Developments in the World
National Institute for Isotopic and
Molecular Technology, Cluj-Napoca
Aleea Tarniţa Nr. 7, Apt. 11
400659 CLUJ-NAPOCA , ROMANIA
The various activities associated with the
production of electricity from nuclear
reactions are referred to collectively as the
nuclear fuel cycle . The nuclear fuel cycle
starts with the mining of uranium and ends
with disposal of nuclear waste.
At the start of 2006 in the world there were
352 nuclear units in operation, ten units
were in construction and 17 units were firmly
committed for construction, almost all in the
Pacific region. All of these require uranium
enriched in the 235U isotope for their fuel.
Uranium is a slightly radioactive metal that occurs
throughout the earth’s crust, of about 500 times more
abundant than gold and about as common as tin. It is
present in most rocks and soils as well as in many rivers
and in seawater, and also, in concentrations of about four
parts per million (ppm) in granite, which makes up 60% of
the earth’s crust. In fertilizers, uranium concentration can
be as high as 400 ppm (0.04%), and some coal deposits
contain uranium at concentrations greater than 100 ppm
There are a number of areas around the world where the
concentration of uranium in the ground is sufficiently high
that extraction for use as nuclear fuel is economically
Uranium found in nature consists largely of two isotopes,
235U and 238U. The production of energy in nuclear
reactors is from the “ fission ” or splitting of the 235U atoms,
a process which releases energy in the form of heat. 235U
is the main fissile isotope of uranium.
Natural uranium contains 0.72 % of the 235U isotope. The
remaining 99.3 % is mostly the 238U isotope, which does not
contribute directly to the fission process.
235U and 238U are chemical identical, but differ in their physical
properties, particularly their mass. The nucleus of the 235U atom
contains 92 protons and 143 neutrons, giving an atomic mass of
235 units. The 238U nucleus also has 92 protons and 146 neutrons
- three more than 235U, and therefore has an atomic mass of 238
The difference in mass between 235U and 238U allows the isotopes
to be separated and makes it possible to increase or “ enrich ” the
percentage of 235U. All enrichment processes, directly or indirectly,
make use of this small mass difference.
In the most common types of nuclear reactors, a higher
concentration of 235U than natural is required. The enrichment
process produces this higher concentration, typically between 3.5%
and 4.5% 235U, by removing a large part of the 238U (80% for
enrichment to 3.5%).
The product of a uranium mill is not directly usable as a fuel
for a nuclear reactor. Additional processing, generally
referred to as conversion , is required.
At a conversion facility, uranium is converted to either
uranium dioxide, which can be used as the fuel for those
types of reactors that not require enriched uranium, or into
uranium hexafluoride (UF6), commonly referred to as “ hex ”,
which can be enriched to produce fuel for the majority of
types of reactors.
After refining, uranium trioxide is reduced in a kiln by
hydrogen or ammonia to uranium dioxide (UO2). This is
then reacted in another kiln with hydrogen fluoride (HF) to
form uranium tetra fluoride (UF4). The tetra fluoride is then
fed into a fluidized bed reactor with gaseous fluorine to
produce UF6. Removal of impurities takes place at several
of these steps.
An alternative wet process involves making the UF4 from
UO2 by reaction with aqueous HF.
UF6 is a solid at room temperature, but becomes a
gas when heated above 570C, suitable for use in the
enrichment process. Particularly if moist, is highly
corrosive. At lower temperature and under moderate
pressure, the UF6 may be liquefied and the liquid
runs into special designed steel shipping cylinders,
which are thick, walled and weigh up to 15 tones
when full. As it cools, the liquid UF6 within the
cylinders becomes a white crystalline solid and is
shipped in this form.
The sitting and environmental management of a
conversion plant requires no special arrangements
beyond those needed for any chemical processing
plant involving fluorine chemicals.
Conversion plants are operating commercially in USA,
Canada, France, UK, and Russia.
Uranium enrichment is a critical step in transforming natural
uranium into nuclear fuel to produce energy. A number of
enrichment processes have been demonstrated in the laboratory but
only two, the gaseous diffusion and gas centrifugation are operating
on a commercial scale. In both of these, UF6 gas is used as the
Molecules of UF6 with 235U atoms are about one percent lighter
than the rest, and this difference in mass is the basis of both
processes. Large commercial enrichment plants are in operation in
France, Germany, Netherlands, UK, USA and Russia, with smaller
The capacity of enrichment plants is measured in terms of
“separative work units” or SWU . The SWU is a complex unit, which
is a function of the amount of uranium processed and the degree to
which it is enriched, i.e. the extent of increase in the concentration
of the 235U isotope relative to remainder. The unit is strictly:
kilogram Separative Work Unit (kg SWU), and it measure the
quantity of separative work (indicative of energy used in
enrichment) when feed and product quantities are expressed in
kilograms. The unit “ton SWU” (t SWU) or “million SWU” (M SWU) is
For instance, to produce one kilogram of uranium enriched to 3%
235U requires 3.8 SWU if the plant is operated at a tails assay 0.25
%, or 5.0 SWU if the tails assay is 0.15% (thereby requiring only
5.1 kg instead of 6.0 kg of natural U feed.
About 100,000 - 120,000 SWU is required to enrich the annual fuel
loading for a typical 1000 MWe light water reactor (LWR).
Enrichment costs are related to electrical energy used. The
gaseous diffusion process consumes about 2,400 kWh (8,600 MJ)
per SWU, while modern gas centrifuge plants require only about 60
kWh (200 MJ) per SWU.
Enrichment accounts for approximately one third of the cost of
nuclear fuel and about 10% of the total cost of electricity generated.
It can also account for the main greenhouse impact from the
nuclear fuel cycle, if the electricity used for enrichment is generated
from coal. However, it still only amounts to 0.1 % of the carbon
dioxide from equivalent coal-fired electricity generation, if modern
gas centrifuge plants are used, or up to 3% in a worst-case
1. Gaseous diffusion
At present the gaseous diffusion process is the most widely used
method, producing over 30 M SWU. The process separates the
lighter 235U isotope from the heavier 238U. The gas is forced
through a series of porous membranes with microscopic openings.
Because the 235U molecules are lighter than 238U molecules they
move faster and have a slightly better chance of passing through
the pores in the membrane. The UF6, which diffuses through the
membrane, is thus slightly enriched, while the gas, which did not
pass through, is depleted in 235U.
