NASA TECHNICAL MEMORANDUM

A STATUS OF PROGRESS FOR THL LASER lsofopE SEPARATION (11 SI PROCESS

+ t e a r 1976

NASA

George C. Marshdl

M d r ~ b d l Space Flight Center Space Fb$t Center, Alabama

lLSFC - Form 3190 ( R e v June 1971)

https://ntrs.nasa.gov/search.jsp?R=19760026408 2018-05-21T15:27:23+00:00Z

REPORT STANDARD TITLE PACE I nEPMTn0. 3. RECIPIENT*$ CATILOC NO.

NASA TM X-73345

An overview of the various categories of the LE3 methodology is given together with illustrations showing a simplified version of the LIS tecbnique, an example of the two-phoiin photoionization category, and a diagram depicting how the energy levels of various isdope influence the LIS process.

A&icatlons have been proposed for the LIS system which, in addition to the use to enrich uranium, could in themselves develop into programs of tremendous scope and breadth. Such applications as treatment of radioac ' --e wastes from light-water nKzlear reactors, enriching the deuterlum isotope to make heavv-water, and enrlchhg tik light isotopes of such

10 TITLE UO S U T l T L t I S . REPORT DATE

17 K E t WORDS 18. DISTRIBUTION STATEMENT

September lS76 I

6 PERFWYIIIG W G U I Z A T I O * CQOE I A st.tUaof Progress for the Iaser isotOpe &paratian (LIS)

Unclassified Unclassified 20 I

George C. M8ralmll!3gam Flight Center I M a r W Flight Center, Alabama 35812

NTIS

I 1. COUTRUT OR am yo.

National Aemutics and Space Administration Washingtan, D.C. 20546 I Tecbnid Memormdum

I

Prepared by Systems Aaalysis and Integration Iaboratory, Science and Engineering

5ECUQlTY C L A S S I F . Ff t h h PI*) 21 NO. OF PAbFS 22 P R I C E

PREFACE

Since the publication of t& first Tech id hiemomxitun (TM X-64947) on the Laser hotope Separation (LE) process in May 1975 [l], there b b e e n a virtual explosion of available information on this process. Articles have been publiskd in a widely varyiag degree of sophistiCatian, r8nging from the recent article in tbe popular science fictioa m a g a z b Analog to the prestigious Science Journal, all of which contain information on the LE process. As a matter of fact, the LIS process is not a single metbdology - but a series of techniques, each of which has its own unique set of critical pammeters. Discussion will be primarily from an engineering point of view, althougb it is recognized that the field lies heavily in tbe discipline specialty of optical physics. An attempt wil l be made to simplify tbe technical descriptions and to present the inforrmticm from the viewpoint of people with a diverse background of specialties.

The trade journal, Laser FOCUS, is to be commended for its role in serving as the source for all late technical information on the evergrawhg list of laser applications.

i i

VAPORIZED URANIUM ATOMS

235

APPROXIMATE WAVELENGTH OF *% ATOM8

TUNABLE LASER

0 0 238 U ATOM

FREQUENCY OF LASER IS TUNED TO MATCH ABSORPTION WAVELENGTH OF THE DESIRED ISOTOPE. OBJECTIVE IS TO RAISE ENERGY LEVEL OF ISOTOPE TO IONiZATION LEVEL.

SIRIPLIFIED SCHEAIATIC DIAGRAM OF THE LIS PROCESS

TABLE OF CONTENTS

page

INTRODUCTION ................................... 1

DISCUSSION OF LIS METIIODOL4XY 2 ..................... ........ OTHER TECHNlQUES FOR SEPARATION OF ISOTOPES 6

PARTIAL LISTING OF APPLICATIONS OF THE LIS PROCESS .... 7

ECONOMIC COMPd9RISONS ............................ 8

CONCLUSIONS AND RECOMMENDATIONS .................. 10

REFERENCES. 12

BIBLIOGRAPHY ................................... 14

....................................

