we have today Dr. Joe Bonometti today's speaker is Robert Hargraves
today we have Kirk Sorensen
Thorium is an element, slightly radioactive is a metal, has a very wide liquied range
some other interesting properties
thorium is not really commercially used for anything of much these days - this is a log scale
of what's available in the earth's crust the uraniuim that you're really interested in
the one fissile material
its orders of magnitude less - nuclear fission is an incredibly dense source of energy
nature gave us three options for fuel
the one of the top is what we use all the time and now put yourself in the late 1930s early
1940s all 3 of these can be made to make nuclear energy
what's the distinction between them? well it's a wartime scenario so to the first question was
how do we turn it into a weapon? this to me is one of the great tragedies
of nuclear energy - it was discovered in the context of a war
we went from weapons to Nautilus
Eisenhower's atoms for peace program but you're using the same infrastructure
the same people - it wasn't exactly atoms for peace - what's the best way to produce
electricity - these were initially evaluated in terms of their destructive potential
natural uranium isolate that U235 and they can make a bomb out of it and that was Hiroshima
take the remaining uranium irradiate it you can make plutonium you can make a bomb with it
now what about thorium? could you irradiate that and make a bomb out of it? really bad idea
it is inevitably contaminated with U232 U232 is decaying and throwing off gammas
and basically screwing up your weapon
thorium is no good for nuclear weapons
you can take some thorium put it in a normal reactor you get some benefits out of it but
it is not an end-all it doesn't extract all the energy out of that thorium
and it doesn't mitigate all problems you have with today's nuclear power
here's what happens in today's light water reactors we start off with about 250 tonnes
of uranium some of it is enriched
about as many fission products come out as go in makes sense - most of the stuff that
comes out is U238 it's not burned up but there's about 1 tonne of fission products
and about 0.23 tonnes of plutonium that come out of a typical gigawatt plant
but for thorium reactor it only uses a ton of thorium because we burn all of it
this thing we get about 0.0001 tonne
about 100 grams of plutonium uranium-232 had a much
lower atomic mass then does uranium-238 and in order to make plutonium you need
many more neutron absorptions successively so the probability of making plutonium in
that kind of reactor is much much less
uraniuim and thorium both have the same energy density if you fission them up
the real advantage is the ability to fission up thorium all the way in a thermal reactor
Enrico Fermi argued for the plutonium based economy - one of the reasons is
you've got 3 neutrons on average per fission and you need at least 2 you: 1 splits and
1 breeds your next fuel using fast neutrons coming off the reactor from the fission
and you can see this number really climbs very good which means you get a whole lot more
than 2 which means you get production of plutonium
for that reason all the emphasis was turned towards the uranium-plutonium cycle because
of the necessity of making nuclear weapons Enrico (Fermi) said nah not such a good idea
thermal fission is the way to we want to slow down neutrons
by doing that we'll have safer and easier to control reactors and the only way to do
this was to use thorium
this is a fork in the road back during the Manhattan project 1 guy went off 1 direction
to go work uranium-plutonium the other guy went the other direction to work thorium-U233
and the reason a thermal reactor is so different from a fast reactor is
this is what these nuclei look like to neutrons
here on the top row that's the thermal spectrum
big targets and the blue represents if you hit it you cause a fission and the red
represents if you hit it, it's just going to absorb the neutron
look plutonium is a big target
but a 3rd of the time you hit it you're just going to get eaten rather than cause a fission
U233 most of the time you hit it you're going to cause fission rather than an absorption
look down here at the fast spectrum - you can't see it at this scale but
most the time you hit the nuclei you're going to have a fission
the problem is you don't hit it very often so a thermal reactor gets
a lot better fuel efficiency - you need
a lot less fuel to get the same amount of heat the upshot of that is a thermal reactor
like LFTR can get about 5 X more heat per unit of fissile fuel than a fast reactor can
look at the uranium cycle compared to the thorium cycle - you start out with
a whole lot more mining with the uranium cycle
you have a whole lot of yellowcake that you make and then enrich that
and then make these pellets it is a very expensive process
you end up with a whole bunch of depleted uranium - you need a very big plant, a vessel
that can hold all the steam or any explosion that can happen here - very high pressure
and you produce a whole lot of spent fuel you need Yucca Mountain for 10,000 years
the thorium cycle you need one tonne this is for the same amount of energy 1 GW
for 1 year - much smaller plant - low pressure - breatons are much smaller, much
more effecient - but the big deal here is in ten years most of that 83%
is going to be back down to safe background levels
and the remainder only needs 300 years for storage
you can imagine finding many places around the world that can handle that and you can
imagine making storage vessels that can last three hundred years
Weinberg called it the burning the rocks you could literally mine rock
just for its energy content - a cubic meter of average Earth's crust has about 12 grams
of thorium in it and that would be enough to power your life for about 10 - 15 years
we have 3,000 tons in storage owned by the United States government that were isolated
during the Manhattan project and certainly at least 400,000 tons more of reserve
in the United States today so it's plentiful
going back to Eugene and Enrico - he asked a really logical question - how are you going to
prevent losses because protactinium-233 will gobble up your neutrons?
