Gérard MOUROU
CPA Transmutation of Nuclear Waste
https://bigthink.com/technology-innovation/laser-nuclear-waste
04 April, 2019
Lasers
could cut lifespan of nuclear waste from "a million years to
30 minutes," says Nobel laureate
Physicist
plans to karate-chop them with super-fast blasts of light.
by Robby
Berman
Gérard Mourou has already won a Nobel for his work with fast
laser pulses.
If he gets pulses 10,000 times faster, he says he can modify
waste on an atomic level.
If no solution is found, we're already stuck with some 22,000
cubic meters of long-lasting hazardous waste.
Whatever one thinks of nuclear energy, the process results in
tons of radioactive, toxic waste no one quite knows what to do
with. As a result, it's tucked away as safely as possible in
underground storage areas where it's meant to remain a long,
long time: The worst of it, uranium 235 and plutonium 239, have
a half life of 24,000 years. That's the reason eyebrows were
raised in Europe — where more countries depend on nuclear energy
than anywhere else — when physicist Gérard Mourou mentioned in
his wide-ranging Nobel acceptance speech that lasers could cut
the lifespan of nuclear waste from "a million years to 30
minutes," as he put it in a followup interview with The
Conversation.
Who is
Gérard Mourou?
Mourou was the co-recipient of his Nobel with Donna Strickland
for their development of Chirped Pulse Amplification (CPA) at
the University of Rochester. In his speech, he referred to his
"passion for extreme light."
CPA produces high-intensity, super-short optical pulses that
pack a tremendous amount of power. Mourou's and Strickland's
goal was to develop a means of making highly accurate cuts
useful in medical and industrial settings.
It turns out CPA has another benefit, too, that's just as
important. Its attosecond pulses are so quick that they shine a
light on otherwise non-observable, ultra-fast events such as
those inside individual atoms and in chemical reactions. This
capability is what Mourou hopes give CPA a chance of
neutralizing nuclear waste, and he's actively working out a way
to make this happen in conjunction with Toshiki Tajima of UC
Irvine. As Mourou explains to The Conversation:
"Take the nucleus of an atom. It is made up of protons and
neutrons. If we add or take away a neutron, it changes
absolutely everything. It is no longer the same atom, and its
properties will completely change. The lifespan of nuclear waste
is fundamentally changed, and we could cut this from a million
years to 30 minutes!
We are already able to irradiate large quantities of material in
one go with a high-power laser, so the technique is perfectly
applicable and, in theory, nothing prevents us from scaling it
up to an industrial level. This is the project that I am
launching in partnership with the Alternative Energies and
Atomic Energy Commission, or CEA, in France. We think that in 10
or 15 years' time we will have something we can demonstrate.
This is what really allows me to dream, thinking of all the
future applications of our invention."
While 15 years may seem a long time, when you're dealing with
the half-life of nuclear waste, it's a blink of an eye.
https://theconversation.com/conversation-avec-gerard-mourou-prix-nobel-de-physique-2018-104338
An
idea for nuclear waste
The one that is particularly close to my heart is the treatment
of radioactive waste with our laser techniques. Let me explain:
take an atomic nucleus: it is composed of protons and neutrons,
if you put an extra neutron or if you remove one, it changes
absolutely everything. It is no longer the same atom, its
properties will then totally change. The lifespan of this waste
is fundamentally changed: it can be reduced from a million years
to 30 minutes!
We are already able to irradiate a lot of material with a
large-flow laser at once, so the technique is perfectly
applicable and theoretically nothing opposes industrial-scale
use. This is the project I am launching in collaboration with
the AEC. We believe that in 10 or 15 years we will be able to
show you something.
This is really what continues to make me dream: all the future
applications of our invention. When we work, it is the passion
that drives us, not the hopes of Nobel Laureates. It's our
curiosity that we have to satisfy. After my prize, I'm going to
keep going!
https://www.nobelprize.org/prizes/physics/2018/mourou/facts/
Gérard
Mourou
US10049778
Arrangement
for generating a proton beam and an installation for
transmutation of nuclear wastes
[ PDF ]
The invention relates to an arrangement for generating a proton
beam and an installation for transmutation of nuclear wastes,
particularly from nuclear reactors.
