CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

6 Data assimilation with EDF neutronic
models
The collaboration between the department SINETICS of EDF/R&D and CERFACS on data assimilation
has started in 2003 with the ADONIS project (2004-2007). This first collaboration was followed by the
ARTEMIS project (2008-2010) aimed at using data assimilation schemes to improve the modelling of the
neutronic state of power plants nuclear cores as well as the estimation of model parameters. The various
results provided during this period led to an extension of those researches within the ARTEMIS 2 project
(2011-2014). Making the most of this collaborative work, data assimilation is becoming a constitutive
part of neutronic studies and several prototypes were already built on top of the new neutronic model
COCAGNE.
6.1 Data assimilation for field reconstruction (B. Bouriquet,
O. Thual)
These experiments proved that the assimilation of the observed neutronic state with the BLUE algorithm
allows the correction of the neutronic state itself, namely the thermal flux of neutrons ([23]). These
results were presented in [24, 21] and corroborate the previous studies carried out on the neutronic model
COCCINELLE. This work have been extended to the new COCAGNE code for various detailed studies in
[15, DA21]. This work was improved using an extensive study on the modelling of the covariance matrix
reported in [16].
6.2 Robustness of data a assimilation respect to the number of
measurements (B. Bouriquet, O. Thual)
Knowing the quality of the field reconstruction through data assimilation study the robustness of the method
when the amount of measured information decreases. We then study the influence of the nature of the
instruments and their spatial repartition on the efficiency of the field reconstruction. It was shown that the
slopes of the reconstruction quality is mainly governed by the repartition of the instruments. Depending on
the chosen repartition, the decrease consists in two or three distinct phases. The behaviour with two phases
within the decreasing quality of the reconstruction as a function of the number of instruments removed is
understood in term of repartition effect, but not quantified yet. Those studies have been reported in [15] and
have been published in Nuclear Instrumentation and Method A [DA11].
6.3 Determination of the most important instrument for nuclear core
reconstruction (B. Bouriquet, O. Thual)
The previous studies prove that global activity fields of a nuclear core can be reconstructed using
data assimilation and that robustness is depending on the instrument network design. We present and
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