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Appendix A
OVERVIEW OF THE AVLIS PROCESS
HISTORY
Dunog World War II, the United States invested significant financial and personnel resources in the
Manhattan Project in order to develop large-scale isotope separation capabilities to produce clinched uranium
for the manufacture of nuclear weapons. The present technological legames of this Herculean effort are the
gaseous diffusion plants at Oak Ridge, Tennessee; Paducah, Kentucky., and Portsmouth, Ohio, which have
produced most of the enriched uranium used in civilian nuclear power plants in the free world. Through the
mid-1970s, these plants were periodically upgraded and had a virUlal monopoly on enrichment services in the
international marketplace. In this time penod, a significant growth rate in nuclear power plant deployment was
berg projected. Since the gaseous division process is very energy intensive (~80% of operation costs), the
United States supported the development of advanced eng~neenng and scientific approaches for uranium
enrichment to provide additional enrichment capacity by using more energy-e~cient technology. In l9T7,
President Carter initiated a program to build the next increment in enrichment capacity in the United States
by using gas centrifuge technology. Advances made in this technology since its early evaluation in the 1940s
promised nearly an order of magnitude reduction in power consumption and a substantial improvement in total
processing costs. Both gaseous diffusion and gas centrifuge development were being pursued aggressively by
several western European countries to provide them with nationally independent enrichment capabilities. In
those assessments, there was also a general understanding that more efficient and lower-cost enrichment
processes were possible and that it was important to develop and deploy them.
The Soviet Union has been installing gas centrifuge technology since the 1960s and is now using fourth-
generation machines. Private U.S. interests have decided to add enrichment capacity based on the Urenco gas
centrifuges. Centrifuges are being installed in Japan, and Asahi Chemical Industnes has a pilaf plant that uses
a chemical process that it claims is competitive with the gas centrifuge. The French have a different chemical
process that is claimed to be better than their present diffusion plant.
Among a number of possible chemical, aerodynamic, electromagnetic, and photophysical uranium
enrichment processes, three processes involving four organizations were explained in depth ~ the United States
in the late 1970s and early 1980s to demonstrate the best process. All three were funded by the U.S.
government, and two, the atomic vapor laser isotope separation (AVLIS) and molecular laser isotope separation
(MLIS) processes, were pursued independently by EXXON in the private sector. EXXON withdrew from active
participation in 1981. After intensive review In the early 1980s, two of the processes, an MLIS process, developed
at Los Alamos, New Medico, and an electromagnetic plasma separation process (PSP), developed at TRW
Corporation, were eliminated from further competition. In 1985, the AVLIS program managed by the Lawrence
Livermore National Laboratory (LLNL) was chosen as the only advanced uranium ennch~nent technology
program in the United States after a competition with an advanced-design gas centrifuge under development by
an industrial team composed of Boeing Aircraft Company, Garrett AirResearch Corporation, the Oak Ridge
Gaseous Division Plant, and Goodyear Corporation. Figure A-1 summarizes these events as well as the
projected activities of the next 7 years.
From the beginning of the LLNL AVLIS program, the primary goal was to understand and develop a
process that could enrich uranium at a price substantially below the existing market price. An early commitment
to high-be~-quality and high-puIse-repetition-frequen~ (Prf) dye lasers was a fundamental difference between
LLNL and Jersey Nudear AVCO Isotopes, Inc. In 1980, the Department of Energy (DOE) judged the LLNL
design to be more cost-competitive in the long-term market.
27
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As the technical feasibility of us~gAVLIS to separate uranium became clear in the late 1970s, scientists
at LLNL applied the technology to the mission of purifying DOE-owned plutonium up to weapon-grade
specifications by removing unwanted plutonium isotopes. After a peer-review competition in 1983 against an
MLIS process sponsored by Los Alamos National Laboratory, AVLIS was chosen as the nation's technology
for plutonium isotopic enrichment.
A large and successful plutonium AVLIS scientific and engineering development program has been in
effect at LLNL since the early 1980s. Milestones in this effort were (1) extended plutonium isotope separation
runs in plant-scale hardware in 1984 and (2) extended isotope separations of surrogate metals in engineered,
plant-ready hardware in 1989.
