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Enhancing Nuclear Safety


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BESTAIR project

Last update on September 2015



The BESTAIR (Beryllium Source Term due to an Accident in the ITER Experimental Reactor) project was led by IRSN in 2013-2014, with the aim of better assessing the potential release of beryllium into the environment in the event of an accident at the ITER facility. It received the IRSN Research Creativity Award in 2015.
 
 
Context and objectives
 
The international ITER project seeks to demonstrate the technological feasibility of producing energy by thermonuclear fusion from tritium and deuterium plasma. This involves the confinement of plasma at several hundred million degrees Celsius in a 2000 m3 vacuum vessel with tungsten and beryllium walls for several hundred seconds, using superconducting magnets maintained at a very low temperature. The vacuum vessel also has a water cooling system.
 
In normal operation, the tritium not consumed by the fusion reaction and several hundred kilograms of tungsten and beryllium dust produced by the erosion of the vessel's inner walls will accumulate in the vessel. In the event of an accident associated with a loss of containment caused by either air intake following breach of one of the vacuum vessel's openings or water caused by a ruptured coolant pipe, the (extremely toxic) berylliated and tritiated dust and gas may be released into the environment. The facility features filtration systems to mitigate the effects of this eventuality.
 
The BESTAIR project sought to improve knowledge of the berylliated and tritiated chemical species in the reactor vessel and to model their behavior in the event of an accident in order to better assess the efficiency of the filters that should be used for the ITER facility. The chemical scope of previous studies was limited to oxygen, tritium and hydrogen, whereas this project also takes into account beryllium and should help predict all berylliated and tritiated species that could form and be accidently released from the facility.
 
 
Project outline and results
 
The BESTAIR project focused on the study of thermodynamic data for gaseous species in the Beryllium-Oxygen-Hydrogen-Tritium (Be-O-H-T) system as most beryllium and tritium releases into the environment (source term) will be in gaseous form.

To this end, BESTAIR first drew on critical analysis of existing experimental results in the bibliography before using calculations from theoretical chemistry to supplement missing data.
 
Four steps were followed:
  • the first step consisted of conducting a more precise reassessment of the enthalpy of formation of gaseous oxides  (BeO, Be2O, BenOn where n < 7) and hydroxides (BeOH et Be(OH)2), on the basis of calculations of the structural and vibrational constant geometrics of the gaseous molecules, and a new interpretation of experimental spectrometric data available in previous research;
  • the second step focused on defining and validating a methodology for the theoretical characterization of the Be-O-H system on the basis of theoretical chemistry calculations for the species considered to be the most well-known. These calculations were made using various methods based on the Density Functional Theory (DFT)1 and helped increase the confidence level for calculating the predicted thermodynamic properties of berylliated species of interest;
  • the third step sought to determine missing or unreliable thermochemical data (particularly data for tritiated species) using the previously defined methodology;
  • the final step drew on work from the first three steps and consisted of determining the most stable components in the Be-O-H-T system under accidental conditions with the loss of containment in the ITER facility



    Outlook

    Given the very large mass (around 500 kg) of beryllium dust in the vacuum chamber, the heterogeneous interactions between this dust and the tritium must be considered. This work requires an approach that draws on both solid-state physics and theoretical chemistry to develop predictive hydrogen absorption/desorption models. It is the topic of a thesis by Laura Ferry, begun in October 2014 at IRSN.



    1. Quantum calculation method for the exact study of the electronic structure of a molecule.


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