Development of Revolutionary and Accurate Methods for Safety Analyses of Future and Existing Reactors

Start date 01/01/2013
End date The project is closed: 31/12/2017


Illustration of the multi-physics nature of nuclear reactor cores, where neutron transport, fluid dynamics, and heat transfer need to be simultaneously modelled.


The design, licensing, and operation of nuclear reactors heavily rely on state-of-the-art modelling tools. These tools are used to demonstrate that such systems can be run safely and economically during normal and off-normal situations. This applies to both the existing fleet of nuclear reactors, as well as future nuclear reactors.

By essence, nuclear reactors are complex systems, involving different strongly-coupled physical phenomena at different scales. More precisely, the temporal and spatial distribution of the neutrons is strongly influenced by the temporal and spatial distribution of the density and temperature of the different media constituting such systems. Likewise, the distributions of the density and temperature depend on the energy released by fission, which in turn depend on the distribution of the neutrons throughout the nuclear core. In order to guarantee a reliable prediction of the behaviour of nuclear systems, the different physical fields have to be solved simultaneously at all scales, and calculations of the transport of neutrons, of the dynamics of the fluid cooling the system, and of the transfer of heat throughout the system have to be performed in a concurrent manner.

With the rapid development of the computer capabilities in the 70ies, different sets of computers codes and modelling strategies have emerged. For historical reasons, they nevertheless all rely on solving the different physical fields and different scales separately, i.e. different codes are used to separately resolve the different physical fields and different scales. Such codes are only thereafter coupled in an a posteriori fashion in order to handle the inter-dependence of the different physical fields and their different scales. The current modelling tools all rely on such an approach.

Although this modelling strategy works satisfactorily for steady-state conditions, it is challenged by the new designs of the fuel assemblies being introduced in the existing fleet of nuclear reactors, and by the new reactor concepts being investigated for near-term and long-term deployment. Moreover, in case of non-steady-state conditions, such a strategy leads to simulations of rather poor reliability, since the non-linear coupling terms existing between the different physical fields are actually not resolved.

The present project tackles the modelling of nuclear reactor systems from several innovative viewpoints. The multi-physics and multi-scale aspects of these systems are taken into account right from the start in the modelling process, by accounting for the interdependency of the different physical fields and their different scales. The latest advances in numerical methods are used for resolving the strong non-linear coupling existing between the different physical fields. In order to use a set of consistent methods for performing both steady-state and non-steady-state simulations, fast running coarse-mesh methods are used to resolve the different physical fields. The multi-scale phenomena are handled in two different manners: for neutron transport, a fine-mesh solver is embedded into the coarse-mesh solver, and both solvers work in tandem in order to model the impact of large scale phenomena on small scale ones and vice-versa. For fluid dynamics, subgrid models are used to provide the necessary small scale information the coarse-mesh solver cannot by itself recover.

In contrast with how the existing codes being used were developed, the present project gathers a team of experts in nuclear reactor simulations, neutron transport, fluid dynamics, heat transfer, and numerical methods, working in an integrated and collaborative manner. With the innovative approach highlighted above to resolve the different physical fields and their different scales, they try to bring the simulation of nuclear reactor systems to an unprecedented level of reliability and sophistication.

Project leader
Professor ​​Christophe Demazière, Subatomic and plasma physics
Antoni Vidal-Ferrándiz, Post-Doc, Universitat Politecnica de Valencia
Sebastian Gonzalez-Pintor, Post-Doc, Subatomic and Plasma Physics, Department of Physics
Anders Ålund, Fraunhofer-Chalmers Centre
Fredrik Edelvik, Accociate Professor, Fraunhofer-Chalmers Centre
​The Swedish Research Council

Published: Thu 09 Jan 2020.