Unified nuclear core activity map reconstruction using heterogeneous   instruments with data assimilation
  Evaluating the neutronic state of the whole nuclear core is a very important topic that have strong implication for nuclear core management and for security monitoring. The core state is evaluated using measurements. Usually, part of the measurements are used, and only one kind of instruments are taken into account. However, the core state evaluation should be more accurate when more measurements are collected in the core. But using information from heterogeneous sources is at glance a difficult task. This difficulty can be overcome by Data Assimilation techniques. Such a method allows to combine in a coherent framework the information coming from model and the one coming from various type of observations. Beyond the inner advantage to use heterogeneous instruments, this leads to obtain a significant increasing of the quality of neutronic global state reconstruction with respect to individual use of measures. In order to present this approach, we will introduce here the basic principles of data assimilation focusing on BLUE (Best Unbiased Linear Estimation). Then we will present the configuration of the method within the nuclear core problematic. Finally, we will present the results obtained on nuclear measurement coming from various instruments. 
Bertrand Bouriquet, Jean-Philippe Argaud, Patrick Erhard, Ang\'elique   Pon\c{c}ot
physics.data-an nucl-ex