Authors: (Piyush Sabharwall, Eung Soo Kim, Idaho National Laboratory, Idaho Falls, Idaho, USA)
Abstract: The next generation nuclear reactor will likely be a helium cooled gas reactor with an outlet temperature of about 750–800°C for the first of a kind, further increased to 900–950°C for the nth of a kind. These reactors will not only produce electricity, they will also provide process heat for applications such as hydrogen production, coal gasification, etc. Helium was selected as the coolant for this reactor because it is inert and relatively easy to handle, has a low macroscopic neutron cross section, and can be operated at high temperatures without high pressurization. In order to overcome the inherent disadvantage of lower heat transfer and heat transport characteristics of gas coolants and obtain higher thermodynamic efficiencies (Brayton Cycle), it is necessary to operate the fuel elements at highest temperatures as possible (fuel centerline temperature being the limit) and permit high gas temperature rise in the reactor by reducing the mass flow rate and pressurizing the gas. Gas reactors because of the capability of transmutation of fertile transuranics, could also be utilized for deep burn, which provides profound benefits in terms of better use of uranium resources, reduction in long term nuclear materials proliferation risks and high level storage requirements.