Reasoning about Nuclear Energy
I try to present facts and logic and solutions rather than just opinions.
Please send any reasoned disagreements to me.
If your facts and logic are convincing, I'll change my mind !
Nuclear in general
Stuart Gary's "Fusion vs fission: clean, green nuclear energy technologies explained"
Why building new nuclear energy is a bad idea:
- We STILL haven't figured out how to handle the waste POLITICALLY; it mostly piles up next to power plants.
There are technical solutions, but we haven't used them, either for cost or political or arms-control reasons.
New reactors designs may fix this, but getting a new design prototyped, approved, built, and into service is a LONG process.
Fukushima showed us some dangers of letting waste pile up.
(Relevant story involving nuclear weapons recycling:
Mark Strauss's "Failed Nuclear Weapons Recycling Program Could Put Us All in Danger")
And the future costs of waste disposal may be higher than predicted:
Joel Stonington's "Sticker Shock: The Soaring Costs Of Germany's Nuclear Shutdown"
- Decentralized, flexible power is the way of the future. Massive centralized power plants that
take a decade to permit and build, must run for several decades to pay off (while costs of other energy sources are decreasing steadily),
then take decades to decommission, are bad (inflexible, single point of failure, slow to deploy, hard to upgrade, etc).
And they are excellent targets for terrorists or natural disasters.
- Even countries we thought were good at running their plants (such as Japan) turned out to be
taking shortcuts on safety and training.
Kirsten Korosec's "At Tokyo Electric, a History of Shortcuts, Near Misses and Coverups"
Paul Brown's "'Nuclear Industry in France in Crisis', 20 Reactors Shut Down"
- If something goes wrong with a nuclear plant, sometimes the result is catastrophic (plant totally ruined,
surrounding area evacuated for hundreds of years). With renewables, only failure of a huge hydro dam is remotely comparable.
John Timmer's "Fukushima cost estimates nearly double, approaching $200 billion"
Kimberly Amadeo's "Chernobyl Nuclear Power Plant Disaster: Economic Impact"
- Apparently Wall Street thinks nuclear is a bad investment; they won't invest unless govt provides big subsidies and liability caps.
Richard Black's "UK 'subsidising nuclear power unlawfully'"
"Want to Reduce the Debt? Cut the Billions a Year In Nuclear Subsidies"
T. A. Frank's "Nuclear Reactionaries"
- Soon cost of power from renewables will be same as cost of power from nuclear, and probably keep going and
be cheaper than nuclear after that. Renewables-plus-storage will follow 5 years later.
See for example:
Brian Mann's "Unable To Compete On Price, Nuclear Power On The Decline In The U.S."
Megan Geuss's "Power company kills nuclear plant, plans $6 billion in solar, battery investment"
Joe Romm's "New study reaches a stunning conclusion about the cost of solar and wind energy"
- Similarly, new-design nuclear such as thorium or fusion won't be ready any time soon, and won't be price-competitive
with renewables plus storage by the time (if any) they are available.
- Note that I am NOT making any argument based on average safety. Nuclear plants are quite safe and clean until
something unusual goes wrong. They are safer than having people install solar panels on rooftops,
or letting a coal plant pour pollution into the atmosphere. Although I'm sure mining for nuclear fuel
carries some safety risks, as does mining coal or drilling for gas.
We still have to keep using existing nuclear for a while, but we shouldn't invest any new public money in nuclear.
Put the money in renewables, storage, non-crop carbon-neutral bio-fuels, energy-efficiency, etc.
From former US Navy nuclear technician on
I eventually changed my mind on [favoring nuclear power], however, for essentially one reason. I don't think humans
are ready for the long-term responsibility of waste storage. The US government is the most powerful organization
humans have ever created, and they're responsible for the regulation and ultimately, the handling of a very
large quantity of nuclear waste products for the foreseeable future (and much, MUCH longer) ... yet they can't
even pass a budget for even a single year. If our most powerful human institutions can't plan even one year ahead,
we have no business creating substances that require us to be responsible for their safeguarding for millennia.
I've been called "anti-science" or even a Luddite for pointing this out on Reddit in the past. I can only assure you
that this isn't the case. You'll have to take my word for it that the Navy isn't typically in the habit of training
Luddites to operate nuclear reactors on board their submarines, and people that "just don't understand science"
don't make it through Naval Nuclear Power School. And while I understand the dangers of climate change as well,
I don't think trading one long-term problem for another is the solution. I think we just have better options
at this point. I'm 100% behind further research into fusion, and even thorium fission reactors, but I think
our best bet, for now, is renewables and more research. Maybe one day we'll find the solution to rendering
the waste completely inert, but until then, building more nuclear capacity or continuing to operate at current
levels makes no more sense than taking up smoking on the assumption that lung cancer will be cured before it kills you.
The video [posted by someone else] says that we've yet to build a deep storage facility for nuclear waste, but this isn't technically true.
We've yet to complete it, but one is currently being built in Finland. Even this ambitious project, the only of its kind (that I'm aware of),
which has long been touted as the ultimate "long-term" solution for the waste problem, has its problems.
I'd encourage anyone who's actually interested in this topic to watch the excellent documentary on Onkalo (the
storage facility in Finland) and the problems with the long-term storage of nuclear waste products in general:
From Wikipedia's "Economics of nuclear power plants":
EIA's "Decommissioning nuclear reactors is a long-term and costly process"
[Decommissioning:] In the United States, the Nuclear Regulatory Commission (NRC) requires
plants to finish the process within 60 years of closing.
The cost of the Fukushima disaster cleanup is not yet known, but has been estimated to cost around $100 billion.
[As of 11/2016:
Yuka Obayashi and Kentaro Hamada's "Japan nearly doubles Fukushima disaster-related cost to $188 billion"
In terms of nuclear accidents, the Union of Concerned Scientists have stated that "reactor owners ... have never
been economically responsible for the full costs and risks of their operations. Instead, the public faces the prospect
of severe losses in the event of any number of potential adverse scenarios, while private investors reap the
rewards if nuclear plants are economically successful. For all practical purposes, nuclear power's economic
gains are privatized, while its risks are socialized".
Paul Dorfman's "How much will it really cost to decommission the aging French nuclear fleet?"
From Jerry Taylor's "Nuclear Energy: Risky Business":
[Published 2008, but some points still valid today.]
