•'-I •£>
INi.S-mi-.-]
LASER ISOTOPE SEPARATION A .NEW CLASS UF CHEMICAL PROCESS
by K.8. Woodall, L. Mannlk, J.A. O'.Neill, D.L. .'•'ader, S.iJ. Xickerson, J.R. Robins and F.E. Bartoszek Ontario Hydro Research Division 800 Kipling Avenue, Toronto, Ontario, M8Z 5S4,
and
D. Gracton Ontario Hydro Design and Development Division 700 University Avenue, Toronto, Ontario, M5G 1X6
-..y.TKACT 2.0 EXPENSIVE LASERS PRODUCE EXPENSIVE CHEMICALS
Lasers are being used industrially in applica- Laser energy is considerably more expensive i Luna tnal include cloth cutting, semiconductor than process heat because lasers are driven by .jineuiing, mecal welding, cutting and drilling and electricity rather than heat and they convert •iven the etching of identifying marks oa bottle electricity to visible, infrared, or ultraviolet .;a;js. Lasers may soon find several applications in light with an efficiency that, in the future, is cr.etnical processing as well. The applications that unlikely to exceed 202, even in the most efficient ::ave attracted the most research funding to dace lasers. (Efficiencies of up to 402 have been pre- ii.volve isotope separation for the nuclear indus- dicted for one special class of laser called the ; rv. These isotopes have an unusually high value free electron laser ). The most efficient high 1 ^:i: owii/kg) compared to bulk chemicals ("$l/kg) power laser available today Is the carbon dioxide ma are generally required in very large quanti- laser,. Its efficiency is currently less than fies. In ,i laser Isotope separation process, light ior. In general, laser photons can be consid- is used to convert a separation that is very diffi- ered t,o be very expensive, costing at least cult or even impossible by conventional chemical $l/mole > . By contrast, almost no high volume <-ngi;ieering techniques to one that is readily industrial chemicals sell for as much as $l/mole. nandled by conventional separation technology. For Bulk chemicals typically sell for about $l/kg. For sow isotopes this can result in substantial capi- this reason, the development of chemical processes ;.il and energy savings. A uranium enrichment using lasers have focussed over the last ten years ;>r ji:est> developed at the Lawrence Llvermore on the production of very high value and high vol- i-ii 1MII.II L.ib'ir.it:ory is the closest to conmierclall— ume products such as the separation of isotopes for ' ii I "ii
The rapidly expanding Industrial market for Canadian heavy water production capacity Is lasers* is evidence for Che fact chat industry is about 1.2 million kg/a. Uranium enrichment costs gaining confidence in Che reliability of laser represent 5 to 102 of the cost of producing power cecrmology. Many of these applications such as from light water reactors. Deuterium enrichment cloth cutting, semiconductor annealing, metal costs represent nearly 202 of the capital cost of welding, cutting, drilling, and laser marking CANDU nuclear reactors or about 10% of the cost of (placing identifying marks on packaging) to name producing power ^r8!no .heavy water reactors. only a few examples, make use of Che laser's Considerable research • ~ , particularly in the ability to deliver a well-defined and, if desired, case of uranium, ha3 gone into the development of an intense beam of energy to a precise location. laser based processes as a lower cost alternative But lasers have another property which can make to conventional isotope separation techniques. them useful in chemical processing. They can deliver lighc energy with a very narrow frequency 3.0 LASER ISOTOPE SEPARATION - HOW DOES IT WORK? or wavelength range. In a laser isotope separation process light is used to convert a separation which is very diffi-
334 :ji: 3r eve:: i~foss:ble by conventional chemical Or.tariu Hydro Research that better i!:a:". "i1/: •,; t:ie 1 •'-...i :~.e<-ri ':*; t-'c'r .: : ues into one that is readily Hr/l/F aixtjr.; can be extracted fron !:.•; trifI-.ro- ::j:'.d lei! bv conventional separation technology. se th-i'ie by flowing the s:r»as •,)er a '-.•.-: >,: IOC:UE '•'..ir.y ii the laser isotope separation processes fluoride pellets. The t ri f luur ji<:r.a::e :s -r.df- t'e: ::^ sc-:dieu involve the use of a laser to selec- tected. Note that this process .jpp'-i'?^ 1-jser r i .-.-1 .• brej.k up or iissociate nolecules containing energy selectively to the desired J.sot.;c bv proper : ..c desired isotope vhiie leaving molecules tuning of the laser. This is the key - .1 -.