Fig. 8-4 Concept of the AVLIS Process Metallic uranium is first heated and vaporized by an electron beam in the linear metal evaporator. This forms streams of gaseous uranium atoms (evaporation process). The 235U atoms in the gaseous uranium streams are selectively excited and ionized by the irradiation from the tunable wavelength lasers in the multistep photoionization process (photoionization process). Finally, 235U ions are collected on the enriched uranium electrode and the nonionized uranium atoms, mainly 238U, are collected on the depleted uranium electrode (recovery process).

The development of Atomic Vapor Laser Isotope Separation (AVLIS) technologies progressing. The advantages of this enrichment system appear to be in its low capital and operating costs, its low consumption of electricity, and its need for a minimum amount of raw material. These advantages result from this system high separation coefficient, which is higher than those of the gaseous diffusion and gas centrifuge methods. The fundamentals of this uranium enrichment process are shown in Fig. 8-4. To apply the AVLIS method for uranium enrichment, the following R&D program has been conducted. In the first phase (1987 ~ 1992), basic spectroscopic and separation data were obtained and an enrichment of 5% and a separation power of 12 kg SWU/y were achieved to evaluate AVLIS performance. In the second phase, which started in 1993, an advanced separation process was introduced to develop a more economical process for enrichment and to extend the data base for separation technology. Data on evaporation, photo reactions, photo propagation, and ion extraction processes have systematically been collected. In the advanced separation process, the optimum combination of wavelength for the multistep photoionization and laser beam intensity has experimentally been studied to maximize economy. The ion extraction rate has been increased by a factor of slightly more than two.

Reference T. Arisawa et al., Studies on Photoionization Process in Atomic Vapor Laser Isotope Separation Appllied to Heavy Elements at JAERI, J. Mass Spectrom. Soc. Jpn. 41 (51), p.253-276 (1993).

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