V

TECHNICAL MEMORANDUM X-73345

A STATUS OF PROGRESS FOR THE M E R ISOTOPE SEPARATION (LIS) PROCESS

INTRODUCTION

Apparently due to a change in the classification policy [ 21 , tbere has been a noticeable change in the details concerning Laser Isotope Separation (LIS), technical and economic. Surprisingly, the principle of "detente" was never more accurately applied than in the Soviet Journal of Quantum Electronics [ 31. The cost values of isotope enrichment by the gaseous diffusion process are released for public utilization. A t one time this value ( 8 5 per gram of U-235) was classified top secret, as were cost VaIues pertaining to the consumption of electrical energy, capital costs of gaseous diffusion plants, and maintenance costs for the diffusion plant cascade.

Also, the classification o r categorization of the several methodolog.les for LIS has shown a noticeable progress .%ring the past 18 months [4]. The various subcategories of the LIS process are outlined approximately as follows:

Laser Isotope Separation:

Single-Photon Photoionization

Two-Photon Photoionization

Three-Photon Photoionization

Two-Step Photodissociation

Two-Stcp Photoc hcmi s t ry

Raman-Scattering Proccss

Autoionizatlon

h) Others.

Of these several techniques, only those represented by b), c ) , and f) he indicated significant progress in the information which bas been released up to the present time. Of the several processes outlined here, some are based on atomic unit processing while others are based on the separation of molecular units, e.g., UF6 or PUF6. The efforts at the LQS Alamos Scientific Laboratory

have been concentrated on the molecular system of isofope separatiou, whereas the activities at Lawrence Livermore Laboratory (also Exxon, Avco, etc. ) mainly utilize the atomic methodology in their laser separation schemes. The main point hem is the question concerning the accumulation of technology related to the chemical processing of uranium to yield the desired molecular form of L'F6 versus the relative difficulty of processing uranium in the metallic state (atomic). Vas t facilities already exist at Oak Ridge to process ~ i ; f U&+ into the vaporizable UF6 [ 51 and also to reduce the enriched "%Jfback to the parent metal; therefore, this part of the nuclear fuel cycle is considered well in hand.

Also, still to be reckoned with in the isotope separation sweepstakes is the category of processes for enrichment of isotopes by the method of photo- chemistry. Several groups have participated in th is specialty [ 6,7,8]. Much promise is held for this approach which naturally falls into the molecular cate- gory, and applications to other arcas of chcrnistry (other than nuclear) are virtually unlimited.

DI SCUSSION OF L I S METHODOLOGY

Overall progress in application of the laser to separate isotopes has been excellent in the past 18 months. Much of this progress has been reported by the teams a t Los Alamos and a t Iawrcncc Livcrmorc [ 7). Laboratories in forcign countries have also madc significant contributions [ 3,9, lo].

The techniquc whcrcby a particular atom, e. g., 23%J, is selectively energized by the application of a laser tuncd to the specific characteristic bandwidth of thc isotopc in question has bccomc a principle subjx t of discus- sion. The application of thc lascr tuned to a discrctc bandwidth at a predeter- mined powcr lcvcl and at a suitable pulsc ratc has bccome the standard approach.

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Many variations in this approach have been reported and others arc being added. Inherent in this LIS approach is the choice of a feed material. Basically. this is the choice between UF6 or the use of metallic or atomic uranium. hlany prefer the UF6 form because this is the only compound of uranium that can be rendered in the gaseous form at a slightly elevated temperature (6OOC). As was mentioned previously, facilities already exist to process the uranium into the UF6 form and to reduce it to the metallic form i f desired. The vast gaseous diffusion process is based on the UF6 form of uranium feed. If a process in LIS based on a UF6 feed material could be accomplished then that part of the nuclear fuel cycle would be simplified [ 5,111.