This process is repeated many times in a series of diffusion stages
called a cascade . Each stage consists of a compressor , a diffuser
and a heat exchanger to remove the heat of compression. The
enriched UF6 product is withdrawn from one end of the cascade and
the depleted UF6 is removed at the other end.
Commercial uranium enrichment was first carried out by diffusion
process in the USA. The two US Enrichment Corporation plants in
that country have a capacity of some 19 M SWU per year. At
Tricastin (France), a more modern diffusion plant, EURODIF, with a
capacity of 10.8 M SWU per year has been operating since 1979.
This plant can produce enough 3.7% enriched uranium per year to
fuel some ninety 1,000 MWe nuclear reactors.
2. Gas centrifugation (I)
A centrifuge comprises an evacuated casing containing a cylindrical rotor, 1
- 2 m long, and 15 - 20 cm diameter, which rotate at high speed (50,000 70,000 rpm) in an almost friction-free environment. The uranium is fed into
rotor as gaseous UF6 where it takes up the rotational motion. The centrifugal
forces push the heavier 238U closer to the wall of the rotor than the lighter
235U. The gas closer to the wall becomes depleted in 235U whereas the gas
nearer the rotor axis is enriched in 235U. The gas flowing within the rotor
can be produced by a temperature gradient over the length of the centrifuge.
UF6 depleted in 235U flows upwards adjacent to the rotor wall, whilst UF6
enriched in 235U flows downwards close to the axis. The two gas streams
are removed through small pipes.
To obtain efficient separation of the two isotopes, centrifuges rotate at very
high speeds, with the outer wall of the spinning cylinder moving at between
400 and 500 m/s to give a million times the acceleration of gravity.
The enrichment effect of a single centrifuge is small, so they are linked in
cascades similarly to those for gaseous diffusion. In the centrifuge process,
however, the number of stages may be only 10 to 20, instead of a thousand
or more for gaseous diffusion. Passing through successive centrifuges of a
cascade, the 235U is gradually enriched to the required assay - usually
between 3 and 5% - and the depleted uranium is reduced to 0.2 to 0.3%
235U. Once started, a centrifuge runs for more than 10 years with no
2. Gas centrifugation (II)
Enrichment by centrifuge is energy efficient - consuming a tiny
fraction of the energy used by the older gaseous diffusion method.
The gas centrifuge process has been developed to a commercial
level by URENCO Group, developed from a joint Dutch, German and
British initiative set up in the 1970’s following the signing of the
Treaty of Almelo. Since this time this Group has been one of the
leaders in the field of uranium enrichment by centrifuge. Today,
URENCO is a global supplier of uranium services, delivering more
than 10% of the worldwide enrichment requirements. On March 26,
1998, URENCO opened a new E23 enrichment plant at Capenhurst.
The centrifuge is more than twice as fast and an order of magnitude
longer than the early pilot plants and will have an output around 50
times as large as the earliest production machines .
Russia’s 10 M SWU per year enrichment capacity is also
centrifuge-based. In Japan, PNC and JNFL operate small centrifuge
plants. The total production of Russia + URENCO + JNFL is over 14
3. Laser enrichment
Laser enrichment processes have been the focus of
interest for some time. They promise lower energy
inputs, lower capital costs and lower tails assays,
hence significant economic advantages. Although
they may become significant in time none of these
processes is yet ready for commercial use.
In 1985, the US Government chooses Atomic Vapor
Laser Isotope Separation (AVLIS) as a new
technology to replace its gaseous diffusion plants as
they reach the end of their economic lives, as one of
the most promising new technologies for improving
the economy of uranium enrichment.
Principle of the AVLIS-U method
In an AVLIS-U process a supersonic beam of atomic uranium vapor
is produced. The ground-state atoms are excited by a sequence of 3
visible photons from dye lasers operating at wavelength λ1a, λ2,
and λ3. The metastable atoms are first excited by a fourth laser of
wavelength λ1b, then by λ2 and λ3. The final photon absorbed by
the uranium atom produces an auto-ionizing state, which rapidly
decays into a uranium ion and a free electron. The auto-ionizing
state is used because the optical excitation cross-section to that
state is much larger than the photo-ionization cross section to the
continuum. The narrow bandwidth in each of the selected
transitions means that each of the laser wavelengths must be
accurate to within one part in 1 million before enrichment appears.
Negligible excitation of 238U atoms occurs when lasers are
optimized to excite 235U. Because of the high selectivity,
enrichment from 0.2% to 3.2% can be achieved in a single step;
thus the atomic vapor process is particularly suitable for stripping
235U from depleted tails. Naturally, with appropriate plant design
parameters, the AVLIS can also enrich natural uranium.
Principle of the AVLIS-U method
The positively charged ions of 235U are then attracted to a
negatively charged plate and collected as liquid metal. Guard plates
are used to prevent unionized uranium atoms of the beam from
striking the product collector plates. The uranium vapor density
must be so high that appreciable charge exchange occurs during
the acceleration of the 235U to the collecting plates. Care must also
take to ensure that the sputtering of uranium atoms from the
collector plates does not seriously degrade the isotopic selectivity
of the process.
The major building blocks of the AVLIS process are the separation
chambers, laser and optical systems, computer controls, and
uranium handling system. Each process is optimized to perform with
low capital and operating costs.
The separation process uses finely tuned, high power lasers to
tag the fissile isotope of uranium, 235U, by removing one of its
electrons. Result a positive 235U ion. Collecting these ions as well
as a portion of the feed material on charged plates forms the
product stream. Uranium depleted in 235U forms the tails stream.
This process takes place in a vacuum chamber in which uranium is
vaporized and exposed to the lasers. Both streams are removed as
small nuggets of solid uranium metal. Further chemical processing
and fabrication yields finished fuel for nuclear power reactors.
The status of R & D of AVLIS-U method in
some countries of the world.
AVLIS IN BRASIL
The aim of the AVLIS Program at Instituto de Estudod
Avansades, Centro Tecnico Aeroespacial (IEAv/CTA), Sao Paolo,
was to demonstrate the technical viability of process using, as long
as possible, resources available in Brazil. It implicates not only on
studying related processes but also on the development of critical
associated technology. The effort has been focused mainly on two
actuation areas: copper vapor and dye laser development and
Laser development: The natural candidate that fills the
requirements to deliver tunable in the visible beams with high peak
power at high repetition rates is CVL pumped dye laser. In this
case, both laser systems works in the Master Oscillator Power
Amplifier (MOPA) chain configuration.
