Patent Publication Number: US-2010111800-A1

Title: PRODUCTION OF NUCLEAR GRADE ENRICHED GADOLINIUM AND ERBIUM USING VOLATILE Gd OR Er SPECIES USING AN AERODYNAMIC PROCESS

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application Ser. No. 61/110,650, filed Nov. 3, 2008 entitled, PRODUCTION OF NUCLEAR GRADE ENRICHED GADOLINIUM USING VOLATILE Gd SPECIES FROM AN AERODYNAMIC PROCESS. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to use of Gd and Er volatile molecules in the production of Gd and Er isotopes in an aerodynamic separation process. 
     2. Description of the Prior Art 
     Processes for separation of vapor phase isotope mixtures utilizing, in part, nozzle-like openings are well known in the art and taught, for example, in U.S. Pat. No. 2,951,554 (Becker). Enhanced nozzle separation is taught in U.S. Pat. Nos. 5,255,404 and 4,297,191 (both Chen). Double deflection nozzles are taught in U.S. Pat. No. 4,551,157 (Becker et al.). The main problem in using these techniques for separating the isotopes of gadolinium and others below is the lack of a volatile molecule containing gadolinium. 
     In Biro (U.S. Pat. No. 4,565,556), molecular and isotropic fractionating processes for gaseous mixtures are described. The gas mixture to be fractionated is subjected to a helicoidal path and interfered in its free circulation by means of aerodynamic elements to obtain fractions of different weights. 
     Isotope separation has been practically limited to a few elements due to the fact that the methods commonly available such as nozzle separation, centrifuge or diffusion require a stable, volatile feed material. The use of molecular laser isotope separation (MLIS), such as generally shown in U.S. Pat. No. 3,951,768 (Gürs) provides even more limitations. In addition to requiring a stable compound that is volatile, the compound must also possess absorption bands that are isotopically active in order to work. The use of atomic vapor laser isotope separation (AVLIS) eliminates the need for stable volatile compounds but has difficulties in that the boiling point of gadolinium metal is ˜3200° C. which is difficult to achieve and that making a product that can be readily separated when activated due to its very fine particle size. In addition, AVLIS operations usually require at least two colors of operation (infra red IR) as well as ultra violet (UV)) wavelengths which tremendously increases costs as well as introducing technical issues with timing and product separation. Isotope separation using activation of a chemical reaction or delayed nucleation (CRISLA) are also known and generally taught in U.S. Pat. No. 5,108,566 (Eerkens). 
     Isotope separation by ion cyclotron resonance (ICR) is also taught by Louvet in U.S. Pat. No. 5,422,481. This method of separation, while technically feasible, is economically unattractive due to its very low production rate and very high capital investment. In addition, the very high boiling point of gadolium and erbium makes this approach very difficult. Producing isotopically separated gadolinium, uranium and many other elements has been a particular problem in this regard. There are many elements with no known, simple (and therefore economic to produce) volatile and stable compounds to work with. Those that have been identified have huge molecular weights such that the weight difference between the different isotopes is very small and the isotopic separation difficulty therefore increases. 
     Uranium isotope separation has been taught, for example, in U.S. Pat. No. 4,097,384, where attractive volative uranium compounds for use in isotope separation include U(By 4 ) 4 ; H 2 C(C 5 H 4 ) 2 U(BY 4 ) 2 ; (C 5 H 5 ) 3 U(BY 4 ); (CH 3 H 5 ) 3 U(BY 3 C 2 H 5 ) and (C 4 H 4 N) 3 U(BY 4 ) where Y=H or D (deuterium). Most lower molecular weight Gadolinium compounds (valance +3) are solids: GdCl 3 , 6H 2 O m.w. 371.76-wh.pr; GdF 3  m.w. 214.30 gelat; Gd 2 O 2  m.w. 362.60 amor.powd.; and Gd 2 S 2  m.w. 410.78 yel.mass.h.yg. Most lower weight Erbium compounds (valence +3) are solids: Er(NO 3 ) 3  6H 2 O m.w. 461.76 red. cr; and ER 2 O 3  m.w. 383.28 red powd. ( Concise Chemical and Technical Dictionary , Ed. H. Bennett, 1962, pp. 368 and 420-421). 
     Gadolinium and also erbium are extremely valuable rare earth metal isotopes, for use as neutron (“poison”) absorbers in nuclear reactors, as is well known in the art, and are important to the nuclear industry. Gd 157  has excellent neutron absorption capabilities, as described in U.S. Pat. No. 7,318,899 (Lemaire et al.) where such isotopes are separated in an aqueous medium by treating soluble compounds of gadolinium with a ligand designed to complex with at least one of the isotopes and nanofiltering the treated aqueous medium to separate the isotopes. A somewhat similar process was described in U.S. Pat. No. 5,470,479 (Snyder et al.). U.S. Pat. No. 5,595,714 (Ripa et al.) also involves recovery of Gd and its complexing agents from aqueous solutions. Paisner et al. (U.S. Pat. No. 5,202,005) also recognized the importance of Gd 157  and Gd 155  as useful burnable poisons in light water nuclear power reactors. They were enriched by selective photoionization using linear parallel polarized laser beam energy. 
