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2019-06-06 10:05 by Karl Denninger
in Energy , 154 references
[Comments enabled]  

Meh.....

More than 50 U.S. companies are developing advanced reactor designs that will bring enhanced safety, efficiency and economics to the nuclear energy industry.

X-energy, located just outside the nation’s capital in Greenbelt, Maryland, is working on a pebble bed, high-temperature gas-cooled reactor that the company says can’t meltdown.

X-energy is developing its Xe-100 reactor and specialized uranium-based pebble fuel that could be available in the market as early as the late 2020s.

Who gives a ****?

Seriously, I mean it.

This design does have advantages -- don't get me wrong.  It's also not new.  The premise is that you construct fuel "pebbles" (about the size of a cueball, so more like "fuel rocks" rather than pebbles) that contain the fuel inside an allegedly "impervious" sphere.  The pebbles, being spherical, allow gas (Helium in this case) to pass between them, which takes the reaction heat away, and you use that to produce electricity through a traditional heat exchanger mechanism.  The moderator is graphite and in the reactor vessel; the fuel is cycled through from top to bottom, which means it is continually refueled in operation, with each fuel unit running for about three years.

Traditional water-cooled reactors use zirconium for the fuel rods.  Zirconium is "transparent" to neutrons; that is, it neither interrupts their passage nor does it get "activated" (absorbing them and becoming a radioactive isotope.)  This is good; you want what looks like a window to the sun for neutrons, because they have to get into the fuel in order to cause fission.

But zirconium has some problems.  Chief among them is thermal tolerance.  This is not a problem provided the reactor remains flooded with water, since water has a critical point of ~3200psi and ~705F.  Therefore you must keep the pressure below that and the temperature below it too, since water is also the moderator.  Above 705F it's steam no matter the pressure.  For this reason water-cooled reactors tend to run around ~1,000psi in normal operation for a BWR and ~2,200psi for a PWR.  BWRs are simpler in that as water boils it loses its moderation; this is a negative feedback on the power level and makes designing control systems, and their inherent safety, easier.

However in the event of loss of circulation (the ability to dump heat) or coolant (e.g. pipe break, etc) you have a severe problem because zirconium melts at ~3,300 F -- and once it does, you're screwed.  Silicon carbide, which is what the pellets in a pebble-bed reactor have their outer shell made of, doesn't melt until nearly 5,000F.  That's a huge safety factor.

But, there's a rub.  The "safety analysis" has run tests that postulate that in an accident the temperatures should not exceed 1,800C.  I note that this is below the melting point of zirconium, yet as we know in Fukushima and elsewhere, that temperature is indeed exceeded in bad situations.

There are also general issues with graphite moderators; they're manageable however, albeit at some cost.

So how safe is this thing?  Well, good question.  But in the end, it doesn't matter.

No fission design is safe end to end, which is all that matters, until and unless you have a closed fuel cycle.  The problem is that the burn-up in a TRISO fuel reactor -- that is, a pebble bed, while much better than a BWR or PWR (20% .vs. ~10%, roughly) still sucks in that 80% of what you put in there comes out and has to be reprocessed somewhere or discarded as high-level waste.

There is no reprocessing in the United States today, and hasn't been since Jimmy Carter shut it down.  Therefore any plant design that does not inherently separate and reprocess its own fuel as an inherent part of its operation is manifestly unsafe and unsuitable for deployment until and unless there is a viable reprocessing cycle available in the United States.

There is only one way to safely deal with most transuranics, which remain dangerous for tens or even hundreds of thousands of years.  You have to put them back into a reactor and burn them up.

Short-lived isotopes that reach a stable, non-radioactive element with half-lives in the range of single-digit years or less we can deal with.  After 10 half-lives basic mathematical theory tells us that the substance is no longer dangerous no matter how high-level of radiation it emitted originally.  But that's not something you can fudge; anything with half-lives in the tens, hundreds or thousands of years has to be returned to a reactor and reduced in this fashion until it reaches either a stable isotope or one with a half-life of less than 10 years.

Period.

Now there will always be a small amount of waste that isn't amenable to this, but if it's small enough in volume it never has to leave the plant until the plant is decommissioned.  What we cannot accept is a no-reprocessing paradigm, which is what we have now, where fuel comes out of these units full of hundred or thousand-year or more half-life highly-radioactive elements for which we have no rational disposal mechanism.  Without reprocessing we cannot put those elements back into a reactor and burn them up and we have nowhere we can safety put them either.

