Liquid Fluoride Thorium Reactors
without equations
∑x<+-=-*±
An overview of liquid-fueled liquid-cooled thermal
spectrum Thorium breeder reactors and why they
matter.
Rob Morse
Science Engineer- Nuclear Option
2012
1
Power makes a difference.
2
Fuel for a lifetime?
You consume a ball of coal
10 meters in diameter…
…or a ball or thorium 37mm in diameter.
LFTR wo Equations. Thorium
power conference, Oct 2009
3
Reactor Basics
 Reactors make heat through fission and decay.
The heat is then converted into mechanical power
and then to electrical power.
 Fission is controlled by the neutron population
around the nuclear fuel. More neutrons produce
more fissions and more heat.
 The neutron economy is tightly controlled by
material properties, physics, and design.
4
The Absolutes
A power source must be Self regulating when it is ON
 “Walk away” safe when it is OFF
 Inherently safe in case of an ACCIDENT
LFTR wo Equations. Thorium
power conference, Oct 2009
6
The Relative Strengths
Little or no radioactive waste
No bomb materials
Low cost per power delivered
Small physical size
Power on demand
A wide choice of building sites.
LFTR wo Equations. Thorium
power conference, Oct 2009
7
Core Options
 Standard pressurized water reactor (PWR)
– Water flows over a core of ceramic fuel pins.
Water acts as coolant and moderator.
Reactivity is controlled by the moderator density
and by control rods.
 Liquid Fluoride Thorium reactor (LFTR)
– A liquid fuel flows though a core of graphite.
The fuel acts as coolant, the graphite as
moderator. Reactivity is controlled by the fuel
density.
8
LFTR Processing Details
Metallic Thorium feed stream
Bismuth-metal
Reductive
Extraction Column
Pa-233
Decay Tank
Fluoride
Volatility
233UF
6
7LiF-BeF2
Uranium
AbsorptionReduction
Pa
Recycle
Fertile Salt
Recycle Fuel Salt
7LiF-BeF -UF
2
4
UF6
Fission
Product
Waste
Return
Two-Fluid
Reactor
Hexafluoride
Distillation
“Bare”
Salt
Core
Blanket
232,233,234
Vacuum
Distillation
Fertile
Salt
xF6
Fluoride
Volatility
Fuel Salt
MoF6, TcF6, SeF6,
RuF5, TeF6, IF7,
Other F6
Molybdenum
and Iodine for
Medical Uses9
Metal Reduction Column
10
Temperature Stability
A power plant with a built in thermostat!
inlet
outlet
Fuel-coolant
Graphite
Moderator
reactivity
temperature
LFTR wo Equations. Thorium
power conference, Oct 2009
11
Improved reactor design
reactivity
temperature
LFTR wo Equations. Thorium
power conference, Oct 2009
12
The Reactor at “idle”
Fuel Loop
LFTR wo Equations. Thorium
power conference, Oct 2009
13
Walk-Away Safe
14
Size matters!
Your nuclear waste is the size of a few grains
of rice!
LFTR wo Equations. Thorium
power conference, Oct 2009
15
Uranium vs Thorium as a Fuel
 0.7 % of Uranium is fissionable. The rest
becomes nuclear waste.
 Thorium is isotopically pure and converted
to U233 for fuel.
 For fuel cycle side-reactions seehttp://en.wikipedia.org/wiki/Thorium_fuel_cycle
16
Lets Make Power
 This is a picture of the waste heat coming from the original
LFTR test cell.
 The heat transfer fluid (molten salt) is at low pressure.
 We can use a gas cycle, like a jet engine, to convert heat
into mechanical power. (highly efficient)
 These plants can run at partial load.
LFTR wo Equations. Thorium
power conference, Oct 2009
17
Fuel or Waste
We want the fuel to fission rather than
transmute.
U233- 90% fissions
U235- 83% fissions
P239- 50% fissions
P241- 25% fissions
LFTR wo Equations. Thorium
power conference, Oct 2009
18
Myth of Half Life
 What makes a radioactive material dangerous?
– Even low energy beta decays can break organic bonds.
 Is a material with a 1 second half life dangerous?
– It is very dangerous..today. Tomorrow it is inert.
 Is a 15 billion year half life dangerous? (Half of it
has decayed since the big bang.) It has a very low
activity, and we used it for hundreds of years.
 How about a thousand year half life? It is both
active and persistent.
19
Myth of Creating Radioactivity
 If radiation is dangerous then we should do
what we can to eliminate it from the
environment. That is exactly what nuclear
reactors do. They are the nuclear analog to
chemical catalysis reactors; they accelerate
natural processes.
 The only way to “create” nuclear radiation is
with particle accelerators. Conventional
reactors simply accelerate decay towards
stable elements.
20
Myth of Concentration
Thorium and uranium are dispersed in nature
and they decay naturally. We concentrate
them, and so concentrate their natural
toxicity.
For safe disposal, should we re-disperse
them and lower their effective activity, or
sequester them and decrease our contact?
21
References
http://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor
http://www.scribd.com/doc/59204103/Thorium-presentation-GreenEnergy-Forum-2008-07-25
http://www.thoriumenergyalliance.com/ThoriumSite/resources.html
http://moltensalt.org/references/static/downloads/pdf/NAT_MSBRrecycle.p
df
Thorium in 5 minutes (remix video)
http://www.youtube.com/watch?v=uK367T7h6ZY
22
Outline






Motivations for Nuclear Power
LFTR overview
Nuclear Chemistry
Chemistry
Myths
Questions
23
Binding energy
24
Cross Section
The probability that the neutron interacts with the
nucleus depends on the neutron’s speed. We
describe the probability as an apparent SIZE of
the nucleus. The larger the apparent size, the
higher the probability. This is a geometric
interpretation of a probabilistic quantum
mechanical event.
Reaction equations are of the formNumber of events/time = (neutron flux) (spatial
density of target nuclei) ( cross section for the
event )
Moderation and Rx Probabilities
Neutron Cross Sections
barns (10e-28 m-sq)
500
400
300
200
100
0
Fast U-233 fission
Fast Thorium absobtion Thermal U-233 fission
Thermal Thorium
absorbtion
>>Fast to Slow>>
LFTR wo Equations. Thorium
power conference, Oct 2009
26
Speed?
LFTR wo Equations. Thorium
power conference, Oct 2009
27
Nuclear Fission
28
Chart of the Nuclides for LFTR
Fissile Fuel!
Ref: http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=90&n=142
Uranium (92)
~27 days half-life
Protactinium (91)
~22 min half-life
Thorium (90)
Raw
Material!
+N
29