I am trying to find reliable information and comparisons about the energy production of renewable energy technologies, specifically, how solar and wind alternatives compare to nuclear fusion.

Why is it generally consider, as I have read, that nuclear fusion is the ultimate renewable energy? Is it really that clean? Would a fusion reactor be safe? Is the infrastructure required cheaper than solar and wind (considering long-term returns)?

If the answer to all or some of the above questions is affirmative, then why countries around the world invest anything at all in solar and wind? Why aren't the efforts directed to obtaining nuclear fusion?

I'm guessing a reasonable answer to these questions could be the inmediate mitigation of ongoing climate change and shortage of non-renewable resources. But then we should say that solar and wind alternatives are a 'transition' towards nuclear fusion. In this case, the main objective for countries worldwide should be obtaining nuclear fusion. But, in the future, when we harness nuclear fusion, wouldn't solar and wind become obsolete?

P.S. I just asked this question in Physics and it wasn't well received by some user because it is about 'politics'. Please, note that I am not interested in a political opinion, but a scientific assessment. The political and economic issues that may be involved are inevitable given the nature of the question. I posted here because now I think it is more appropriate for this site.

  • $\begingroup$ There's an interesting implicit assumption in the question "Would a fusion reactor be safe?". The most common construction injury is falls from height - osha.gov/oshstats/commonstats.html classes falls as number one in a 'fatal four' causes ( 364 out of 937 total deaths in construction in 2015). Wind energy almost invariably features tall structures with poor access. What does safe mean? A wind turbine is clearly unlikely to take out a city (which is not to say that a fusion reactor is likely to do so) but the implication that it's automatically safe is interesting. $\endgroup$ – achrn Jul 13 '17 at 10:08
  • $\begingroup$ @achrn What I meant by 'safe' is that it is well known (Chernobyl, Fukushima...) that fission reactors can be 'super' unsafe for millions of people if you compare it with falls as a result of dangerous maintenance jobs. Nuclear fusion doesn't have this problem with radiation, but could a reactor, for instance, explode like, incidentally, an H-bomb? $\endgroup$ – Alberto Jul 13 '17 at 10:22
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    $\begingroup$ The point made by @achrn is still valid. It sounds like you came into this already discounting nuclear fission but it is generally not "super unsafe" as you say, and is actually a quite viable technology if you don't get caught in the politics. There have been relatively few nuclear accidents, and (in the US, at least) every incident that does occur including ones that don't make the news, is required to be evaluated by live sites to evaluate lessons learned. Furthermore, almost all of the big incidents were the result of bypassing safeguards. $\endgroup$ – Secundus Jul 13 '17 at 11:40
  • $\begingroup$ This is a very broad question/series of questions, you could probably break this down into several individual questions such as "What properties of fusion energy production make it inherently safe?" or something along those lines. For your some of your other questions, such as why we aren't directing all our efforts into developing fusion power, the answers are going to be opinion-based and likely rooted in politics and economics (risk vs. reward) $\endgroup$ – BarbalatsDilemma Aug 2 '17 at 18:43
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    $\begingroup$ Since you are still interested, you might enjoy reading up on hydroelectric power. As far as sustainability goes, it's a very "green" method as well. Yes, there are caveats such as fish migration and the separation of ecosystems, but the water is flowing a given direction whether you benefit or not. Another concern with wind is that energy is being robbed from performing it's natural function within weather cycles, while taking kinetic energy from water is less impactful. $\endgroup$ – Secundus Aug 4 '17 at 0:06

Fusion is widely extolled by advocates as being safe (but is that collective opinion justified)?

I would prefer to begin my discussion comparing fusion with renewable energy systems with an examination of safety as in my opinion, safety should always come first when we compare energy alternatives.

Some Reasons offered why Fusion should be Safe - - Only tiny amounts of fusion fuel are inside a fusion reactor at any one time. Continuous operation of a fusion power plant is maintained by continual refuelling with the fuel mixture (deuterium-tritium or deuterium-deuterium), so the fuel inventory in the plasma chamber at any time is gram quantities or less and sufficient only for about one minute of operation. The ITER tokamak will contain only grams of fusion fuel as it runs. A NIF laser fusion capsule contains only about 0.17 milligrams of Deuterium-Tritium fuel (Basic premise – If the fuel is not inside the reactor, it can’t even theoretically explode inside the reactor or become a factor in an accident)

-No greenhouse gasses produced

  • No reactor meltdowns or decay heat burn downs (Chernboyl, Three Mile Island, Fukushima incidents cannot happen)

  • No mining of fuel (fuel is extracted from water)

  • Billions of years of fuel available on earth (versus hundreds for fossil fuels)

  • 1/1000ths of the radioactive waste of fission power. Nearly all materials become activated to some degree by energetic neutron bombardment. Neutron reactions in DT fusion reactors will inevitably create radioisotopes. The principal radioactive materials present in a DT or DD fusion reactor will therefore be tritium and neutron activated structural materials surrounding the reaction volume in the fusion chamber.