Nuclear power safety is not solely about meltdown safety, although pebble bed designs look promising in that regard.  In addition these designs have other challenges, one of them being that they use Helium as a coolant -- and Helium is a non-renewable gas that is in short supply and in addition it's a very small molecule so it leaks like crazy.  Helium, incidentally, is used as a coolant in these units for a number of reasons -- among them is that it is not easily activated (that is, it doesn't capture more neutrons easily) and when it does it decays extraordinarily quickly, so it doesn't form dangerous reaction products.  This means that if it's released (e.g. due to a pipe break) it won't hurt anyone as any activated isotopes will decay before it can get out of the building.  It also has a pretty good specific heat ratio; that is, it carries heat well as gases go (much better than air, for example), so it's a good choice for that reason as well.  Being inert it has no reactive issues with the various materials inside the reactor either, which is a big bonus.  And it has a very low neutron cross-section, so it doesn't interfere with the fission reaction itself.

Finally, due to the use of gas as a coolant and the much higher temperature tolerance of the fuel these units run at materially higher temperatures than a common PWR or BWR, which means they're materially more thermally-efficient.  It also means they can, at least theoretically, be run in places where large-volume water cooling is not available (e.g. inland, and not near oceans, fault lines or huge lakes) with reasonable overall efficiency.  That's a plus.

But on the downside our supply of Helium is basically all from natural gas wells, where it's a trace component of what comes out of the hole.  It's completely non-renewable and non-capturable, in that it is so light it effectively disappears into the upper atmosphere when released.  For this reason consumption of it is a serious long-term problem since our ability to get more of it is inherently tied to natural gas production.

Nonetheless the big problem with all of these types of reactor designs remain -- there is no sane means of dealing with the waste products out of these units.  Of the fission designs currently known and on the board there is only one that is amenable to continual, on-site reprocessing that burns up basically all of the high-level reaction products as part of its normal operation.

That's the LFTR, which uses Thorium as its fuel, is started on Uranium (since Thorium is fertile and not directly fissile) and since the fuel is dissolved in the working fluid it can be reprocessed chemically online in the plant itself, thereby allowing on-site burn-up of most of the high-level reaction products.

Oh, and it is also passively safe since are no fuel pellets or rods that can overheat, crack and release the material inside, and we know that passive safety system works because it was run for several years at Oak Ridge in the 1960s and when the scientists went home for the night they literally just turned the power off to the systems and walked away.

I wrote an article on a viable hydrocarbon replacement strategy here, and also covered it extensively in my book Leverage in Chapter 10.  It's as valid today as it was then; go read it.

The LFTR was abandoned, incidentally, because being Thorium fuel-cycle based it is almost entirely unsuitable for the production of nuclear bombs -- and we wanted dual-use nuclear technology.

Go figure.

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Ok, if you've listened to Pickens and the Ratigan show, you know that they seem to think that we can fix things with natural gas and perhaps with some renewables.

That will never work.  Nor will drilling here - we can replace some of our demand, but not all of it.  Further, the amount of oil we have is finite.

Indeed, all of the various energy resources are finite.  Even The Sun is finite.  It will eventually run out of fuel and "die."  It just won't happen for a very, very long time.

We have about ten years of natural gas supplies in proved reserves at present rates of consumption.  But "growth" is a nasty thing; it's a compound function, and I discuss this often - compound functions cause trouble, and usually quickly.

Pickens wants to move trucks (at minimum) to natural gas.  Nice sentiment.  But he's talking his book and pushing something that, if we double our consumption - and if we replaced gasoline and diesel we would - the "solution" would only last five years, make him filthy rich, and still leave us screwed.

There has to be a better way.  We need a solution that will last at least a hundred years.

What if I told you that there is one?

It's coal.

But not how you think of coal.

We think of coal as going into a power plant that makes electricity.  But that's wasteful, believe it or not.

Here's the math on gasoline, diesel and coal.

1 lb of gasoline contains about 2.2 x 10^7 Joules of energy.
1 lb of coal contains about 1.1 x 10^7 Joules of energy.

These are reasonably-comparable; another way to look at this is that you need about 200% of coal (in pounds) as you do in gasoline for the same energy content.

Edit: Numbers vary on coal depending on type.  Changed to reflect the most-pessimistic reasonable observed number - 4/1 1:44 pm

We currently consume 378 million gallons of gasoline a day.  At 6lbs/gallon (approximately) this is 2,268 million pounds.  Reduced to short tons (2,000 lbs) this is 1.134 million short tons of gasoline/day, or 414 million short tons a year.  Converted to coal, this is 828 short tons.

The most-current value I can find for distillate (diesel fuel) is 3.794 million barrels a day.  At 42 gallons to the barrel, this is 159 million gallons of diesel fuel.  Diesel contains about 20% more BTUs per gallon than gasoline, but is about 17% heavier at 7lbs/gallon, so if we convert simply based on weight we get close.  So we have 1,113 million pounds of diesel daily; reduced to short tons that's 0.557 million short tons of diesel daily, or 203 million short tons a year.  Converted to coal, this is 406 million short tons.