... electricity markets have a very peculiar pricing mechanism that makes it harder for nuclear to maximize returns
compared to gas-powered or other plants. In essence, there are two electricity markets: a market for base-load power
(electricity sold 24-hours a day) and a market for peak power (electricity sold as needed during peak demand periods
like hot summer days). Much of the demand for new power - and thus much of the profit available to investors today - is found
in the peak market. But nuclear power plant construction costs are so high that it would take a very, very long time
for nuclear facilities to pay for themselves if they only operated during high demand periods. Hence, nuclear power
plants are only profitable in base-load markets. Gas-fired power plants, on the other hand, can be profitable in
either market because not only are their upfront costs low but it is much easier to turn them off or on unlike nuclear.
... investors in new nuclear power plants are making a multi-billion dollar bet on disciplined construction schedules,
accurate cost estimates, and the future economic health of the region. Bet wrong on any of the above and the company
may well go bankrupt. Bet wrong on a gas-fired power plant, on the other hand, and corporate life will go on because
there is less to lose given that the construction costs associated with gas-fired power plants are a small fraction
of those associated with nuclear plants.
Investors are also wary of nuclear plants because of the construction delays and cost over-runs that have historically
plagued the industry. For instance, the Areva/Siemens nuclear power plant being built for TVO in Finland - the first
nuclear power plant to be built in a relatively free energy market in decades - once scheduled to be operational
within 54 months, is now two years behind schedule and 60% over budget. Nor have these construction delays had
anything to do with regulatory obstruction or organized public opposition.
If nuclear power plants are so uneconomical, how then to explain the blizzard of permit applications for the construction
and operation of new nuclear power plants that the Nuclear Regulatory Commission has received? Easy: These applications
cost little and oblige utilities to do nothing. Industry analysts maintain that federal approvals will not translate
into actual plants without a federal promise to private equity markets that, in case of default by power plants,
the taxpayer will make good on the full sum of all bad nuclear loans.
Nuclear supporters often counter that construction costs would be a lot lower if regulators didn't impose insanely
demanding safety standards, byzantine and time-consuming permitting processes, or endless public hearings,
any one of which could result in the plant being stopped in its tracks. Investors would also be more likely to invest,
we're told, if there were a high-level waste repository in place or more political support for nuclear power.
I would love to tell that story. I do, after all, work at the Cato Institute, and blaming government for economic problems
is what keeps me in business. But what stops me is the fact that those complaints are not echoed by the nuclear power industry itself.
Given all of this, how do France, India, China, and Russia build cost-effective nuclear power plants? They don't.
Government officials in those countries, not private investors, decide what is built. Either these governments
build expensive plants and shove them down the market's throat - or they build shoddy plants and hope for the best.
Nuclear energy may well be safer, in terms of deaths per year, than other forms of energy.
Solar installers fall off roofs, wind-generator maintenance people fall off wind-generators, coal miners die from accident or illness.
Of course, there are some deaths in the uranium mining and processing and transportation industries.
And some people died from the accidents at Chernobyl and Fukushima.
Nuclear energy may emit less greenhouse gas than solar energy ?
Seems unclear. For example, if you look in
Wikipedia's "Life-cycle greenhouse-gas emissions of energy sources",
you find three sets of numbers, the first showing utility-scale solar emitting 4x as much GHG as nuclear,
second showing solar PV emitting about 3x as much as nuclear,
third showing solar PV emitting 1/2 as much as nuclear.
And in the first set of numbers, emission for solar PV has a range (min to max) of 10x and nuclear has a range of 30x.
So I'm not sure what to think.
Nuclear energy may well be better than coal energy, which directly pumps pollutants (including CO2, acid-forming chemicals,
radioactive materials, particulates, mercury and other metals) into the air, leaves toxic ash/sludge afterward, and often involves
massive environmental damage from mining, and health damage to miners. But "at least we're better than COAL" is not a ringing endorsement.
Some new nuclear reactor designs may fix some of the problems with current nuclear power plants.
But we're not using those new designs yet, and may not be for a couple of decades to come.
Many of these "new" technologies or designs have been studied or prototyped for 40+ years now,
and still haven't become commercial. MSR experiments were done at ORNL in 60's,
thorium has been studied by US in 60's and many countries since 70's and operated in Germany in the 80's (THTR-300),
fusion has been worked on with big money since the 70's. We'd probably be better off investing in new renewable
energy technologies rather than new nuclear technologies.
Use of nuclear energy may well be necessary for decades to come. Only certain types
of renewable energy (geothermal, tidal) can serve as "baseline" (continuous, dependable) energy,
until some storage mechanism (pumped hydro, stored heat, flow batteries, etc) is used along with variable renewable sources (solar, wind, etc).
But there continues to be great progress made on development of new storage and improvement of solar photovoltaic power.
Other technologies (wind, hydro, etc) don't have as much room for improvement, and still others (nuclear, coal) offer
the chance of improvements in safety or pollution but maybe not efficiency or cost.
Shauna Theel's "Myths And Facts About Nuclear Power"
Wikipedia's "Economics of nuclear power plants"
Ian Sample's "Fukushima two years on: a dirty job with no end in sight"
Mark Cooper's "The Economic Failure of Nuclear Power ..." (PDF)
The Economist's "Half-death"
Joe Romm's "Why James Hansen Is Wrong About Nuclear Power"
Mark Diesendorf's "Renewable energy versus nuclear: dispelling the myths"
CANDU from discussion on reddit 5/2017:
There are a few reasons why we don't see more:
- They use very expensive heavy water as a moderator.
- They have higher emissions of tritium into the environment. While the levels are safe, they exceed the minimums for many countries.
- The tritium can also be captured and used in fusion weapons, posing a proliferation risk.
- Like many other reactor designs, they have proved very costly to refit, as Ontario has discovered.
- The most recent designs are a generation behind in safety. While pioneers of independent safety systems,
they still lack true passive, walk away for a week safe elements seen on Gen III+.
They are also really expensive to run. The maintenance costs are huge; there are so many subsystems to maintain.
Which feeds into the tritium problem.
CANDU reactors are not perfect. It costs $300M to fill a CANDU reactor with D20. And in CANDU reactors,
fuel gets shuffled around a lot and that can add to proliferation risk in a different way than what you mentioned with H3.
From /u/lie2mee on reddit 6/2018:
I think it is worth mentioning that the French only reprocess a third of their spent fuel,
that the effort actually increases the volume of waste by roughly a factor of six due to machinery exposure
to plutonium and subsequent wear and disposal, and that the effort creates 100 million liters of liquid waste
that is disposed of in the ocean in remote dumping sites all over the world from the English channel
to the Arctic to Antarctica to the indian ocean. In barrels. That are leaking all over the place.