we're going to build a fluid filled reactor that's how
as a chemical instead he was used to dealing with everything in fluid form
when you use chemicals, when you use reactants, when you've got a solid you usually turn it
into a liquid - when you're done you turn it back into a solid but you do everything as a
liquid - when you do this in solid form you run into those problems of U232 and some others
but there's one - Xenon 135 is the biggest neutron poison was we know of
it just loves to eat neutrons it's like looking at Jupiter next to Pluto or something like that
I mean it is just huge
Eugene Wigner realized in liquid form that Xenon being a gas would just come right out
reactor operators would be happy to tell you of troubles they have battling Xenon in solid
fuel reactors it's a real pain in the tail
so off they went in different directions Fermi's group building the first liquid metal
fast breeder reactors and Wigner's group building an aqueous homogeneous reactor: uranium & water
it had a lot of advantages but it had one basic disadvantage
there was no aqueous form of Thorium you couldn't dissolve thorium into water
you could dissolved uranium into water but you couldn't do it with thorium
well they had this program to build an aircraft reactor
most of them thought it was pretty hokey they didn't think it was a good idea
in fact Alvin Weinberg who ran the lab said it wasn't like we all suddenly believed that
nuclear airplanes were a good idea
it was the only way we can build reactors a high temperature reactor could be useful
for other purposes even if it never propelled an airplane
boy that was super hard you can only imagine if you're flying a nuclear bomber over siberia
and you run the reactor too hard and the engineer comes back and says:
captain we're going to shut down for 9 hours because the Xenon is overriding our reactivity
control. i'll just put down on the snowfields of Siberia & wait for our Xenon to decay away
they learned quick they needed a reactor which did not have that problem
how are we going to do this? because we know this (light) water version isn't going to work
hey, what about a fluoride? salt!
salts are really chemically stable because they're so darn happy being what they are
they can go to really high temperatures and they don't have to have high pressure
this is birth of fluoride reactors: to ask can we dissolve uranium & thorium in salt?
