nuclear fusion technology · nuclear fusion the phenomenon of fission is a good source of nuclear...
TRANSCRIPT
Nuclear Fusion Technology
Dr. BC Choudhary, Professor
Applied Science Department,
NITTTR, Sector-26, Chandigarh-160019.
Content Outlines
Review of Nuclear Processes
Nuclear Fusion Reactions
Fusion Reactor Technologies
Technological Developments
Pros and Cons
Foreseeable trends
Four Forces of Nature
Systematic Information about Nucleus
Nuclear density at the centre of the nucleus
0 1044 nucleons/m3
Density of nucleons (r) in the inner region of the nucleus is about
same for all nuclei.
Surface thickness of all nuclei are very similar
Radius of nucleus, R = R0 A 1/3 , small variation in radii
NOT ALL NUCLEI ARE SPHERICAL.
Energies of nucleons in nucleus 10 MeV
ALL NUCLEI ARE NOT STABLE
Nuclear Stability
Stable nuclei
Proton unstable
Neutron unstable
Stable n:p = 1.2 –1.4
Measure of Nuclear Stability
• Nuclei with the largest binding energy per nucleon are the most stable.
• The largest binding energy per nucleon is 8.7 MeV, for mass number A = 60.
• Beyond Bismuth, A = 209, nuclei are unstable.
EB(Z,N) = {ZMp+NMn - M(Z,N)} c2
Binding Energy per nucleon
We can release energy by creating nuclei that are more
strongly bound (increasing Eb)
Fusion: Lightest nuclei
combine to form heavier
nuclei.
Fission: Heaviest nuclei
split into smaller fragments. 56Fe
1H
238U N
Eb
N
Nuclear Processes
Both the processes evolve large amount of energy.
Nuclear fission:
A large nucleus splits into several
small nuclei when impacted by a
neutron, and energy is released in
this process
Nuclear fusion:
Several small nuclei fuse
together and release energy
Nuclear Fission and Fusion
Electricity from Nuclear Fission
Nuclear power plants account ~17 percent
of the worlds power.
Nuclear Fusion
The Phenomenon of fission is a good source of nuclear
energy. However, a considerable larger amount of
energy can be obtained by fusion of light elements to
heavier ones.
The energy yield per gram in fusion is about 8 times
that in the fission.
In order to effect the fusion of two or more nuclei, they must
be brought so close together against the force of electrostatic
repulsion that they face within the range of nuclear forces.
This will occur only if the interacting nuclei have K.E. of
about 0.1 MeV or more.
This energy is undoubtedly provided by Accelerators, but
their use is limited to small number of nuclei.
Nuclear fusion at very high temperature
Thermonuclear Reactions.
To produce fusion of large mass of material, the K.E. must be
due to the thermal motion of the nuclei, which could in
principle result from a sufficient increase in temperature.
To impart the particles energies as high as 0.1 MeV, its
temperature shall be raised to 107 K.
The SUN
Sun is radiating energy at the rate of 41016 J/s for several
billion years without showing any sign of cooling off
Chemical reaction (combustion of
carbon) cannot account for energy at
above rate for long time.
Fission process can also not be
expected- because of small
abundance of heavy nuclei in the
sun
Hydrogen and Helium constitute 90% of sun’s mass in almost equal
proportion.
Probable that certain nuclear processes involving H and He may be
actual source of Sun’s energy.
Thermonuclear reactions in the core of the
Sun produce its energy
• At extremely high temperatures and pressures, 4 Hydrogen atoms
combine to make 1 Helium atom and release energy in the process
according to E = mc2
4H He + energy : HYDROGEN FUSION
In 1938, Bethe proposed a set of nuclear reactions to
accounts for energy produced in sun and other stars.
The C-N-O cycle dominates in stars
heavier than the sun
The Proton-proton chain
dominates in stars: the size
of the sun or smaller.
Fusion of in Laboratory
In order to overcome Coulombic repulsion, must have very
energetic (~70 keV> 800,000,000 oC) D, T nuclei.