The CVL development started in 1985, with a first prototype of
a externally heated copper bromide system that delivered about 100
mW at a repetition rate of 100 pps. From this system the work
evolved to self heated true CVL’s, with maximum average output
power ranging from 5 W, from a compact air cooled system, to 40
W, for conventional water cooled system.
Spectroscopy: In this field has been obtained the necessary
experience to start the investigation of the multi-frequency
absorption in the atom of uranium, in order to get convenient line
sequences for the AVLIS process.
2. AVLIS IN CHINA (I)
AVLIS in China started in 70’s and got rapid development since 1985. The
research ranges from uranium spectra, dynamic process of excitation and
ionization of uranium atoms under laser radiation field, extraction of ions
from plasma, to R & D of facilities such as copper vapor laser (CVL), tunable
laser and electron beam heating and separator.
Thanks to exploring in basic and development of facilities, a
systematic scientific data and some important experimental results have
been reached. In three-step, three-photon process, a high selective
ionization was attained, and a macroscopic quantity of enriched uranium
sample has been collected which characterizes by its about 10%
concentration of 235U and its collection rate of few mg/h. The experiment
demonstrate that an effective depletion down to 0.4% could be reached,
together with a high enrichment good extraction percentage of ions and
excellent separation coefficient.
Basic research: The basic research activities relating to AVLIS are
mainly executed in some institute and universities and can be summarized
- Measurement and identification of energy levels, level life, branch
ratio of transition lines, cross section of absorption, isotope shift and
hyperfine structure, Rydberg state and auto-ionization state;
- Interaction between atomic system and strong laser radiation;
- Plasma of uranium atom induced by pulse laser and ion dynamics;
- Mathematical and physical model for ion extraction and collisions in
2. AVLIS IN CHINA (II)
Facilities: The facilities necessary for AVLIS were prepared
in two different channels. A few were built through
modifying the existed equipment, and the most were
specially designed, tested and manufactured. The facilities
are mainly composed of lasers and separator.
CVL: Two models, 20 W and 40 W CVL has been
successfully made, the first has been applied in separation
experiments. The typical performance of CVL-20 is listed
Output: 20 W; ratio of yellow/green: ~ 1:2; spot size: Φ = 30
mm; repetition rate: 6 kHz; pulse duration: ~ 30 ns;
divergence: 1 mrad; tube length: 1.2 m; input power: 4 kW;
conversion efficiency: 0.5%.
6 sets of CVL have been integrated to form oscillationamplification chains: one set is used for oscillator, and the
rest 5 sets constitute two chains of amplification.
2. AVLIS IN CHINA (III)
Separator: It is a special facility composed of 10 kW e-type electron beam
gun, uranium crucible, irradiation zone and collectors for thermal ions as
well as laser induced ions. All of these components are installed in one
cylindrical vacuum chamber of 1x0.5 m. Uranium metal is put into one watercooled crucible and heated through electron beam. The atomic density at a
distance of 10 cm over the crucible was of around 10 tera (T) /cm3.
Linear electron beam facility : Is composed of a vacuum chamber,
linear gun, magnetic coil and HV power supply: Typical performances: beam
power: 20 kW; beam size: 10x0.2 cm; power density: 10 kW/cm2; deflection
radius: 5-10 cm; deflection angle: 180-270 degrees .
The electron beam set up of power 50 kW has been put into operation
Separation experiment : Experimental demonstration of three-color
three-photon process. Mass spectrometers measurement shows separation
coefficients of 1,000-2,000 which demonstrates the high selectivity of AVLIS.
Applying four-color three-photon process instead of three-color threephoton process, the total ionization probability can be increased by 30%.
Thanks to various measures, the concentration of samples reaches
30%, and the depletion reduces to 0.4%. The total ionization probability is
high up to 42% with separation coefficient of 100.
Prospects: The development of a project of AVLIS and to establish one
comprehensive set-up with higher separation capacity.
3. AVLIS (SILVA) IN FRANCE (I)
- Long term goal with a priority for a high performance process,
available when world stocks of enriched uranium are exhausted and
aging enrichment plants have to be shut down. In reach this goal,
the French Atomic Energy Commission has focused since 1985 on
AVLIS (SILVA), in agreement with the industrial operator, COGEMA.
- A network of co-operation supports the program with advanced
technology companies, particularly in the field of lasers, optical
components, and materials, power supplies.
Technical program :
- Basic research in each field with models developments adjusted
through specific and integrated experiments;
- A progressive development of components with specific facilities;
- Integrated experiments, especially with the pilot facility for
- A general process model including operational and economical
3. AVLIS (SILVA) IN FRANCE (II)
- Uranium spectroscopy:
The multi-step photo ionization of uranium atoms implies to
choose an irradiation scheme and this choice is only possible if the
following spectroscopic parameters and specific effects are known:
oscillator strength, isotope shift, hyperfine structure, lifetime, autoionization spectrum, effect of electric and magnetic fields, effect of
laser polarizations, effect of multiphase processes upon selectivity.
Since the oscillator strengths determine the laser fluencies needed
to efficient atomic photo-ionization this parameter has been
accurately measured. It enables to choose the best wavelengths,
selected by appropriate criterions.
- Light matter interaction:
Several computing codes have been
set up for coherent interaction calculations (Bloch equations) in
order to compute ionization yield and its variation with the pulse
- Evaporation: Optimization of the uranium vaporization by an
electron beam is one of the keys of the SILVA process. Experiments
are made on several benches of different sizes including process
scale seize (HORUS)
3. AVLIS (SILVA) IN FRANCE (III)
- Vapor flow: All vapor properties must be known in all
regions where laser-vapor interactions take place, as they
take part in the process optimization. Monte-Carlo
computing codes have been developed in order to interpret
the vapor measurements.
- Extraction: In order to choose the best extraction system,
beside experimental set-up, a Monte Carlo computation
code applied to charged particles has been performed.