It is known that the transmutation of nuclear wastes from
nuclear reactors needs to deposit a large amount of neutrons and
gamma photons on hazardous nuclear isotopes. The conventional
approach is to use fast neutrons generated by fast breeding
reactors or a dedicated high power and high energy accelerator
to bombard a spallation heavy weight target to produce high flux
of neutrons which will induce transmutation of these isotopes.
A conventional arrangement for transmutation of nuclear wastes
has the short-comings that it is very bulky and expensive. Its
size may exceed the one of the nuclear reactor itself.
The invention has the object to overcome these shortcomings.
For reaching this object, the arrangement proposed by the
invention is characterized in that it is constituted by a laser
driven accelerator of protons adapted to produce a beam of
relativistic protons of 0.5 GeV to 1 GeV with a current in the
order of tens of mA, such as a current of 20 mA.
According to a feature of the invention, the arrangement is
characterized in that it comprises a laser pulse source adapted
to produce a beam of short pulses having a duration of hundreds
of femtoseconds and an intensity greater than 10<23
>W/cm<2 >with a high-average power of the order of tens
of MW and a proton target on which the laser beam is focused on.
According to another feature of the invention, the arrangement
is characterized in that the duration of the laser pulses is in
the order of 30 femtoseconds.
According to still another feature of the invention, the
arrangement is characterized in that the high-average power is
in the order of 20 MW.
According to still another feature of the invention, the
arrangement is characterized in that it comprises a laser pulse
oscillator producing ultra-short pulses having a duration in the
order of tens of femtoseconds and an energy in the order of
nanojoules and a single mode optical fiber amplifier device into
which the produced laser pulses are fed in, comprising a
multitude of optical fibers in view to form a coherent
amplification network system.
According to still another feature of the invention, the
arrangement is characterized in that said coherent amplification
network system comprises a series of successive amplifier stages
each comprising a bundle of single mode fiber amplifiers, in
which the fibers are spaced from one another in view to allow
passage of a cooling medium there between, the bundle of one
stage comprising fibers which have been obtained by splitting of
the fibers of the preceding stage bundle.
According to still another feature of the invention, the
arrangement is characterized in that in the downward end the
portion of the coherent amplification network, each fiber
comprises two fiber sections, an amplifying fiber section
belonging to the last amplifier stage in which the fibers are
separated from one another for cooling reasons and a transport
fiber section made of very low loss fiber, the transport fibers
allowing to transform the great diameter bundle of the amplifier
stage into a small diameter output bundle where the fibers are
kept as close as possible from each other to make the overall
output pupil diameter as reduced as possible.
According to still another feature of the invention, the
arrangement is characterized in that the proton target is a
solid target formed by a film of a substance such as hydrogen,
helium or carbon.
According to still another feature, the laser pulses source is
adapted to produce laser pulses having a repetition rate in the
order of Khz, such as 10 KHz.
The installation for transmutation of nuclear wastes is
characterized in that it comprises the arrangement for producing
the beam of relativistic protons and a spallation target for
producing a beam of neutrons of 0.5 GeV to 1 GeV, which is
directed towards nuclear waste, said spallation target being
irradiated by the ultra-relativistic proton beam.
In accordance to an advantageous feature, the spallation target
is a liquid target of Pb—Bi.
According to another feature, the installation is characterized
in that the spallation target comprises an entrance window of
high-stress steel and a cylindrical tube filled by a liquid of
Pb—Bi alloy, the liquid alloy being used as cooling medium.
Other features and advantageous of the invention will become
apparent from the description given below which only serves as
an example and is in no way limiting the scope of the invention,
with references to the attached drawings, wherein:
FIG. 1 is a schematic diagram of an installation for
transmutation of nuclear waste, according to the invention;
FIG. 2 is a view of an arrangement for producing a
high-intensity and high-average beam of protons, according to
the invention;
FIG. 3 is a schematic cross-section view of the optical fibers
architecture of the transport fiber assembly along the line
IV-IV of FIG. 2; and
FIG. 4 shows an installation according to the invention for
transmutating nuclear waste.
The invention will be described below in its application to
transmutation of nuclear waste. This application however serves
only as a non-exclusive example. It is to be noted that the
invention covers all applications using a beam of relativistic
protons obtained by the laser based method proposed by the
invention.