The approach by Lawrence Livermore Lab, Exxon, and Avco-Everette has by contrast been based upon using the atomic uranium as the feed material with the uranium in a metallic state being heatcd in an oven to the molten state (Fig. 1) [ 121. A similar approach was used by Israel as described in a patent disclosure 191. According to this patent disclosure, 7 gm of 23%J (at a purity level of 60 percent) were separated in a 24 h period. Due to the very corrosive characteristic of molten uranium (2000 K) , it is necessary to have the atmos- phere for the oven in a rare gas atmosphere, e . g. argon. In spite of the prob- lem with the corrosive nature of molten uranium, there is at least one sipifi- cant advantage to the use of atomic wanium as the feed material - the charac- teristic laser wavelengths are much bctter defined o r distinct for the atomic uranium. Each isotope of uranium, or any nthcr element, has a distinct wave- length or bandwidth for each of its isotopcb:;. The energy level of a chosen isotope may be increased by matching the frcqucnrv o r bandwidth of a suitable laser to the characteristic wavelength of the isotopc. The energy level of a particular isotope may be increased by application of a suitable laser until a point is reached where the continuum is realized - at this point, thc isotopc in question emits an electron and beconics an ion. As illustrated in Figure 1, the ions a re collected by thc use of a negatively chargcd plate. Also, as shown in Figure 8, t b e atoms of uranium may bc brought up to the continuum level in step-wise fashion by either two, three, or more lasers tuned to the appropriate bandwidth. As pointed out in the "Laser E'ocus" [ 2) , the LIS could bc accom- plished with "3 single highpower pulsed lascr, tuned to one isotopic transition" 1131. The mode of actual recovery of the product will depend upon whcther the isotope is being scparatctl in atomic or molecular forni.

In thc photodissociation p r L nss, thc sigiiificant action is the physics of selectively hrcaking chemical bonds in a two-step process. The first reported application of two-step photodissociation to isotopc cnrichmcnt was the scpara- Yon of nitrogcn isotopes 14N and 15N 1.11, Other molecular csamplcs have also 5ccn reported [2 ,4 ,G, 111.

LASER ISOTOPE SEPARATION (LIS)

AT

0’ EXCITATION

U S E R BEAM

IXENOCII)

COLLECTED QNR URANIUM

2%

(NEGAT~VELY CHARGED) L n Y Figure 1. Two-photon photoionization.

CONTINUUM LEVEL 1

2 PHOTONS

2 A

ATOMIC IONS

A+ + e-

.E PHOTON

Figure 2. Energy level diagram.

In the selective photochemical process, the critical activity [SI is the influence of the laser on the chemical reactivity of a particular element during a chemical reaction. Several isotopes have been reported enriched during chemical reactions which involved enhancement by lasers ("N, 3sCl, "CI) .

In the autoionization scheme, the p r w e s s relies upon the greater cross section for autoionization (by the isotopes) than for conventional photoionization. Consequently, a considerably weaker laser can be used for the final ionization step. This method is considered a variant of the photoiocization technique [9].

5

In the Raman-scattering mode of laser isotope separation, the process depends upon an amplification process in which the simultaneous irradiation by a dye laser is tuned to the difference between the pump frequency and the fre- quency of the Raman-scattering component of the selected isotope.

In the final analysis, the "isotope separation sweepstakes" break down into two different camps. The advantages and disadvantages of each approach (as previously outlined) indicate that considerable development and some additIona1 research will be needed before the process of LIS can be reduced to the pilot plant stage by specific methodology [ 111. For the atomic approach, there are the problems of the corrosiveness of high temperature uranium vapor and the tendency of ionized 235U atoms to recombine. In the case of the molecular approach, there are several problems: 1) the energy states of the molecular form UF6 a re close together, tending to overlap, so that it is almost impossible to find a wavelength a t which 23%JF6 will absorb light (from a laser) but '%F6 does not; 2) few of the UF, molecules will be found in the '(ground state" (a necessary condition for laser excitation) ; and 3) perhaps the most important drawback to the molecular mcthod is the lack of commercially available lasers with sufficient power and at the desired wavelength to do the job.