Nearly a dozen countries have formally requested that the French stop their disastrous reprocessing activities
to reduce French nuclear pollution in their sovereign territorial waters and their fisheries.
LFTR (Liquid Flouride Thorium Reactor) from discussion on reddit 1/2014:
I think one of the biggest problems is not feasibility, but cost. Development of new nuclear power systems
is extremely expensive and comes with incredible amounts of regulation. Power companies already have proven
designs and don't have a lot of incentive to invest in unproven designs that will take decades to be profitable,
assuming that there isn't some inherent flaw being overlooked that ends up making the idea infeasible.
It's not a big conspiracy, just economics.
To add: LFTR would require a complete rewrite of the regulatory rulebooks. The NRC is very familiar
with PWR designs and even sodium fast-reactors. But molten salts? They haven't the slightest idea. It is too different.
Then there is the reprocessing issue. As it stands now it is a no-no. Not in law but by regulation.
Getting the well-understood PUREX processing going for current nuclear waste is damn near impossible.
LFTR requires a brand-new fluoride volatility Uranium separation system, a vacuum distillation step
to recover the salt, plus possibly a pyroprocessing step to keep the actinides out of the waste stream.
The NRC hasn't the first idea how to regulate any of that. Again, because it is too different.
You would have to build it all (reactor, reprocessing, power systems, etc) small-scale and test it for years,
then have the NRC write the regs, then you could finally scale up the thing for commercial power.
It is a technology that is in its infancy and decades away from commercial production if it was to be pursued.
But if we ever figure out how to build and operate it cheaply ... sheesh ... we wouldn't need anything else.
Medium-lived waste stream with inexhaustible fertile material.
Based on the way the NRC has been lately, it would take them over a decade just to figure out how to make
rules for a LFTR even with unlimited resources. Of course this includes all the anti nuclear lawsuits that will hold up the process.
Most of the obstacles facing LFTR are not in fundamental physics, however they are more political or cultural in nature.
Most of the nuclear industry as well as most nuclear engineers are trained to handle solid fuel elements.
LFTR's, on the other hand, operate primarily in the fluid phase like a chemical plant, at much higher temperatures.
As a result, much of the actual day-to-day skills of nuclear engineers do not translate. Besides the fact that
light water reactors and LFTR's both rely on nuclear fission, the technologies are very different from the engineering perspective.
The biggest issue with the technology that I can see is that it doesn't seem to offer any massive benefit
over modern reactors, at least in the near term (the fuel supply issue makes it more tantalizing in the really long (100+ years) run, though).
One compelling advantage that it seems to offer versus a modern light-water thermal reactor.
It seems much, much harder to catastrophically break the primary plant, thanks to the lower pressures involved.
On the flip side, it seems to have more potential for lower level radiological problems, but as long as those
can't make hundreds of square miles uninhabitable, that may be a good tradeoff.
The big disadvantage that I see in the LFTR is the inability to recover from some types of plant casualties
gracefully. For instance, a steam rupture or other massive, secondary-induced over-power transient could
cause the coolant to freeze, which would easily drop an entire loop, and possibly put the entire plant
into a complete loss of coolant flow (and potentially dead-heading and then burning out your pumps,
making it totally impossible to recover from). The answer to that seems to be just dumping the combined
fuel/coolant mixture into an unmoderated holding tank, which seems like it would work, but breaching your
primary containment boundary is hardly a good solution to a reactor plant casualty, imho.
In short though, it seems like every other thought-out form of nuclear power: possible, viable,
but not without some risks, and not nearly the panacea that its proponents make it out to be.
From Edwin Lyman (expert on nuclear terrorism and nuclear safety, works at UCS, doctorate in physics) on
[About LFTR:] We are aware that there are many types of reactor designs other than light-water reactors,
the current standard. These concepts all have advantages and disadvantages relative to light-water reactors.
However, most competitors to light-water reactors share one major disadvantage: there is far less operating
experience (or none at all). Molten-salt reactors, of which the LFTR is one version, are no exception.
The lack of operating experience with full-scale prototypes is a significant issue because many reactor
concepts look good on paper - it is only when an attempt is made to bring such designs to fruition
that the problems become apparent. As a result, one must take the claims of supporters of various
designs with a very large grain of salt.
With regard to molten-salt reactors, my personal view is that the disadvantages most likely far outweigh the advantages.
The engineering challenges of working with flowing, corrosive liquid fuels are profound. Another generic problem
is the need to continuously remove fission products from the fuel, which presents both safety and security issues.
However, I keep an open mind.
From /u/theskepticalheretic on reddit:
We built one in the US at Oak Ridge national laboratory in TN. The reactor experienced multiple accidents, some fatal,
and was primarily an experiment in the feasibility of the design. The biggest challenges to widespread adoption
are techniques used to make the components, chemical separation of 'neutron sinks' (daughter products that slow
to stop the reaction like protactinium), and the construction materials. Further, the medium used to move the
heat for power production is nasty, nasty stuff. Molten salt is highly corrosive, making containment of the heat
transfer medium very, very difficult (which was coincidentally what many of the facility accidents involved).
From /u/cark on reddit:
[About thorium in general:]
... there is the issue of supply chain. Getting from uranium ore to the uranium pellets used in nuclear plants
is a whole industry. Much R&D went into that. It is also a profitable industry.
The startup cost for a new supply chain is enormous. You need the ore, the thorium extracted, then conditioned,
and on top of that you need the power plants to sell it to. A bit of a chicken and egg problem if you will.
To make any of it commercially viable. Each of these steps requires costly R&D, then a lot of hardware investment.
Public funding is often required for such high cost research. For the uranium supply chain, there was a will. Not so much for thorium.
From /u/whatisnuclear on reddit:
From /u/Versac on reddit:
[About why don't we have thorium power:]
The main reason is momentum. Nuclear energy isn't like software in that you can just have rapid transformations overnight.
The industry moves at a snail's pace in innovation these days. It's so hard to even make small changes to conventional
reactors with all the people suing and all the regulators being extra careful to protect the public. The Navy developed
light water reactors to propel submarines as a war-time need. This development transferred over to industry and we've
kinda been stuck with it. Forays into advanced reactors were made. The USG spent a lot of money on liquid-metal cooled reactors,
but they became politically unpopular and very over-budget and were eventually axed by Congress. Smaller efforts were made to
develop molten salt reactors that are good with Thorium. Reasons for their cancellation have been quoted as:
- The existing major industrial and utility commitments to the LWR, HTGR, and LMFBR (AKA other advanced reactors).