  • Radioactive waste, mostly neutron activated fission chamber structural material remains radioactive ~20 years versus hundreds of thousands of years for Minor Actinides in spent fuel produced by fission reactors. DT fusion reactors would however burn and require storage of significant quantities of Tritium, a moderately radioactive nuclear isotope of hydrogen. Tritium gas is hard to secure and small leaks in reactor tanks and plumbing could result in some loss of tritium to the environment. Tritium decays while emitting weak Beta radiation and under most circumstances is not seriously hazardous to humans. The deuterium-deuterium (DD) fusion process, dispensing with tritium as a fuel and the requirement for Tritium storage. DD fusion does however produce Tritium as part of the DD fusion reaction, but this Tritium does not tend to accumulate but is immediately burned in place inside a DD fusion reactor.

  • Fuel for energy would no longer be a geopolitical issue (huge benefit for humanity)

  • No nuclear weapons from waste products (again, huge benefit for humanity)

To have success in fusion and renewable energy innovation -

you have to get the BIG PICTURE right

The ultimate potential of D-D Fusion is very great and eclipses the potential of all other forms of energy production including nuclear fission and renewable energy systems-

Fusion Energy longer than the earth has existed or the sun will burn

The complete conversion of deuterium nuclear fuel releases an energy content of 250 x 10^15 joules per metric ton of deuterium. The quantity of deuterium in the world’s oceans is estimated at 4.6 x 10^13 metric tons. Deuterium present in seawater will yield around 5 x 10^11 TW-years of energy. In the year 2016 the entire planet consumed around 17 TW-years of energy, which means that the energy content of the deuterium in seawater would be enough for 29.5 billion years of energy supply.

To give all 10 billion people expected to live on the planet in 2050 the level of energy prosperity we in the developed world are used to, a continuous average use of power of 6 kilowatts per person as is typical in Europe, we would need to generate 60 terawatts as a planet—the equivalent of 900 million barrels of oil per day.

The time since the earth first formed = 4.54 billion years.

The time until the sun burns out = 5 billion years.

The deuterium in the sea is capable of completely powering planet earth at a level of 60 Terawatts for 8.33 billion years

(longer than the earth has existed or the sun will burn).

D-D fusion of pure Deuterium separated from sea water is a practical fusion reaction and practical fuel for ICF fusion

When talking about near term prospects for fusion, fusion scientists frequently neglect to mention that mankind's first successful terrestrial release of fusion energy (Ivy-Mike experimental test shot of 1952) produced in excess of an exawatt of fusion power from D-D (not D-T) fusion. Use of cheap and ubiquitous Deuterium separated from sea water was the very first fusion reaction to work. Futher, it deserves to be pointed out that Ivy-Mike D-D fusion worked the very first time it was tried, and never failed to work.

Hundreds of Magnetic Confinement Fusion devices that have been built over the course of 60+ years have never once even for milliseconds produced break-even fusion power or fusion with energy gain. ICF fusion of cheap and common Deuterium from sea water worked the first time it was tried (Ivy-Mike 1952) and thereafter never failed to work in hundreds of underground nuclear tests held at NTS and on the Pacific Test Range (Marshall Islands).

Large tokamak magnetic fusion designers often tend to discount the deuterium-deuterium (D-D) fusion reaction because it is not possible to achieve the necessary fusion reaction rates and break-even energy with D-D fusion using tokamaks and stellarator devices such as we currently are able build. The situation is different, however, with Inertial Confinement Fusion which typically employs fusion plasmas that are literally 10^11 times more dense than the typical ion plasma densities used in MCF tokamaks or stellarators.

The power than can be drawn from a plasma at fusion conditions is proportional to the second power of the plasma ion density. Even small improvements in plasma ion density will result in significant improvements in the performance of a fusion experiment.

There is an impressively large Range of plasma density in current and planned fusion experiments Plasma ion density of typical current fusion experiments

There is literally a factor of 10^10 to 10^11 difference in plasma ion density between MCF and ICF fusion experiments. This large difference has implications for commercial fusion technology as the denser the plasma, the more power that can be realized from a fusion burn and the smaller the physical fusion reactor can be while achieving fusion energy with energy gain.

The D-D reaction takes place at higher temperatures than can typically be achieved in magnetic confinement tokamaks and typically has a lower fusion cross section leading to lower fusion reaction rates on earth relative to D-T fusion .

