Reasoning about Nuclear Energy

Diagram of a nuclear fission power plant I try to present facts and logic and solutions rather than just opinions.

Contact me If your facts and logic are convincing, I'll change my mind !

Nuclear in general

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 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.

John Laforge's "Nuclear Power Can't Survive, Much Less Slow Climate Disruption"

From former US Navy nuclear technician on reddit 5/2017:
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: Into Eternity.

From Wikipedia's "Economics of nuclear power plants":
[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".
EIA's "Decommissioning nuclear reactors is a long-term and costly process"
Paul Dorfman's "How much will it really cost to decommission the aging French nuclear fleet?"
Michael Barnard's "UK Has £10 Billion Per Nuclear Reactor Decommissioning Bottomless Pit"
Half as Interesting's "Why It Takes 7+ Years to Shut Down a Nuclear Plant" (video)

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.

From /u/ISpendAllDayOnReddit on reddit 9/2020:
... as a civilization, it seems as though we've lost the ability to do large construction projects. Every single project runs massively over budget and has a ton of delays. The main airport in Berlin, Tegal, was built in 90 days. The airport they're building to replace it was meant to open in 2011 (they started in 2006). It was meant to take 5 years to build and they've currently been working on it for 14 years and it's still not open. And of course the airport is already riddled with problems and the budget exploded. There's a lot more red tape now. Parts of projects get subcontracted out and those 100 different contracting companies don't talk to each other so there ends up being inconsistencies which need to be fixed. In an effort to make things as cheaply as possible by contracting everything out, we've ended up crippling our ability to actually build anything large. This is why solar and wind is actually working. Because one company just does it from start to finish. If we could actually fix the construction industry, so we could build things like we did in the 60s, then nuclear power would be amazing. But I don't see that happening. Small reactors are probably the best option because the large ones will have so many different contractors that nothing will get done.

From /u/jascottr on reddit 9/2020:
I have a bachelor's in Nuclear Engineering, and have some knowledge on the problems of recycling used nuclear fuel. The issues, from what I understand, come down to mostly three things: economic feasibility, total waste utilization, and regulation changes.

The first is just that storing waste indefinitely and mining more fuel is currently cheaper than recycling. This is unfortunate, since it removes one of the primary (realistic) driving forces that could cause a push for used nuclear fuel recycling.

The second part involves the many, many different isoptopes present in nuclear fuel after it comes out of a reactor. There are places (some US facilities in the recent past) that recycle the uranium and plutonium out of this fuel, but leave everything else for disposal. Methods have been developed for extracting many of the other serious isotopes such as strontium or cesium (notably by Oak Ridge National Lab in the mid 1900s), but these aren't currently used anywhere that I know of. Even if those two were extracted as well, there will still be radioactive waste as a by-product, and it will be in a less ideal form for storage after all of the extraction processes. The final issue regarding is that even if we did extract everything that we could from the waste, we would have a lot of isotopes and probably nothing to use them all for; some of them are obvious, like the actinides being recycled into new fuel, but what about the strontium? It makes a decent fuel for RTGs in the form of Strontium Titanate, but is very active and we don't really have use for that many RTGs right now.

Finally, at least in the US, used nuclear fuel recycling faces major regulation issues. To the best of my knowledge, there isn't really any robust regulation in the US as there currently is for, say, reactor operation. This would be a very involved and drawn out process, even if everybody involved was completely on board and agreed on everything. As I'm sure you're well aware, nuclear energy has a ton of red tape around it, and is taken incredibly seriously from a safety perspective, and this is a major limitation when pushing for advances in the technology for the industry.
From /u/Doppeldeaner on reddit 9/2020:
One of the big things missing from nuclear waste disposal in the US is an economic incentive. Many people do not understand that all nuclear waste (including spent fuel) is legally owned by the Federal Government. Commercially, the waste is taken care of by the power plant that generated it, but the Feds own it. It has been this way since day 1. The Federal Government decided that civilian nuclear power could exist but proliferation risks were so great that they should own all used fuel. The Federal Government then entered into a contractual relationship with all operating nuclear power plants. "Y'all give us a tenth of a cent on the dollar, and we promise that we will get rid of the spent fuel, you don't have to worry about it". So all the power plants are in this deal, perpetually paying the feds to dispose of the waste, then suing the government for the costs of storing it due to breach of contract.

The government has no political incentive to deal with the stuff, nor do they have a monetary incentive to reprocess, recycle or otherwise make physical use of it. The power plants themselves don't have any legal standing to do any of those things either. So it just sits in limbo.
From /u/Puzzleheaded_Tax_856 on reddit 9/2020:
Not one ounce of nuclear waste in the world is in permanent storage. It's all in temporary storage that leaks and degrades even over 50 years, let alone until the material is safe again.

