of the control rod and accurate prediction of the control
rod worth are essential to determine the shutdown margins and to ensure
In this work (Part II of II), two different homogenization schemes are com-
pared. One is based on the traditional reactivity-equivalence procedure in 2D,
and the other a newly implemented 3D version of the reactivity-equivalence
procedure, with approximations based on the results in a companion pa-
pers (Part I). The deterministic results are compared with a Monte Carlo
Both of the cross section sets, from the two homogenization schemes, yielded results within the requested 5% error margin in reactivity. The
largest discrepancy was found for the classical procedure for the case with a
slightly inserted control rod (normal operating conditions).
Both sets of cross sections yielded similar power profiles in the fuel sub-
assembly neighboring the control rod within the 2 Monte Carlo standard
deviation. Neither of the cross section sets were able to predict the large
gradients in capture rates close to the internal control rod interfaces.
The study showed that the traditional 2D reactivity-equivalence proce-
dure produces homogenized cross sections which yield reliable results in a
CFV-type core. One exception from this was found for slightly inserted con-
trol rods, where the effect of the follower/absorber interface could not be fully
captured by the 2D scheme, and for such cases, 3D modeling is recommended.