Production of Pa-U fuel with proliferation resistance by 14 MeV neutron for long-life core

Protactinium-231 has an attractive potential to reduce the initial excess-reactivity and to be effectively converted to the fissile nuclide 233U through 232U. Thus, 231Pa serves as the burnable fertile material helping to achieve a long-life core. However, the natural abundance of 231Pa is negligible. Therefore, the production of 231Pa has been studied in a fusion blanket with a ThO2 zone, which is irradiated by 14 MeV neutrons to cause the (n, 2n) reaction in 232Th at a neutron wall load of 1 MW/m2. The mass balance of 231Pa shows that the one fusion reactor with approximately 1.1 GWth and 195 t of ThO2 supports the one pebble bed-type gas cooled reactor with approximately 1 GWth and 10-year lifetime (700 GWD/t). It is also shown that the attractive fertile nuclide 231Pa is produced with a fissile nuclide 233U and a small fraction of 232U which enhances the proliferation resistance for the fissile product 233U due to the generation of high decay heat an strong gamma rays. In the present study, the isotopic fraction of 232U is increased to over 2.4 % by controlling the neutron spectrum in the ThO2 zone. As a result, the fissile nuclide 233U could be always protected by 232U throughout the thorium fuel cycle based on 231Pa. (author)