- The lack of incentive for industrial investment in supplying fuel cycle services, such as those required for solid fuel reactors.
- The overwhelming manufacturing and operating experience with solid fuel reactors in contrast with the very limited involvement
with fluid fueled reactors.
- The less advanced state of MSBR (thorium) technology and the lack of demonstrated solutions to the major technical problems
associated with the MSBR concept.
Source: AEC's "An Evaluation of the MSBR" (PDF)
Nuclear innovation takes a very long time, lots of money, and very serious commitment. It's just not popular enough
to get these in current democratic societies.
It's not my specialty, but last I heard there still wasn't a good answer to the problem of neutron embrittlement
without unacceptably compromising operating temperature, just to name one issue. I suppose I'm confused as to
why you're attributing the lack of commercial thorium to industrial momentum when there are still significant
technical issues. This is still experimental technology.
From /u/DropBear25 on reddit:
Nuclear engineer here - it never ceases to amaze me how often people keep repeating this idea that thorium is this
magic bullet fuel and even worse that it would all just magically be ok if not for evil governments wanting to make plutonium.
The engineering challenges to make a profitable thorium have not been overcome. End of story. It's a totally different reactor fuel
cycle that requires special designs to be functional, the practicalities of which would be a huge investment. You have the potential
to create some really nasty transuranic isotopes as part of the fuel cycle and also major sinks for neutrons which
if not dealt with properly mean your reaction isn't sustainable.
Tinkering with it in government-funded test reactors is one thing, a profitable commercial reactor is something else.
And if you're the person trying to fund these things you're going to go with the design that has a proven track record.
I'm working on the new UK reactor and it's going to cost an estimated £16B to build, and that's for a reactor that's
already largely designed and was only an evolution of standard pressurised water reactor technology in the first place. These things aren't cheap.
I'm all for science advancement and the above is the exact reason why public funding of this stuff is important because it shouldn't
be all about the bottom line when you're talking about the future of civilisation, but people seriously have to stop oversimplifying
the rhetoric on thorium.
From /u/bigmike827 on reddit:
Oh look, OP has stumbled upon Thorium. You know, OP, 5 years ago I found similar numbers and watched similar documentaries.
I decided Thorium and nuclear would save the world and that I should dedicate my life to helping in the effort.
4 years later and hundreds of hours of studying I finally got my degree in nuclear engineering. I'm still all for nuclear
and how it will ween us off coal, petroleum and natural gas, too. But f*ck thorium. F*ck the people who want it to happen.
F*ck the people obsessed with it and f*ck the people halting research and development. Thorium is next to impossible to control,
next to impossible to burn efficiently, and next to impossible to refine.
Nothing short of a perfect reactor made of next-next-next-gen materials would be able to make Th useful, let alone efficient.
So please, OP, don't let the idea of thorium make you hopeful. We'll have perfected fusion before we can handle thorium and molten salt reactors.
From /u/whatisnuclear on reddit:
[Why do we hear about thorium all the time
(at least on reddit):]
Ooh I can totally answer this with my non-nuclear knowledge. My buddy Dave sent me this book once that explains why stories like the Thorium one stick. It says that to have a sticky message, the message should be:
- Simple: "Put this fuel in a reactor and all problems of nuclear go away"
- Unexpected: "Hey there's a energy source that solves all our problems that you've never heard of!"
- Concrete: "All you have to do is switch fuels from uranium to thorium!"
- Credible: "Tons of national lab scientists actually proved it works in the 60s"
- Emotional: "The only reason we don't do it is that the powers that be are holding it back, but we can fix this!"
- Story-filled: "We only don't have it because it can't make bombs" is a common story (albeit false)
As you can see, Thorium fits all the needs of a sticky story. Everyone knows we have an energy problem so when this pops up,
it captures people. As I've written a lot, most of these one-liners are nuanced and often misconceived.
From /u/Hypothesis_Null on reddit:
> Why aren't we using one of the many more efficient
> and safer reactor designs (including thorium) ?
A short and incomplete answer is that we've made essentially one type of reactor for commercial use for the last 50 years.
That's 50 years of operating hundreds of plants, that have let them identify points of failure and design redundancies
and minimum tolerances to make them safe.
Right now building a nuclear plant is a very risky proposition just from an economics standpoint. And that's building
a reactor you know will work. There are hundreds of problems that could be run into building the first commercial version
of something like a Thorium plant. Other reactor designs can be more efficient - and at first glance you'd think that
would provide some economic incentive to try the new models.
But this is where nuclear's prime advantage works against itself, so to speak. The cost of running a nuclear reactor
is almost entirely running all the personal and safety mechanisms and general operation. The fuel cost is a very tiny
fraction of operating costs. This is good, because it means fluctuating fuel prices don't really impact electricity prices,
like they can with coal and oil. But it also means that a more efficient plant doesn't give much of a profit advantage.
TL;DR The current type of reactor we have comes with 50 years of experience, making them 50 years safer and 50 years more predictable.
Because fuel costs are so tiny compared with the overall cost of running a nuclear reactor, a design with more efficient use
of fuel doesn't really add to the bottom line enough to justify the risk.
From /u/dizekat on reddit:
Pretty much any thorium breeder reactor design could just as well run off depleted uranium instead (which costs nothing,
i.e. a lot cheaper than thorium), getting similar mileage. So if someone's focussing on thorium in particular, it is a BS conspiracy theory.
The reason those reactor designs aren't used are complex, mainly having to do with fuel costs being only a small fraction of
reactor operational costs; if you reduced fuel costs to zero but increased maintenance by a few percent due to more
corrosive environment, you'd be worse off. Reducing costs is all about using materials that are least corrosive and
most chemically straightforward (and for which there exists experience), hence boiling water trumps everything.
Yes, you can set up a reactor that will need less uranium and/or could use thorium; the advantages of such are very
easily negated by even a minor increase in failures requiring maintenance.
Stainless steel in hot water is a very well-studied topic. Materials in a mixture of fluorides of half the elements from
the periodic table are not, not to mention that it is far more complex chemically than water. Materials in molten sodium
are not either, but at least you don't have half the periodic table attacking your pipes.
From /u/choppedbeef on reddit:
If you're asking why we aren't switching over to thorium today, cost and technology are the two main prohibiting factors.
- Any new nuclear power plant is extremely expensive to build, and requires going through a rigorous approval process with the NRC.