The Los Alamos group has reported successful separation of isotopes of SF6 by the development of a more powerful laser with the desired bciidwidth [ 111.

system, but for UF6 proof of the methodology must await

Recent reports have placed the dcsircd wavelength for enrichment of uranium as apprcximately 16.1 pm (for UFO) [ 141. It has been reported that more precise specification of the wavclength beyond three digits is classified (e. g. , 16.13483).

OTHER TECHNIQUES FOR SEPARATION OF I SOTOPES

Although considerablc disclosurcs have bcen made, certain classified facts rdated to the isotope separation still remain. Naturally, only the information based on published rcports can be discussed.

The mainstay of thc American nuclear industry has been and continues to be the gaseous diffusion (also for thc Frcnch) . There have been several challenges to this process which arc dcscrilxd in general in Reference 1s

and in detail in Reference 5. The main advantage is that it is a proven tech- nology and has been for over 25 years. The disadvantages are: a) capital investment cost, b) power consumption cost, e ) land usage, and d) maintenance costs. A recent contender for the uranium enrichment business has been the centrifuge which has been used by a European consortium and by the Japawse. The centrifuge reiies upon certain physical properties of the isotope to effect the separation. The process, though still under development in the United States (and is largely classified), does show considerable promise with enrich- ment factors in the range of 1.5 to 2.0, as compared with 1.004 for gaseout diffusion [ 111. The power consumption for an equivalent amount of product would also be reduced considerably.

There is also anothnr process, about which little is known, in Germany, This is based upon the passage of a gas ( UF6) over an airfoil by a nozzle. The reported disawantage of this process is the excessive consumption of power. South Africa and Brazil a r e reportedly utilizing tho technology of this isotope separation methodology.

PARTIAL LISTING OF AFPLICATIONS OF THE L I S PROCESS

The principal candidate for application of thc LIS has been to separate 235U from natural uranium. This mcthodology promises to be 1000 times more efficient than the current technique of gaseous diffusion [ 151. The enrichment of the 235U isotopc from its naturally occurring percentage of 0.711 pcrcent to the 2 to 4 percent lcvcl is currently important bccausc of the ever increasing demand as fuel elcmcnts for the light-water reactor.

Also potcntially important is thc application to enrich deuterium. The naturally occurring concentration of deuterium in watcr is o;ily 0.015 percent, too low for a technique based on mass difference to work efficiently. Applica- tions for heavy-water a r e wcll known, but thcrc is , for cxaniplc, the Canadian derived CANDU rcactor (a heavy-water type) which uses hca.v,y-watcr and also the wcll known application i n thc fusion proccss.

Treatment of nuclear wastc materials was used to scparatc thc isotopes af ulutoniuni PU-238 and PU-239. Also, the lascr could bc vcry uscful in thc separation of certain actinid:is f i w: t!ic wastc mztciial s from reactor systcnis

7

to make the storage of those waste materials a i d subsequent handling easier. Since many of the actinides are so close together in the periodic table, separa- tion by chemical means becomes very difficult. An alternative for this applica- tion is not known at the present time.

Other less important uses are as follows:

a) Separation of 'OB to usc in light-water reactor control rods.

b) Separation of 6Li for u e in the fusion reactor system.

c) Savings in weight by scparation of the light isotopes of, e. g. , Titanium for aerospace application. Light isotopes could also be useful for applications where weight of a moving part limits its performance, e.g., turbine blades and rotors.

Since the gaseous diffusion method leaves a significant portion of the 235U isotope (M 40 perccnt) unseparatcd, a final consideration for application is that it is possiblc to rcmovc practically all of the selected isotope with the laser methods. Tbis fact alone will rcsult in approximately a 67 percent increase of our effccilve uraniim rescrvcs [ 151. The tails from the gaseous diffusion plants could all be worlccd to remove the remaining radioactive portion.