- Collecting flows : High temperature liquid metal collecting
of enriched product and waste tail was one of the most
difficult task of this process from material and technology
points of view. It is also connected with various
fundamental problems linked to material and liquid material
interaction (adhesion energy, wetting angles, chemical
interactions), and hydrodynamics (film, drop, stability under
3. AVLIS (SILVA) IN FRANCE (IV)
Uranium vaporization and management facilities:
CEA has quite numerous specific facilities, each of them
devoted to one process function. Most of them are located at
- HORUS - devoted to vaporization process optimization;
- Material test and behavior in conditions similar to those
found in a separator was the main aim of CORDY facility. This
facility includes an evaporation apparatus and a thermal control
system. The experimentation concerns two kinds of tests: short
duration tests for checking solutions during their development (6-30
hours) and long duration tests for high performance solutions (time
higher than 100 hours);
- Uranium flow handling outside vapor deposition areas was
studied on a special facility called IRIS, which was used to generate
uranium flows and generates drops and films flows. Various shapes
and slopes of guiding components was tested with this facility;
3. AVLIS (SILVA) IN FRANCE (V)
- Technological studies for ions extraction
and collection was especially undertaken in
ISABEL laboratory (Saclay) with two
evaporation facilities. They are also one of
the pilot facility targets;
- Complete metal-liquid flows
management systems are experimented in
the MAEVA facility, which was the higher
sized SILVA evaporating facility;
- Facilities for material processing are
associated with the previous facilities.
3. AVLIS (SILVA) IN FRANCE (VI)
Nominal optical pumping systems utilize copper vapor lasers
(CVL) developed by CILAS Company. The first lasers produced
(MNT 40) constitute the pumping system of the pilot facility A2. The
next (ASTER) include 100 W laser modules. For 100 W CVL,
individual running times are several thousand hours;
- Dye oscillation and amplifiers (developed by CEA) and
studies on pumping schemes using solid lasers;
- Laser chain, optical components and associated automations
(developed by CEA).
Pilot process facility A2:
The facility includes two main parts: the laser system named
HERA and the separator named ANDROMEDE. More than 90 test
runs have been achieved, each run corresponding to evaporation
duration between 2 and 20 hours. The main test was the followings
- Production test: Production rate between 1 to 10 g/h of
enriched uranium, with uranium enrichment assay up to 5.5%;
- Design optimization for: extraction systems; matter-light
interaction areas; photon management.
3. AVLIS (SILVA) IN FRANCE (VII)
The pilot extension to a higher size facility named ASTER
was going on, planned to include a laser system with a
power output about ten times higher than the present one
and a new separator named ALDEBARAN.
SILVA general schedule:
The SILVA program was periodically assessed from
both scientific and the industrial point of view. The general
assessment was included several demonstrations related to
each of the main process functions (“DEMO”) as well as an
evaluation of the economics.
General schedule: Basic research: 1985 – 1998; Process
demonstration: 1985 – 1999; Technological development:
1987 – 2001; General assessment: 1996 – 1997; Production
demonstration: 1994 – 2005; Industrial deployment: 1997 –
2015. But , in 2000 SILVA Program has been abandoned.
4. AVLIS IN INDIA
Researches on uranium spectroscopy, at Bhabha Atomic Research
Centre, Bombay, as follows:
- Spectroscopic and thermal properties of uranium relevant to atomic
schemes for laser isotope separation (S.A. Ahmad et al., Report BARC
- Two-color three-step photo-ionization of uranium (V.K. Mago et al., 1987);
- Single color photo-ionization in uranium I, (V.K. Mago et al., 1987);
- New high-lying odd levels of U I in a two-color multi-photon
ionization spectrum (B.M. Suri et al., 1987);
- Two color multi-photon ionization spectroscopy of uranium from a
meta-stable state (P.N. Bajaj et al., 1988);
- Study of high-lying odd levels in U I by two-color photo ionization
(V.K. Mago et al., 1988);
- Energy levels, isotope shifts, hyperfine structures, lifetimes,
transition probabilities and other spectroscopic parameters of neutral
uranium atom - update 1987 (S. A. Ahmad et al., Report BARC-1413, 1988);
- New odd-parity Rydberg and auto ionization levels in U I (A.K. Ray
et al., 1990);
- Resonantly enhanced single-color multiphase ionization of uranium
atom (A.K. Ray et al., 1992);
- Two-step single color photo ionization spectroscopy of uranium
atom (V.K. Mago et al., 1993).
5. AVLIS IN ITALY
Studies on the basic principles of AVLIS
along with some spectroscopic aspects of
this method, some experimental data, and
the uranium photo ionization process (CNENCSN Casaccio Centre):
- AVLIS (P.Benetti et al., Report CNENRT/FI(80)16, 1980);
- The isotopic separation of uranium by laser
method: spectroscopic aspects
et al., Report CNEN-RT/FI(80)19, 1980).
6. AVLIS IN JAPAN (I)
The R & D of AVLIS started when the ad-hoc committee of Japan
Atomic Energy Committee (AEC) stated that this process might have great
potential as leading process for future uranium enrichment, and issued a
directive, which mandated that feasibility study of this process can be
completed as soon as possible. Since domestic demand for enrichment is so
limited, the process must be shown to be profitable on a moderate scale,
such as 1000 t SWU per year .
AVLIS study in JAERI .
JAERI has been working in this field for many years aiming at the
basic data acquisition for most adequate separation process especially for
uranium isotopes. In 1984 the technological assessment program has been
initiated based on data, which had been obtained by that time.
For the accomplishment of AVLIS technology, both the development of
tunable light source and the development of separation process are
inevitable. Tunable light source with a broad tuning, narrow line width, high
stability and high efficiency has been developed. From point of view of
industrial application, performances such as high repetition rate, high
average power and high efficiency are added to the quality above mentioned.
For these purposes, copper vapor lasers or excimer lasers has been used as
a pumping source, and high repetition rate dye laser has been developed as
a tunable source.
6. AVLIS IN JAPAN (II)
For the development of the AVLIS, energy levels,
isotope shifts, hyperfine structure and photoabsorption cross-section are the basic parameters,
which would determine the laser specification.
An AVLIS Test Plant has been studied by Laser
Atomic Separation Research Association of Japan
(LASER-J), founded in 1987. The main objectives of
LASER-J was as follows:
- To develop engineering-scale components;
- To construct the test plant;
- To conduct enrichment tests in the test plant.
