17 research outputs found
Optimal design of measurement network for neutronic activity field reconstruction by data assimilation
Using data assimilation framework, to merge information from model and
measurement, an optimal reconstruction of the neutronic activity field can be
determined for a nuclear reactor core. In this paper, we focus on solving the
inverse problem of determining an optimal repartition of the measuring
instruments within the core, to get the best possible results from the data
assimilation reconstruction procedure. The position optimisation is realised
using Simulated Annealing algorithm, based on the Metropolis-Hastings one.
Moreover, in order to address the optimisation computing challenge, algebraic
improvements of data assimilation have been developed and are presented here.Comment: 24 pages, 10 figure
Variational assimilation for xenon dynamical forecasts in neutronic using advanced background error covariance matrix modelling
Data assimilation method consists in combining all available pieces of information about a system to obtain optimal estimates of initial states. The different sources of information are weighted according to their accuracy by the means of error covariance matrices. Our purpose here is to evaluate the efficiency of variational data assimilation for the xenon induced oscillations forecasts in nuclear cores. In this paper we focus on the comparison between 3DVAR schemes with optimised background error covariance matrix B and a 4DVAR scheme. Tests were made in twin experiments using a simulation code which implements a mono-dimensional coupled model of xenon dynamics, thermal, and thermal–hydraulic processes. We enlighten the very good efficiency of the 4DVAR scheme as well as good results with the 3DVAR one using a careful multivariate modelling of B
Differential influence of instruments in nuclear core activity evaluation by data assimilation
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
Exact and efficient solutions of the LMC Multitask Gaussian Process model
The Linear Model of Co-regionalization (LMC) is a very general model of
multitask gaussian process for regression or classification. While its
expressivity and conceptual simplicity are appealing, naive implementations
have cubic complexity in the number of datapoints and number of tasks, making
approximations mandatory for most applications. However, recent work has shown
that under some conditions the latent processes of the model can be decoupled,
leading to a complexity that is only linear in the number of said processes. We
here extend these results, showing from the most general assumptions that the
only condition necessary to an efficient exact computation of the LMC is a mild
hypothesis on the noise model. We introduce a full parametrization of the
resulting \emph{projected LMC} model, and an expression of the marginal
likelihood enabling efficient optimization. We perform a parametric study on
synthetic data to show the excellent performance of our approach, compared to
an unrestricted exact LMC and approximations of the latter. Overall, the
projected LMC appears as a credible and simpler alternative to state-of-the art
models, which greatly facilitates some computations such as leave-one-out
cross-validation and fantasization.Comment: 21 pages, 5 figures, submitted to AISTAT
Best linear unbiased estimation of the nuclear masses
This paper presents methods to provide an optimal evaluation of the nuclear
masses. The techniques used for this purpose come from data assimilation that
allows combining, in an optimal and consistent way, information coming from
experiment and from numerical model. Using all the available information, it
leads to improve not only masses evaluations, but also to decrease
uncertainties. Each newly evaluated mass value is associated with some accuracy
that is sensibly reduced with respect to the values given in tables, especially
in the case of the less well-known masses. In this paper, we first introduce a
useful tool of data assimilation, the Best Linear Unbiased Estimation (BLUE).
This BLUE method is applied to nuclear mass tables and some results of
improvement are shown
Robustness of nuclear core activity reconstruction by data assimilation
We apply a data assimilation techniques, inspired from meteorological
applications, to perform an optimal reconstruction of the neutronic activity
field in a nuclear core. Both measurements, and information coming from a
numerical model, are used. We first 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
Theory of fusion hindrance and synthesis of the superheavy elements
The two-step model for fusion reactions of massive systems is briefly
reviewed.By the use of fusion probabilities obtained by the model and of
survival probabilities obtained by the new statistical code, we predict residue
cross sections for 48Ca+actinide systems leading to superheavy elements with
Z=114, 116 and 118.Comment: 7 pages, 4 figures, Halong Bay meeting proceedin