Sébastien Massart

On the Merits of Using a 3D-FGAT Assimilation Scheme with an Outer Loop for Atmospheric Situations Governed by Transport

Abstract Three-dimensional variational data assimilation (3D-Var) with the first guess at appropriate time (FGAT) appears to be an attractive compromise between accuracy and overall computing time. It is computationally cheaper than four-dimensional (4D)-Var as the increment is not propagated back and forth in time by a model, yet the comparison between the model and the observations is still computed at the right observation time. An interesting feature of the 4D-Var is the iterative process known as the outer loop. This outer-loop approach can also be used in conjunction with 3D-FGAT. But it requires the application of the 3D-FGAT analysis increment at the beginning of the assimilation window. The pros and cons of using this unusual 3D-FGAT variant are illustrated in this paper on two applications focused on the transport, one of the main phenomena governing the atmospheric evolution. The first one is the one-dimensional advection of a passive tracer. By three representative situations, it shows the ben...

Use of 3D-VAR and Kalman filter approaches for neutronic state and parameter estimation in nuclear reactors

Abstract In this paper, data assimilation (DA) techniques that have proven to be efficient in the fields of meteorological forecast and oceanography are applied to neutronics problems. Two applications, the techniques of which can be used to enhance optimization, are presented: three-dimensional (3-D) neutronic field interpolation in online core monitoring, and parameter estimation in code qualification procedures. First, the main bases of DA theory are shortly presented. Calibration and estimation procedures that are in use today at Electricité de France (EDF) are then briefly introduced. We also analyze the main limitations of these procedures and the potential improvements that the use of various DA techniques can provide. We present the MANARA mock-up, which computes a 3-D field interpolation and has been implemented in PALM, a DA-dedicated coupling platform developed at the Centre Européen de Recerche et de Formation Avancée en Calcul Scientifique (CERFACS). Result validation and comparison with former interpolation procedure CAMARET are also presented. Next, the principles of the KAFEINE mock-up, based on an extended Kalman filter approach, are displayed. This application covers the field of optimal parameter calibration using the in-core measures. In conclusion, these first two applications to neutronics, carried out in partnership between CERFACS and EDF Research and Development, seem very promising, especially considering the new generation of neutronic solvers that are being developed in the frame of the DESCARTES project.

Differential influence of instruments in nuclear core activity evaluation by data assimilation

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