D-D fusion is more complex and proceeds with multiple fusion side reactions, but when all of the side-chains run to completion, D-D fusion actually produces more energy than D-T fusion per starting mass of reactants. D-D fusion produces T and He3, which in a secondary reaction burn with D. This was practically demonstrated in early thermonuclear tests like the 15 Megaton Ivy Mike fission triggered deuterium experimental test in 1952.

D-D fusion does normally produce Tritium

D-D Fusion of Deuterium fuel produces energy through four reactions:

D + D -> He-3 + n + 3.268 MeV

D + D -> T + p + 4.03 MeV

(side chains)

D + T -> He-4 + n + 17.588 MeV

He-3 + D -> He-4 + p + 18.34 MeV

The net effect of these four fusion reactions taken together is:

6 D -> 2 He-4 + 2p + 2n + 43.243 MeV

Fusion and neutrons -

DT and DD fusion release large amounts of their fusion energy in the form of fast neutrons.

The task of shielding fast neutrons requires

• Fast Neutrons (E >1 MeV) must first be thermalized with high

neutron scattering materials (typically materials that have a high percentage of light atoms like hydrogen)

• These thermal neutrons can then be absorbed or shielded with material having high cross sections for neutron absorption

Absorption of thermalized neutrons can be done by relatively light materials like polyethylene plastic unlike gamma radiation that require lots of high-z material (lead, concrete, water) to absorb the penetrating gamma. LLNL's Dr. Ralph Moir has pioneered several molten salt fusion reactor concepts (HyLife II and PACER Revisited). A thick liquid falling wall of molten salt loaded with a neutron absorber like 50 micron particles of Boron Carbide as a slurry can absorb damaging fast neutrons. Such a thick falling wall of molten salt can effectively protect fusion chamber structure and largely prevent neutron activation of fusion reactor materials. This permits molten salt ICF fusion reactors to have long 30+ year commercial lifetimes and to at reactor end of life produce little or no neutron activated waste.

Energy Density

The issue of producing fusion with energy gain while simultaneously achieving a high enough power density are dominant themes of the near future in selection of which energy technology is best suited to produce competitive power plants that communities will want to build to produce safe and dependable power.

Comparison of fusion and “renewable” energy systems from the standpoint of energy density

Source Joules per cubic meter

Solar Radiation = 0.0000015

Geothermal = 0.05

Wind at 10 mph = 7

Tidal water = 0.5-50

deuterium in the form of D2O (heavy water) = 6.88 x 10^10 MJ/cubic meter

note: about 20% by mass of heavy water or D2O is deuterium Deuterium is a gas at standard temperature and pressure but heavy water D2O is a easily and safely stored as a liquid. D-D fusion is in excess of million times more energy dense than any renewable energy system.

Practical fusion will always be 50+ years ago (not 50 years away)

Mankind came into possession of a practical way of generating energy from fusion over 50 years ago with the Ivy-Mike nuclear test that produced fusion energy from pure Deuterium via DD fusion. Practical fusion will always be 50+ years ago (not 50 years away) Today, there are smaller pure fusion devices designed to make clean energy (not blast effects) from pure DD fusion of Deuterium separated from sea water. One such design is called mini-Mike, which produces a small predictable controlled energy yield of 250 GJ.

Note: Deuterium separated from sea water is totally non-radioactive and fusion of this fuel produces only totally non-radioactive nuclear waste

Inertial Confinement Fusion has already been PROVEN to work and produce fusion ignition and fusion with energy gain

Both LANL and LLNL were successful in producing full ICF fusion ignition during the last years of the cold war era. ICF fusion is experimentally demonstrated and proven to work and this places ICF fusion in a different category than any other form of fusion..

The energy needed to ignite an inertially confined thermonuclear fusion reaction in liquid (or solid) deuterium-tritium (DT) is not that large; it is on the order of not more than 10 MJ or about the same amount of chemical energy stored in about 1.25 cups of automotive gasoline. The problem is that this energy must be compressed in space (focused down to an area less than a 2 mm) and in time (to less than 3 nanoseconds).

Pure Inertial Confinement Fusion that does not use nuclear fission to produce the conditions for fusion is today driver limited.

It is still not experimentally possible to build a laser (or ion particle accelerator) large enough to produce DT fusion ignition. Still, many people, including Congress, in the late 1980s and early 1990s wanted to know for certain if inertial confinement fusion would ultimately work and actually produce net energy from fusion. To answer this question, in the final few years on underground nuclear testing, both LANL and LLNL designed a series of test shots called Halite-Centurion. Halite-Centurion series shots were fusion related add on shots piggy-backed onto shots already on the schedule. These shots were designed to utilize a small portion of the X-rays produced from the primary of an experimental device through a line of sight to a remote fusion experiment housed some distance away in the underground experimental test canister. Lasers and Ion-beam fusion drivers such as were available at that time could not provide the driver energy required to produce fusion ignition - but X-rays from a remotely ignited fission device could provide the driver energy needed (>10 MJ energy delivered into a spot of about 2 mm in a time of less than 3 nanoseconds) .