It's been around 20 years since a new commercial reactor was brought online (though political movements have a lot to do with that,
and it's possible a new one may be brought online this year).
- Far more research is needed before commercial LFTRs can be built. Many issues, including graphite moderator lifetime and
corrosion caused by fluoride salts, need to be addressed. Some of this research could take decades, even if it were well-funded
(most of today's research goes into improving upon current reactor designs, making improvements to reactors already in use,
and developing novel reactor designs other than LFTRs).
- To start up a LFTR, you would need a critical mass of U-233. There are currently no U-233 enrichment facilities,
so these would need to be constructed.
If a business were to build a new reactor today, they would likely want to choose a well-understood design
that they knew they could get NRC approval for, that operators and engineers have experience with, and that
uses a fuel that can be obtained through an existing supply chain.
If you're asking why humanity decided to pursue U-238 water-cooled reactors instead of LFTRs early in the
developing of nuclear power, the short answer is that it is much easier to obtain material for nuclear weapons
from the waste products of a U-238 reactor than from those of a thorium reactor.
From /u/whatisnuclear on reddit:
> Are these advantages of Thorium over Uranium true ?
> 1- Thorium reactors can't melt down as catastrophically.
> 2- Thorium can't be turned into nuclear weapons in the
> same way that Uranium can.
> 3- We have lots of Thorium basically just sitting
> around as it was a byproduct of mining or something.
> 4- The moon has lots of Thorium so it would be ideal
> power generation technology for a lunar base.
Those are almost all the points we answered on our
Thorium Myths and Misconceptions page
- Low pressure reactors like Thorium-MSRs and a bunch of uranium fueled advanced reactors have major benefits
over conventional water-cooled reactors in passive safety. If you put thorium in a regular reactor, it would be basically as catastrophic.
- False. It needs a different mechanism but it can definitely be turned into a nuclear weapon.
- True. Also true for Uranium. We can run the entire USA on pure nuclear for 200 years using the depleted
uranium sitting around as cold-war enrichment tails if we used breeder reactors. So, it's an advanced nuclear thing, not uniquely a thorium thing.
- Haven't looked into it. Definitely possible. But a lunar base will probably start small. A nuclear submarine powers
itself for a good 30 years on one small batch of fuel so it may not be necessary to set up mining infrastructure on the moon
for the first few lunar bases.
From /u/totallylumberjacked on reddit:
> Why would a MSR be cheaper than an
> existing fission reactor ?
With a pressurised water reactor the fuel coolant needs to constantly be under like 100 bar of pressure.
The architecture of the plant and the safety systems is all centred around what happens in the unlikely (but non-zero)
chance that containment is lost. For example, the containment building is about a thousand times larger than the actual
reactor itself because of the volume change from water to steam. The reactor casing needs to be 8 inch thick Hastelloy
cast in one piece, no chance of welding. And the engineering tolerances are necessarily extreme.
Contrast this with an MSR system. At ambient pressure, so the reactor vessel can be far thinner and manufactured in a factory
to be shipped out to where it's needed. A clean salt loop is run through the reactor out to a heat exchanger,
where it then uses a steam turbine basically identical to something you'd find in a coal or gas power station.
And because this type of design can be made in a factory, that means standardisation and economies of scale,
compared to the current clusterf*ck of nuclear where seemingly every new plant (outside of China anyway) is
individually designed, all special snowflakes with insane cost overruns.
From Alan Rominger on Physics.StackExchange's "What practical issues remain for the adoption of Thorium reactors?" 1/2012:
Now, Thorium is vastly more sustainable than natural Uranium, we all agree on that.
But the problem with nuclear power today is not sustainability of the fuel supply
Your question is why we haven't adopted it as a power source. To start with, we have no economic reason to adopt it.
You could ask why we have not adopted the molten salt reactor, for which the answer is a matter of technology evolution.
Also, we don't have many breeding reactors in general which is tied to larger issues like reprocessing.
Thorium fuel cycles offer their own unique approach to a breeding fuel cycle. But to use Thorium is to
use breeding, and we don't do (deliberate) breeding.
At the same time that Thorium has advantages, it has disadvantages. The small number of neutrons per fission
is a drawback
for the design of the reactor. The company Terrapower proposes to make a candle-type reactor
with U-238. You could not do this with Thorium because it doesn't have enough neutrons.
The design isn't neutron-efficient enough. A molten salt rector (MSR), on the other hand,
is one of the most neutron-efficient designs we've ever contemplated. Obviously it matches well with Thorium.
U-238 could be used in a MSR as well, but Thorium could not be used in a Terrapower design.
To summarize my opinion, there is a strong argument for Thorium based on sustainability,
there is a weak argument for Thorium based on the waste, and there is really no argument
for Thorium based on economics. Current designs are based on economics. QED.
From /u/233C on reddit 11/2018:
Warning, nuclear physicist talking.
Anything you watch or read when they talk about Thorium, do the
Protactinium test: Ctrl+F "Protactinium".
If you've heard about Thorium, you might remember that 232Th is not a nuclear
fuel per se, it must be turned into the good stuff 233U; that's the one that will
fission and give you your energy from fission, to turn into heat, steam, etc.
Think of it like a recipe, you have butter and flour, you mix them to get
the shortbread that you want. See how easy it is for everybody to get some shortbread?
Except everybody also likes to gloss over that between the "butter/flour"
step and the "shortbread" step, there's a "white phosphorous neurotoxic napalm"
step that might make things a bit more complicated in the kitchen. That's your
So it goes 232Th+n -> 233Pa -> 233U.
This is when you say: "but wait 233c, this is just like 239Pu is produced
from 238U: 238U+n -> 239Np -> 239Pu, this is happening all the time in
normal nuclear power plants. What's the difference?". The difference is
the same as between 2 and 27.
239Np (the step between Uranium 238 and Plutonium 239) has a half life of
while 233Pa (the thing between Thorium and Uranium 233) has one of
If you leave 239Np in the core it will quickly turn into 239Pu,
but you can't leave 233Pa in the core for a month or it will capture
more neutrons and turn into something else than 233U. (There's also
a matter of cross section: 233Pa has a much higher probability of
capturing neutrons than 239Np). If you leave your butter and flour
too long in the oven you'll get a brick rather than a shortbread.
If you want to use Thorium, you must: expose your Th; extract your 233Pu;
let it decay into 233U; feed the 233U back to your reactor.
By now you should understand why liquifying the fuel makes so much more sense
for Th than for U. It's not "MSR works so well with Thorium", it's "if you want
to continuously extract your 233Pa, you'd better do it with a liquid fuel".
