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30/01/15 The fourth ARCHER Newsletter was released on 30 January 2015. Read online here

21/01/15 The second ARCHER EUROCOURSE, hosted by NRG, was held in Petten from 19-20 January 2015. Click here for more info

26/11/14 The third ARCHER Newsletter was released on 26 November 2014. Read online here

28/10/14 The ARCHER final meeting was held on 21-22 Jan 2015 at NRG in Petten (NL).

27/10/14 The High Temperature Reactor (HTR) Conference was held from 27-31 October 2014 in Weihai, Shandong Province, China. Click here for more info

29/03/14 The second Newsletter was released on 28 March 2014. Read online here

Supported by

European Commission

Promising first results for THINS study on Flow Modelling in a Pebble Bed

Intermediate simulation result of the flow and heat transfer in a limited sized randomly stacked pebble bedThe EU FP7 Thermal-Hydraulics of Innovative Nuclear Systems (THINS) project initiated a study on the detailed flow behaviour in a pebble bed to improve the understanding of heat distribution in a High Temperature Reactor (HTR).

Since experimental data are scarce and provide limited information, NRG has developed a simulation strategy based on Computational Fluid Dynamics, which shows how fluid and heat flows manifest themselves between pebbles.

First, a numerical experiment is performed. The methodology is based on fundamental principles of physics and a very small idealised pebble bed. To this end, after several months of preparation, around 60 computers were used in parallel for eight months. Different increasingly pragmatic engineering simulation methods were then compared to the numerical experiment and showed satisfactory and promising results.

To improve and validate these pragmatic engineering simulation methods, and ultimately the methods at full reactor scale, NRG worked out a multistep simulation validation strategy in which each step moves closer to the real conditions at the cost of the computational approximations.

More ‘realism’ was added by simulating a randomly stacked pebble bed, created in cooperation with Delft University of Technology, containing about 30 pebbles limited in size. These simulations are now running.

This second step should be followed by another simulation of a limited size randomly stacked pebble bed with one of the sides simulating the reactor vessel wall influencing the pebble stacking and giving rise to a bypass flow.

Ultimately, after this step, the available approximation correlations used in the simulation techniques for reactor-scale simulations should be improved, allowing more accurate simulations of a complete HTR reactor core.