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November 05, 2006

Comments

MCrab

Cue drx with more nuclear hysteria.

Followed by Kirk, pointing out that a molten salt reactor fueled with thorium would be a far better project for that DOE money.

I'm with Kirk. :)

amazingdrx

Completion by 2021? That fits my compromise to a T. No reason to rant on this one, hehey.

They are only wasting 8 million so far. No problem. But you know they will waste 80 billion by 2021 given the chance.

Does this one recycle waste? Of course not. Nuclear advocates and boardroom and lobbyist residents are obviously not even reading from the same book, much less the same page.

Let Kirk, Udo , and atomic rod rant against their own.

Kirk Sorensen

The reactor uses a thermal neutron spectrum and a once-through uranium cycle.

In that case, it will consume very little of the energy available in its fuel.

The VHTR is gas cooled and operates at extremely high temperatures, with operational fuel temperatures above 1250°C (2300°F).

But what is the coolant temperature? (since that's what really matters in the thermochemical generation of hydrogen). The Aircraft Reactor Experiment (the first liquid-fluoride reactor) achieved a fuel temperature of 860 C back in 1954. Achieving these kind of temperatures will require fuel with thermal stability and conductivity way beyond what we've got today.

Brian Wang

drx,

Do you debate online for only the purpose of having a debate ?

The fact that there are ideas, timelines energy projects that are not going to help with current pressing problems does not help anyone. The fact that current energy demands are met primarily with coal and will continue to be met by coal is bad news for everyone. Even coal companies and their shareholders do not really benefit. They get some money in the near term but they live here too. They are not immune to the environment and health effects.

We will be lucky to see solar and wind contributing 10% of our power by 2021. 70+% will probably still by coal and oil. Where is your rant. Where is your action to support solutions to chip away faster at that problem? It looks like you are pushing for projects that will make up less than 1% of the answer.

Udo Stenzel

Kirk, a coolant temperature in excess of 1000°C should be well in range. Graphite based fuel elements are certainly capable of this -- those in the German AVR and THTR certainly were. I'd be surprised if a molten salt reactor could sustain operation at this temperature with currently known strutural materials.

How a VHTR is supposed to recycle used fuel is beyond me. Probably marketing speak for "we can run it on plutonium, too", which would be true, but it would neither breed nor eat LWR waste without prior reenrichment. Breeding in a Th/U cycle should be possible, though.

Btw, drx, this isn't about hydrogen as fuel for cars. Most hydrogen that is currently produced is immediately consumed again. The chemical industry needs lots of it for oil upgrading and all sorts of synthesis processes. Electric cars are no alternative there. Also, hydrogen production works with current nuclear power, too. It's just not nearly as efficient.

amazingdrx

Well Brian, you caught me. I'm really hoping the 10 to 20 year delay to prove nuclear power safe and cost effective and able to neutralize it's own waste is a long enough time period for renewables to win.

Thus my compromise proposal.

Wind is already proven safe and cost effective. And that old saw..."We will be lucky to see solar and wind contributing 10% of our power by 2021'..that since renewables are a small part of the energy market now, they can't expand quickly. Well that's pure bunk.

The same kind of bunk that buggy whip manufacturers used to appease their shareholders at the advent of the horseless carriage. only 1% of people use horselerss carriages, therefore buggy whip sales will continue to be strong well into the second half of the 20th century!

Invest in nuclear and fossil power now!! renewables are only a tiny portion of the market.

In the case of nuclear it is like the buggy whippers figured they could maybe build carriages the horse ride inside of on treadmills to power them, in order to keep buggy whip sales going.

Nuclear fuel, fossil fuel. It's still fuel, with plenty of deadly dangerous pollution, climate disaster producing greenhouse gases, and toxic waste.

Abandon your buggy whips, get onto the renwable power bandwagon, the "horseless carriage" of this energy re-evolution.

Nucbuddy

Amazingdrx writes: renewables are only a tiny portion of the market.

Wind and solar do not represent any portion of the energy market.

"windpower is yet another energy sink requiring more energy to develop and maintain a site and to deliver its energy than the energy derived from it."

Dezakin

VHTR is another dead end technology if its using solid fuels. Fluid fuel reactors can achieve temperatures of 1000C with far better neutron economies, passive safety, and 100 times better fuel utilization.

