Laser isotope separation enrichment process

Laser isotope separation is one area where multistep excitation and ionization has great commercial potential. The research and development efforts in atomic vapor laser enrichment of 235y are a major factor contributing to the current research activities in laser excitation and ionization processes. The first paper on selective multistep photoionization of atoms was published in 1971. (.62) Since then numerous review articles( 15, 16 >L7,63 >54, (i5) ave been written on laser isotope separation and, in each review, there is a section on atomic vapor photoionization processes. The subjects of economics and critical parameters have been well covered in previous reviews and will not be discussed in detail here. We... 

Uranium isotope enrichment by LIS has been exhaustively studied and the conceptual outlines of two separate programs have made their way into the open literature. These methods are multiphoton dissociation of UFe and LIS of monatomic uranium vapor (atomic vapor laser isotope separation, or AVLIS). AVLIS was selected by the United States DOE as the process to be used in its separation plants during the 1980s and 1990s, but, once again due to the present oversupply of separated uranium, the plant has recently been closed. 

There also have been gaseous diffusion plants built in other coimtries, some still in operation, but the gaseous diffusion process is gradually being replaced by the gas centrifuge process. Another method of enrichment, laser isotopic separation, has generated interest in recent years. 

Two recent papers by Letokhov (38) and by Moore (39) contain excellent and detailed discussions of the application of lasers to isotope separation. The approaches fall into two broad categories which may be characterized as one-step and two-step processes. The one-step process is particularly simple conceptually but not as generally applicable. It involves selective excitation of a suitable molecule to an upper pre-dlssoclative state. This upper state is a non-dissociative one whose potential energy surface intersects another surface corresponding to a dissociative state. Such a system is illustrated in Figure 13. If the dissociative lifetime is shorter than the radiative lifetime, then selective photo-excitation can produce isotopically enriched... 

The Energy Research and Development Agency (ERDA), the forerunner to the DOE, through the late 1970s to 1981 supported the study of three new experimental processes for uranium enrichment. Two were based upon laser separation, and one on plasma separation. Jersey Nuclear-Avco Isotopes Incorporated (subsidiary of Exxon) and the LLNL worked on atomic uranium vapor. LLNL referred to it as AVUS. The LANL and a group at Exxon Research Laboratories (not connected with Jersey-Avco) worked on molecular UFg. TRW Incorporated pursued research work on a plasma separation process. Union Carbide Nuclear Division (UCC-ND) supported each in their efforts. In 1981, the AVLIS process at LLNL was selected as the process to be developed further and the other processes were subsequently phased out. 

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