Production of Pa-U Fuel with Proliferation Resistance by 14 MeV Neutron for Long-life Core

Abstract

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 1MW/m². The mass balance of ²³¹Pa shows that the one fusion reactor with approximately 1.1 GW_th and 1951t of ThO₂ supports the one pebble bed-type gas cooled reactor with approximately 1 GW_th 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 and 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 ²³¹ Pa.

KEYWORDS:

• protactinium 231
• proliferation resistance
• fusion neutrons
• long-life core
• thorium cycle
• high burn-up
• uranium 232
• uranium 233