->.:-? containing the other isotope untouched. high cost laser light competitive witn low cost process heat. Molecules vlbr3te with one or more character- istic frequencies. They absorb light at these Figure 2 illustrates some jf the other key frequencies and transmit light of other frequen- details of the process. The supply of trifluoro- cies. An Infrared absorption spectrum is a record ae thane is far too small to provide the large of the characteristic vibrational frequencies of .1 quantities of deuterium required for a single CANDl" molecule. If a laser is tuned to one of these nuclear reactor. (Approximately 5 x 1C" kg of frequencies, the laser energy will be absorbed. If heavy water are required.) The deuterium content the laser energy Is Intense, the molecule will of the trif luoronethane oust be replenisneii by jbiurb enough energy to dissociate Into fragments deuterium exchange with an .ibund.mt ir .t-: r: -jm t'l.it 'ldvo physic.il and chemical properties that s.,ur.:e, wjter. I'.r-ll + HI;o - '',V.\i ~ ii^V. .'..1., can litt'T greatly l'rnia those of the original molecule. be done in a counter-current flow exchange tjwer using sodium hydroxide as a catalyst. The exch.i.ue Just as placing a lump of putty on one prong can take place at moderate teaiperat ires (~"VCj n a tuning fork lowers the characteristic vibra- if a rate enhancing solvent (.diiaethyl sulf oxide J is tional frequency of the tuning fork, substituting added to the exchange liquid or at, higher tempera- .me itoo of a nolecule with a heavier isotope tures (130°C) without the solvent' . Ir. order to changes the characteristic vibrational frequencies avoid separating the components of the exchange ol the molecule. A small portion of the absorption liquid loop, the deuterium content of this strean spectra' of CFj H and CF3D, illustrates this iso- can be replenished by passing water vapour counter- topic shift (Figure 1). In principle a laser can current to this liquid stream in another aultiplate be selectively tuned to preferentially dissociate counter-current flow contacting tower. molecules containing the low abundance isotope. I'nlike conventional separation processes where This process is in a relatively early stage of energy is expended equally on all molecules, a development. The steps in Figure 2 have been laser Isotope separation process expends laser energy preferentially on the minor component in the demonstrated on a laboratory scale only. mixture. Because of this, expensive laser radia- tion can be considered for chemical processing. 4.2 Comparison With Conventional Deuterium Separation Technology
i.O EXAMPLES OF ISOTOPE SEPARATION PROCESSES Deuterium is currently separated from lake water in a process Involving deuterium exchange 4. 1 Deuterium Separation between hydrogen sulphide and water. Advantage is 10 taken of the fact that the distribution of deuteri- Research at Lawrence Llvermore Laboratories um between hydrogen sulphide and water varies with and Allied Chemical " in the United States, and at temperature. Hundreds of separation stages are Atoxic. Energy of Canada Limited and Ontario required in large (90 m high by 9 m in diameter) Hydro'' in Canada has contributed to the develop- counter-current flow exchange towers which contain ment of laser deuterium separation processes. The 20 atmospheres of toxic, corrosive hydrogen most attractive separation process is based on the sulphide gas. The laser process uses a non-toxic, dissociation of trifluoromethane (CF3H) with carbon non-corrosive process gas and strips four times dioxide laser radiation. more deuterium from lake water than the hydrogen sulphide process does and enriches It in a single The reaction CF3D + nhv * CFz + DF has been separation stage. Cost estimates based on computer shown to be at least 10 000 times more probable modelling and bench scale experiments predict that than the reaction CF3H + nhv * HF + CF2 when the heavy water could be made for as low as half the carbon dioxide laser la tuned to a wavelength in cost of heavy water from an as-yet unbuilt hydrogen the 10.2 urn to 10.3 um region. About 30 laser sulphide plant. However, costs of three or four photons are required for each dissociation. The times this low level cannot be ruled out because of OF;; radicals combine to form tetrafluoroethylene, a many uncertainties involved in scaling up this valuable chemical byproduct. In a single step a, process. Larger cost reductions are not thought stream of CF3H molecules containing 0.019% CF3D can possible because a substantial fraction of the be converted to a stream of CF3II molecules con- total process cost must be used to transfer taining about 0.0019% CF3D mixed with a stream of deuterium to the process gas using conventional HF molecules containing approximately 50SI DF. technology. It will be difficult to achieve large Simply by exposing the trlfluoromethane stream to coat breakthroughs via laser isotope separation for Intense Infrared radiation, an extremely difficult Isotopes valued at substantially below Sl,0OO/kg, separation of two nearly Identical molecules (CF3H especially when process gas recycle is required. and CF3 D have boiling points differing by only a few tenths of a degree) is converted to the much simpler separation of highly polar molecules (HF or Development of new deuterium separation tech- DF) from a trlfluoromethane stream with an almost nology has slowed considerably due to the recent 100°C lower boiling point. It has been shown at drop in electrical load growth throughout Canada