At this temperature, D,T nuclei are ionized, forming a charged
plasma
No material can withstand this temperature How to confine?
The easiest fusion reaction to attain is
Deuterium + Tritium:
3H + 2H 4He + 1n
D + T +n
Lawson's Criterion for Fusion
The closest approach to Lawson's criterion has been at the
“Tokamak Fusion Test Reactor ( TFTR)” at Princeton.
Has reached ignition temperature and got in very close to
Lawson's criterion, although not at the same time.
Once a Critical ignition temperature for nuclear fusion has been achieved, it
must be maintained at that temperature for a long enough confinement time ()
at a high enough ion density (n) to obtain a net yield of energy.
Deuterium - Deuterium
fusion n 1016 s/cm3
Deuterium- Tritium
fusion n 1014 s/cm3
Lawson’s criterion
for fusion
In 1957, J. D. Lawson showed that the product of ion density and confinement
time determined the minimum conditions for productive fusion, and that product
is commonly called Lawson's criterion. Commonly quoted figures for this
criterion are
Three Confinement Methods
High-power laser confinement
Nuclear Fusion and Plasma Confinement
FUSION REACTOR
Types of Reactors
• Magnetic Confinement Fusion (Tokamak)
• Inertial Confinement Fusion (ICF) : Laser Ignition
MCF is about 20
years ahead of ICF
TOKAMAK
Charged plasma can be confined by large magnetic
fields, requiring super conducting electromagnets.
• Fusion reaction occur,
and the energy released
makes the He byproduct
more energetic, thus
keeping the temperature
of the plasma hot enough
to ‘burn’ D,T
Magnetic Field Configuration
Tokamak
Scheme of the tokamak principle:
arrangement of magnetic field coils and
the resulting magnetic field that confines
the plasma.
Trajectory of "trapped particles".
Charged particles travel in tight "gyro-
orbits" around magnetic field lines. In
some cases, due to the gradient of the
magnetic field, their trajectory traces
out banana-shape orbits.
Cross-section
showing the
toroidal, poloidal
and divertor coils
FUSION ENERGY-TOKAMAK
Magnetic Fusion Reactor
Schematic of a Fusion Reactor –Tokamak Design
Tokamak
Problems
• Helium only carries 20% of energy, neutron escapes
plasma
• Energy lost from the core due to radiation, and this
energy is proportional to Z2
Containment vessel = high Z material
• Plasma is chronically unstable
“confining a plasma using magnetic fields is like confining
Jell-o with elastic bands”
TOKAMAK
Results:
The energy that goes into heating and confining the plasma
is MORE than the energy that is produced
Rate of energy loss > the rate of energy gain.
Break-even: Eout > Ein
• The energy recovered by burning some amount of fuel is
greater than the energy required to get it to burn.
• Analogy : The energy gained by eating a sandwich is greater
than the energy of chewing, digesting
TOKAMAK
Ignition : P out, avg > Pin, avg
• In steady state, the average power output is greater
than the average power input
• Analogy : Using a match to light a fire that gives off
lots of heat as long as there is fuel, i.e. it is self-
sustainable
TOKAMAK
For best Fusion burn, want :
High density plasma (N)
Hot Plasma (T)
Long burn time ()
Inertial Confinement
Conditions for controlled fusion reactions;
Extremely high temperatures (108 K) and pressures
very hard to produce
Possible through use of high energy Laser pulses from many
directions simultaneously Inertial Confinement
Argus Laser System, USA,
Shiva System – 20 lasers
directed from 20 directions
Delphin System in USSR- 256 beams launched through 256
amplifiers.
Laser Fusion Projects:
Based on Nd:glass lasers
Inertial Confinement Fusion
Multiple high power lasers or ion beams are focused on a
freeze dried pellet of D and T
Pellet absorbs energy and heats up dramatically, causing an
imploding shockwave that crushes the D, T nuclei together
Rapidly shrinking nuclei with increasing temperature causes
fusion reaction
Pellet and laser system must be designed for most of the D-T
fuel to fuse before pellet explodes.
