A SYMBIOTIC SYSTEM OF A LARGE FAST BREEDER REACTOR AND SMALL-SIZED, LONG LIFE, THORIUM SATELLITE REACTORS - General Introduction -

Responding to the rapidly increasing growth of energy demand in the less- developed and developing countries, use of fission nuclear energy best mixed with other primary energy resources is inevitable short- and mid-term options. However, requirements of high capital investment and high technological capabilities, further burdened with safety, high level radioactive waste and nuclear material proliferation issues are challenging factors which have to be resolved by the countries themselves as well as by the vendor countries (mainly consist of developed countries) and international institutions through bilateral and multilateral collaborations. To contribute in resolving part of this global problem, in this study we proposed a symbiotic system consists of large scale, sodium-cooled, fast breeder reactors (3000 MWth) operated in “nuclear parks” located in developed countries or proper internationally controlled areas, and small-sized, long life, thorium satellite reactors (30 to 300 MWth) shipped to and deployed in developing countries. The FBRs owing to their leading neutron economy and breeder capability have the role of breeding their own fuels while producing 233 U fissile materials required by the small-sized thorium satellite reactors. A uranium-thorium mixture core is proposed where uranium and thorium metallic fuel pins are arranged side by side to achieve higher production rate of 233 U fissile material. The satellite thorium reactors with their fissile materials supplied by the FBRs should have simple design features such as long life and without on-site refueling activity, since they are expected to be deployed in countries or regions with less-established infrastructures and resources. As for the small-sized satellite reactors we studied the feasibility of pressurized water reactors (PWR) and block-type gas-cooled reactors (HTGR) for meeting small demands of electricity and process heat, operated under thermal neutron spectrum and thorium fuel cycle. Adoption of thorium fuel is attributed to its better neutron economy in thermal energy region (a key design factor for long life core and without on-site refueling feature), large abundance, less long-lived trans-uranium nuclides produced, and negative void reactivity coefficients.