The JAERI, which has been developed the AVLIS
process since 1976, was in charge of obtaining
fundamental data regarding this process, in close
cooperation with the LASER-J.
6. AVLIS IN JAPAN (III)
When LASER-J started, components of the AVLIS
system available in Japan were limited to small scale
ones, and the performance was not sufficient for an
engineering-scale test. It was first necessary to
develop the hardware components, such as lasers
and electron beam guns, before to start the
construction of the test plant. By now, these hardware
components of the AVLIS process were developed
and the original goal has been achieved. In addition,
R & D on physical processes, such as uranium
vaporization, photo-ionization and ion recovery have
also been undertaken. Construction of the test plant
was completed in May 1990 and the first stage test
was to obtain physical data for processes such as
photo-ionization and ion recovery. For this purpose a
small separator with an array of instruments has been
6. AVLIS IN JAPAN (IV)
A single unit of a CVL could produce a power of 122 W
powers, an improved CVL, 211 W, in case of MOPA, the
system used in the test plant produced 318 W, and with an
improved CVL MOPA, 488 W. Repetition frequency of a CVL
was of 5 kHz.
For the electron beam gun has been developed a 300 kW
power linear type gun. Acceleration voltage was as high as
50 kV and the width of the electron beam, less than 5 mm.
The separator system has been used at a temperature
higher than the uranium melting temperature of
approximately 1,400 K. The uranium vapor density was of
10 at 13/cm3 at the stand distance of 50 cm, vaporization
efficiency being of 3 - 4% .
The next stage will be the enrichment test, which will
employ a larger separator. The purpose of this test is to
demonstrate the enriching capability of approximately 1 t
SWU/year, and also to obtain engineering data of the AVLIS
6. AVLIS IN JAPAN (V)
From a recent economical evaluation and optimization
on an AVLIS plant of 1,500 t SWU/year, it would be
sufficient a CVL unit power output of about 500 W .
If LASER-J could clear the process, it would go to the
last step of building a set of Demo Facility and
making Enriching Demonstration Test thereof.
Studies on AVLIS are also performed at Institute of
Laser Engineering (ILE), Osaka University and
Institute for Laser Technology (ILT), Osaka. These
studies are concentrated on developments of highpower CVL and dye laser, fundamental studies on
high-resolution spectroscopy and coherent dynamics
of excitation and ionization of atoms, resonant and
near-resonant effects in laser beam propagation and
studies on atom-ion collision in the atomic vapor
7. AVLIS IN ROMANIA (I)
Here has been elaborated a database on AVLIS. It contains 20
internal reports (in Romanian), as follows:
1.- Program Project for uranium enrichment by laser methods
(G.Vasaru et al., Report ITIM-AVLIS-1, 15 Dec. 1987, 87 pp);
2.- Revised edition of the Program (G. Vasaru et al., Report ITIMAVLIS-2, 26 May 1988, 42 pp);
3.- Project for a laboratory scale plant for the study of selective
photo-ionization of the uranium vapor (G. Vasaru et al., Report
ITIM-AVLIS-3, 20 Oct. 1988, 129 pp);
4.- Isotope separation by AVLIS method (G. Vasaru, Report ITIMAVLIS-4, 1 March 1989, 79 pp);
5.- The components and the characteristics of a laser spectroscopy
plant for the study of selective photo-ionization of atomic vapor (G.
Vasaru et al., Report ITIM-AVLIS-5, 15 April 1989, 45 pp);
6.- Thermodynamic of the vaporization of the metallic uranium (G.
Vasaru, Report ITIM-AVLIS-6, 15 December 1989, 128 pp);
7. AVLIS IN ROMANIA (II)
7.- High-lying odd levels of U I in the range 34000-43000 cm-1
identified by a single-color three-photon ionization technique (G.
Vasaru, Report ITIM-AVLIS-7, 15 March 1990, 14 pp);
8.- High lying odd levels in U I by two-color three-photon photoionization in the range 34000 - 37000 cm-1 and 39900 - 41600 cm-1
respectively (G. Vasaru, Report ITIM-AVLIS-8, 15 November 1990,
9.- Energy levels of neutral atomic uranium (U I) (G. Vasaru, Report
ITIM-AVLIS-9, 5 August 1991, 164 pp);
10.- Isotope shifts and hyperfine structure of neutral uranium atom
(U I) (G. Vasaru, Report ITIM-AVLIS-10, 10 November 1991, 98 pp);
11.- Transition probabilities, oscillator strengths, branching ratio,
and absorption cross-sections of neutral uranium atom (U I).
Lifetimes of the odd and even levels of U I (G.Vasaru, Report ITIMAVLIS-11, 5 November 1992, 106 pp);
12.- Thermal properties of uranium, (G. Vasaru, Report ITIM-AVLIS12, 15 May 1993, 48 pp);
13.- Ionization processes of uranium atom (G. Vasaru, Report ITIMAVLIS-13, 15 October 1993, 46 pp);
7. AVLIS IN ROMANIA (III)
14.- Copper vapor lasers, (G.Vasaru, Report ITIM-AVLIS-14, 1 April
1994, 98 pp);
15.- Dye for lasers. Photo-physical and photo-chemical properties
(G. Vasaru, Report AVLIS-ITIM-15, 1 October 1994, 63 pp);
16.- Laser systems for the uranium enrichment (G. Vasaru, Report
ITIM-AVLIS-16, 15 December 1994, 91 pp);
17.- Physics of the vaporization process of metallic uranium (G.
Vasaru, Report ITIM-AVLIS-17, 10 May 1995, 67 pp);
18.- Laser-atomic uranium vapor interaction. The selective resonant
multi-photon photo-ionization process (G. Vasaru, Report ITIMAVLIS-18, 10 October 1995, 43 pp);
19.- Laser systems for AVLIS-U. I. Kinetics of CVL. II. Physical and
technological conditions for laser systems of AVLIS-U (G. Vasaru,
Report ITIM-AVLIS-19, 30 November 1995, 65 pp);
20.- Uranium vaporization system for AVLIS-U (G. Vasaru, Report
ITIM-AVLIS-20, 15 December 1995, 13 pp).
8. AVLIS IN RUSSIA (I)
The scientific activity of the Institute of Molecular
Physics (Moscow) included researches on laser
methods for isotope separation.