As shown on FIG. 1, an installation for transmutating nuclear
waste such as waste from nuclear reactors comprises an
ultra-relativistic intensity pulse-laser source 1 susceptible to
produce a laser beam 2 of ultra-short laser pulses having a
duration of for instance 30 femtoseconds (fs) and an intensity
greater than 10<23 >W/cm<2 >with high-average power
of the order of 20 MW, a proton target 3 on which the laser beam
2 is focused on and from which a beam of relativistic protons 4
of 0.5 GeV to 1 GeV with a current for instance of the order of
20 mA is produced. The latter irradiates a spallation target 5,
for instance a liquid target of Pb—Bi where neutrons 6 of 0.5 to
1 GeV are spallated from. The neutrons are directed towards the
nuclear waste 7 to be transmutated, such as spent nuclear fuel,
in order to transmute the waste's radioactive isotope, i.e.
lower actinides, into much safer materials or elements with
significantly shorter half-lives.
With reference to FIGS. 2 to 4, the ultra-relativistic intensity
pulse-laser source 1 will be described here-below in a detailed
manner.
As can be seen on FIG. 2, the source 1 comprises an oscillator 8
adapted to produce short pulses of for instance femtoseconds
(fs) duration and energy in the order of nanojoule (nJ). The
produced laser-pulse is fed into a single mode optical fiber
amplifier arrangement comprising a multitude of optical fibers
in view to form a coherent amplification network (CAN) system
providing simultaneous high-peak and high-average powers with
high efficiency greater than 30%, i.e. the laser beam 2 shown on
FIG. 1 which may have an intensity greater than 10<23
>W/cm<2>.
Concerning the coherent amplification network system reference
is made to the publication “Euronnac, May 2012 Meeting CERN”,
IZEST, Ecole Polytechnique, Palaiseau of Gerard Mourou and
Toshiki Tajima, and to the publication “Coherent Beam Combining
of 1.5 μm Er Yb Doped Fiber Amplifiers”, Fiber and Integrated
Optics, 27(5) (2008) of S. Demoustier, C. Bellanger, A. Brignon
and J. P. Huignard, and of “Collective Coherent Phase Combining
of 64 fibers” Opt. Express, 19, Issue 18, 17053-17058 (2011) of
J. Bourderionnet, C. Bellanger, J. Primot and A. Brignon.
More precisely, the laser-pulse produced by oscillator 8 passes
through a pair of diffraction gratings 10 which are represented
in form of a boxes the structure of which is precised beneath
and which stretch it by about 10<5 >times in a manner
known per se. The stretching separates the various components of
the stretch pulse, producing a rainbow in time. The pulse after
stretching is at the millijoule (mJ) level.
The stretched pulses are coupled in a first amplifier stage 13
to a multiplicity of for instance 10 to 100 fibers 14, each
constituting a single mode fiber amplifier. Each fiber will
amplify the input pulse to the millijoule level. The amplified
fibers are kept to form a bundle wherein the amplifying fibers
are at a relatively large distance from one another in order to
allow efficient cooling by an appropriate cooling medium for
evacuating heat produced by the fibers.
The same operation is repeated in a second amplifier stage 15
where each fiber amplifier of the first stage 13 feeds a
multiplicity of for instance 10 to 100 single mode amplifiers 16
of the same type as the ones of the first stage. Each fiber will
amplify the input, which is a corresponding part of the output
of the fiber from which it is obtained by splitting, to the
millijoule level.
The same process is repeated in successive series of amplifier
stages, one of which is furthermore shown in 17 on FIG. 2 which
comprises a larger diameter bundle of fibers 19 spaced from one
another for enabling efficient cooling of the fibers.
It results from the foregoing that by splitting and branching
each single “seed” pulse a matrix of thousands of lasers is
obtained. In each stage of the successive series of amplifier
stages, the phase of each pulse is preserved.
The very great number of fibers of the last stage, on FIG. 2 the
stage 17, are combined and phased with one another so as to form
a single pulse, which is compressed by a pair of gratings in a
manner known per se. The pulse energy can be now of tens of
Joules, the pulse duration corresponding to the initial pulse
duration of 30 femtoseconds of the present example.
