A neutronic evaluation of VHTR and LS-VHTR

VHTR (Very High Temperature Reactor) and LS-VHTR (Liquid Salted - Very High Temperature Reactor) reactors were analyzed and compared from the viewpoint of the neutronic parameters. The multiplication coefficient (k_inf), the fuel and the moderator temperature coefficients (α_TF and α_TM, respectively) and the hardening spectrum (φF/φT, fast flux/total flux) parameters were analyzed focusing to understanding better the VHTR and LS-VHTR neutronic behaviors. The experience obtained performing this work will be used in the future to study and to simulate the possibility of such systems for fuel reprocessing and recycling always analyzing how the process can affect the hydrogen production efficiency. The preliminary analyses have demonstrated that the VHTR reactor has a safer behavior in comparison with to the LS-VHTR one considering the evolution of the safety parameters along the burnup using WIMSD simulations.