Innovative thorium fuel cycles in a generation IV very high temperature hybrid system - 5407

Nuclear energy faces 4 important issues to be successful as a sustainable energy source: nuclear safety, economic competitiveness, proliferation resistance and a minimal production of radioactive wastes. Actually, an innovative generation of nuclear energy systems and fuel cycles are under investigation in order to solve these challenges. Very High Temperature Pebble Bed Reactors together with fuel cycles based on thorium could offer the opportunity to solve these challenges. This paper shows the results of the use of a hybrid system formed by a Very High Temperature Pebble Bed Reactor (VHTR) and two Pebble Bed Accelerator Driven Systems (ADSs) using a variety of fuel cycles with thorium (²³²Th+²³³U, ²³²Th+²³⁹Pu and ²³²Th+U) under a deep burn scheme. Parameters related to the neutronic behavior as nuclear fuel breeding, Minor Actinides stockpile and the radiotoxicity of the long-lived wastes were used to compare the fuel cycles using the well-known MCNPX ver. 2.6e computational code. A benchmarking exercise using a benchmark announced by IAEA-TECDOC-1694 was performed utilizing the available results of the critical experiments performed at the ASTRA critical facility. This benchmarking exercise was solved in order to validate that the developed models with MCNPX code and the available library in XSDIR are adequate for studies of thorium fuel cycles in a Very High Temperature Pebble Bed Reactor. (authors)