In early 1990, the Secretary of Energy announced a decision to indefinitely postpone construction of the
plutonium AVLIS (special isotope separation) production plant at the Idaho National Engineering Laboratory.
This action was based entirely on the Ranged nations needs for plutonium, not on any shortcomings of the
AVLIS "ethnology. In fact, the desire to find alternative uses for this sophisticated "ethnology prompted this
study.
The following sections describe AVLIS technology in terms of uranium enrichment. The reader should
recognize that the same technology, and much of the same hardware, has already been applied to the separation
of plutonium isotopes and isotopes of several heavy metals and can be applied to the separation of isotopes of
other elements. As a result of the plutonium AVLIS program, process-ready hardware is available at LLNL
for the separation of selected metallic elements on a gram to kilogram scale.
PROCESS DESCRIPTION
The AVLIS process developed at LLNL consists of two major subsystems: a laser system and a
separator system (Figure A-2~. In the separator, unenriched metallic uranic is vaporized by an electron beam
that creates an atomic 235U/238U vapor stream that rapidly moves away from the uramum melt. At the "me
time, dye lasers produce beams of red-orange light precisely tuned to the colors that will selectively photoioni7~.
235U isotopes. Powerful copper lasers emit beams of green-yellow light that energize the dye lasers. Ibis
configuration produces powerful beams of tuned red-orange light to illuminate the uranium atomic vapor inside
the separator.
235U isotopes absorb the tuned red-orange light, but 238U isotopes do not. The excited 235U isotopes
eject electrons (become photoioni~ed) and retain a net positive charge. The 235U ions can then be moved
preferentially by an electromagnetic field to condense on the product colDector. The 238U isotopes, which remain
uncharged, pass through the collector section to condense on the tails collector. The separated uranium
condensates are collected in metallic form. Presently, the technology is being developed to convert the AVLIS
product to a uraniums oxide form suitable for fabricating nuclear reactor fuel elements.
The primary goal of the AVLIS program is to develop a process that can enrich natural (and/or tails)
material at less than half the cost of any other competing technology. After numerous reviews by peer groups
and h~gh-level government advisory panels, AVLIS has been judged to have the potential for processing natural
uranium at a cost of between $25 and S50 per separative work unit (SWU).* Each of the major subsystems is
described below in enough detail to identify performance and operational characteristics that have potential in
other applications.
*The standard measure of both the capacity of urban enrichment plants and the amount of
enrichment required for a particular task is the SWU. For example, about 4 SWU is required to produce 1 kg
of 3% enriched uranium starting Tom natural uranium (0.7%), assuming a waste or tails uranium concentration
of 0.25%. Similarly, about 200 SWU is required to produce 90% enriched uranium from natural uranium. Thus,
an enrichment plant with a capacity of 1 minion SWU/yr could produce either ~250,000 kg of 3% enriched
material or ~5,000 kg of 90% enriched material. The cost of enrichment is commonly Even ~ dollars per SWU
[see reference Ad.
OCR for page 30
30
- \
Dye master oscillator \ Metallic uranium is melted and vaporized. The
\Laser system vapor is illuminated by visible laser light that
_ ~\ photoionizes the selected isotope. The ion is
_ \ then electromagnetically extracted.
_ ~
Pump laser ~
Pump laser 7\~ \ \
| roduct :~ collector
I\ - Laser
~ Vapor
\ ~
\Vaporizer
~ Dye amplifier
FIGURE A-2 Illustration of the AVLIS process.
Separator system
-
-
-
-
OCR for page 31
31
AVLIS is not a single-market technology limited to the separation Of 235U from 238U. The periodic
table shown In Figure A-3 shows that most elements can, in principle, be separated in this way. Separation of
uranium isotopes, which potentially bears great economic benefits, Is an obvious application for AVLIS.