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.

John Timmer's "Why are nuclear plants so expensive? Safety's only part of the story"
Brian Potter's "Why are nuclear power construction costs so high? Part I"
Shauna Theel's "Myths And Facts About Nuclear Power"
Austin Vernon's "Why is the Nuclear Power Industry Stagnant?" 1/2022
Austin Vernon's "Nuclear Power's Challenges in less than 1000 Words" 3/2023
Wikipedia's "Economics of nuclear power plants"
Ian Sample's "Fukushima two years on: a dirty job with no end in sight"
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"
Hyman Rickover on Nuclear Designs

SMRs (Small Modular Reactors):
Michael Barnard's "Small Modular Nuclear Reactors Are Mostly Bad Policy"
Arjun Makhijani and M.V. Ramana's "Why Small Modular Nuclear Reactors Won't Help Counter the Climate Crisis"
Mark Cooper's "The Economic Failure of Nuclear Power ..." (PDF)
Michael Barnard's "What Drives This Madness On Small Modular Nuclear Reactors?"
From /u/Agent_03 on reddit 3/2023:
Part of the challenge with small-core designs is that they're up against nuclear physics: energy output increases with the cube of core size, where cost of the pressure vessel increases with the square of core size (plus some sizeable fixed costs for pumps etc). Neutron economy (and thus fuel burn-up) improves with larger cores as well. This means building fewer, bigger cores comes with a large built-in economy of scale. There are a few factors that partially offset that, such as the ability to rely more heavily on convection for cooling and easier handling of decay heat. But historically attempts to make small reactor cores cost-effective have failed for this fundamental reason.

NuScale has already had to increase their cost estimates from $58/MWh to $89/MWh, and if it follows the normal trajectory for new reactor technologies the final construction price will be at least double the estimates -- which would make their SMRs more expensive per unit energy than orthodox large-core reactor tech.

SMRs only end up becoming cheap if they achieve economies of scale, and that is unlikely. They're already more expensive than renewable energy today and the first construction won't finish until nearly 2030. At that point renewable energy and storage will be considerably cheaper, give current trends. So SMRs are going to be trying to scale production (to achieve cost-efficiency) on a timeframe when they're going to be massively undercut on costs by competing energy technologies.

SMRs are an interesting approach which may be really useful in a few niche applications, but they are unlikely to make much of an impact on energy markets. My personal estimate is the total amount of SMRs deployed will end up < 4 GW. Or about the size of a single large nuclear powerplant with several large reactor units.

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.

The nuclear lobby pushes "we need nuclear power to fight climate change". But

From /u/rethinkthegrid on reddit:
Here's a little thought exercise. Just to replace The current energy we get from fossil fuels, we would need in the region of 15TW of power operating 24/7. A normal nuclear plant produces around 1GW of power, meaning that we would need and 15,000 nuclear power plants to be built (mind, this is only to satisfy current needs, not accounting for any growth in energy usage). That means that if we built a nuclear power plant every day, it would take 40 years to fully power our current needs. Of course nuclear power plants need to be recomissioned every 50 years or so, so that cycle is going to continue indefinitely.

This is just to provide a bit of perspective. Do we need nuclear energy? Maybe. But it's certainly not going to single handedly solve the problem. Energy sources like solar certainly should not be discounted. Every hour over 100PWh of solar energy hit the earth, almost as much as we use in a whole year. Obviously we can't capture all of this, and the same argument I made above regarding nuclear power can be applied to solar power, but it is not a resource that can be ignored.

Finally, the prospect of grid scale energy storage, I don't think, is nearly as far away as this article implies. There are not only a plethora of interesting research avenues into energy storage, but with the explosion of electric cars, batteries are becoming cheap enough to be viable for grid scale storage.


LFTR (Liquid Fluoride 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 reddit 3/2014:
[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:
[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:
  1. The existing major industrial and utility commitments to the LWR, HTGR, and LMFBR (AKA other advanced reactors).

  2. The lack of incentive for industrial investment in supplying fuel cycle services, such as those required for solid fuel reactors.

  3. The overwhelming manufacturing and operating experience with solid fuel reactors in contrast with the very limited involvement with fluid fueled reactors.

  4. 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) (1972)

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.
From /u/Versac on reddit:
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:
  1. Simple: "Put this fuel in a reactor and all problems of nuclear go away"

  2. Unexpected: "Hey there's a energy source that solves all our problems that you've never heard of!"

  3. Concrete: "All you have to do is switch fuels from uranium to thorium!"

  4. Credible: "Tons of national lab scientists actually proved it works in the 60s"

  5. Emotional: "The only reason we don't do it is that the powers that be are holding it back, but we can fix this!"

  6. 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.

