  The global activity fields of a nuclear core can be reconstructed using data
assimilation. Data assimilation allows to combine measurements from
instruments, and information from a model, to evaluate the best possible
activity within the core. We present and apply a specific procedure which
evaluates this influence by adding or removing instruments in a given
measurement network (possibly empty). The study of various network
configurations of instruments in the nuclear core establishes that influence of
the instruments depends both on the independant instrumentation location and on
the chosen network.