ECONO: .; C COMPARI SONS

One might ask "with a proven technology that has bccn opcratbg for over 25 years*1' why take the chancc with onc more way to enrich uranium? This would be cspccially truc whcn you coiisider that for power plants, thc operating costs a rc alrcady chcapcr than for conventional fossil fuels. Tne reasons are rather obvious when you considcr that the owra l l investmcnt costs a r e roughly 30 t imes higher for thc prcscnt method, which is gaseous diffusion. It would only be fair to say that thcsc statistics a re based on the currently reported inforrratim and arc in thc: naturc of projections bccausc there is no L E plant to cpmpare dircctly with the gaseous diffusion plants located i n Oak Ridge (Temessee) , Paducah ( K e n t x k y , , and Fortsmouth (Oldo). The Tsble is, however, based on the best ir.fr,miation available at the present time and is assumed on the basis of 1976 dollars 1 151.

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TABLE. COST COMPARISON OF GASEOUS DIFFUSION VERSUS LE ENRICHMENT P W T S

Assumed Capacity = 8.75 X 10' !kparative Work Units/Year, $ = Billions of

1976 Dollars

Caseous Capital Investment Diffusion

Enrichment Plant $3.1

1.4 Power Plant - Total Capital 44.5

LE

$0.130

0.013

$0.143

-

Operating Costs

Electric Power $0.426

Other 0.036

Total Operating Costs $0.462

Land Use = 90 acres

$0.004

0.016

$0.020

= l acre - ~ ~~ ~

Note: The gaseous diffusion plant must also be located closc. to a river o r somc other source of cooling water. An LIS plant cmld presumably bc located at any geo- grapluc location.

So far as enrichment of uraniuin is conccrned, the WS is the choice .r a wide margln on most points of comparison - capital invcstment, operating costs, laL1d use, or cvcn choice of thc plant site to bc close to a river. The cost comparisons with the ccntrifugc process would be less impressive - but since the data are still classified, none' can be made.

9

Cost comparisons concerning the application to treatment of nuclear wastes cannot be made because there is no known competitive system. The cost of deuterium enrichment is still unavailable, so no comparison can be made.

Based on current projections and assuming currently planned use of nuclear power plants, the demand fer enriched uranium will begin to exceed supply sometime behveen 1980-1983. A decision must be made 80<111 as to tbe type of enrichment plants that must be built and whether it will be haneed by the L'nited States Government or private enterprise.

CONCLUSIONS AND RECOMMENDATIONS

As has been outlined, the LIS process is really a group of related tech- niques rather than a single method. The inherent simplicity of the approach is the thing that attracts much attention. Also, the economic question is perhaps the aspect of the methodology that attracts the most interest. Millions and perhaps even billions of dollars might be saved by applicatic.. of the LLS process to the uranium reactor fuel system alone.

The q3estion of whether the molecular or the atomic form of separation will prove to be most practical must be answered. Them are several dis- advantages as well as advantages inherent to each of the forms of feed material. Also, there remains the problem of scaling the laboratory-sized operations up to the pilot plant size and then industrial plant size.

Other applications of the LIS process to such approaches as treatment of nuckar wastce to effect a separation of actinides, etc., and to enrich deuterium for heavy-water applications show exceptional promise. The treat- ment of the tails from the Oak Ridge gaseous diffusion appears to be a simple way to extend the volume of our uranium reserves.

In thc area of rcconmondatims, thc laser part of the system appears to be the way to progress i n most all of the categories which have been pre- viously detailed. It would thoreforc appear frugal to concentrate development efforts on the laser itself. In such efforts thcre are two principal laser hard- ware parameters which should receive attcntion:

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a) Tunability of the laser

b) Power levels.

The savings in uranium enrichment can be very important by application of the LIS process; however, laser-influenced chemistry holds forth a much broader application range because laser-induced chemistry can be applied to all the elements of nature and to coniplex molecules as well. The laser would in effect become a "super-cataIyst,*' to influence the speed of chemical reac- tions, etc.

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REFERENCES

1.

2.

3.

4.

5.

G.

7.