This is where you say "Ok, but I still don't see the issue, you just pump and
filter your fuel to recover the 233Pa, and let it decay in a tank,
and pump/filter the 233U back in for it to fission".
I'm going to assume that you know what a Becquerel and a Sievert are.
Remember the 27 days? With the density of 233Pa, that translates into
(Tera is for 1012 , that's a lot), and because of the high energy gamma
from our friend 233Pa, that also means a dose rate at 1m from a 1g teardrop of 233Pa of
. Starting to get a picture?
Notice how all the numbers I've used are not "engineering limits" that a few millions
in R&D can bend, those are hardwired physical constants of Nature: half life,
density, neutron capture cross section, gamma energy. Good luck changing those
by throwing $ at them.
Now try to imagine technicians working in those plants, like doing some maintenance,
replacing a pump (I haven't even touched the complex chemical separation system
you need to extract your 233Pa from your fuel or 233U from your 233Pa, which
will definitely need maintenance). Let's put it this way: if there is 1mg of
233Pa left in the component they are working on, they'll reach their annual
dose limit in 1h.
Now try to imagine the operating company of those plants, if you have the
tiniest leak, like a tiny puddle, you can't send anybody in for months,
meaning you are losing months of revenue because of a tiny leaky seal failure,
what would be a trivial event anywhere else (did I mention that molten salts
also have corrosion issues).
When they say "Thorium has been used in research MSR", they mean
"we've injected some Thorium and detected 233U" or maybe even just
"we've injected 233U in the fuel".
So my humble opinion is that playing with it in the lab is one thing,
turning it into actual power plants is slightly more problematic.
are more numbers trying to imagine an industrial scale Thorium reactor.
TL;DR: Thorium will probably never leave the labs to reach industrial,
electricity production scale. The physics is sound, the engineering and
actual practical operating constrains just kill the concept.
> What if we don't have humans doing the maintenance?
That is indeed a very good question.
As I mentioned, 1g of 233Pa gives a dose rate of about 21Sv/h.
So it would take 25.5g to reach
the highest dose level ever measured
where basic cameras and instruments fail within hours.
So even assuming an army of robots (either independent or remote controlled)
to do the maintenance, you can be sure that you would have to throw them away
and buy new ones after each outage, see how that impacts your $/kWh.
And you'll have to convince your regulator AND your bankers that you'll be able
to do it before starting building it, otherwise your plant is unsafe and/or inoperable.
> than constantly producing permanent waste than could fuel nuclear bombs
Are you suggesting that Thorium does not produce radioactive waste or bomb-grade matrerial?
The thing is, it does both.
It is true that Th/233U produces less minor actinide (the waste that remain
radioactive for millions of year), but still produce some, and fast Pu reactors
can reduce them even more.
As for bomb material, Th/233U is even worse than U/Pu, because, with U/Pu,
your 239Pu that you want for the bomb is always contaminated with other Pu
and you have to separate it and it is diffcult and costly; whereas, as I explained,
for Th, you need to isolate 233Pa to have it decay to 233U, when doing so,
you get pure 233U, perfect to make a
is a good summary of the proliferation risk from Thorium.
I'm not saying it's impossible, rather "Why bother??" when U/Pu can do the
trick without the radioprotection and robots, and complexity.
Physics Central's "Thorium Nuclear Power"
Nick Touran's "Myths and Misconceptions about Thorium nuclear fuel"
Wikipedia's "Liquid fluoride thorium reactor"
Wikipedia's "List of thorium-fueled reactors"
Noel Wauchope's "Don't believe thorium nuclear reactor hype"
Physics Stack Exchange discussion
Jan Beranek's "Exposing the thorium myth"
Open University's "Thorium: Proliferation warnings on nuclear 'wonder-fuel'"
ThorCon page explaining some of the technical issues
Union of Concerned Scientists Statement on Thorium-fueled Reactors (PDF)
Richard Martin's "China Details Next-Gen Nuclear Reactor Program"
Most of this applies to "big" fusion, a big reactor producing heat to drive a steam plant
and electric generator, similar to today's fission and coal power plants.
If we ever get a huge breakthrough and someone invents a non-thermal fusion process
that produces electricity directly, that would change everything.
Problems with fusion power:
- It won't be working any time soon. Think 2025 or later. We haven't achieved
break-even in a lab, much less built a reactor prototype.
- It won't be commercially available any time soon. Think 2050 or later.
- If it does become commercially available, by then it won't be economically viable. It might not be economically viable even it was
commercially available right now.
What are the benefits of fusion versus fission ?
Fuel is about 30% of the operating cost [not LCOE] of producing electricity via fission
Does that mean electricity from fusion reactors would be 30% cheaper than electricity from fission reactors ?
About the same cost to build each type of reactor ? The controls for a fusion reactor seem to be more complex
and expensive than those for a fission reactor (in fusion, you have to heat and confine and control the plasma,
and feed in new fuel continually). Fresh fuel transport much easier.
No waste-handling problem while the fusion reactor is operating.
No danger of fuel meltdown. No on-site spent-fuel storage. I assume decommissioning a fusion reactor
would be cheaper because of far less radioactivity.
Maury Markowitz's "Why fusion will never happen"
Jon Excell's "Nuclear fusion financially viable in decades claim researchers"
Daniel Jassby's "Fusion reactors: Not what they're cracked up to be"
C. Bustreo's "Fusion energy economics" (PDF)
From /u/Rannasha on reddit 10/2015:
Barring any unprecedented breakthrough, we're still very far (read: decades) from using nuclear fusion in a commercially viable manner.
We can already do fusion in experimental reactors. That's not new. We can also do fusion in a way that more energy is produced
than is used in H-bombs. The problem is combining the two :)
A nuclear fusion reaction is rather hard to achieve and the essence of the problem is one of scale: The larger and more extreme the setup,
the higher its efficiency. Current experimental reactors are too small to produce more energy than they consume. So the goal is to make
a reactor that is bigger and operates at even higher temperature and pressure to go beyond the threshold of "Q = 1" (Q is the ratio
between output and input energy, if Q > 1 then more energy is produced than consumed).
The current big project is ITER, this is planned to be the first fusion reactor to achieve Q > 1. The design goal is to reach Q = 10.
But targets for continuous operation are only in the order of magnitude of hundreds of seconds (several minutes). Large parts of ITER
and supporting infrastructure are currently being built in southern France. The project is scheduled to have its first plasma operations
inside the reactor in 2020 and start fusion reactions in 2027.