TL;DR is:
  1. 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.

  2. False. It needs a different mechanism but it can definitely be turned into a nuclear weapon.

  3. 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.

  4. 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 233Pa.

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 2 days, while 233Pa (the thing between Thorium and Uranium 233) has one of 27 days. 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 769TBq/g (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 20,800mSv/h. 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.

China MSR 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 difficult 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 bomb. THrisks 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.

From /u/Bleabot on reddit 12/2018:
Thorium reactors still use uranium. Thorium isn't fissile, so it cannot be used as an energy source. Thorium reactors would breed Uranium 233. That would be the actual energy source.

[Can thorium reactors be smaller than other reactors ?] As far as I know, a thorium reactor would be subject to the same restrictions. (Yes they have been designed to be smaller, but there are also tons of designs for small modular "traditional" reactors. Design is one thing. Implementation is another.)

[Cheaper ?] The primary reason thorium isn't used is because it would be prohibitively expensive for the industry to switch. It's not some huge conspiracy. Building the first-of-its-kind of anything is an enormous investment and there is absolutely no economic reason to do so. H*ll, there is very little economic incentive to build the reactors we're already familiar with!

I'm not trying to sh*t on thorium here. The thorium reactor is a really cool piece of technology, but it's not this miracle cure that people make it out to be. It has many of the same issues traditional reactors face, and many of the benefits that proponents tout (especially regarding waste and safety) have already been achieved with next-generation designs.

From /u/veemondumps on reddit 6/2022:
The only "advantage" of a thorium reactor is that it's harder to turn the waste products of the reactor into a nuclear bomb. It's not impossible to do so, nor would it be prohibitively difficult for a nation looking to acquire nuclear weapons. But it is technically harder. Exactly what country would actually consider that to be an advantage is up to you to figure out.

The disadvantages are significant:

1) Uranium reactors need to be refueled every 18-24 months. Thorium reactors need to be refueled every 3 months. Refueling using a conventional mechanism takes about a month, during which the reactor is out of service. That isn't economical to do on a reactor with a 3-month refueling cycle, so you need a mechanism that allows for the reactor to be refueled while in operation. Those are either substantially more expensive to build and operate, substantially more dangerous for the people refueling the reactor, or both.

You also burn through a lot more fuel doing this (which also means that the reactor is a lot less efficient on a per fuel mass basis).

2) Going along with how thorium reactors are less efficient - thorium itself can't be used as the sole fuel in the reactor - you also need to blend it with at least some enriched uranium. So you still need all of the enrichment infrastructure that you need for a conventional plant, plus the infrastructure to blend the thorium and uranium into fuel. Creating thorium fuel rods is not trivial and adds a substantial amount of cost to the already-expensive fuel.

3) You can't use water as a coolant in a true thorium reactor. The coolants that you can use are things such as liquid sodium or liquid lead - both of which have significant problems in terms of maintenance and safety. Also they're much more expensive to use than water.

There are some water-cooled reactors, such as the CANDU Reactor, that can incorporate some thorium into their fuel, but the fuel is still predominantly uranium.

The possibility of using thorium in the CANDU Reactor is more a gimmick than anything else - as mentioned above, it makes it harder to turn the reactor's waste products into nuclear weapons. That's a "selling point" of the reactor, though it's worth noting that no country that has built a CANDU Reactor has run it with any thorium blended into the fuel.

All 3 of those disadvantages are due to the basic physics of the thorium fuel. There is no way to engineer them out of a reactor - any reactor using thorium will have those disadvantages relative to a uranium reactor.

So you basically have reactors that are much more expensive to build, much more expensive to run, and much more dangerous than a conventional uranium reactor. And you're taking on all of those costs and risks for a single benefit that is of extremely dubious value to any country looking to build a nuclear reactor.

The only countries that have ever shown interest in thorium reactors are China and India. The reason both countries have shown interest in using thorium is because neither country has domestic uranium reserves, while they do have some thorium reserves. Despite the limited interest that both have shown, neither has seriously moved forward with plans for thorium reactors because of their significant downsides.

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'"
Union of Concerned Scientists Statement on Thorium-fueled Reactors (PDF)

World Nuclear News' "Chinese molten-salt reactor cleared for start up" (8/2022)


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 overall system break-even in a lab, much less built a reactor prototype.
    Former fusion scientist on why we won't have fusion power by 2040 (video)
    How close is nuclear fusion power? (video)

  • 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 (Wikipedia). 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.

    From Austin Vernon's "Why is the Nuclear Power Industry Stagnant?" 1/2022:
    The reactor portion of the [LWR fission] plant is only ~25% of construction costs.

