Apres ORIENT, A P and T-based new resource strategy in nuclear fuel cycle

The Apres ORIENT research program, recently initiated in 2011, will deal with transmutation of radioactive FPs to create rare metals/rare earth (RE) elements (defined as secondary Nuclear Rare Metal, ^2ndNRM) by (n, γ) reaction succeeded by β^- decays: _Z^AFP(n, γ)_Z^A+1FP (β^- decay) ⟶ _z+1^A+1NRM. Target _Z^AFP are radioactive FPs and any created _z+1^A+1NRM should be more valuable and non-, or significantly less, radioactive than the _Z^AFP. In the case of transmutation of radioactive Ba (i.e., non RE element) to La (i.e., light RE), the yield of ¹³⁹La was low <3.5% with 5 years irradiation at thermal neutron energy conditions. However, by neutron irradiation in the fast reactor blanket region corresponding to a resonance energy range of 10 ∼ 100 keV with an expected cross section, σ_γ=0.27 b, of ¹³⁹Ba a higher transmutation rate of more than 12%/5 y was obtained when the neutron flux is 1.0x10¹⁵ n/cm²-sec. Created La will be perfectively non-radioactive (< 0.001 Bq/g) despite that natural La is slightly radioactive ca. 1 Bq/g. To facilitate Ba/La separation various kinds of crown ether (CE) resins were tested. The highest separation of Ba²⁺/La³⁺ was obtained by a newly synthesized Benzo-18-Crown-6 (BC18) -substituted resin indicating SF_Ba/La > 1,000 at 5 mol/l HCl medium. To confirm scientific feasibility on such new P and T, actual irradiation tests by various target materials in a test reactor and separation and analysis of the products are required. While the test reactor available at UC Irvine has a steady state flux on the order of 1.0x10¹² n/cm²-sec which is at least 2 orders of magnitude lower than a conventional power reactor, proof-of-concept investigations will be carried out since the production of nuclides should scale up linearly with the neutron flux. (author)