8.

9.

l o .

Delionback, Lcon hI. : Possible Application of Laser Isotope Separation. NASA Tbl X-649.17, hlay 1975.

Jensen, Reed J.: Backscattc . h s e r Focus, vol. 12, no. 7 , July 1976, p. 8.

Letohov, V. S. and Rloore, C. Bradley: Laser Isotope Separation (Review). C)uantum Electronics, Fcbruary and bLqrch 1976 (Soviet Journal), translated by Anlcrican h s t i t u t c of Physics.

Aldrige, J. P., Bircly, J. 11.. et al. : Experimental and Theoretical Studies of Laser Isotope Scpn- rtion. Report No. LA-UR-75-2368, Rev. 1, 1975.

AEC: Gaseous Diffusion Plant Qwrations. ORO-684, ljSAEC Technical Information Center. Oak Riclgc, Tcnncsscc 37830.

Lyniaii, John I,. and Jcnscn, Rcctl J. : Iascr Driven Chemical Reac- tions of Dinitrogcn TetrafIuoridc* with IIytlrog:.cn and Sulfur Ilcxafliloride with Iiytlrogcn. Thc Journal of Physical Chcmistry, vol. 77, no. 1973.

Jacobs, Stcphan F.,ct 31. : Iascr I'hotoch?niistry, Tunable Lasers (and othcr topics) . Atldison-\Vcslcy 1'uI)lishing Cr,. , Rcading, Massachusetts, 1976.

%arc, Richard h'.: N r w s in 1;ocus. Julv 1976, p. 12.

I a w r l'ociis, vol. 12, no. 7,

K;c.t)cnznhl, I . and L A ! v ~ v , M. : A Process for Isotope Separation. Gc~rman Patotit N o . 3, 212, 1'34, Octolwr 4 , 1973.

‘.1. Metz, William D. : Laser Enrichment: Time Clarifies the Difficulty. Science, vol. 191, March 1976.

32. Levey, Richard H. and Janes, George S. : Method of and Apparatus for the Separation of Isotopes. United States Patent No. 3, 772, 519, November 13, 1973.

i 3. Jensen, Reed J. Marinuzzi, John G., et al. : Prospects for Uranium Enrichment. Laser Focus, vol. 12, no. 5, 1976.

14. Scalable 16-m Laser Developed at NRL Could Aid Uranium-Enrichment Studies. Nava l Research Laboratory, Laser Focus, vol. 12, no. 3, 1976, p. 11.

15. Robinson, C. Paul and Marinuzzi: Laser Isotope Separation. Report No. LA-UR-76-198, February 3, 1976.

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B I 3L I OGRA PHY

Altschuler, S. J. : Possible Applications of Laser Isotope Separation to Nuclear and Conventional Technologies. Dow Chetr.icai Co., Golden, Colorado 80401.

Hecht, Jeff: Enriching Isotopes with Lasers. Analog, VOX. XCVI, na. 9, September 1976,

Kimmel, PA. and Speiser, S. : The Stimulated Ximan Scattering Process for Possible Use in Photoselective Isotope Enrichment. Chemical Physics Letters, vol. 28, no. 1, Septembcr 1, 1974.

Weinberg, Alvin M. : The Maturity and Future of Nuclear Energy. The American Scientist, vol. 64, January-February 1976.

APPROVAL

A STATUS OF PROGRESS FOR THE LASER ISOTOPE SEPARATION (LIS) PROCESS

By Dr. Leon M. Delionback

The information in this report has been reviewed for security classi- fication. Review of any information concerning Department of Defense o r Atomic Energy Commission programs has been made by the MSFC Security Classification Officer. This report, in its entirety, has been determined to be unclassified.

This document has also been reviewed and approved for technical accuracy.

I

11. E. 'I'HOMASON Director, Systcms Analysis and Integration Laboratory

15 eU 5 . G O V C A N M C N T PRINTING O F F I C E 1076 740-049/7 R E G I O N NO 4