335 ••hi.:is nas resulted in large projected heavy vcter 5.1 Zirconium surpluses fur tJie remainder of this century. Nuclear reactors use zirconiua alloys tor internal *.j L ratii um enrichment reactor parts (.fuel cladding in light water reac- tors and fueL cladding, pressure cubes
Altnougn detaiLs of the US government uranium 5.2 Tritium enricnment programs are classified, some informa- tion has been released15 which indicates that a The tritium separation processes that are substantial cost breakthrough is predicted using being studied closely resemble the deuterium sepa- laser technology. ration process described earlier. Separation of trace quantities of tritium from large amounts of Table I hydrogen is required to creat the waste streams of nuclear fuel reprocessing plants and future nuclear Comparison of Uranium Enrichment Costs fusion plants. Highly selective dissociation of CFjT in the presence of CF3H has been demon- strated15. T/H separations with other fluoro- Relative Relative carbons (C^FcT and CF,CFC1T) are aiso being Capital Energy Operating studied10.'^. Process Costs Requirements Costs Nuclear reactors that use heavy water modera- '.jseous UiJrtusion high high tor accumulate Inventories of tritium. In order to t Convent ional (-1.0) (-1.0) low reduce the radiological hazard of chronic and acci- Technology) dental leaks, processes are required that separate T from D. A laser process has been developed at uds Centrifuge nigh low Lawrence Livermore National Laboratories based on (Developmental (-1.33) (-0.042) moderate the selective laser dissociation of chloroform, Technology) CCI3T, which shows some promise of being superior to conventional cryogenic distillation technol- Laser Isotope ogy18. The recovered tritium has a value of Separation low low SIO,OOO,OOO/kg. It is used as a fuel in fusion 5.3 Carbon 14 The two new processes (gas centrifuge and Laser isotope separation) are expected to substan- Heavy water reactors produce substantial tially lower the energy requirements of iranium quantities of '""C as a waste product. Carbon 14 enrichment. The laser based process also offers enrichment by selective dissociation of formalde- the prospect of substantially reduced capital costs 11 hyde, *CH2O, has been demonstrated at Ontario as well. Hydro Research19. Recovered carbon 14 has a value of greater than ?10,Q00,000/kg. It is used as a Even though there is surplus uranium enrich- tracer in medical and biological research. ment capacity available today, development of ad- vanced uranium enrichment technology is proceeding 5.4 Carbon 13 rapidly because of the potential for very large cost reductions with these new processes. A Russian process based on selective dissocia- tion of CF3I has been reported20. Considerable 5.0 OTHER ISOTOPES cost reduction compared to the conventional method of producing carbon 13 by cryogenic distillation of Several other Isotope separation processes are carbon monoxide has been claimed but no laser pro- being studied. Ma,ny o£ these have applications duced carbon 13 has reached North America as yet. within the nuclear power industry. 336 over the next iu years we can IOOK for im- jtve1-p-ent or an alternative process using a provements in laser reliability and ti:i:ii;::^v r CJS: r.;ej material is being studied at the ar.d reductions in capital ind jperalin^ c-o'.i, JUJI 5.7 Isotopes for Medical Research and Treatment 5. J.I. Davis, M. Feld, C.P. Robinson, J.I. Steinfeld, N. Turro, W.S. Watt, It may be possible to produce small quantities J.T. Yardley. "Laser Photochemistry and of many isotopes which have high value as medical Diagnostics, Recent Advances and Future diagnostics and relatively small demand (<1 kg) on Prospects". Report on National Science a small scale using low cose lasers. Several Foundation, Department of Energy Seainar, radioisotopes (eg, thalliutn-203 and zinc-68) cur- June 4-5, 1979. rently separated by high coat calutrons (electro- nu^netlc separators; at Oak Ridge are candidates 6. J.I. Davis, J.Z. Holtz, M.L. Spaeth. "Status tor laser Isotope separation process development2"*. and Prospects for Lasers in Isotope Separa- tion". Laser Focus, September 1982, p 49. 