Add these two and we get 1,234 million short tons a year of coal equivalent.

Why is this important?

Because according to the EIA, again, we consume about 1,073 million short tons of coal a year, virtually all of it being burned to produce electrical power.

How much coal do we have?  According to the EIA the total reserve base - the reasonable commercially recoverable coal, is about 489 billion short tons.  That's roughly four hundred years worth of supply at current rates of use.  If we assume our population will grow at about 1% a year and per-capita energy use remains roughly constant, we should have enough coal to last at least 200 years.

Now stay with me a minute.

Remember, we consume about that amount in coal-equivalent between both gasoline and diesel.

Consider this: There is 13 times as much energy in coal in the form of Thorium as there is available by burning the coal, and right now we literally throw it away in the ash pile!

What is Thorium?  It's a fertile material.  That means that when struck by a neutron in a reactor it transmutes via a nuclear process to an element that is capable of fission.  Note that Thorium itself is not fissionable - that is, it will not (directly) split and release energy.  Instead it captures thermal neutrons and turns into Uranium-233.  U-233 is fissile.

There is a type of nuclear reactor that utilizes this fuel cycle.  Instead of the traditional nuclear reactor which uses water as a moderator and coolant (either a boiling or pressurized water reactor) these reactors use a liquid salt.  In the vernacular they're called "LFTR"s, pronounced "Lifter." 

You've probably never heard of them.  But they're not pie in the sky dreams.  Our nation ran one for nearly four years in the 1960s at the Oak Ridge National Laboratory.  It was scrapped in favor of the traditional uranium fuel cycle we use today because the fuel it produces is very difficult to exploit for nuclear weapons, and it breeds fuel at a slow rate.  The natural process of the nuclear reactions in the core of such a unit produces a byproduct that is a very strong gamma emitter that is difficult to separate from the other reaction products.  For this reason - and because we wanted both nuclear power and nuclear weapons - we built the infrastructure for uranium and plutonium rather than thorium.

Thorium-based reactors have several significant advantages and a few disadvantages.  We have much less experience with LFTRs than traditional nuclear power, simply because we stopped working with them for political and war-fighting reasons.  They use a fluoride salt which is quite reactive when in contact with water, but the reactivity is a bonus in all other respects, because it tends to encapsulate the reaction products (the nasty fission products that you don't want in the environment) through that same chemical process.  It runs at a much higher temperature (typically 650C) than a traditional reactor and unlike a traditional reactor the fuel and the working fluid is the same - there are no fuel rods that can melt and release their nasty fission product elements, as the fuel is dispersed in the coolant.

Finally, the unit is intrinsically safe.  It does not require high pressure; the working fluid and coolant is a liquid at ordinary atmospheric pressure.  This gets rid of the need for high-pressure pumps, pipes and similar materials.  Without the moderator the reactivity is insufficient to sustain a chain reaction, and the moderator is in the reactor vessel itself through which the fuel/coolant is pumped, so criticality is impossible outside of the reactor vessel and inside the vessel the fuel and coolant are the same, and a liquid.  The working fluid is contained in the reactor loop by an actively-cooled plug.  If power is lost cooling ceases and the plug melts; the working fluid then drains into tanks by gravity under the reactor and cools into a solid, as it cannot maintain criticality outside of the reactor itself (there's no moderator in the tank or the plumbing.)  As the fuel is in the fluid, there is no core to melt as occurred in Japan and being dispersed over a much larger area the working fluid naturally cools from liquid to solid without forced pumping and cooling.  This safety feature was regularly tested in the unit at Oak Ridge - they literally turned off the power on the weekends and simply went home!

There are some downsides.  The working fluid requires special metals made out of Hastelloy.  But these are no longer particularly-special materials, being used in other chemical plants where highly-corrosive material is commonly handled.  They are expensive, but then again so are traditional reactor pressure vessels which require high-pressure integrity and thus special welding and inspection techniques.

Why did I just spend all this time talking about LFTRs?

Let's remember two facts from up above:

  • There is 13 times as much energy in coal in the form of Thorium as there is available by burning the coal.

    and

  • We use 1,234 million short tons a year of coal equivalent in gasoline and diesel fuel which is approximately - within 20% - of the amount of coal we burn now.

One final piece of information: The Germans figured out how to turn coal into synfuel - gasoline and diesel - before WWII.  This process, called Fischer-Tropsch, requires energy to drive it and is currently in commercial use in some places that have a lot of coal but little or no oil, such as South Africa.  Malaysia also has an operating plant.  Typical operating temperatures for this process are in the neighborhood of ~350C.