However, as the teleology improves, as costs decrease, and as demands for the new isotope products increase,
new markets may well appear. For example, markets might develop for the separation of gadolinium (for use
In power reactors) apt for the isolation of radioactive xenon (to use for radioiodine production). Markets
already exist for small-scale medical diagnostic, and research uses of a number of stable and radioisotopes. The
SWU costs projected for a uranium AVLIS plant, $~5-$50/SWU, translate directly into a cost of $30 $60/mole
Of product with a typical away concentration of 32%. A rough estimate of the cost per mole of product in other
isotope separation missions can be obtained by scaling these costs by the ratio of the fraction of the product that
is processed as photoions in the mission to that fraction for the uranium mission (i.e., 0.0323. For missions that
are on a smaller scale than that for uranium, costs can exceed these estimates, depending on how the laser and
separator systems are union. It is important to realize that each element requires a unique set of frequencies
and that many will present unique materials handling problems related to vaporization, separation, and collection.
Each element will require a substantial independent development effort. Elements requmng vacuum ultraviolet
radiation may not be tractable.
TECHNICS
Numerous technologies are required to construct and operate an AVLIS process. Table A-1 is a top-
level summary of the scientific and eng~ncenug disciplines that have been developed In the major programmatic
areas. Note Mat the copper lasers and uranium separators share many common problems and technology
requirements. Both operate at low pressure and high temperatures with corrosive liquid metals (uranium being
much more corrosive than copper), but copper lasers operate at a temperature several hundred degrees higher.
To engineer the AVLIS copper lasers and uranium separators, the AVLIS staff has expertise in selecting,
motiving, and testing refractory metals, ceramics, and h~gh-effic~engy thermal and electrical insulators and in
constructing electrically and mechanically complex precision mechanisms. To rewires the AVLIS system together,
very sophisticated optical design capabilities have been developed that allow transport of high-average-power light
with meal absorption, Fresnel, scattering, diffractive, or aberration losses. Many optics elements
simultaneously have absorptions of <10-5, transmittance or reflectance losses of <0.0003, scattering of
< 10-5, rms wavefront errors on the order of 0.01 optical wavelength and the ability to operate continuously at
optical power densities of more then 104 W/cm2. Deformable optical elements whose surfaces An be adjusted
have been develop to preserve the inherent optical quality of laser beans with enough power to thermally
a- . . ~ ~ ,' ~ ~ · ,- . ~ . ~ ~ · _ _ 1 _ __ ~ 1 _ _- _ t _ ~ _ mat-__ ~ ._ ___- I_
distort even very low loss optics. Sophisticated measurement techniques have then designed and ut~zeo to guide
the development and evaluation of optical and electro-optical subsystems and to provide precise control
capability. Highly integrated, efficient, user-friendly microprocessor and computer networks and associated data
bases have been deveiope<] and deployed to mate and record the thousands of operations that take place in
the AVLIS process. Since AVLIS must operate as a cost-competitive continuous industrial process, detailed
understanding of cost and reliability eng~neenag, user-friendly product development, integrated refurbishment,
and preventive maintenance has had to become part of the AVLIS culture. The capabilities of some of the
AVLIS subsystems are outlined below to aid in identifying new applications of this technology to industrial,
scientific, medical, or military moons.
Lasers and Optics
After more than 15 years of sustained development of very complex high-average-power laser, optical,
and materials processing systems for the AVLIS program, LLNL now has a mature and comprehensive capability
to design, engineer, construct, integrate, activate, operate, m~nta~n, and On prove indus~ial-grade laser and
optical delivery systems for cost-competitive commercial processes. Because of the inherent complexity of the
AVLIS process and the absolute requirement that the lasers not represent a performance or cost problem, the
kinds of laser systems developed have characteristics that surpass the performance and reliability of most
presently available commercial systems.
Because the funded applications of AVLIS at LLNL have been for nuclear materials, dissemination of
information and technology transfer have been controlled by DOE classification polimes derived from the Atomic
Energy Act. With a few key exceptions associated primarily with the details of a specific materials process, this
OCR for page 32
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laser and electro-optical system capability is not limited to the processing of materials that have an impact on
national security and may be of broad use In the industrial sector.
