Interactions between radio-nuclides and sodium aerosols formed during an accident in a sodium-cooled nuclear reactor

PhD student : Ankita Jadon

In the context of Gen IV reactor development, the consequences of a severe accident in sodium cooled fast nuclear reactor (SFR) have to be investigated. One critical risk of a severe accident (SA) is the core disruption accident and production of contaminated aerosols in the containment building by ejection of primary-coolant-system sodium through the reactor top vault. Being pyrophoric, the ejected sodium droplets react with oxygen first oxidizing then burning, with a significant release of heat of combustion and regarded as a potential threat to the integrity of the containment vessel. Beyond the effects of pressure and temperature, it is important to analyze the chemistry of interaction of the sodium aerosols and radio iodine in order to monitor their effect. Moreover, this analysis is an essential step in the analysis of the source term.

The different and successive species of sodium aerosols formed are sodium peroxides/hydroxides/carbonates are very reactive in nature and they can readily react with the fission products which are also present in the containment of an SFR. In addition to being toxic (in oxide form), the aerosol will then become radioactive. If such aerosols are leaked in the environment they can contaminate the environment and pose danger to the humans and plants in the vicinity.

The aim of this doctoral research is to study the interaction between sodium fire aerosols and iodine for a more quantitative source term prediction in case of a SA in an SFR. Theoretical investigation as well as experimental tests are planned that will serve to improve the modelling of containment phenomenology in the simulation code currently developed in the IRSN for computing severe accidents.

In order to carry the experiments dedicated to study the interaction between sodium aerosols and radio iodine, surface energy calculations of different sodium fire aerosol compounds like carbonates and bicarbonates will be first performed using the density functional theory; VASP (Vienna ab initio simulation package). These calculations will provide us with the entropies and standard enthalpy of formation of these compounds at and their interaction with iodine.

Laboratory:  ​Corium and Radioelement Transfer Research Laboratory - cf PC2A