In-vessel source term calculation using chemical equilibrium approach for a medium sized sodium cooled fast reactor

• Published in: Nuclear engineering and design 2020-06, Vol.362, p.1-11, Article 110583
• Main Authors: Patel, Parthkumar Rajendrabhai, John Arul, A
• Format: Article
• Language: English
• Subjects: Accidents; Alkali metals; Antimony; CDA; Chemical equilibrium; Europium; Free energy; Gases; Heavy metals; Lanthanides; Mathematical analysis; Metal fuels; Nuclear fuels; Optimization; Radioisotopes; Radionuclide; Rare gases; Reactors; Release fraction; Severe accident; Sodium; Sodium cooled reactors; Source term; Strontium; Vessels
• ISSN: 0029-5493; 1872-759X
• DOI: 10.1016/j.nucengdes.2020.110583

•First time application of thermochemical equilibrium approach to calculate in-vessel source term of oxide-fuelled FBR core.•Release behaviour of various chemical species formed at constant volume is analysed for different temperatures.•An open source, modular code capable of calculating equilibrium species at constant (T, V) or (T, P) is developed.•Comparative validation of code is presented.•The differences in release fractions between a metal and oxide fuelled reactors are studied. Quantifying the severe accident in-vessel source term for a fast reactor is a computationally challenging task owing to the complex phenomena and wide range of accident paths to be studied. A chemical equilibrium approach offers a relatively accident path independent way to quantify the source term. Here we follow a thermochemical equilibrium approach to the determination of in-vessel source term for a medium-size oxide-fuel sodium-cooled fast reactor. Assuming a uniformly mixed molten corium at a given temperature and volume, the quantity of radionuclides released to the cover gas volume in gaseous form is determined. The development of a modular code in Python for the calculation of equilibrium species in different phases from specified initial inventory at given thermodynamic conditions and its validation are discussed. From the calculations, it is observed that strontium, europium and other lanthanides form stable oxide species in the sodium as opposed to the elemental form in metal fuel reactors. As is the case with noble gases, almost complete inventory of alkali metals and antimony could be released to the cover gas in elemental form (Cs, Sb). The differences in release fractions between metal fuelled and oxide fuelled reactors are brought out in the study.