Transcript AKissTalk3.ppt

Safe and Abundant Energy from
Accelerator-Driven Nuclear
Fission
by Alex Kiss
Energy Issues
• World population and economy are
growing fast
• Coal, oil, gas are non-renewable
resources, when these sources run out . . .
• New sources of energy (mainly electrical
energy) will eventually be needed
• Nuclear fusion, an almost unlimited source
of energy, is not expected to be developed
for decades if it is at all.
Nuclear Fission
• Nuclear fission reactors are a good source of
energy, but their current methods are creating
long-lived radioactive waste with half-lives of
thousands to millions of years
• However, new developments on earlier ideas
have sprung a new energy option:
Accelerator and Fission reactor technologies
merged into a single system that deals with the
problem of long-term waste.
How It Works
• A high energy proton beam produced by
the accelerator strikes a target, producing
neutrons used to drive a blanket assembly
containing fissionable fuel (1 p+, 20-30 n0)
• Blanket assembly is like a reactor in that
fission is the source of power but unlike
one because it is sub-critical and cannot
sustain a chain reaction without the
accelerator
Blanket
• Energy producing, resembles nuclear
reactor
• Consists of moderator and fissile fuel
• Moderator: made of graphite, used to
slow the fast neutrons down to thermal
energies to be most effective in producing
fission in the fuel
• Fuel: liquid, molten salt that flows through
the moderator
Target
• The target which the proton beam hits
must be compact yet capable of handling
the several megawatts of energy from the
beam
• It would consist of a central vessel filled
with molten lead
• The beam enters through the top of the
vessel and penetrates deep into the lead,
producing spallation neutrons
Fissile Fuel
• The fuel is thorium, which occurs naturally
and abundantly as the element 232Th, with
a small amount of enriched uranium
• The thorium is readily transmuted by
neutrons to the easily fissionable 233U
• The molten salt fuel is made of
LiF:BeF2:ThF4 equal to 70:18:12 by mole
% along with a small fraction of 238UF4.
Blanket Processes
• Once the accelerator is turned on and
neutrons are produced, the 232Th becomes
233Th, which beta-decays to 233Pr, after 27
days this then beta-decays to the easily
fissionable 233Ur (It takes a while for the
233Ur to be produced so a small amount of
238Ur is added to the startup fuel)
• Heat exchangers located in the blanket
produce electrical energy with steam
Reuse of Waste
• Radioactive byproducts formed during
fission continually separated from the salt
• Long-lived isotopes are extracted from the
stable, short-lived ones and returned to
the system to be reused and converted to
stable, short-lived ones
• So the real waste is almost all stable,
short-lived isotopes and not a problem to
store, perhaps even at the site.
Other Uses Besides Energy
• Destroy both the surplus plutonium
accumulated in the weapons stockpile as
well as spent commercial nuclear fuel
• With this accelerator-driven system, large
amounts of electrical energy would be
produced to pay for solving the problem of
radioactive waste disposal