SIGMA: The first intrinsic proliferation resistant uranium enrichment technology

Full text: The problem of proliferation using originally peaceful nuclear systems is a challenge that the nuclear energy must solve, if it is wanted that the nuclear energy could play a major role in the energy basket for all the planet that want to peacefully use it. Technology restrictions that finally reflects resources transfers, or competitiveness advantages obtained by countries that will have both, peaceful and military use, could become a major obstacle if its really wanted that in the future, nuclear energy could be a massive option like modern gas turbines or even piston motors. To deal with this challenge, different international and national efforts (INPRO, GEN IV, etc.) proposed to open the discussion about new 'proliferation resistant' approaches, in order to help a sustainable large scale use of nuclear energy in the future. Now is clear that proliferation resistance is a feature that is useful only if its applied to all the nuclear system itself, and includes the nuclear power plant together with all fuel cycle facilities. At present there are many proliferation resistance concept proposed for future advanced nuclear systems, new reactors and back end fuel cycles facilities, but up to now there are no new proposals for present front end of nuclear fuel cycle. In general, nuclear material present in the front end of LWR fuel cycle has been taken as very low attractiveness material because it must be enriched significantly to be usable in a weapon. But there are strong concerns about that plants designed to enrich LEU could be easily modified to produce HEU. As was stated previously, it was a well-known issue that ultracentrifuge could be easily used to potentially produce, in a short time, significant quantities of direct usable weapon grade fissile material. All these issues could be seen as minor problem if the final proliferation risk could be addressed by institutional safeguards without significant cost. But leveled fuel cycle safeguard cost could share up to 80% of all the safeguard efforts (for Once Through NPP) if in the future all the enrichment will be produce with ultracentrifuges (UC) in safeguards (75% of this safeguards cost comes for enrichment plant alone). Up to 0.2 mills/KWh will be the leveled safeguard cost of ultracentrifuges. For the long term, this situation could be even worst. The enrichment gain and capacity of the UC method strongly depends on the peripheral velocity of the rotating machine and its length. This characteristic is conditioned by the material resistance, or by the ultimate tensile stress over density (UTS/ρ) rate of the desired material. The difference could be significant, and different advanced materials could multiply the enrichment gain of the UC process, just incrementing the rotating velocity. Due to this possibility of increment in the separation, great efforts are focused on the R and D of new materials and UC construction engineering. All these technology improvements increase the inherent proliferation risk of a UC plant and then more safeguard cost could be expected for advanced UC plants. UC are very cheap in power and O and M, but very expensive in capital, then increase enrichment gain and capacity decrease the capital cost, and finally the economical advantages override any other requirement, like inherent proliferation resistance features. In order to cope to this challenge, Argentina developed a totally new technology based on the proved Gaseous Diffusion (GD) Physics. This technology overcomes the problems of the enrichment known technologies, lessening the total SWU cost to 60% of its actual level. This new concept is called SIGMA. As long as the cascade paradigm of the GD does not allow any significant changes in the plant economy, the SIGMA technology changed the cascade concept itself. This change opens a new design path and allows a new set of optimal design points. In the SIGMA concept, non proliferation is a central issue: the safeguards systems are included in the design itself, using all the non proliferation advantages of the GD, multiplied by some innovative features that allows the use of NDA techniques for on-line hold-up control. The SIGMA technology inherits all the proliferation resistant features from GD, and incorporates new innovative features that results in the first proliferation resistant enrichment technology. The SIGMA innovative features for proliferation resistance are: - Easy to check fissile material inventory; - Long characteristic times; - There is no reconfiguration capacity to produce more than 20% of enrichment; - Low cost NDA probe, that allows on line control of the amount and enrichment of the Uranium being processed; - All in process or I/O fissile material could be remotely checked on real time, 24 hr per day, 365 days per year for safeguards; - The remote safeguard results are clear and unambiguous. This last point, with a remote safeguard control system could enable the transference of the operation of the SIGMA plant to a country, without transferring the technology itself. The economical advantages of UC compared with classic GD are very well know. So it looks like the market forces are selecting a cheap technology jeopardizing the proliferation risk. This could be supported in the long term only if UC will be used in nuclear weapon states or a small group of developed country. The sustainability of this approach for the long or even the medium term is very low, and it's only motorized by the lack of alternatives. The SIGMA concept, could overcomes all this requirements and maybe becomes the unique overall solution of the enrichment market dilemma, using market forces to help to reduce the proliferation risk. (author)