    The rest of the facility is typical power plant components like heat exchangers, pumps, cooling towers, turbines, generators, etc. Nuclear plants have requirements like cobalt-free components, but other processing industries have similar limitations. These technologies are already far down a learning curve measured in hundreds of years, limiting potential cost declines.


    Most fusion concepts are just a more complicated way to heat water. They fall victim to the heat engine problem and will not revolutionize human energy use.

    The exception is the few startups that rethought generating electricity within their design, like Helion. Helion's cost goal is $10/MWh instead of $50/MWh because they don't need a traditional electricity generation setup.

    If you ever wonder about fusion, ask: "How does this technology/company generate electricity?" You can stop reading if it looks like a traditional thermal power plant.

    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)
    Real Engineering's "The Problem with Nuclear Fusion" (video)
    Brian Potter's "Will We Ever Get Fusion Power?"

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?

From /u/crnaruka:
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.
From /u/VeryLittle:
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 abundant 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:
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.
From /u/edemdee on reddit 5/2017:
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.
Re: "building cookie-cutter reactors": we've been using fission reactors for 60 years and still haven't managed to do this for them.

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 reddit 3/2016:
[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.

From someone on reddit 7/2022:
... there are leaks of tiny amounts of tritium at some fission plants and people lose their minds. Fusion reactors will have many orders of magnitude more tritium. Will people not lose their minds just the same? Tritium is notoriously hard to contain since it's so small. It can permeate through metal like a hot knife through butter.

Also, lots of people worry about fission and nuclear weapons proliferation. So does fusion get around this? Not really. In fact it's worse. Did you know that the two materials you need to make thermonuclear weapons are tritium and plutonium? Tritium breeding is required by almost all practical fusion power plants (the other reactions are 100s to 1000s of times harder ...

Plutonium is made by irradiating natural uranium from the dirt with neutrons. Practical fusion reactors have lots of neutrons. Really high energy ones too.

From someone on reddit 4/2019:
> Can someone ELI5 two things:
> 1- Is fusion power generally considered something that is feasible
> and will basically replace all other forms of electricity generation,
> giving us basically free unlimited power, once we crack certain hurdles,
> or is it largely viewed as a pipe-dream?
> 2- If it does become commercially viable, are the usual stories about
> "well energy companies will suppress it because they rely on people buying
> electricity from conventional power sources we control" simply bullsh*t
> conspiracy theory?

I actually work at one of these fusion startups so I think I can give some insight.

1) From a technical standpoint, fusion is completely within the realm of possibility. The technology to make DT fusion work has been know for years and the ITER project will probably get it working in the next 20 years. However, the problem is that it is very hard and will be so ungodly expensive that no one will ever build a commercial one. There are many problems with DT fusion. The neutron production is huge and will require enormous amounts of shielding and remote handling. Also, the feasibility of breeding tritium (the T required in the DT reaction) is dicey as well. That being said, DT is the easiest reaction to do and is probably our best shot. Advanced fuels are called that for a reason, they are advanced. Trying to get them to work before we master DT is a fools errand. It's like trying to work with jet fuel before you've built the internal combustion engine. The pb11 reaction is ridiculously hard and I have no idea how TAE has sold it to people (really good marketing). No serious person in the nuclear industry thinks that is possible. Also their FRC method (although interesting) has not been proven to work and certainly can't achieve the conditions for pb11 fusion which is three orders of mangnitude harder than DT. Additionally most of the energy of the reaction is in the form of hard x-rays, and I've read that you would need to capture an enormous percentage of this energy to make the process viable. This is something that no one has even come close to addressing and really goes to show how good TAE is at spewing BS. I literally laughed out loud when I heard their CEO say commercial fusion was 5 years away. I pick on them because they are the largest fusion company, but certainly others have tenuous claims as well.

2) This is a thinking trap that I think many proponents of conventional nuclear fall into as well. The idea of why there aren't fusion and fission plants everywhere is because outside influences (hippies and greedy corporations) have conspired to make them non-viable. The real problems are much more simple and they are cost and feasibility. Fusion is hard and expensive. Even if they get it working, I do not see it solving any of the cost problems that have caused conventional fission plants to stagnate. The capital costs are going to be huge for a fusion plant. The superconducting magnets alone are going to cost a billion dollars. Coupled with the fact that the machine will break down every other week because you have to replace the first wall which has turned to Swiss cheese. The capacity factors of fission plants are the only reason they are even remotely viable in today's energy landscape. Fusion will not even come close to running as frequently as those.

This all comes from someone who works in the fusion industry. There is a ton of BS hype that comes from people in this industry. I suggest you Google the term "fusion woo". Fusion is certainly a noble goal and could change a lot if we ever getting it working right. It could be the power source of 2200 but in the 21st century I just do not see it solving the fundamental problems that fission plants have today.

Giant fusion reactor in the sky