Neutronic features of the GT-MHR reactor

The design of a Gas Turbine-Modular Helium Reactor (GT-MHR) of 600 MWt power is being developed in frames of "The Agreement between the Government of the United States of America and the Government of the Russian Federation on Scientific and Technical Cooperation in the Management of Plutonium That Has Been Withdrawn from Nuclear Military Programs" signed on July 24. 1998. The reactor concept is based on the deep burnup of initially loaded plutonium fuel at its single use in core and the subsequent disposal of the spent fuel without additional processing. The present paper describes the analysis of the basic features of the GT-MHR reactor core fueled by plutonium: 1. The annular type core design is used to decrease fuel temperature in accidents without active heat removal. 2. Unlike other alternatives for plutonium disposition (MOX fuel), in the basic variant of GT-MHR reactor design no fertile materials such as U-238, or Th-232 are used. Erbium is used as a burnable poison and means for ensuring the negative reactivity temperature coefficient. 3. Deep fuel burnup (640 MW day/kg on the average) leads to the significant accumulation of Pu-241 during irradiation of weapons grade Pu fuel. This fact determines the specific time dependence of the multiplication factor in the end of the fuel lifetime. 4. Rather hard neutron spectrum in the annular-type active core, and the essentially thermal spectrum in the reflectors cause a peak in the power distribution near the core-reflector boundary. Fuel and burnable poison zoning are used to control power profile. 5. The movement of control rods located in the side reflector noticeably deforms the power distribution in the core. 6. The temperature coefficient of reactivity depends both on the temperature and burnup level. In the GT-MHR reactor with plutonium fuel the temperature reactivity coefficient has values close to zero for temperatures less than 400 degreesC at the end of the partial fuel cycle. 7. Deep fuel burnup, achievable through the use of fuel particles with multilayer coatings, and high efficiency of transforming the thermal energy into electricity allow the effective utilization of plutonium in the GT-MHR reactor. (C) 2003 Elsevier Science B.V. All rights reserved.