AVLIS needs about 6 eV to ionize the uranium atom.
The IMP laboratory separation facility is based on
using copper vapors lasers (CVL) pumped dye lasers
(DL) to generate radiation with needed wavelengths.
The investigated process scheme involves two steps
of successive photo-excitation and photo-ionization.
Recent experiments have demonstrated rather
promising results on laser equipment improvement,
optical scheme optimization, evaporating set-up and
collection method development.
8. AVLIS IN RUSSIA (II)
It has been shown that production of low-enriched (3-5 %)
or highly enriched (90%) uranium-235 is industrially
feasible. The pilot version of industrial AVLIS module for
uranium isotope separation is now under development. The
experiments on the module will give the information for
evaluation commercial potential for the industrial
application of AVLIS technology. It's generally supposed
that this technology is preferable in case of using lowenriched starting raw materials.
It seems reasonable to use the AVLIS method for
separation and commercial production some expensive
stable isotopes, which cannot be separated by the
centrifuge method. The Institute has achieved considerable
progress in development of the AVLIS method for isotopes
separation of Nd, Gd, Zr, Yt, and some other elements.
Another interesting field of AVLIS method application is
production of isotope mixture depleted with definite
9. AVLIS IN UK (I)
Work on methods of enriching isotopes using laser techniques
started in 1974 within UKAEA. Both the molecular and atomic route
was studied. In 1983 a decision was taken to concentrate on the
atomic route (AVLIS) as offering the greater economic potential. In
1986 a collaborative agreement on AVLIS was entered into by BNFL
and the UKAEA.
The program of work has included:
- Theoretical considerations of photon-atom interaction, including
the effects of HFS and magnetic field (Zeeman effect) and cross
sections for excitation transfer and charge exchange;
- Experimental work to find theoretically favorable transitions
between the levels in the atom and to measure relevant transition
parameters using initially, low density uranium vapor;
- Development of techniques for the precision tuning and
stabilization of suitable lasers, obtaining the required bandwidth,
and amplifying light to required power;
- Materials and technology related to high-density vapor production;
9. AVLIS IN UK (II)
- Theoretical and experimental work on efficient
separation of selectively generated ions from a vapor
- A watching brief on laser development, with active
initiation of development for specific purposes.
Later, the UKAEA and BNFL moving towards
integrated development. It was envisaged there
would be five main areas for development:
- Vapor production using electron beam guns;
- Selective ionization of 235U;
- Separation and collection of product and tails;
- Engineering of laser facility.
9. AVLIS IN UK (III)
BNFL has installed a test facility for evaporating uranium,
which, together with other equipment will be used for
studying uranium vapor properties, electron beam gun
development and feed system development. The CVL, which
provide the light power needed for the process, was
planned to be developed for higher power and longer life.
Spectroscopic work will be continued by UKAEA with the
objective of finding energy levels, which would enable 235U
to be ionized more efficiently. In addition, work will be
carried out on the light transmission characteristics of the
envisaged systems. Techniques for the separation of the
ions from uncharged atoms are being explored by the
UKAEA. Application of these techniques to uranium vapor,
and subsequent problems of product and tails collection and
handling are also being investigated.
9. AVLIS IN UK (IV)
In addition to the theoretical and experimental work reestimation of the plant costs of AVLIS which take into
account of improving knowledge of key parameters such as
transition rates, process and geometric efficiencies,
process modeling and hardware-related costs are taken into
consideration. Comparison is then made with the URENCO
future centrifuge costs (BNFL being one of the partners). At
present the result of this comparison is that BNFL continue
this AVLIS research and development program. The overall
target is that BNFL should achieve technical competence in
this area such that consideration of the construction of a
laser enrichment plant. This target is entirely consistent
with BNFL and URENCO aim of progressive technological
advance. The plan to exploit AVLIS methods jointly with the
partners of URENCO remains; discussions of the economic
exploitation advantages have been held and a collaborative
program is being pursued.
10. AVLIS IN USA (I)
The USEC - AVLIS Program:
One of the key aspects in assuring that nuclear energy option
remains economically competitive for the future is the provision of
an economic, reliable supply of fuel. Nuclear fuel costs for a power
plant include natural uranium, conversion services, enrichment
services, fuel fabrication and transportation. Of these fuel cost
components, one of the largest is enrichment service. The AVLIS
technology option for enriching uranium has been considered to
provide the potential for stable or declining nuclear fuel costs in the
The US has developed the AVLIS process, both to assure
availability of the nuclear option and as a key element of a strategy
to ensure US competitiveness in the uranium enrichment business
in the twenty-first century. This technology, which uses the
selective laser excitation and ionization to separate the isotopes of
uranium, has rapidly advanced by US AVLIS team providing a
database to support deployment of the technology as required by
10. AVLIS IN USA (II)
AVLIS has high potential for achieving mature production costs that
are $20 to $50 per SWU, lower than production costs from gaseous
diffusion, and that are lower than any other process known today.
As a result of this significant economic promise, all major
participants in the international enrichment business are developing
In the mid-1970s, DOE began R & D of a new generation of
technology to produce enriched uranium for civilian energy
production. One technology involved the use of high-energy lasers
to separate vaporized 235U from 238U and process it into fuel.
The AVLIS technology was designed to operate on a smaller scale
than existing gaseous diffusion plants and produce a cheaper
product. In 1988, DOE began running “commercial scale” uranium
enrichment tests using AVLIS facilities built at LLNL in California.
10. AVLIS IN USA (III)
AVLIS was a program of the largely self-financing US Enrichment
Corporation (USEC), created by Congress in 1992. In 1994, the US
Enrichment Corporation announced it would proceed with
commercial development of a $2 billion AVLIS program, despite
debate over whether the Livermore AVLIS experiments had proven
its commercial viability.
AVLIS team: AVLIS is an advanced uranium isotope separation
process under development by USEC. The laser-based technology
has the potential to be the most economic method of enriching
uranium fuel for commercial nuclear power plants. A full-scale
system has been tested at the LLNL.
USEC planned to initiate commercialization of AVLIS in the
near future. Working with USEC on team AVLIS are: Allied Signal
Corp., BWX Technologies, Bechtel National Inc., Cameco Corp.,
Duke Engineering Inc., GE Nuclear Energy, Lockheed Martin Inc.,
Parsons Engineering and LLNL.