This light bulb should be coming on about now: We can replace our gasoline and diesel consumption, plus replace the coal-fired plant electrical generation, and have lots of energy left over - all while completely eliminating the requirement for foreign petroleum from anyone!

Now let's put the pieces together.

We'll start with the same amount of coal we burn today.

We have the fuel energy in the coal, and we have 13x that much energy which we are going to extract from it in the form of the thorium naturally contained in the coal.

Let us assume we consume twice the fuel content of the coal extracting the thorium.  We have 11x the original energy left (once in combustion of the coal, and 10x in thorium energy content.)

We will then use the Fischer-Tropsch process to turn the coal into synfuel - gasoline and diesel.  We will be rather piggish about efficiency (that is, presume we're not efficient at all) and assume we put in twice as much energy as the coal contains in fuel content converting it.  Since the process heat from the reactor is of higher quality (higher temperature) than the Fischer-Tropsch reaction requires by a good margin, we can do so directly without first converting to electricity (which would introduce more losses.)

We now have all of our gasoline and diesel fuel, and we also have 8x the original BTU content of the coal left in thorium energy content.

We will then use the remainder to generate electricity.

So what do we have out of this?

A nuclear and physical technology that:

  • Replaces all of our gasoline and diesel fuel requirements.  This ends our foreign oil imports.  It also allows us to remove all foreign military activity related to securing that foreign oil.  It is essentially a lock that we can drop $200 billion a year off our military budget this way, and it's not unreasonable to expect that we might be able to cut the DOD in half.  Over 20 years this is at least $4 trillion in budget savings, and might be as much as double that.  Those funds should do nicely to build the plants involved.

  • Continues to use liquid hydrocarbons for light and moderate transport needs.  Sorry folks, there's nothing better.  I wish there was too.  There isn't.  Some day there might be, but that day is not today.  The problems with the alternatives are all found in thermodynamics as a consequence of energy density and those are laws, not suggestions.  The energy and money required to produce a plug-in vehicle or hybrid is, for most users, greater than the incremental cost of the fuel over the entire lifetime of the car.  Hybrid and all-electric vehicles make no sense unless you have no rational way to produce the liquid hydrocarbons.  We do have the ability using the above.

  • Reduces our carbon emissions by the amount of the former oil imports that were burned.  We still burn the gasoline and diesel, but that's in the form of the converted coal.  Since we're only using half the hydrocarbons we used before between coal and oil, our CO2 emissions go down by the amount of the formerly-burned petroleum.  I'm not an adherent of the global warming religion but if you are you have to love this plan for that reason alone.

  • Provides us dramatically more electrical power than we have now, and more-efficiently on a thermal-cycle basis.  Conventional nuclear power uses Rankine-cycle turbines.  This is one reason why they need access to large amounts of water.  Due to the higher temperature of operation these reactors can run combined-cycle generating turbines, which makes practical siting them in places where they are air-cooled yet they can still achieve reasonable thermal efficiency.

  • Is sustainable for two full centuries, even assuming our historical 1% population growth rate and no decrease in per-capita energy use.  Within 200 years we should be able to get fusion figured out.  200 years is a long time for technology to advance.  This much is absolutely certain: There is no other option that is reasonably feasible with today's technology and which has an exhaustion horizon of more than 100 years available at the present time, allowing for our historical population growth and no dramatic reductions in per-capita energy consumption.

  • Is not subject to the same constraints and risks that exist for today's reactors, even though this has nuclear power at its core.  The accident in Japan, for example, cannot occur with these units because they do not require active cooling after being shut down to remain safe.  The working fluid also tends to bind any reaction products, which inhibits the spread of any material if there is a pipe break or other release into the environment.

  • Produces much less high-level nuclear waste than conventional reactors.  Most waste is burned up in the reactor via continual reprocessing on-site.  The final waste product produced is a tiny fraction in volume of that from conventional plants.  It is not zero to be sure, but these units present a much-smaller waste profile than do traditional uranium/plutonium cycle nuclear plants.

The biggest disadvantage is that we've only built one of these reactors, at Oak Ridge, and then we stopped because a decision was made to pursue "conventional" plants due to their dual-use capability.  But the challenges presented by LFTR technology are known, and the ability to build and operate such a plant is not "pie in the sky"; we've performed all of the necessary technical parts of assembling this alternative individually and ran one of these reactors for four years.

Are their engineering challenges in this path?  Yes.  Is it "free energy"?  No.

Can this be made to work given what we know now, at a reasonably-competitive price?  YES.

If you're going to propose something else then show me the math. If you can't, then get on board, because this is the bus that will work.

Incidentally, China and India appear to have figured this out as well; I'm not the only one with a brain.

We had better lead on this or we're going to get trampled.

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