3.d other Isotopes 7. R.G. Denning. "Laser Isotope Separation The Isotopes of oxygen, nitrogen, and sulfur Techniques". Phys. Tech., % 242, 1978. ire examples of stable isotopes required in small quantities for research purposes. Laser isotope H.L. Chen, J.I. Davis. "Lasers In Chemistry separation may lead to reduced costs for some of Hearing the Breakthrougn?" Photonics Spectra, tiiese isotopes. October 1982, p 59. CONCLUSIONS 9. R.L. Rawls. "Laser Separation of Uranium Chosen for Scale—up". Chemical and Engi- Laser radiation can be used to promote separa- neering News, May 17, 1982, p 30. tions that are extremely difficult by conven- « tional technology. It is particularly appli- 10. (a) I.P. Herman and J. Marling. Chem. Phys. cable to Isotope separation where the product Lett., ^4, 75, (1979). produced has a very high value (ie, >S1 ,UUO/kg) . (b) I.P. Herman and J.P. Marling. J. Cliem. Phys _72> 516 .(1980). The rirst large scale Industrial use of lasers for isotope separation is expected to be the (c) J.fi. Marling, I.P. Herman, and uranium enrichment process developed at S.J. Thomas. J. Chem. Phys. T2, 5bO3, Lawrence Livermore National Laboratory. This 1980. process Is planned to be operational in the (d) I.P. Herman. Chem. Phys. ±5_, 121 , (1983). 3. An attractive research area for the 1980's will be the development of processes to 11. A. Hartford and S.A. Tucclo. Chem. Phys. separate small quantities (<1 kg) of high cost Lett., _60, 431, (1979). isotopes with lasers. These processes will in oust cases not require any improvements or 12. D.K. Evans, K.D. McAlpine and H.M. Adams. J. scale-up of existing laser technology. Chem. Phys., TT_, 3551, (1982). 13. (a) L. Mannlk, S.K. Brown. J. Appl. Phys., 53, 6620, (1982). 337 (SJ J.A. O'Neill, J.R. Robins, published. (a) E.A. Synons, M.J. Clermont. J. Am. Chea. Soc.,_lO3, 3127, (1981). (b) E.A. Symons, M.J. Clennorit, L.A. Coderre. J. Am. Chem. Soc, 103, 3131, (1981). (c) E.A. Symons. unpublished data. 15. K. Takeuchi, J. Inone, R. Nakane, Y. Nakide, S. Kaco, P. Tomitiaga. J. Chea. Phya., _70. 398 (1982) and references cited therein. Y. Makide, S. Kato, T. Toralnaga, K. Takenchi. Applied Physics, 28, 341 (1982). O. t^urihara, Tak.euc.hi, S. Satooka, Y. Makide. Paper accepted for publication in J. Suci. Sci. Techno!. Hay, 1983. 18. J.L. Halenscneln, F. Hagnotta, I.P. Herman, F.T. Aldrldge, P. Hsiao. '•Tritium Removal from Contaminated Water via Infrared Laser 1020 1000 980 960 340 Multiple Photoa Dissociation". Paper pre- sented at the 5th Topical Meeting of the Technology of Fusion Energy, Knoxville, Laser frequency (cm" 1 Tennessee, April 26-28, 1983. 19. L. Mannik. Unpublished data. Figure 1 20. V.S. Letokhov. "Laser-Induced Chemical Processes". Physics Today, Sov 1980, p 34. Infrared Absorption Spectra of CF.,U and The large Isotopic shift associated with substitution of a D atom for a H atom is 21. P.A. ilackett, C. Willis and M. Gauthler. shown. Note that the spectrum of CF^ti "Mulciphoton Decomposition of Hexafluoroace- has been amplified by 100 times by :one. Effects of Pressure, Fluence, Wave- recording it at a much higher pressure. length, and Temperature ou the Decomposition The positions of some carbon dioxide Yield of C-13 and 0-18 Isotopic Selectivity". laser lines are also indicated. J. Chea. Phys., Tl_, 2682. J. riecht and C.B. Hltz. "Govemraetit Research Funding". Lasers and Applications, June 1983, p 55. 'I'S. M. Yamashita, H. Kashiwagi. "Method for Sepa- ration and Enrichment of Lithium Isotopes by Laser". US Patent 4,149,077 April 10, 1979. S.C. Stiason. "Supply Problems Cloud Ouclook for Kadioisotopes". C&E News, May 31, 1982, p 14. 338 BOILER VAPOUR DRYER CONDENSER COMPRESSOR FEED WATER C F :h I ' ?0ppmD LASER ABSORPTION CELL CF3H-H1O DEUTERIUM SELECTIVE CFjD EXCHANGE OISSOCIATIOH TOWER CF ;H I 19ppmD] • DFC 501D] DF SEPARATOR J ippmD LOOP 1 LOOP : LOOP i Water Peed Loop Water • D-Excnan'je Process Gas Catalyst Loop I Trif luoroiH'thane ) Li.»op Figure 2 Trifluoromethane Laser Heavy Water Process The three loops in the trlfluoromethane laser deuterium separation process. In loop 3, the CF3D nolecules are aelectivelv dissociated to DF and CF2. The DF is recovered by selective absorption on sodium fluoride pellets and then chemically converted to water and distilled to 99.9% reactor ^raae nejvy wacer. Loops 1 and 2 are required to replenish the deuterium content ot the tririuorometnane by deuterium exchange with water. TAILS COLLECTOR URANIUM FEED Figure 3 Livennore Uranium Enrichment Process A beam of uranium vapour intersects a laser beam which selectively photoionizes the 235U component. An electromagnetic field collect the ions at Che product collector while the unionized •d3BU atoms pass through the field unaffected and freeze out on the tails collector. 339