Brian M.

drx,

Interesting analogy (albeit a little overused and rather cliché). I would say, however, that a more relevant analogy than your "buggy whip" story is the following. To me the assertions of those advocating spending time and money on developing and building wind farms are about as ridiculous as someone in the eighteenth or nineteenth century arguing that steam engines should not be developed for industry, rather the world should instead make more efficient water wheels. In fact, the wind farm arguments are even more ridiculous than that, because we have the advantage of hindsight.

The truth about wind farms is

(1) They consume huge amounts of land -- something to consider if your are a conservationist.

(2) They consume very large amounts of resources to build. For example, to build the equivalent amount of electrical generation capacity (not production; if you want to take capacity factors into account then multiply these estimates for the wind farm by about three) as the 1600 MW reactor that is currently being built in Finland, a wind farm with the latest large "efficient" turbines would require about 30% more reinforced concrete than what is going into the nuclear plant. I don't care to speculate on the amount of land that would be required.

(3) They are not economical. Wind generation only begins to become (barely) cost effective if one includes the production tax credits being offered in the US. Without that (and various mandates for renewables passed by state governments), they are a bust and nobody would invest in them. And by the way, does this cost analysis for the wind farm include the cost of decommissioning and the disposal of all of that concrete? My guess is no.

As for safe? Well, I guess so, as long as you are not a bird.

Let's face it, wind has had it's day. Just as modern navies no longer use wind power, why should the rest of us?

As for the relative merits of a gas-cooled reactor versus a molten-salt-cooled reactor, there is plenty of room for debate, but in the end it comes down to the size of the plant that you want to build. The molten-salt reactor is going to be larger; it has to be. If you consider the production of hydrogen to be important, however -- which is one of the main advantages being put forth these days for high temperature reactors -- then it is conceivable that a large number of smaller plants, more widely dispersed for better distribution of the final product (whether for hydrogen-fueled vehicles, for chemical plants, or for refineries), might be a better option, and I think that this is part of the DOE's thinking when looking into the gas-cooled route for now.

Also, keep in mind that, although the DOE is currently looking at a uranium-fueled design, the only commercial high-temperature gas-cooled reactor ever built in the US used a uranium-thorium fuel cycle. Certainly, it can be done, and there is already experience with thorium for these designs, both in the US and in Germany.

Kirk Sorensen

As for the relative merits of a gas-cooled reactor versus a molten-salt-cooled reactor, there is plenty of room for debate, but in the end it comes down to the size of the plant that you want to build. The molten-salt reactor is going to be larger; it has to be.

I'm not sure where you get that, since the gas-cooled reactor has to operate at very high pressure and low core power density, whereas the molten-salt reactor operates at ambient pressure and can have a high core power density. The molten-salt reactor should be much smaller AND lighter than a gas-cooled reactor of the same power rating.

Have you ever seen a cross-sectional view of the prestressed concrete vessel for gas-cooled reactors like Fort St. Vrain? Baby they're big.

Dezakin

On the issue of reactor size, fluid fuel reactors are scalable small. The prototype for the airborne nuclear reactor program was a liquid flouride reactor because of the ambient pressure and high power densities. The ORNL prototype was in the 8MW range.

But even if they were only built big, how is that a hinderance for hydrogen production. In hydrogen production you want as big of a reactor as you can get to realize economies of scale, and you arent limited to grid intertie connections as traditional nuclear power plants.

Udo Stenzel

Wind is already proven [...] cost effective.

Care to explain why Germany is massively subsidizing wind power then?

Jim Hopf

.

Jim Hopf

The long timescale for the plant is indeed frustrating. The time it takes DOE to get anything done, be it the VHTR or Yucca Mtn. seems inexplicable. The reactor is definitely worthwhile though.

The reactor's outlet temperature will be ~1000 C, enough to generate hydrogen at a thermal efficiency of ~55% to 60%; much higher than converting the heat to electricity and then using electrolysis.

It's true that the spent HTGR fuel would be hard to reprocess. It may be possible to reprocess LWR fuel and then feed the resulting mixed-oxide (MOX) fuel into the HTGR for a single, second cycle. Then you would bury the HTGR fuel.

This issue is not much of a problem, however. The HTGR fuel form is much better at containing radionuclides over very long time periods than Zircaloy-clad fuel, with containment over millions of years being realtively easy to demonstrate. The harder HTGR spectrum will reduce the quantity of long-lived actindes anyway, and they will then be much more easily contained.

