Advanced In-Core Fuel Cycles for the Gas Turbine-Modular Helium Reactor

Abstract: In 1789 a German chemist, Martin Heinrich Klaproth, announced the discovery of a new element: uranium; few years later, the head of father of the modern chemistry, Antoine Lavoisier, was swept away by guillotine: a new era was destined to be opened, either where energy would have been produced in large scale by nuclear processes delivering hundreds of times the energy of chemical processes or where a mass of people, revolutionary or not, would have been melted down into a couple of seconds. After a quite long time, on the 2nd December 1942, the first nuclear reactor has been put into operation by Enrico Fermi in Chicago; few years later, came also the dark side utilization of fissile materials in Hiroshima and Nagasaki. Since those moments, three power plants generations succeeded, until the current one which is the generation IV of nuclear reactors. The latter has the goal of generating electricity in a safe manner, for the core is designed to provide an effective passive cooling of the decay heat. Amid generation IV of nuclear power plants, the Gas Turbine – Modular Helium Reactor, designed by General Atomics, is the only core with an energy conversion efficiency of 50%; the above consideration, coupled to construction and operation costs lower than ordinary Light Water Reactors, renders the Gas Turbine – Modular Helium reactor rather unequaled.In the present studies we investigated the possibility to operate the GT-MHR with two types of fuels: LWRs waste and thorium; since thorium is made of only fertile 232Th, we tried to mix it with pure 233U, 235U or 239Pu; ex post facto, only uranium isotopes allow the reactor operation, that induced us to examine the possibility to use a mixture of uranium, enriched 20% in 235U, and thorium. We performed all calculations by the MCNP and MCB codes, which allowed to model the reactor in a very detailed threedimensional geometry and to describe the nuclides transmutation in a continuous energy approach; finally, we completed our studies by verifying the influence of the major nuclear data libraries, JEFF, JENDL and ENDF/B, on the obtained results.