yeah, you can. it's real easy in fact so they built the aircraft reactor experiment
this was the first liquid flouride reactor it ran for about 100 hours
at some of the highest temperatures ever achieved by nuclear reactor and what's
even cooler about it - it did it at atmospheric pressure. this wasn't some
high-pressure reactor, this was running in essentially ambient pressure
and they found that it was self controlling as the salt expanded, there was less fuel
in the core so reaction rate would slow down as the salt got cooler it got denser
there was more fuel in the core & the reaction rate would increase this reator just basically
ran itself as they would increase heat removal it would power up as they would decrease the
heat removal it would power down you didn't have to move
control rods around it was self controlling and it was chemically stable
you could have fission and it would still not screw up the fuel. fluoride fuel is the
only way to build a high-temperature high-power-density reactor. if you use solid
fuel you're going to be fighting your xenon
I love this quote
until then I had never quite appreciated the full significance to the breetdr but now I
became obsessed with the idea the humanity's whole future depended on the breeder
now when he says breeder he means the ability to burn up thorium
we tend to think of liquid metal breeders really that's what he's talking about
I understand that kind of passion because I feel the same way myself - indeed to have
sustainable industrial society on this planet it is going to be dependent on this technology
this is what the molten salt reactor experiment looked like it was a bunch of graphite fuel
elements in that tank and then they would flow the fluoride fuel through it
and they ran this reactor for about five years from 1965 to 1969
during that time they demonstrated a lot of the features that we would want ultimately in LFTR
online refueling, they did it. this is actually a capsule and they would load it up with new
fuel and they would just drop it in the reactor
fuels in the capsule would just dissolve away when they want to take out the uranium they
used fluorination they could remove all the uranium and they had this fantastic safety feature
called the "freeze plug" - because the fuel's so hot if you cool it down it will freeze
it will lock-up in the pipe so they had a little blower over a
flattened section of pipe and it kept part of the salt frozen right there in the pipe
if you lost all power to the reactor if you turned all the lights off, all the juice off, the freeze plug would melt
and your salt would drain out into a drain tank that was passively cooled
in most reactors you have to take the coolant to the reactor in an emergency situation
that makes them hard to build because you've got to have the regular core run and make power 99.99% of the time
but then in an emergency case, you've got to get emergency coolant in and override everything else designed for your normal operating times
this reactor was the complete opposite
you let the core do just what it was supposed to and if there was an emergency, it would send the fuel where it would be passively cooled
these guys, on Friday afternoon they'd go and turn off all the power
the salt plug would freeze everything would drain into the tanks it would freeze up over the weekend
they come back on Monday, they'd turn the heaters on, they pump it out of tanks back into the core
they did this over & over & over again a working example is worth stacks of documents people go, how do you know this will work?
well, they did it, this really worked they demonstrated most of the features that are pertinent to this reactor
well after doing that they really wanted to investigate how to build the real thing
they began to go through different design concepts this was about where they stopped on this design
the really appealing thing about this approach was they had this super simple fuel cycle
you would make the fuel you flourinate it out
you would introduce it to the core and burn it up when it was time to reprocess the core
you take at the fuel you distill off the good stuff and you're just left with fission products
that's a super simple closed nuclear fuel cycle
the real problem they had was with graphite it would contract, then it would swell under radiation
and they began to realize a lot of their plans for how they were going to build the reactor just weren't going to work
just because of tolerancing and how graphite is going to change the reactor had a plumbing problem
the plumbing problem has got to be understood and managed I think and that it can be I have some really good ideas on that
but the overall appeal of the two fuel reactor is still great and it really comes from that very, very simple fuel cycle
all right so what happened to this? the atomic energy commission was being run by a guy named Milton Shaw
he was a very driven to build a nickel metal fast breeder reactor
these were Weinberg's words, he said: "Woe be unto anyone who stood in his way, Milton was like a bull."
"He enjoyed congrassional confidence so his position in the AEC as unassailable."
"Tt was clear he had little confidence in me or in ORNL, after all, we were pushing Molten Salt, and not the fast breeder."
"Moreover that, we were being quite troublesome over the question of reactor safety." Admiral Rickover, and his program...
a gigantic organization including not only the Nautilus but the entire nuclear navy he did a very good job establishing safety
the Navy is excellent in that inherently is not found in the reactor it is found in the very strict rules,
the very well trained sailors that run these reactors Alvin Weinberg invented light water reactor
he holds the patent on that design which is so prevelant in the world today
he knew its capabilities and it's limitations he felt like this was a better approach
there was a congressman who ran the joint commission on atomic energy, Chet Holifield. and they were having a coversation
congressman Holifield became exasperated he said "Alvin, if you're so concerned about the safety of reactors..."