Long-term uranium supply is simply not an issue. The amount of fuel available before ore prices would significantly impact the cost of power are more than enough to last for hundreds of years, even under very high growth assumptions. We will have breeders, or fusion, long before then. Thus, a electricicy/hydrogen producing reactor that uses a once-through or semi-once-through cycle is just fine.

One more thing, the reason why one shouldn't expect that renewables will be able to do it all in the near future (making other alternatives like nuclear unnecessary) is not simply because it generates a tiny (< 1%) fraction of generation now. It's because there are real reasons why its contributions will be limited in the future. The primary reason is intermittantcy, but persistent, high costs are also a factor for many renewables other than wind (e.g., solar). Even the American Wind Association says that the most wind will be able to provide (optimistically) by 2020 is ~6% of all generation. Solar will be far less.

It's also unfair to describe nuclear as a polluting energy source. Nuclear has always been held to impeccible standards. Nuclear is required to emit no pollution during operation, and to also demonstrate that it's waste stream will never do so at any time in the future. The only environmnental impacts are from mining and perhaps hot water release, both very minor in the grand scheme of things (i.e., compared to global warming and ~25,000 deaths from fossil plant emissions every year in the US alone). Nuclear has never had any measurable impact on public health (i.e., has killed noone) and emits negligible CO2.

BTW, I agree with the author completely on how the real answer will be plug-in hybrids (or pure electrics) along with baseload power from LWRs or renewable sources. This is true, at least over the short-to-mid term, especially given the depressing schedule. Of course, any such H2 will be used (at refineries, etc..) to make liquid fuels, and not used directly in some fuel cell car....

Udo Stenzel

Brian says:

if you want to take capacity factors into account then multiply these estimates for the wind farm by about three

Make that six (average availability of the German wind farms in 2005 was 16%) or even ten (average availability of Californian wind farms last summer).

I'd love to see Storm van Leeuwen and Smith do a life cycle analysis for wind farms based on that amount of concrete. Should be good for a chuckle.

Kirk Sorensen

Jim, there's a number of reasons why the abundance of uranium and thorium should not be taken as an excuse to waste them, but the most compelling (in my opinion) is the need to reduce the volume of high-level waste and eliminate the production of long-lived transuranic isotopes.

If the Democrats take the Senate and Harry Reid becomes majority leader, Yucca Mountain will probably be toast and the US will have to get serious about a closed nuclear fuel cycle much more quickly. Thorium and the liquid-fluoride reactor offer the faster, safest, and simplest path to achieving that goal.

The fluoride reactors can completely burn thorium, have sufficient temperature to produce hydrogen, can produce electricity at 50% efficiency (with a helium gas turbine) and will be smaller, lighter, and more power-dense than gas-cooled reactors.

Jim Hopf

Kirk,

While conserving even abundant natural resources is always a good idea, conserving uranium is a far lower priority for me than making sure nuclear plants are built in the future as opposed to coal plants, given that they cause ~25,000 premature deaths every year in the US alone, and are the leading single cause of CO2 emissions (whereas nuclear has never had any significant public health or environmental effect). We can't afford to "wait" for these ideal reactors while Rome (coal) burns.

If Yucca Mtn. is "toast" as you say, the (political) effect will be a lot less nukes, and a lot more coal in the near to mid future. This will be a tragedy for our nation for many reasons (global warming, air pollution, increased energy dependence (gas), higher cost energy and worse balance of trade).

Keep in mind that no matter what type of reactor we choose, or whether we reprocess or not, Yucca Mtn. will still be necessary to thake the fission product waste, if nothing else. The main benefit of reprocessing is that it will allow us to get by with only one repository, even if nuclear grows alot. I do believe that we will eventually reprocess. I would even describe it as necessary. I just don't believe that we need to rush and start reprocessing in the near future. Additional repositories can be avoided even if we wait until ~2050 to start reprocessing. In the shorter term, it is imperative that Yucca go forward.

Anyway, this whole discussion was about reprocessing HTGR fuel. I still don't believe the reprocessing problems are enough to justify abandoning a reactor will so many positive features, such as high thermal efficiency, process heat and H2 applications, and inherent safety. How many of these other reactor designs can survive a complete loss of their (liquid) coolant w/o any consequences?