But these are just schedules and delays can't be excluded since there is a lot to figure out still. The conditions inside the fusion plasma
will be unlike anything we've made so far and even though magnetic fields will be used to prevent the fusion plasma from touching the vessel
walls, making a reactor vessel that can withstand such stresses and still allow for energy to be extracted is a challenge, to say the least.
And while ITER is designed to generate more energy than it consumes, it's still very much an experimental device, set up for scientific
purpose and not commercial application. The followup to ITER, called DEMO, is a prototype of a potential commercial plant built on the
same principles as ITER, but slightly larger. Its very tentative schedule has first operation starting in 2033, with an upgrade/expansion
already planned afterwards and the second, final phase of operation starting in 2040. But this very strongly depends on whatever we learn
with ITER. And DEMO is still a demonstration model, not something that will be mass-produced.
Next to ITER and DEMO, which will use a technique called "magnetic confinement fusion" in a "tokamak reactor", there are several
other avenues being explored. The donut-shaped tokamak reactor has an alternative in the so-called stellarator, which also uses magnetic
fields to confine the plasma. In addition to magnetic confinement, fusion has been achieved using inertial confinement,
which essentially involves a fuel pellet being forced to implode due to exposure to lasers, causing the outer layers being pushed
inwards and confining the fusion reaction in the inner layers of the pallet.
All these techniques work, but none work at an efficiency that allows for commercial application. Currently tokamak reactors are in the
lead when it comes to scientific attention, as evidenced by the ITER megaproject, but the jury is still out on what'll end up winning the race.
You hear cold fusion being mentioned from time to time as an easy and affordable alternative that does not involve effectively putting
the sun in a small box and hooking it to the powergrid. In the late '80s there was some buzz about scientists allegedly finding fusion
reactions taking place in conditions close to room temperature.
However, these findings were quickly disproven. These days, there's still a fringe community that revolves around the notion that cold fusion
is possible in the way that was described back then. They also use the term "Low Energy Nuclear Reaction" (LENR). From time to time,
some news article appears claiming a new device delivering practically free energy using something related to cold fusion / LENR.
Unfortunately, there has been no independent scientific proof of such a device actually delivering on its promises. When tests are being
published, they're often of very poor quality, done by people affiliated by the creator or done without the researchers having full access
to the device (At one point a test report described a cable being attached to the device without the researchers being allowed
to see where the cable lead or to unplug it).
So for now, cold fusion / LENR is fringe activity that is riddled with scammers and people that are a bit too trusting.
If cold fusion or something similar would be possible, it would be the holy grail to solve the energy puzzle. Because while "regular"
nuclear fusion is a perfectly achievable process, actually getting useful power out of it is a large challenge it's unlikely that
it will be the source of widely available, virtually unlimited clean energy this century.
From discussion on reddit:
Why is fusion such a big deal when we already have fission-based power plants?
The short answer is that fusion power can potentially give us energy more efficiently than what is achievable using fission,
it relies on a far more abundant source (hydrogen vs. uranium), and most importantly it avoids the risk of catastrophic
meltdowns and the hassle of dealing with mountains long-lived radioactive waste. For this reasons fusion could
truly be the definitive solution to the world's energy needs, producing almost unlimited energy in a fairly safe manner.
The problem is just getting the damn thing to work ...
Now let's look at these potential benefits a bit more closely. The most striking advantage of fusion when compared to fission
is that fusion can give you a much bigger bang for your buck (more energy per mass of inputs). ...
Another major advantage of fusion over fission is when it comes to safety and waste management. Carrying out controlled fusion
is actually very, very, hard, which is why there is still not practiced on a mass scale. Essentially for fusion to occur at all,
conditions need to be just right, or else pretty much nothing will happen. However, from a safety standpoint, this situation
presents an advantage. Unlike nuclear fission where runaway reactions can lead to a meltdown, this simply couldn't happen with fusion.
In addition, the reaction products are far more easily manageable for fusion power than is the case for fission.
The reason is that while fission produces a sludge of long-lived radioactive waste, fusion generally only results in the production
of helium (which is utterly inert), and some tritium. While tritium is radioactive, its short half-life (~13 years) makes its handling
far more manageable.
This is spot on. Everything about the fuel is cleaner and safer.
The components and waste don't stay dangerously radioactive as long. The fuel is literally hydrogen - you can get it from water.
It's not like turning a mountain upside-down to get uranium ore.
In plasma confinement reactors your reactor won't melt down. If there's a breach the plasma expands and cools and the reaction ceases.
As you said, the only major risk is a tritium leak. Since it's hydrogen it forms water, and you don't want people drinking tritiated water.
While it's harmless outside your body, beta decays inside your body are bad news.
One thing that can be said for fission though is that the "sludge of long-lived radioactive waste" is often the only source
of a lot of those isotopes on earth, and many of them have useful applications. Traditional fission reactors can produce Molybdenum-99
which has a half-life of days and produces Technetium-99m. That 'm' means it's metastable and spits out a gamma ray, so it makes a great
radioactive tracer for medical imaging. It works like an X-ray, except the gamma rays are originating inside your body. There's really
no other source for this stuff, and with such a short half-life it can't effectively be stockpiled.
From /u/Hypothesis_Null on reddit:
Fusion does not give us limitless energy. It gives us a way to release energy from a very abundent fuel source.
It still takes expensive facilities, and people, performing constant operation and maintenance, to produce a limited
amount of power at each power station. And this power still has to be delivered using a network of wires and substations
that also have limitations and also need maintenance.
Nuclear Fission Reactors, many of which which have been operating for over four decades now, do the exact same thing.
Average price of electricity is ~$0.10/KWH, of which 1-3 cents is profit. Of the $0.08/KWH in cost and operations,
about 1-2 cents go towards the actual fuel cost.
Considering how much more difficult fusion is than fission, it seems reasonable to assume that a fusion plant's operation
will not be cheaper than a fission plant's operation for similar levels of power generation.
So if we are generous and assume the costs are all the same, minus the cost of fuel, then Fusion power will cost $0.08 cents per kilowatt-hour.
Think of the world-changing possibilities with prices like that!
Oh, actually there really aren't many. Space travel may get denser fuel for ships large enough to warrant a fusion-reactor.
And proliferation won't be an issue so the technology can probably be shared and implemented more freely.
But no, we don't magically get an Iron-man Super Power Source that lets us air-condition the outdoors and turn Lead into
Gold just for the h*ll of it.