If the laser systems developed for AVLIS are examined by subsystem, there are many laser and/or
optical systems, components, and engineering capabilities that can address many processing problems much less
sophisticated than AVLIS. Many Department of Defense applications require sources of reliable high-intensity
~llun,~nahon that range from nonspectrally sensitive target iBum~nators to narrow-band frequengy-stable optical
laser radars Pith multispectral scan capabilities. Cost-compet~tive high-average-power lasers with kilowatt-per-
aperture capabilities have numerous applications In cutting, welding, marking, and heat treating. These
applications include common construction materials such as iron and aluminum and range to complex material
matrices used In the semiconductor and computer industries. The Prf (~1-30+ p~Hz]) and the moderate-
pulse-energy (03 05 J/pulse) capability of the copper laser or copper-laser-pumped tunable dye lasers milt be
appropriate for generating practical x-ray plasma sources for submicron-level lithography needed for the next
major advance in computer memory and processing technology.
The primary issue with any AVLIS mission is the value of the material to be processed relative to the
capital and operating cost of a high-technology laser system. Since the primary goal of the uranium AVLIS
program has always been to develop a minimum-cost process, the associated laser systems developed within the
LLNL program are engineered to be cost-competitive in a commercial environment. On the basis of costs
projected for a uranium-scale AVLIS plant, fixed-frequenc~r copper laser photons (green and yellow) can be
procluced for $150-$250/mole, and t~able dye laser photons (yellow and red) can be produced for $10-
$18/mole. Accounting for inflation and increased equipment costs over the past decade, the costs for producing
these photons in replicated hardware similar to that operating at LLNL today are twice as great as the values
gnen above, depending on system size and date of deployment. Other applications of the laser capability
developed in the AVLIS program become practical only after the technology leaves the laboratory and the
prototypical hardware reaches its true economic potential in the commercial world. These applications include:
~ . ~ ,~ _ ~ ~_ ,
Control of chemical and biological processes.
Environmental monitoring.
Direct line-of-sight communication
Nondestructive testing.
Commercial laser radar.
A wide variety of scientific and commercial applications of spectral analysis and control.
To provide an appreciation of the broad rate of transferable capabilities developed In the AVLIS
program, the laser system, components, and engineering capabilities are described below In terms of products
and/or capab~t~es.
System Description: Ind~strial-Grade High-Average-Power Risible Laser Systems, Components, and Technology
The laser facility shown in figure AT Is constructed by using a modular integration of copper and
tunable dye lasers. The performance characteristics of the copper laser system and the copper-laser-pumped dye
laser system are given below. Characteristics of this system include:
Parallel architecture for high availability (>99%) and continuous operation.
Discrete optical component or fiber-optic cable power transport and delivery.
· Manual or computer-controlled power, wavelength, beam position, thermal, and environmental control
.
Integrated diagnostic and data management system.
For the replication of all or portions of this system, one or more of these options could be used.
OCR for page 35
35
W^~<
\
\
· Copper laser system
· Optical systems
· Instrumentation and control systems
· Laser support systems
· Dye laser system
· Refurbishment facilities
FIGURE AN Industrial-grade high-average-power visible laser system.
OCR for page 36
36
Subsystem Descap~on: Modular Copper Laser Chains win Beam Multiplexing Optics
A copper laser chain (Figure A-S shows six copper laser chains in a comdor) is capable of providing
high average power for optical pumping' headug, x-ray generation, and other missions. Typical operating
characteristics are s~nnmarizect in Table A-2.
TABLE A-2 Operating Charactenstics of AVLIS Copper Lasers
Optical power
System
Single amplifier cham
Wavelength
Frequency bandwidth
Operational mode
Prf
Pulse duration (FWHM)
Beam quality
Laser head ~F)
Efficiency, electrical to light
Power stability
Photon cost
Capital cost
Up to ~10,000 W
600 to ~1500 W
511 and 578 (nary)
~8 (GHz) at 511 am;
~12 GHz at 578 am
Continuous, 24 in/day
2 to ~30 kHz; typically =5 kHz
20 to 60 (us); 50 ns typical
2 to 15 x diffraction limited
~ 1,000 hours
~1%
Y%/day
+L5%/week
~ $28/kW~h
~ S630/W
Subsystem Description: Tunable Dye Laser Systems
Copper-laser-pumped dye laser osciDator/=nplifier chains are visible, wavelength tunable, narrow-
spe~ral-bandwidth, high-average-power lasers for spectrally sensitive optical excitation, coherent illumination,
and materials processing missions. The typical operating characteristics of a tunable dye laser system such as
the one shown in Figure AT are summarized In Table A-3.