Interestingly, whereas unreprocessed HTGR fuel would have a higher heat generation rate and would thus raise the repository temperature, the HTGR fuel itself would easily be able to withstand those higher temperatures. The problem would be that the hot HTGR fuel could affect the spent LWR fuel buried next to it. Perhaps we could give HTGR fuel its own drift (repository section), or even have one additional repository specifically for HTGR fuel. Of course, if we only buried reprocessed (vitrified) LWR spent fuel along with HTGR fuel, I'm sure we can design an HLW waste form that could take the heat.

Brian M.

Kirk Sorensenon wrote:

"... the gas-cooled reactor has to operate at very high pressure and low core power density, whereas the molten-salt reactor operates at ambient pressure and can have a high core power density. The molten-salt reactor should be much smaller AND lighter than a gas-cooled reactor of the same power rating.

"Have you ever seen a cross-sectional view of the prestressed concrete vessel for gas-cooled reactors like Fort St. Vrain? Baby they're big."

Not physical size. I'm talking economics. I'm talking about the difference between a 1000 MWe molten-salt reactor (that's the reference size for the Gen. IV concept) versus a <300 MWe modular high-temperature gas-cooled reactor.

G. R. L. Cowan, boron combustion fan

I think we need 10000, 50000, 200000-MW reactors -- oil-refinery-sized or larger, since it is oil they'll be replacing. The idea of turning their heat output into electricity or hydrogen, things that are very difficult to store, has traditionally prevented people from seeing the advantages of much larger scale, but if some people retain that tunnel vision and others do not, the end result is just as if no-one had.

Liquid lead cooling is interesting.

Kirk Sorensen

Not physical size. I'm talking economics. I'm talking about the difference between a 1000 MWe molten-salt reactor (that's the reference size for the Gen. IV concept) versus a <300 MWe modular high-temperature gas-cooled reactor.

There's no reason you can't build a 300 MWe (or smaller) fluoride reactor. The technology scales exceptionally well. The reason that the MHTGR is confined to 300 MWe or less is because of the passive cooling scheme they employ for a loss-of-coolant accident...any bigger and that passive cooling trick is less and less effective. The passive cooling technique used for fluid-fuel reactors, of any size, is a core drain into a non-critical, passively-cooled configuration. That scales to any size.

How many of these other reactor designs can survive a complete loss of their (liquid) coolant w/o any consequences?

Liquid-fluoride reactors can survive horrible accidents (loss-of-coolant, breach of containment, intentional sabotage) with no adverse consequences to the public. Read "Safety Options Galore" on my blog. Furthermore, these safety features scale with the reactor size, unlike the passive safety features of the MHTGR.

Kirk Sorensen

Keep in mind that no matter what type of reactor we choose, or whether we reprocess or not, Yucca Mtn. will still be necessary to thake the fission product waste, if nothing else.

We need a repository, but not a Yucca Mountain. Yucca is designed for 10,000 year isolation, which is driven by the long-lived transuranics in the waste. We need nuclear plants that produce no long-lived transuranics--unfortunately that eliminates all of our thermal-spectrum uranium-fueled reactors today.

But fluid-fueled thorium reactors can be operated in ways that produce no long-lived transuranics in the waste stream. You'll still need a repository, but it won't have to be certified for 10,000 yrs like Yucca Mountain. A few hundred years of monitored storage will be just fine if all you've made is fission products. And we have zillions of salt mines that could fit the bill for that.

G. R. L. Cowan, boron combustion fan

Is the absence of long-lived transuranics enough to make monitoring unnecessary after a few hundred years, Mr. Sorensen, or would all manmade alpha-emitting isotopes with lifetimes of a century or more have to be absent too?

(The truthful answers are yes, no, and monitoring is unnecessary much earlier than that, for any fission plant waste. It looks as if Sorensen is counting on petrolist cant about nuclear waste to remain strong, but not too strong.)

Brian M.

Kirk Sorensen wrote:

"There's no reason you can't build a 300 MWe (or smaller) fluoride reactor. The technology scales exceptionally well."

The technology might scale exceptionally well, but what about the economics? You might have the perfect design for the perfect reactor, which scales to whatever size, but if it's too expensive to build -- guess what? -- nobody is going to build it.