AVLIS development: The basic AVLIS concept development of
the laser-based AVLIS enrichment technology has been under way
at LLNL since the mid - 70s. In 1990 the DOE transferred the
proprietary rights to AVLIS to USEC in the largest transfer of
technology ever in the US by the DOE.
10. AVLIS IN USA (IV)
AVLIS used a system of high-powered lasers, tuned for a specific
wavelength, to ionize only 235U isotope of uranium. The ionized
235U atoms are positively charged and are attracted to negatively
charge collecting plates. The recovered enriched uranium alloy is
sent to a conversion facility to be charged into uranium oxide
pellets which are loaded into metal fuel assemblies for be used as
fuel at nuclear power plants.
Separator process: The AVLIS process begins with uranium
alloy being fed into a large separator vessel in the form of solid
rods. The separator is a vacuum chamber in which a high-energy
electron beam vaporizes the uranium rods. Light from a precisely
tuned laser selectively ionizes the 235U atoms in the vaporized
uranium, giving them a positive electrical charge while leaving the
undesired 238U isotopes neutral. As the isotopic mixture moves
through the separator, the positively charged ions are attracted to a
negatively charged plate. The ions collect on the plate as enriched
uranium and then flow into a collector. Now are three full-scale
separators one which is capable of operation. Six production lines
would be used in a commercial AVLIS plant with each line
consisting of 14 separators.
10. AVLIS IN USA (V)
Pump lasers: Solid-state lasers are used to convert
electricity into light energy for the process lasers. The
solid-state lasers convert electricity into green light,
which is used to energize (pump) the process lasers.
The light is routed to process through fiber optics.
The small bore CVL is at plant size today (40 W) and
the dye system can achieve plant requirements by
joining existing units. Optimally, the maximum power for
large bore CVLs will be scaled from 300 W to 700-1000
The AVLIS CVLs are joined together in master oscillator
power amplifier (MOPA) chains that supply laser power
to the dye lasers. Six of these chains are organized into
a corridor that has grown capacity from a few hundred W
to 2500 W.
10. AVLIS IN USA (VI)
Process lasers: A process laser provides the precise
frequencies of light to ionize uranium vapor. Since 235U isotope
has a slightly different absorption spectrum than the 238U, it
will absorb the laser light while the 238U will not. The absorbed
energy from the laser light will excite, or energize, the 235U
atom knocking off an electron and giving it a positive charge.
The process laser is often referred to, as a dye laser because it
uses a dye to produce the specific wavelengths required
ionizing the uranium vapor.
The control room: The AVLIS process operated from the
control room. This high-tech facility continuously monitors key
characteristics of the AVLIS process such as laser beam shape,
wavelength and pulse frequency, separator operating
temperatures and pressures, and other essential components.
One control room in the plant can be used to run both the laser
and separator systems for two production lines. A commercialsize enrichment plant would require six production lines with
three control rooms.
10. AVLIS IN USA (VII)
Feedstock: The AVLIS feed material consists of metal
rods of uranium-iron alloy. USEC is working with the
Cameco Company, a leading uranium producer based
in Canada, to develop a cost-effective process for
converting uranium ore concentrate to uranium-iron
feed rods for use by a commercial AVLIS plant.
Product: The enriched uranium metal produced by
AVLIS is in the form of small nuggets. The AVLIS
product is sent to a conversion facility, which purifies
and converts the uranium alloy into uranium dioxide,
which fuels most of the world’s commercial nuclear
power plants. The purified uranium dioxide can then
be made into pellets and inserted into metal rods for
use as reactor fuel. This conversion process is being
developed by USEC jointly with GE Nuclear Energy.
10. AVLIS IN USA (VIII)
AVLIS enrichment plant : Was an architectural concept of a
commercial-size AVLIS uranium enrichment plant, capable
of producing up to 8.7 M SWU per year. The facility was
planned to occupy one-tenth the space today’s uranium
enrichment plants employing gaseous diffusion technology
and consume only 5-10% of the electricity of a gaseous
The modular design of AVLIS allows a flexible
deployment, enabling capacity to be added in enrichments
to meet market demands.
Commercialization: USEC is expected to deploy
commercial-size AVLIS feed production, enrichment and
product conversion plants early in the 21st century.
Construction of the three plants will begin after completion
of the testing, design and licensing activities, with the goal
of full commercial operation by 2005 .
The possible introduction of AVLIS-U as a competitive industry
constitute, at this time, an open problem.
In June 10, 1999, USEC Inc. announced that it is suspending
further development of its AVLIS enrichment technology. USEC’s
Board of Directors and management reached this decision after a
comprehensive review of operating and economic factors. In making
the announcement, William H. Timbers, Jr., President and Chief
Executive Officer of USEC Inc., said, "We commend Lawrence
Livermore National Laboratory (LLNL) for their concerted research
and development efforts on AVLIS. However, we have reexamined
the AVLIS technology, performance, prospects, risks and growing
financial requirements as well as the economic impact of
competitive marketplace dynamics. We now have enough data to
conclude that the returns are not sufficient to outweigh the risks
and ongoing capital expenditures necessary to develop and
construct an AVLIS plant."
Later, CEA France stopped also the SILVA R&D Program.
And very possible other countries…
Illustrative figures on
uranium isotope separation.
Why enrich uranium?
Most commercial and research reactors and
all nuclear weapons that use uranium for
fission require enriched uranium.
Only 0.72% of natural uranium is U-235 – the
fissile isotope. A tiny fraction is U-234.
Over 99% is U-238.
Without a very efficient moderator, such as
heavy water or very pure graphite, a chain
reaction cannot be sustained in natural
uranium – U-235 is too sparsely distributed.
Mining & Milling
Uranium is found in several
types of minerals:
Pitchblende, Uranite, Carnotite,
Autunite, Uranophane, Tobernite
Also found in:
Milling: Extraction of uranium
oxide from ore in order to
Uranium tetrachloride (UCl4) is vaporized and ionized.
An electric field accelerates the ions to high speeds.
Magnetic field exerts force on UCl4+ ions
Less massive U-235 travels along inside path and is
Inefficient: Typically less than half the feed is converted to U+
ions and less than half are actually collected.
Process is time consuming and requires hundreds to thousands
of units and large amounts of energy.