I think it may be time for you to leave nuclear energy
Alvin Weinberg got fired his opinions were at variance with those of the atomic energy commission congressional leadership
Alvin called nuclear energy a faustian bargain and became a promoter of moten salt breeders the program was canceled in 1974
a bunch of oak ridge guys did try to kind of keep the torch burning
probably into the eighties led met with some of the old-timers there's really almost nobody
there now who was involved in this the vast majority of them are dead there's no reason why any reasonable
sized country couldn't go and make this happen quite successfully with their national resources
it's a low fuel price, low capital cost, long life, low maintenance you've got homogeneous mixing
which means you don't have any hot spots which are a real concern in conventional reactors
one spot gets hotter and it continues get hotter until you have a meltdown
you get to burn up all the fuel because it is constantly moved around in the reactor and no fuel shutdown, you fuel this continuously
the cost of this whole system would be a significantly less than the existing nuclear power plants
we've got spent nuclear fuel accumulating from our nuclear reactors this is the amount of spent nuclear
fuel we have it's not going to be long before our rate of generation spent nuclear fuel is going to have Yucca pretty full
if we start building more light water reactors then we're going to hit those limits a lot sooner
our current approach to nuclear reprocessing is based on dissolving nuclear fuel
in nitric acid and it's a very complicated expensive process the first thing you do is take a solid and turn it into a liquid
and then once you turn it into a liquid you're trying to seperate all the piece parts all the components out
and at the end you try take this liquid and turn it back into a solid again now the French have really mastered this
I mean they have a facility at La Hague where they do this but it's a big facility they spent a lot of money to make this work
we know it's possible but it's difficult on the other hand reprocessing fuel in fluoride reactors is really simple
we just fluoridate the blanket we introduce it into the core so this is a complete nuclear fuel cycle
boiled down to just a handful of steps
this should scale up and scale down onto the back of a semi-trailer if you really want to use other processes
when it is mobile it can go to a site for shell oil extraction. it couples very well with desalination for water processes
hydrogen production as well because of the high temperature nature of the reactor core
what's the biggest obstacle? is it funding? is it political? one of the basic problems is this stuff
is completely different than what they do in the nuclear world today
a few weeks ago was of the American Nuclear Society Conference
I mean this is like the nexus of all of your best and brightest engineers in the field
nobody knows about this stuff I don't mean that in a disparaging way these are very smart people
I have almost finished my master's degree in nuclear engineering in that time I have
had one course that talked about breeding and during that course about ten minutes of the talk was about Thorium
and none of it mentioned fluoride reactors it is entirely possible to go to nuclear engineering school and get a PHD
and to never been exposed to any of this stuff
that when you do go get in the field and you learn how to run real reactors and solid core and control control rods
and feed water and all this other kind of stuff
it's like the difference between a typewriter and a word processor you get the same thing in the end
but what's under the hood is just utterly and completely different
so I think the real nuclear industry looks at this and they go "what are we gonna do with it?"
they'd be starting from scratch it's great for an entrepreneur it is rough for the legacy folks
the nuclear energy industry today makes all their money making fuel elements it's very expensive, it's very exacting
little zirconium cans with precisely measured oxides inside
this would make all the fuel kind of at the plant that revenue stream would go away
the incumbent players are not really interested in designing a reactor that cuts off their future revenue stream
a lot of times back in the sixties reactor vendors would sell reactors at a slight loss
in order to lock in a long-term fuel fabrication contract the razor blades approach
the whole cost structure around today's nuclear is really not amenable to this cheap simple easily processed fuel
we know that to tackle global warming we're going to have to go after #1 coal, then #2 transportation
between this and electric cars we can make a big difference
as an engineer I can look at this and go there are really tangible, easy to do, already been demonstrated steps
based on well understood chemistry that has been around a hundred years
we can go and do it and make this happen this isn't that hard
in conclusion this gives us options for inherently safe, proliferation resistant, economic nuclear power
that can last thousands if not millions of years this really could be
the silver bullet that enables us to power our industrial society. and this also offers real options for solving the long-term issues
surrounding our existing spent nuclear fuel and ultimately preventing the formation of new transuranic wastes
and finally I want to thank Google
I love gmail, I love your search engine and almost all the stuff I've done on this
has been thanks to Google and you didn't even charge me for it
you guys are awesome and thank you for having me today