I'm sorry, but unless you are able to provide believable, reasonably detailed (at least, beyond hand waving) cost analyses to demonstrate that the economics of the thing works out, I'm not going to take you but so seriously. A reactor that looks great on paper is just that -- a paper reactor. But some paper reactors are closer to reality than others. Reactor designs that are somewhat similar to previous commercial plants and designs that have test reactors already built and currently running score points. If you have to go all the way back to the 1950's to cite examples of your design's capabilities, you lose points.

You are quick to point out the advantages of your favorite design, but you tend to skip over the challenges, or perhaps you do not think that developing and qualifying materials to operate in a corrosive, high-temperature environment while being exposed to radiation is a challenge. Sure, it can be done, but at what cost?

Look, I'll admit that molten-salt reactors have some really cool features. They might be the future of nuclear power. However, keep in mind that a good part of this thread has consisted of complaints that the new reactor designs are not available quick enough. Sure, HTGR's are not perfect -- they have their limitations and shortcomings -- but at least they are something that has the possibility to be designed, sold, and built for commercial operation sometime in the near future (~30 years). No matter how perfect they are, you can't say that about liquid-fluoride reactors.

Kirk Sorensen

You are quick to point out the advantages of your favorite design, but you tend to skip over the challenges, or perhaps you do not think that developing and qualifying materials to operate in a corrosive, high-temperature environment while being exposed to radiation is a challenge. Sure, it can be done, but at what cost?

The corrosiveness canard is one that seems to come up a lot with respect to the fluoride reactor. I can't speak for every salt composition, and I can't speak for every container material, but when it comes to LiF-BeF2-UF4-ThF4 salt and Hastelloy-N, the ORNL folks put this issue to bed in the 70s, through extensive testing and experimentation:

ORNL-TM-5783: Compatibility Studies of Potential Molten-Salt Breeder Reactor Materials in Molten Fluoride Salts

ORNL-TM-5920: Status of Materials Development for Molten-Salt-Reactors

ORNL-TM-4286: Alloy Compatibility with LiF-BeF2 Salts containing ThF4 and UF4

I apologize for linking you to 30-year-old documents, but active research on this reactor ended in 1976 in the US. But physics is physics, and engineering is engineering. If it's done well, it's still right.

Brian M.

Kirk Sorensen wrote:

"I apologize for linking you to 30-year-old documents, but active research on this reactor ended in 1976 in the US. But physics is physics, and engineering is engineering. If it's done well, it's still right."

I agree, and I think that molten-salt reactors have a lot of potential. It is a shame that not more research is being done to further the various designs. Nevertheless, there is a long road from basic research and a reactor concept to an actual commercial plant. The stepping stones to getting there are seeing that new plants are built and working now and that new designs are brought to market sooner, rather than later. Let's hope in the future and work hard to make this happen.

Dezakin
Keep in mind that no matter what type of reactor we choose, or whether we reprocess or not, Yucca Mtn. will still be necessary to thake the fission product waste, if nothing else.

No, we wont. With fluoride salt distilation, you separate the fission products out into a molten salt bath that is very suitable for high temperature chemical separation. Fully 20% of the fission products are stable xenon isotopes that have immediate market value. Most of the platinum group metals have short half lives and high market value in industry. The zirconium is blessedly free of hafnium and very valuable for nuclear applications, and the technetium has all kinds of industrial/nuclear applications in catalysts and corrosion resistance. The Cs-137 is valuable for food irradiation, and the Sr-90 is valuable for nuclear batteries of all sorts. Its unlikely we would need any offsite repository; Onsite storage of several tens of kg per GW/year is very reasonable.

I'm sorry, but unless you are able to provide believable, reasonably detailed (at least, beyond hand waving) cost analyses to demonstrate that the economics of the thing works out, I'm not going to take you but so seriously.
The cost estimates have allready been done and indicate that liquid flouride reactors based on the ORNL design are significantly less expensive than light water reactors, and in many cases even coal.

https://www.ans.org/pubs/journals/nt/va-138-1-93-95

HTGR's are not perfect -- they have their limitations and shortcomings -- but at least they are something that has the possibility to be designed, sold, and built for commercial operation sometime in the near future (~30 years). No matter how perfect they are, you can't say that about liquid-fluoride reactors.
All the basic research on fluoride has been done. A company with industrial commitment to a fluoride reactor could very conceivably design and build a power plant in a decade and then build hundreds more five years later.

If you want nuclear power today then theres a family of reactors for you now called the LWR or CANDU.

