Study of Thorium Fuel Cycles for Light Water Reactor VBER-150

The main objective of this paper is to examine the use of thorium-based fuel cycle for the transportable reactors or transportable nuclear power plants (TNPP) VBER-150 concept, in particular the neutronic behavior. The thorium-based fuel cycles included Th232+Pu239, Th232+U233, and Th232+U and the standard design fuel UOX. Parameters related to the neutronic behavior such as burnup, nuclear fuel breeding, MA stockpile, and Pu isotopes production (among others) were used to compare the fuel cycles. The Pu transmutation rate and accumulation of Pu with MA in the spent fuel were compared mutually and with an UOX open cycle. The Th232+U233 fuel cycle proved to be the best cycle for minimizing the production of Pu and MA. The neutronic calculations have been performed with the well-known MCNPX computational code, which was verified for this type of fuel performing calculation of the IAEA benchmark announced by IAEA-TECDOC-1349. 1. Introduction There is a growing interest in small reactors, and specifically TNPP. These reactors could represent a solution for developing countries with energy needs on islands, with remotely located areas without interconnected electricity grids or without the infrastructure required for land-based stationary NPP. Various designs have been developed, but most of the TNPP are based on long-term experience acquired with ship propulsion reactors and with larger land-based stationary reactors. Depending on the host state requirements, the plant can be operated by the supplier state or by an entity from the receiving country. The host state can acquire a TNPP to own with all the consequences associated with the use of nuclear energy. In other scenario, the supplier state has additional responsibilities that may include delivery and return of the TNPP and its operation if requested by the host state. All operations with the nuclear fuel are done at the zone of responsibility of the supplier state. Anyway, to implement this, it is necessary to design a reactor core with long operation cycles without on-site reloading and shuffling of fuel, which ensures difficult access to the fuel during the entire period of the reactor installation operation including transportation. Some TNPP being considered today for export, but they are innovative concepts and need effort for the demonstration of their viability [1]. The use of thorium based fuel cycle and the exclusion of on-site refueling provides the solution to the nonproliferation problem; therefore, this category of reactors is very attractive for energy supplies in developing countries.