FIG. 3 shows the arrangement of the fibers in the region of the
downward end of the fiber architecture. As can be seen, each
fiber is realized in two sections, an amplifying section 19 and
a transport section 20 made of very low loss fiber 21. The fiber
amplifying sections 19 which constitute the last amplifier stage
are arranged in a manner to form a great diameter bundle wherein
the different sections are sufficiently separated from one
another to ensure efficient cooling by means of an appropriate
cooling medium. The fiber transport sections 20, since they are
very low loss fibers which need no particular cooling allow to
transform the great diameter bundle in a small diameter output
bundle 21 where the fibers are kept as closed as possible from
each other to make the overall output pupil diameter as reduced
as possible.
The individual laser beams which get out at the ends of the
small diameter fibers form a beam 22 of single pulse, after
having been phase controlled to be in phase such as described in
the before mentioned publication “Euronnac, May 2012, Meeting
CERN, the teaching of which is considered to be included
therein. Each amplified stretched output pulse is then
compressed by means of a second pair of gratings 23
schematically shown on FIG. 2. The resulting pulse has the
ultra-short duration of tens of femtoseconds such as of 30
femtoseconds of the original pulse produced by oscillator 9, but
its energy is enormous of for instance 30 Joules.
Theses pulses are made to hit a parabolic mirror 30 which
focuses it on the proton target 3 as can be seen on FIG. 4.
The resulting pulse is the high-average power and high-intensity
pulse 2 shown on FIG. 1, which is in the ultra-relativistic
regime, i.e. greater than 10<23 >W/cm<2>.
According to FIGS. 1 and 3, these pulses 2 which can be produced
at a repetition rate in the order of KHz for instance 10 kHZ,
due to the efficient cooling of the single mode fiber amplifiers
in their different bundles by means of an appropriate cooling
medium, are made to shoot the proton target 3 which can be a
solid target made of a substance such as hydrogen, helium and/or
carbon, advantageously in form of a film 25. The shooting of the
target produces the high-flux 4 of high-energy protons in the
range of 0.5 to 1 GeV which is made to impinge on the spallation
target 5 in order to be converted in the high-flux of fast
energetic neutrons 6 by spallation process induced in the target
5 which is for instance a high-Z material target. It is to be
noted that 1 GeV proton produces on the target about 30 neutrons
which is a high multiplication factor.
The target 5 consists of an entrance window of high-stress steel
and a cylindrical tube 27 of about 50 cm filled by a liquid
Pb—Bi alloy for neutron production. This liquid alloy can be
made to flow and circulate in a dedicated hydraulic circuit to
maintain the temperature well below its critical value.
Accordingly, the alloy is not only used for neutron production,
but also as coolant.
By appropriate monitoring the corrosion and the stress in the
entrance window as well as of the temperature gradient and the
production of H and He in the target assembly, a safe operation
of the system is insured.
In the conditions described above, the invention allows to
produce efficient relativistic protons by shooting the solid
target of hydrogen and/or helium within a laser at the density
of greater than 10<23 >W/cm<2>. In this radiation
dominated pressure regime, the momentum is transferred to ions
through the electric filled arising from charge separation. In
this regime, the proton component moves forward with almost the
same velocity as the average longitudinal velocity of the
electron component and renders the interaction very efficient,
close to 100%. Moreover, the proton energy is a desired energy
range between 0.5 and 1 GeV to produce the neutrons with the
high-energy in order to achieve the transmutation of the nuclear
waste 7.
It results from the foregoing that the laser based way to
produce neutrons to be directed toward a target of nuclear waste
comprises an oscillator for producing ultra-short laser pulses
in the order of femtoseconds having an energy in order of
millijoules, very far from the level of tens of joules necessary
for the targeted application of the invention, such as
transmutation of nuclear waste. To this end, the invention
proposes to combine a very large number, i.e. 10<4 >or
more fibers coherently in the coherent amplification network
system described above and shown on the figures. The repetition
rate of the laser pulses having the intensity greater than
10<23 >W/cm<2 >can be advantageously in the order of
tens of kHZ due to the use of fibers having a high surface area
and the heat removal ensured by the disposition of the fibers in
large diameter fiber bundles wherein they are separated from one
another to allow circulation of a cooling medium there between.
Since the used single mode fiber amplifiers are the same in each
amplifier stage, and are tested telecommunication components,
the laser pulse generator arrangement and the installation for
transmutating nuclear waste can be realized as relatively cheap
and compact apparatus which can be moved to locations where it
should be used.