Kirk Sorensen

Very good points, Dez. Considering how quickly most fission product isotopes achieve stability, and the relative ease that distillation can be used for chemical separations, this could be a very valuable side stream of income.

Brian M.

Dezakin wrote:

"The cost estimates have already been done and indicate that liquid fluoride reactors based on the ORNL design are significantly less expensive than light water reactors, and in many cases even coal ..."

Okay, I guess I should have been more clear. While I was not necessarily quoted out of context, I suppose that the quote that you have included does not go quite with the intent I was trying to make. I was primarily following up on the claim that molten salt reactors could be built at any size. I had meant to say that I wanted reasonable estimates of the costs of a plant at the smaller sizes that we were referring to.

Sure, I wouldn't doubt that if you made the plant the ideal size (which I suspect is larger than the <300 MWe plant that we were talking about) then the economics work out much better and make the design competitive. Still, I notice that the study that you cite compares the (understandably old) molten salt reactor technology to equally old PWR and coal technology from the 70's and earlier. I suppose that that's fair, but yet it begs the question: what about modern technology? Does the MSR still compare well, and if not, how much is required for it to catch up?

"All the basic research on fluoride has been done. A company with industrial commitment to a fluoride reactor could very conceivably design and build a power plant in a decade and then build hundreds more five years later."

But what company has such an industrial commitment? As I have mentioned before, there is a long road from "basic research" to an actual commercial operating plant. What company out there is willing to take the risk to work toward an actual working commercial product? I'm sure that there are companies that would be willing to study the concept on the government's nickel, but does that get you to a design that will actually be sold and built? I'm skeptical.

Besides, assuming that one can design a reactor in a decade and plan to build them five years later, a company hoping to sell this product would still need to license the design. So add (substantial) additional years for that. As someone who has seen the new plants process from the inside, I can say that it is not as simple as you make out.

The work that has been done on and the experience with gas-cooled reactors is an order of magnitude more than what is available for molten salt reactors, and it is going to be challenging enough to get one of the HTGR's built.

I just don't understand this silly hostility towards the HTGR, except as the classic ubergeek engineer's "my design is better than your design" type of contest. Okay, if that makes you happy, then go for it. As for me, I would like to see as many LWR's and HWR's built today as we can possibly build. After that, I would like to see HTGR technology employed, since I think that it is the next logical step (assuming that liquid-metal fast reactors don't overtake them). Then ... who knows? Hopefully, the molten salt reactor will be able to make a significant contribution to provide the world's need for energy.

Kirk Sorensen

I just don't understand this silly hostility towards the HTGR...

I have no hostility towards gas-cooled reactors, it's just that each application suggested for gas-cooled reactors can be done by fluoride reactors, and then some.

Gas-cooled reactors can achieve high temperatures, thermochemically generate hydrogen, generate electricity at 50% efficiency, and are essentially immune to loss-of-cooling accidents. Fluoride reactors can do each of those things too.

But fluoride reactors can also operate at ambient pressures, have high power densities, and can have closed fuel cycles on abundant thorium with conversion efficiencies greater than unity.

That's not being an uber-geek, it's just looking at the potential of the reactor types. I admit that fluoride reactors have a lot of development and shakedown to go through, but the payoff is pretty compelling.

Udo Stenzel

it's just that each application suggested for gas-cooled reactors can be done by fluoride reactors, and then some.

Unfortunately not, Kirk. For the Sulfur-Iodine-Cycle you need temperatures of at least 850°C, preferably more. Hastelloy-N is a good structural material for molten fluoride systems up to 750°C, beyond that corrosion becomes a problem. 1000°C are no problem for the salt, but no strutural material for the reactor vessel and piping has been tested to date. Carbon composites, carbides and ceramics might work... we'll see in maybe 20 years.

I still think it's about time that MSBR or some similar design be built and operated at least as prototype. It will likely be a good power plant, but the S-I-process is out of reach for some time to come.

Kirk Sorensen

Aren't there other hydrogen-generation cycles that operate at lower temperature?

I forgot to add no fuel fabrication. no excess reactivity, and no xenon transients to the list of fluoride reactor advantages.

Brian M.

Kirk Sorensen asked:

"Aren't there other hydrogen-generation cycles that operate at lower temperature?"

Sure there are. In addition to other theromochemical water splitting methods, there's high temperature electrolysis (HTE) and even steam methane reforming (SMF). The SI process was singled out years ago as the "most promising" of the chemical processes, and that is where most of the research has been done, but some of the other processes have been explored as well.