Working :
ICF- Schematic
An inertial confinement fusion implosion on the NOVA laser creates
"microsun" conditions of tremendously high density and temperature
rivaling even those found at the core of our Sun.
Inside the main chamber of Nova
( National Ignition Facility)
National Ignition Facility (NIF)
America Fires the Most Powerful Laser in History (2010): United
States' National Ignition Facility at Lawrence Livermore National Lab in
California has fired the most powerful laser in history, a record-breaking 2MJ
shot. The laser was originally designed to reach 1.875 MJ, but beat everyone's
expectations set a new world record in the process.
192 laser beams (UV) combined to form the
single shot, initially reaching 1.875 MJs.
Better yet, the blast caused less damage to
the laser optics than predicted, which
allowed the facility to fire another shot just
36 hours after the 2.03 MJs one.
“It's a remarkable demonstration of the laser from the standpoint of its energy, its precision, its power, and its availability.”
- Ed Moses, Director, NIF
Fusion Schematic in NIF
• 192 Laser beams in single shot
Target assembly for NIF's first integrated ignition
experiment mounted in the cryogenic target positioning
system (cryoTARPOS). The two triangle-shaped arms
form a shroud around the cold target to protect it until
they open five seconds before a shot.
NIF and ICF
Inertial Confinement Fusion
Problems :
• With many lasers requiring extreme precision and
power, the firing is not possible more than a few
times each day (optics needs to cool)
• In order to reach power production conditions, the
lasers must be fired more than once per second.
Results :
• Break-even is nowhere close
Safety & Waste Management
It’s so hard to get going, that if you do anything wrong,
it stops.
Massive reactors still have very little fuel in the
machine at any time
• ~0.2 g of D,T produces 1.5 GW
• Small amount of fuel means no chances of container melting
He4 and free neutrons emitted
Containment vessels become activated, though with
short half-lives.
Pros and Cons : Fusion
Pros:
• Near infinite supply of fuel (Deuterium from water,
Lithium can produce Tritium)
• Only emission is Helium
• “ Inherently safe”
Cons:
• Radioactive Core
• High neutron emission for workers
• Not yet viable, will cost billions
Future Fusion Research
ITER Large scale Tokamak being built in France, to be operational
by 2025
2nd largest international scientific collaboration in history
Aim for Q>10, possibly ignition
Fission –Fusion Hybrid
• Using a fusion core to emit fast neutrons that will produce
Pu239 for fission reactors.
National Ignition Facility (NIF)
NIF is the largest and most energetic ICF device built to date.
First "integrated ignition experiments" (which tested the laser's
power) declared completed in October 2010.
ATTRACTIONS: Fusion Vs Fission
Offers a low cost and pollution free energy
Produces less radioactive nuclear waste materials
Light nuclei required for a fusion reaction are
available in abundance on earth than the heavy
elements needed for fission.
If efforts succeed, fusion will be a practically
inexhaustible source of energy.
Fusion Power Technology
ITER : International Thermonuclear Experimental Reactor
• A Joint Project Conducted by: European Union , Russian
Federation, United States, Canada, Japan and India.
• The Purposes of ITER are:
– Demo that electrical power from fusion is scientifically and technically
feasible
– Build and Initially test the Demo System
Two Approaches to achieve Fusion:
Tokamak and ICF
Results of Practical Electric Power from ITER are Probably
10-20 years away.
Though the research in fusion reactors is
extremely costly, but so great are its
advantages- readily available fuel, no military
applications, minor production of radioactive waste
compared with nuclear fission reactor - that
research on fusion reactors continue with the
hope that they will be able to supply much of
the world’s energy needs in centuries to come.
ICF research continues, but magnetic confinement seems
closer to the goal of a working fusion reactor.
Laboratory experiments have given positive results,
however, nuclear fusion reactors remains an unproven
technology after Seven decades of expensive research
FUSION TECHNOLOGY : A Sustainable
Energy Source ?
Future Energy Sources ?