UCl is very corrosive.
Many physicists, chemists, and engineers needed.
Could be hidden in a shipyard or factory – could be hard to
Although all five recognized nuclear-weapon states had tested or
used EMIS to some extent, this method was thought to have been
abandoned for more efficient methods until it was revealed in 1991
that Iraq had pursued it.
Relies on molecular effusion (the flow of gas
through small holes) to separate U-235 from
The lighter gas travels faster than the heavier
The difference in velocity is small (about
So, it takes many cascade stages to achieve
Relies on molecular effusion (the flow of gas
through small holes) to separate U-235 from U-238.
The lighter gas travels faster than the heavier gas.
The difference in velocity is small (about 0.4%).
So, it takes many cascade stages to achieve even
U.S. first employed this enrichment
technique during W.W. II. Currently,
only one U.S. plant is operating to
produce LEU for reactor fuel.
China and France also
Uranium hexafluoride UF6: Solid at
Uses physical principle of
centripetal force to separate
U-235 from U-238
Very high speed rotor
generates centripetal force
Heavier 238UF6 concentrates
closer to the rotor wall, while
lighter 235UF6 concentrates
toward rotor axis
Separation increases with
rotor speed and length.
Gas Centrifuge Main Components
Thin-walled cylinders, end caps, baffles,
Made of high-strength materials:
Maraging steel, Aluminum alloys, or
Composite materials (e.g.,
Other key components
Magnetic suspension bearings, vacuum
pumps, and motor stators
Developed and used by South Africa with German
help for producing both LEU for reactor fuel and HEU
Mixture of gases (UF6 and carrier gas: hydrogen or
helium) is compressed and directed along a curved
wall at high velocity.
Heavier U-238 moves closer to the wall.
Knife edge at the end of the nozzle separates the U235 from the U-238 gas mixture.
Proliferant state would probably need help from
Germany, South Africa, or Brazil to master this
Uses difference in heating
to separate light particles
from heavier ones.
preferentially move toward
Not energy efficient
compared to other
Used for limited time at
Oak Ridge during WW II
to produce approximately
1% U-235 feed for EMIS.
Plant was dismantled
when gaseous diffusion
plant began operating.
Molecular Laser Isotope Separation
16 micron wavelength IR laser excites
uranium-235 hexafluoride gas
Another laser (either IR or UV)
dissociates a fluorine atom to form
uranium-235 pentafluoride, which
precipitates out as a white powder
Laser Isotope Separation
Easy to conceal
Energy costs low compared to centrifuge
Hard to acquire or make proper lasers
Can be significant material losses of U
Basics of the SILVA/AVLIS Process (1/4)
U + 3 photons → 235U+ + e-
Choosing an efficient
photoionization scheme is a
very difficult task
3 wavelengths λ 1, λ 2, λ 3
Laser-Vapor Interaction Modelling in SILVA
2 Isotopes 235U and 238U
• 5 energy levels and 4 transitions
Basics of the SILVA/AVLIS Process (2/4)
( natural U)
Basics of the SILVA/AVLIS Process (3/4)
enriched U collectors
depleted U collector
depleted U stream
electron beam gun
water cooled crucible
Basics of the SILVA process (4/4)
Copper Vapor pump Lasers
and YAG oscillators
(oscillators - Amplifiers)
with closed loop
Milestones of the SILVA Process
1973 : Atomic isotope separation by laser : initial patent
1980 : Basic research at CEA (spectroscopy, evaporation)
1985 : SILVA/AVLIS selected as advanced process :
USA, France, Japan
1994 : Tens of grams produced at the industrial assay
1994-1998 : Technological demonstrations (by parts)
Mid 1999 : AVLIS shut down in US ; early 2003 in
2000 : Decision for a conclusive 4 years program
2000 - 2003 : MENPHIS construction and
2003 : Demonstrations on MENPHIS
Milestones of the AVLIS Process (USA)
1972 : Beginning of the AVLIS Project at Los
1992 : 150 kg (2%); 112 hours (9 hours full flow)
1992-95 : Work on Gd and Er
1997 : 400 hours (280 hours for enrichment)
1999 : the AVLIS program is stopped in USA
2000–2003 Program : Objectives
Complementary R&D on both
illumination and uranium
Building a large scale demonstrator facility
Demonstrating the technical ability for SILVA to
produce at least 200 kg of enriched uranium at an
assay around 3% 235 U
Demonstrating the photoionisation efficiency
over a one kilometer propagation length in the
uranium full density vapor (multiple beam folding
and propagation in several evaporator units)
2000–2003 Program : Menphis construction
Menelas separator (plant
+ laser system
on line product & tail assay analys is lab
2000–2003 Program : Menphis facility
Dye laser chain
Copper vapor laser
Design : 2001
Building : 2002
1st test : early 2003
1st full scale exp. : june 2003
Menphis Enrichment Experiment Results
Main results for the process :
204 kg of enriched uranium at
≈ 2.5 % mean (predicted) value
About 2000 kg natural U evaporated
≈400 “on line” assay measurements
Menphis experiment technological results
≥ 600 hours for each CVL
170 hours for dye laser at full power
Several hundred hours at the operational
temperature and extractor voltage without
significant failures nor material damages
Long time evaporation
Menphis Propagation Experiment Results
Laser beam profile at the separator entrance
Passage numéro 21
Used as initial conditions for calculation (left) and experiment (right)
Result of the calculations by
Prodige 3D code
PLS measurements X,Y profile
After 21 round trip for a very sensitive
wavelength which amplifies distortion
2000–2003 Program : CONCLUSIONS (1/2)
The results of both the preliminary R&D on separator and
illumination, and of the integration large scale experiments
(204 kg of enriched uranium around 2.5 %),
demonstrate the capability of SILVA to produce large amounts of
enriched uranium in one evaporator .
Demonstration to maintain the photoionisation efficiency over one kilometer p ropagation length in the uranium full
density vapor is obtained from a 3D code benchmarked with an experiment in similitude
The scientific and technical feasibility of the process is now established.
2000–2003 Program : CONCLUSIONS
Many countries have demonstrated
with AVLIS a g/h production of low
But only a few have been able to raise the
production up to a few kg/hour (USA, Japon,
To get such a production level : 20 years :
high power electron gun
high laser power
Thank you very much
… for your attention.