TABLE A-3 Operating Characteristics of AVLIS Dye Lasers
Optical power
System
Single amplified chain
Wavelength
Frequency bandwidth
Frequency stability
Operational mode
PI
Pulse duration
Beam quality
Maintenance cycle
Efficiency, pump to dye
Power stability
Photon cost (mclucting Co laser pomp)
Capital cost (including Cu laser pump)
>2,000 W
Up to ~1,500 W
Tumble 500 to 1000 am
~50 MHz
~120 MHz
Continuous, 24 in/day
2 to ~30 kHz
20 to 60 ns
~DifEraction limited
Mission dependent, ~ 100s of hours
20 60%
Typically she as excitation source
~$ 200/kWh
~$5,300/W
OCR for page 37
FIGURE A-S Copper laser corridor showing six copper laser chains.
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38
FIGURE AN Tunable dye laser system.
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39
Other Subsystems
To construct the systems discussed above, many subsystems have been developed and engineered for
routine operation. For example:
.
Tunable TiAI2O3 oscillator/amplifier systems.
Multiwatt tunable continuous-wave dye oscillators.
High-performance-frequenc y measurement and control systems for tunable lasers.
Optical transport system desk and fabrication capability for efficient high-optical-quality distribution of h~gh
average-power lasers.
High-average-power fiber-optics transport and distribution systems for broadband laser light.
Integrated high-performance diagnostic and control systems for laser-based materials processing systems.
Optical, spatial and temporal multiplexing systems.
Low-cost adaptive optics phase-correction systems.
Highly stable three-dimensional optical system architecture design and construction.
High-performance laser electronics, such as:
Higb-reliability (>20,000 hours M=F), high-voltage (~10 kV) switching power supplies.
High-voltage (>100 kV), higb-average-power (~100 kW), short-pulse (~100 ns) modulators.
Smart local microprocessor controllers.
Comprehensive ancillary control and diagnostic systems.
Although each of these capabilities was developed for constructing the integrated AVLIS system, they are
easily applied to other applications with minor interface engineering. The key characteristics that differentiate
these subsystems and components from others in the laser optical field are that they have all been engineered
for continuous operation and cost-effective manufacturability and have been proven in large-system applications.
Separator Systems
The second major subsystem required for the AVLIS process is the separator system, in which the
material to be isotonically enriched or purified is vaponzed, photoionized~ and collected separately from the
. . ,
non~on'~ed or tans vapor tiow stream. DOth the collected product and tans streams condense as liquids and flow
via separate paths to product and tails accumulators. To operate for reasonable processing times, a separator
system must also have provisions to continuously feed material as it is vaporized.
The most visible characteristic of the separator system is the external vacuum vessel, shown in Figure
A-7. Typically manufactured from stainless steel, the vessel provides a high-vacuum envelope for the
vaporization and collection process. Satellite subvessels at each end house the optical system to insert and
control the AVLIS process laser beams' which interact with the vapor flow stream. Since a loss of vacuum or
a water leak can generate a vigorous reaction with liquid metals, the vessel must also be designed to withstand
moderate overpressure and release safely above a defined pressure limit. Because the near-term applications
involve radioactive and/or tone metals, all operations must be engineered to prevent any material release that
could be harmful or hazardous to the workers and surrounding community. Highly engineered airflow and
control systems integrated with a redundant high-efficiengy particulate filter system are a significant part of the
separator system.
Vaponzation is accomplished by focusing an electron beam from high-average-power electron beam guns
onto the working material. These gums are similar to those used in steel or other metal reEning processes. Long
life (hundreds of hours) and nominally constant vaporization at high efficiency are requirements for an AVLIS
process. Generally, the electron beam gun is located out of the direct vapor path and the electron beam is
deflected by as much as 270°. To some degree, the beam is focused by magnetic and electrostatic lenses. An
initial charge of material for the vaporizer is prepared in a metal crucible that is replenished by external feeders
to maintain long-duration, high-volume evaporation rates from a nominal constant-volume crucible with a well-
defined surface level. To begin the vaporization process, the electron bean gun ~n~tiaBy melts the solid material
in the crucible. Once a stable pool of liquid metal is formed, the electron beam vaporizes metal Tom the surface
OCR for page 40
40
FIGURE A-7 Uranium AVLIS separator vacuum vessel.