At least no more than we already have with fission power. Fusion will only give us so much energy as we can build power plants,
and staff them with technicians, and maintain them all, to produce it.
Which is why I find people obsessing over Fusion - as though it will solve all of our problems - perplexing to say the least.
It's a power source with more abundant fuel. It doesn't radically changed the economics of what power sources are,
or what we can feasibly do with them. If Fusion is imagined to be so great, we should be pushing for fission, which
is almost nearly as great, and has already existed for half a century and powers a fifth of the US grid.
But somehow nobody goes after that.
Fusion removes one bottleneck - the fuel bottleneck. But since fuel isn't currently even close to providing a bottleneck for fission,
if a scale-able Fusion plant was delivered to the world today, it wouldn't change much of anything.
Materials, skilled labor, and economic demand would keep Fusion behaving pretty much the same way Fission does now.
... Fusion reactors aren't going to be utterly without radioactivity either. Depending on what kind of fusion and what
materials they use in construction, the activated products might be shorter lived or less dangerous, but when
dealing with nuclear products, it's more a question of proportion than absolute amounts.
From /u/kirime on reddit 5/2017:
From /u/edemdee on reddit 5/2017:
Not cheap and certainly not that clean, at least in the foreseeable future. The only things in which fusion is undeniably better
than fission is safety and abundance of potential fuel.
The main problem is that deuterium-tritium fusion produces a huge amount of fast neutrons, ~hundred times more than fission
for the same power, and those neutrons make the insides of a reactor highly radioactive and greatly reduce the lifespan
of any equipment and materials inside the vacuum chamber. Also, tritium itself is radioactive.
So, even if DT fusion is cleaner than typical fission, it still uses radioactive fuel and produces tons upon tons of radioactive waste.
Aneutronic reactions exist, but their energy requirements are several orders of magnitude higher than those of DT and they often
use more exotic fuels.
And fusion certainly won't instantly make energy free. The cost of nuclear fuel is just a few percent of the total cost of
fission energy, the rest is equipment and construction cost. Fusion reactors are far, far more complex and expensive
than fission ones, and their fuel isn't free either. Unless the prices will go down much further than expected,
thermonuclear energy is going to be more expensive than nuclear, not otherwise.
Re: "building cookie-cutter reactors": we've been using fission reactors for 60 years and still
haven't managed to do this for them.
Yes you're correct, fusion produces many energetic neutrons which decrease the lifetime of reactors compared to fission reactors.
However the materials are radioactive for SIGNIFICANTLY less time than fission. We're talking 50-100 years for fusion while ~1000
years for fission. Not to mention fission reactor produce waste instead so you're actively creating more radioactive material
while fusion has no radioactive waste by product. So I would say that this isn't necessarily the MAIN problem with fusion.
Okay yes tritium is radioactive. But, compared to plutonium/uranium for fission, tritium is nothing. Tritium is much more difficult
to weaponize and much less radioactive. I think saying that both have radioactive fuel and radioactive waste so they're equally bad
is pretty misleading.
Last, there's really no way to tell how much a commercial power plant would cost because we're nowhere near building one.
Yes, as I mention elsewhere, ITER, the biggest reactor being built, has astronomical costs but it's also being built
on cutting-edge science and being somewhat mismanaged. The cost of building cookie-cutter reactors once the science
is all figured out will be much less. Less expensive than fission reactors? I'm not sure, I don't think anyone knows for sure.
So it's a little pessimistic to dismiss fusion as definitely being more expensive than fission. That's like saying the car
will be more expensive than the carriage and isn't viable when we haven't even gotten the model T yet.
While you raise good criticisms of the field, they're hardly deal breakers in my opinion.
From /u/jjs2424 on reddit 5/2017:
> ... how will we USE all of this energy ?
> Will we just use it like we do a fission reactor,
> using the excess heat to generate steam ? ... Or, is
> there some way to use the plasma to generate electricity ...
There are two basic answers, but things are much more complicated for a fusion reactor.
1- Use heat generated by the reaction to generate steam or another hot fluid.
2- Extract energy from the reaction in the form of electromagnetic energy (light, x-rays).
The problem with no. 1 in magnetically-confined fusion is getting the heat from inside the reactor to outside the reactor.
This is easy in fission reactors (just circulate a coolant that absorbs energy from neutrons through the reactor).
In magnetically-confined fusion, the reaction requires generating a plasma in a vacuum vessel, so exposing coolants
directly to the reaction is out. You could heat up the reactor walls with neutrons, but all solid materials we know
of would be physically damaged by highly energetic neutrons and/or become radioactive through neutron activation.
For now the best solution to that problem is to use liquid metal walls (like liquid lithium) inside the reactor to capture the neutrons.
This liquid metal would need to flow continuously. Making this work is tricky.
Number 2 is possible if you switch to fusion reactions which do not produce significant quantities of neutrons and instead
release most of the energy in the form of photons. Problem is that all the candidate "aneutronic" fusion reactions require
much better heating and confinement of the plasma when compared to deuterium and deuterium-tritium fusion, and we still
haven't cracked those two reactions.
From /u/Wendelstein7-X on reddit 2/2016:
> When do you think fusion power
> will become a reliable source of energy?
According to the EFDA Roadmap it is planned that the demonstration reactor DEMO should produce
first electricity 2050 (as usual: if everything works as expected). It will just be a prototype.
After this one can start producing reactors on a large scale. So, the time when fusion power
will become a reliable source of energy then depends how fast further reactors can be build.
But roughly I would say, not before 2060.
Fusion reactors will always be big devices, so you will unfortunately probably never see a Mr. Fusion for your car.
The reason is that a fusing plasma loses energy through its surface area (residual contact with the walls)
and produces energy through in its volume. The larger your device, the better the ratio of volume to surface is,
just like penguins are larger near the poles than the equator to compensate for the higher heat loss there.
[Re: using fusion reactor as a source of helium:]
The amount of fuel fusion consumes, and hence the amount of helium produced, is very small.
The helium we produce will be used in the reactor.
From someone on
[Compared to thorium fission,]
two of the big unsolved problems with fusion power are tritium contamination and the creation
of a fairly large variety of heavy, long half-life isotopes because of the extremely
high energy neutrons flying off the fusion reaction. Even though there is almost definitely
less radioactive material being produced in a mass/volume sense, the radioactive material
is much more chemically diverse and thus harder to separate out and store safely.
So it's still to be seen which is safer. Neither technology will see the light of day
before 2050 anyway, so it's still well up in the air. A lot of it depends on implementation details,
not fundamentally the process itself.
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