     Gd and Er “burnable absorbers” which absorb neutrons during nuclear fission, whose ability to absorb neutrons decreases with increased exposure to nuclear fission are recognized by Grossman et al. (U.S. Pat. No. 5,350,542) are separated by atomic vapor laser isotope separation (AVLIS) developed at the Lawrence Livermore National Laboratory. Problems with AVLIS were generally discussed earlier. 
     Peterson, Lahoda and Weisberg, in U.S. Pat. No. 4,711,768 taught use of a liquid chromatographic column system using an ion-exchange resin and eluent solution to separate Gd isotopes, which Gd is used for nuclear control rods and burnable poison shims, preferably Gd 155  and Gd 157 . Problems herein include the low degree of separation per stage (leading to very large and uneconomic columns due to the high cost of the ion-exchange resin) and the low production rate due to the batch operation of the separation column. 
     Finally, Snyder et al. (U.S. Pat. No. 5,470,479) teaches continuous separation of isotopes of Gd. This method is again not economically feasible because of the very small separation factors that were achieved per theoretical stage. 
     None of these patents address using gaseous Gd(BH 4 ) 3  or similar gaseous Er compounds, in an injector nozzle separation device, to produce isotopes of Gd or Er. Again, the reason for this has been the lack of a volatile low molecular weight compound containing gadolinium or erbium. 
     It is a main object of this invention to provide a method of using gaseous Gd or Er compounds in a process to provide useful Gd and Er isotopes. 
     SUMMARY OF THE INVENTION 
     The above needs have been met and problems solved by providing a method where highly volatile compounds of gadolinium and erbium containing three —BH 4  or —CH 3 BH 3 , ligands/ions, hereinafter “(Gd, Er)·(—BH 4 , —CH 3 BH 3 ) 3  compounds” preferably Gd or Er with —BH 4 , are used in an aerodynamic separation process to separate isotopes of gadolinium or erbium. The term aerodynamic separation process (“ASP”) is herein defined to mean any gas flow separation device such as that described in Biro (U.S. Pat. No. 4,565,556), in U.S. Pat. No. 2,951,554 (Becker), in U.S. Pat. No. 5,255,404 (Chen), U.S. Pat. No. 4,297,191 (Chen) or double deflection nozzles as taught in U.S. Pat. No. 4,551,157 (Becker et al.). A carrier gas is used in the ASP process, and is selected from the group consisting of H 2 , He and mixtures thereof, preferably at a temperature range of between −50° C. and 400° C., at pressures from vacuums such as 0.001 atmospheres, to pressures up to 100 atmospheres. 
     In the method, (Gd, Er)·(—BH 4 , —CH 3 BH 3 ) x , where x=3 is manufactured as a gaseous starting product or starting “Product”. That starting Product is passed to an ASP process, as generally described previously to provide Gd or Er heads and Gd or Er tails. The term “heads” means a product enriched in the concentration of the desired isotopes. The term “tails” means a waste stream depleted in the concentration of the desired isotopes. These heads and tails are then reacted with Cl 2  gases. This is generally shown in the FIGS. 
     More specifically, the invention preferably utilizes Gd(BH 4 ) 3  or Er(BH 4 ) 3  and involves a method of providing gaseous Gd or Er isotopes comprising: (a) reacting a solid starting product material selected from the group consisting of GdCl 3  or ErCl 3  in a reactor with LiBH 4  to provide a reaction product selected from the group consisting of gaseous Gd(BH 4 ) 3 , or gaseous Er(BH 4 ) 3  and solid LiCl; (b) passing the gaseous reaction product into an aerodynamic separation process utilizing an injector nozzle in a stationary reactor to produce centrifugal force/spiraling or swirling gases while utilizing a carrier gas selected from the group selected from the group consisting of H 2 , He and mixtures thereof, to provide heads and tails selected from the group selected from Gd or Er heads and Gd or Er tails; and (c) passing the heads and tails to a reactor to react with Cl 2  to provide BCl 3  and HCl off gases and final solid product selected from the group consisting of  157 GdCl 3 ,  155 GdCl 3  and  167 ErCl 3  rich in Gd and Er isotopes. 
