As ThorCon operates, an intricate dance takes place. Fissile isotopes will split creating fission products. Some of the fission products will decay or be transmuted. Some of the fission products will be removed by the offgas system; some will plate out. Thorium will be converted to U-233. And periodically fuel or thorium will be added as necessary to keep keff very close to 1.0. In order to study the evolution or burn up of the fuelsalt, Martingale used the Serpent package as extended by Politecnico di Milano. Serpent is the remarkable achievement of the Finnish VIT center under the leadership of Jaakko Leppanen. It combines most of the Monte carlo capabilities of MCNP with an extremely fast burn up capability. The extension of Serpent to liquid fuel reactors was done by Manuele Aufiero and his colleagues in Milan. Both groups generously allowed us to use their code.
The drawings shows Serpent’s flavor view of ThorCon. In these drawings, the fuelsalt is shown in red, graphite in green, B4C in purple, concrete in gray, borated water in blue, concrete in gray, and stainless steel in black. The Serpent model is very similar to the MCNP model, but a bit simpler, and very much faster.