HTE cannot achieve the level of efficiency that the SI process can (which may or may not be important), and SMR requires methane, which kind of defeats the purpose of using hydrogen to get away from fossil fuels.

Udo Stenzel

Aren't there other hydrogen-generation cycles that operate at lower temperature?

Seems you're right, Kirk. There's (at least) the Calcium-Bromine-Iron (or UT-3) cycle, which operates at 730°C, and that just happens to be near the preferred operating temperature of an MSR. Efficiency will be limited to about 40% (as opposed to 50% for the S-I-cycle), but this actually looks promising.

(Many MSR fans seem to bemoan the infeasibility of an MSR to drive the S-I-cycle. I wonder if they know of the possible alternatives.)

Kirk Sorensen

I'd like to invite anyone who might be interested to come over to a new discussion forum about thorium as an energy source:

https://www.energyfromthorium.com/forum/

I can assure anyone who might come over and join and post that I will personally make sure that people who post will be respected (no name-calling or trolls) and that all views are welcome.

Sean Holt

Hi All:

Although my comments on this blog are new,
my research into the technologies under
discussion is not.

The debate seems to be hydrogen production
via the thermochemical process and whether
HTGR or MSR technology is better in this
application -no?

A few points on both:

Although HTGR technology will indeed do all
that was previously posted and reactors of
this type have already been built (using
pebble bed cores as opposed to prismatic
blocks). HTGR's still use a single pass
fuel cycle and cannot address the more then
70,000 metric tonnes of reactor waste
already produced in all of North America,
both in Canada and The US in addition to
decommissioned nuclear weapons stockpiles.

As for MSR's, yes all of their good points
have also been mentioned in addition to
their on power reprocessing and closed
fuel cycle not to mention their ease of
breeding thorium. However, the molten
flouride coolant is also the reactant and
is highly radioactive requiring great
attention to shielding in addition to a
secondary molten salt loop before a tertiary
energy loop. This makes the balance of plant
somewhat complex and impacts negatively on
safety. As with the HTGR, several countries
including The US, France and India have
built experimental reactors of this type so
the technology is well understood.

I have a third candidate: The lead cooled
fast reactor. It is capable of the high
temperatures needed for the efficient
production of hydrogen via the thermochemial
process, can employ a closed fuel cycle and
can breed and use thorium. However, lead is
a natural shield to radiation and is not
reactive with either air or water. Thusly
the balance of plant is far simpler as the
energy loop heat exchangers for whatever
working fluid is used (water, helium, CO2 or
nitrogen) can be situated directly in the
molten lead with little consequence should a
leak develope. The coolant remains at
atmospheric pressure and removes heat from
the core simply by convection - no pumps or
plumbing required. Safety is both inherent
using dopler broadening and completely
passive needing no enegineered safety
systems beyond coolant containment. Russia
has by far the most experience with this
type of reactor, having built and operated
at least eight of them inside the alfa
class submarine.

So. Now that we are all familiar with the
likely candidates for future commercial
scale hydrogen production, lets take a look
at hydrogen itself as all of this discussion
may well be moot.

Due to its atomic structure, hydrogen will
penetrate, contaminate and cause degradation
in every material with which it comes into
contact without exception. This means that
the entire hydrogen distribution
infrastructure will need to be replaced
unworkably often. Unless it can be absorbed
or combined with another atom (like carbon)
its use in its pure form as a fuel is
unlikely. Far wiser I think to simply use
the aformentioned reactor technologies to
produce enough electricity, which they
easily can, such that no other energy source
is required globally. My research has found
that fast reactors employing closed fuel
cycles can provide all of humanity with all
of the energy we would ever need for longer
then the predicted remaining life of our sun
using know global reserves of both uranium
and thorium. Hydrogen really isn't needed.

As for timeline: There are no technical
reasons why any and all of these reactors
aren't already in largescale commercial
use. Russia has already been using fast
reactors (sodium cooled) for almost 30
years (BN350) and are currently one of only
two countries still doing so (BN600). France
is the other (Phenix reactor)

If we could just subdue the coal and oil
lobbies we could actually move
constructively forward.

Fat chance!

But if I have to vote - I choose lead cooled
fast reactors!!

Best regards

Sean.

ps: Not like I care but are we supposed to be using our real names?

SWATHI


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