Recent progress in advanced actinide recycling processes

Document in abstract form only. Full text of publication follows: Concerns about environmental preservation have increased the demand for more efficient management, as well as sound and sustainable development, of nuclear energy. Appropriate management of radioactive waste arising at the back end of the fuel cycle is considered to be a crucial issue of long-term environmental concern in relation to the nuclear fuel cycle. Of particular concern - due to long-term radiotoxicity and heat load issues, as well as proliferation risk - is the approximately 0.4 wt.% of spent fuel composed of minor actinide (MA) isotopes. As of the year 2006, it is estimated that about 110 tonnes of MA are being contained in spent fuel storage worldwide, and an additional 40 tonnes are contained in high-level waste products from reprocessing for the future. P and T will be necessary to decrease these amounts. Within this framework, this paper presents recent progress obtained at CEA/Marcoule on the development of innovative MA partitioning hydrometallurgical processes in support of their recycling, either in homogeneous mode (MA are recycled at low concentration in all the standard reactor fuel) or in heterogeneous mode (MA are recycled at higher concentration in specific targets, at the periphery of the reactor core). Recovery performances obtained on recent tests under high active conditions of the GANEX process (grouped actinide separation connected to homogeneous recycling) are presented and discussed, as compared to the demands of P and T scenarios. New results also concern major improvements and possible simplifications of the DIAMEX-SANEX process, whose technical feasibility was already demonstrated in 2005 for americium and curium partitioning (heterogeneous mode). The promising initial results of the EXAm process (extraction of only Am, at a front head step of the partitioning process) are also presented. Since recycling of only the americium could be more easily implemented than the recycling of both americium and curium, EXAm is dedicated to Am recovery at an early stage of the partitioning process, using one hydrometallurgical cycle. The principle of the EXAm process is based on the extraction of americium together with some light lanthanides having close values of distribution coefficients in high nitric acidity, and curium and other lanthanides remaining in the aqueous phase. The TEDGA amide molecule is used in order to increase the selectivities Am/Cm and Am/heavy Ln, because of the complexation of curium and heavy lanthanides by this amide; the overall efficiency of the process is largely improved, with a corresponding decrease in the number of necessary separation stages. A test of this innovative process was carried out at the CEA Atalante facility in 2009, with very satisfactory results, and the concentrations of the radioelements measured during the test are in good agreement with the values calculated with the PAREX code. A complete hot test, from a genuine concentrated spent fuel dissolution solution, is planned in 2011-2012, in order to confirm these promising results. In the coming years, subsequent steps will involve both better in-depth understanding of the scientific basis of these actinide recycling processes, and for the new, promising concepts, the studies necessary prior to potential industrial implementation. (authors)