OCR for page 41
41
of the liquid melt by intense local heating. Thermal control in the crucible is typically provided by careful
thermal design referenced to eternal water and/or gas cooling.
When the vapor Is generated as described above, a dense beam of atoms elands rapidly away from the
surface of the melt until it passes through the laser irradiation zone. When the multiple laser frequencies
(colors) are ad precisely tuned to the absorption lines for the vaporized isotopes of interest and the power
denser ~ each color is above a nominal limit, most of these isotopes become electrically charged wherever all
the multiple laser beams overlap spatially and in the correct temporal format. Collector plates located near the
laser bean path have a negative voltage and attract the ionized isotopes as the atoms flow through the region.
These ion extractors (or, in the case of uranium, product plates) work very efficiently if the geometry, applied
voltage, and number of ions and atoms fall within certain ranges. Typically, the practical limits on ion extraction
are imposed by practical limits on voltage and the amount of heat the extractor plates can dissipate without
having a negative impact on the process. Product purity is dominated by the spatial characteristics of the flow
stream, the collector geometry, and the charge exchange between selected ions and nonselected neutrals. Several
degrading effects (such as charge exchange) scale with the vapor density and set the practical upper limit to
throughput per unit area. Other factors such as ion sputtering must also be accounted for ~ the extractor design
to ensure overall acceptable performance.
Most of the discussion above Is very general since the geometry, materials, many critical dimensions, and
operating points for the electron gun, vaporizer evaporation rate, extractor voltage, and any other parameters
needed to desk an AVLIS process separator are classified. Those having appropriate clearances to obtain more
specific information may find novel applications for the vaporizer and/or material systems developed for AVLIS.
Specific information on vaporizers and separator systems and descriptions of their capabilities will be available
Only to individuals having DOE ~Q~ security clearances and need-to-know approval from DOE.
URANIUM PROCESSING
To operate the AVLIS process, the working material must be in an atomic state and is typically generated
by vapormng a metal. Uranium and many other metals are generally found in nature as mineral compounds,
ounces, sulfides, etc. The miners and refiners provide uranium oxide, which must be converted to metal by an
efficient, environmentally sound process. Once processed by AVLIS, the enriched product must be converted
to an oxide that meets the strict purity and form requirements for nuclear reactor fuel rod elements.
Historically, nearly all uranium enrichment has been performed in gaseous diffusion and centrifuge plants by
using a molecular gas, U[6. Figure A-8 illustrates two technical paths to process naturally occurring uranium
oxide (yellow caked through its venous chemical and enrichment stages and subsequent chemical processing to
an oxide fuel pellet. Clearly, there can be alternative processing options. What has been done in the uranium
AVLIS program, primarily at Martin Marietta Energy Systems, Oak Ridge, Tennessee, Is to evaluate several
practical approaches from many possible options to generate metal from the natural oxide from the wewpo~nt
of minimum process cost, residual waste, and environmental impact. Similar examinations have taken place on
the conversion of ennched metal to an oxide with purity and material properties compatible with the exacting
demands of the fuel rod industry. Similar activities have taken place for processing plutonium in which
significant capabilities have been developed in pyrochemistry, electr~refining, and waste reduction by using
electrochemical processing. Much of this expertise in chemical engineering and analysis can be applied to other
processes In the nuclear fuel complex and to cost and/or environmental problems now being identified In the
chemical industry. Although it would be fortuitous to find an exact match between a developed AVLIS chemical
process and an existing ~ndus~ial requirement, much of the engineering capability that has been developed could
be of significant benefit to industnes now searching for environmentally superior processing approaches.
REFERENCE
A1. Benedict, M., T. Pigford, and H. Levy. 1981. Nuclear Chemical Engineering, 2nd ea., Chapter 2.
McGraw-HiD, New York.
OCR for page 42
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-
al
E
·)
U)
IS
.
,
-
C)
:~
so
o
Coo
Ct
CD
Ct
3
To
-
·=
In
U.
C)
o
·8
o
~4
sol
·~
Coo
CO
LL
Representative terms from entire chapter:
avlis program