     In the above method, the BCl 3  and HCl off gases from step (c) are passed to an electrolysis unit where LiCl from step (a) is reacted with HCl from a separate reactor where H 2  and Li from the electrolysis unit and BCl 3  from step (c) are reacted to provide LiBH 4  which is fed into step (a) and HCl which is passed to the electrolysis unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with accompanying drawings in which: 
         FIG. 1  is a simple, block diagram of the method of this invention involving Gd (valence=+3) isotope separation using a —BH 4  ligand; and 
         FIG. 2  is a simple, block diagram of the method of this invention involving Er (valence=+3) isotope separation using a —BH 4  ligand. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Gd and Er compounds are synthesized using —BH 4  or —(CH 3 BH 3 ) ligands/ions. These compounds of gadolinium and erbium have overcome all the barriers described in the BACKGROUND above. These compounds are relatively stable, have low molecular weights and are simple to produce. Boron (B) has two isotopes with concentrations of 19.9% of B10 and 80.1% of B11. In order to improve the per pass yield in the separation step, a single isotope of boron or more likely an isotopic mix that is enriched in either B10 or B11, could be used (see for instance, U.S. Pat. No. 5,443,732 “Boron isotope separation using continuous ion exchange chromatography” or U.S. Pat. No. 5,419,887 “Separation of the isotopes of boron by chemical exchange reactions”.) The term “isotropic mix” means the same element with more than one isotope. 
     In addition, the use of an aerodynamic separation process to produce a Gd product enriched in Gd157 isotopes overcomes the issues associated with other isotope separation processes. For erbium, the Er167 isotope would be enriched. The aerodynamic process utilizes compressors to increase carrier gas pressure that contains the volatile form of Gd or other element, and carrier gas  25  (either He or H 2 , or their mixture) is then injected by injector nozzle separation device  26  at pressures between 0.001 atmospheres to 100 atmospheres, preferably 2 atmospheres to 10 atmospheres to affect a spinning/swirling motion in the gas, that results in the centrifugal separation of the isotope of Gd or other element of interest by centrifugal force. The carrier gas temperature can range from −50° C. to 400° C., preferably from 25° C. to 200° C. The process does not break bonds, forming lower molecular weight volatile species that are hard to collect and separate from the products as do laser isotope separation methods. It has a much lower cost than diffusion methods. The process can also operate at elevated temperatures, where actual centrifuges are not operable. The process of this invention involves a gas swirling around inside a tank rather than spinning the tank, as well as lower temperatures, for instance −50° C. So, for example, it is possible to operate at any elevated temperature such as up to 400° C., which allows sufficient volatility of the compound whose isotope is being separated. The pressures that are used in the process would range from vacuums of about 0.001 atmospheres to pressures up to 100 atmospheres, as previously mentioned. 
     In this invention, referring to  FIG. 1 , treating the preferred material Gd, GdCl 3  is reacted with LiBH 4  by ball-milling them together at atmospheric pressure at room to slightly elevated (100° C.) in a water vapor free enclosure to provide Gd(BH 4 ) 3  (“Product”:  24 ) in a reactor  10 . The LiBH 4  is manufactured in reactor  12  by combining BCl 3 , Li and H 2  according to the reactions: 
       2Li+H 2 →2LiH; 12H 2 +2BCl 3 →B 2 H 6 +6HCl, and 
       B 2 H 6 +2LiH→2LiBH 4 . 
     The Li is produced in reactor  14 , in an electrolysis process, wherein LiCl product from reactor  10  and HCl product from reactor  12  are reacted with HCl, with the overall reactions: 
       2LiCl→2Li+Cl 2 , and 
       2HCl→H 2 +Cl 2 . 
     In the ASP process reactor  16 , preferably the Gd (BH 4 ) 3  or Er(BH 4 ) 3 , or other “Product,” is mixed with carrier gas (hydrogen and/or helium) and raised to pressures of preferably 2 to 10 atmospheres at temperatures from 25° C. to 400° C. The carrier gas with product is then injected through nozzles  26  and into a stationary, non-spinning collection chamber, generating sufficient centrifugal forces to cause gas swirling and separation of the various isotopes of the gadolinium or erbium. 
     Subsequently, Gd heads and Gd tails, previously defined, are fed to a separate reactor  18  to convert borohydride to chloride by reaction with Cl 2  feed, to form BCl 3  and  157 GdCl 3  or  155 GdCl 3  heads (product  20 ) and GdCl 3  tails (product  22 ). GdCl 3  is a solid and will therefore separate readily from the Cl 2 , HCl and BCl 3 . These reactions will be viable with all components of (Gd, Er)·(—BH 4 , —CH 3 BH 3 ) 3  components. 
     An electrolysis process  14  is used in this invention to convert the LiC to Cl 2  which is fed to reactor  18 , and H 2  and Li is fed to reactor  12 . 
       FIG. 2  provides a similar process for utilizing Er (valence +3, the same as Gd). Such reactions are completely similar; only Er is substituted for Gd in the process. This  FIG. 2  is incorporated into the specification as a duplicate of  FIG. 1  with all reaction parameters in reactors  30 ,  32 ,  36  and  38  being the same and providing similar products  40 ;  167 ErCl 3  and tails  42 . Er (BH 4 ) 3  starting Product is shown as  44 , the injector as  46  and the electrolysis reactor as  34 . 
     Thus, Gd157, Gd155, and Er167 are isotopes of Gd or Er and the product heads are rich in those isotopes in the chemical form of GdCl 3  or ErCl 3  and the waste tails are depleted in those isotopes in the chemical form GdCl 3  or ErCl 3 . 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the breath of the appended claims and any and all equivalents thereof.