Halite-Centurion fusion experiments in the Nevada desert worked and reliably and repeatedly and produced full fusion ignition of small sub-gram samples of DT fuel (in small filled spheres). These experiments were once classified but DOE allowed senior scientist Dr. John Lindl to declassify and reveal about half of the fusion related project information. Halite-Centurion experiments are referred to in a fundamental document for the design of the NIF facility: the 91 pages paper of John Lindl entitled “Development of the indirect-drive approach to inertial confinement and the target physics basis for ignition and gain”, published in 1995 in the AIP/Physics of plasmas. Halite-Centurion success was used by LLNL managers to sell the NIF program to Congress in the mid-1990s.

What is lacking in current ICF fusion experiments to support building of practical ICF fusion power plants is a fusion driver with characteristics close enough to the driver employed by LANL and LLNL in Halite-Centurion tests to permit full fusion ignition with energy gain. A driver capable of delivering greater than 10 MJ into a focused area less than a 2 mm in time of less than 3 nanoseconds. The current NIF driver laser driver is capable of delivering about 2 MJ total energy and is only able to achieve "alpha heating" phase of fusion operation - a stage that immediately precedes fusion ignition. LASNEX and HYDRA computer simulations on which LLNL based the engineering design of the NIF laser were overly optimistic in predicting the required fusion driver characteristics to produce ignition. Failure of the LASNEX and HYDRA simulations resulted in NIF being built too small to achieve the goal of fusion ignition and for NIF to serve as the basis of LIFE ICF fusion power plant technology.

Source documents (with links where possible) - NY Times article published at the time of Halite-Centurion field tests - Secret Advance in Nuclear Fusion Spurs a Dispute Among Scientists http://www.nytimes.com/1988/03/21/us/secret-advance-in-nuclear-fusion-spurs-a-dispute-among-scientists.html?pagewanted=all

The following document contains what John Lindl was permitted to release publicly regarding Halite-Centurion ICF by DOE "Development of the Indirect‐drive Approach to Inertial Confinement Fusion and the Target Physics Basis for Ignition and Gain." John Lindl. Page: 3937. AIP Physics of Plasma. American Institute of Physics, 14 June 1995.

Light ion driver pure fusion power plant concept

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    $\begingroup$ This answer, while containing lots of information about fusion power and how it may or may not be produced, does not really answer the original questions, which are "Why is nuclear fusion considered safe?" and "Why aren't we pursuing feasible fusion over solar and wind technology?" This answer reads as an extended article on the feasibility of nuclear fusion, and the technologies that may enable it. This answer could be improved by tightening its focus to specifically answer the questions in the OP, without digressing into a long discussion on fusion power $\endgroup$ – BarbalatsDilemma Aug 2 '17 at 18:54
  • $\begingroup$ @BarbalatsDilemma I do not agree, I think this answer provides sufficient information to answer pretty much everything I have asked above. It presents information and numerical comparisons of the technologies in question (which was the original question, the first two paragraphs). As for the rest (the most controversial part), as I said, I didn't want a political opinion, just data and scientific assessment. $\endgroup$ – Alberto Aug 2 '17 at 22:12

The reality of generating electricity from nuclear fusion on an industrial scale is still a very long ways off. It is speculative high cost, high risk venture, with a potential high payoff far off into the future. Test reactors alone are >$100 million.

The existing technical problems and challenges with nuclear fusion are very complex. We're talking about generating the equivalent of the suns core at will in a controlled manner here on Earth vs. harnessing the energy of the actual sun from 93 million miles away. Only one of these can be put into practice now and for the foreseeable future.

  • $\begingroup$ The reality of generating electricity from nuclear fusion on an industrial scale is still a very long ways off. [...] Only one of these can be put into practice now and for the foreseeable future. Those claims are false according to this. Apparently based on fairly reliable sources and talking about dates we can consider the foreseeable future $\endgroup$ – Alberto Jul 13 '17 at 9:54
  • $\begingroup$ And let me add, getting nuclear fusion by the end of this century is not a very long ways off having other renewable energy alternatives as 'transition', as I mentioned in the original post. $\endgroup$ – Alberto Jul 13 '17 at 10:00
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    $\begingroup$ Solar is an incredibly dirty technology on the manufacturing and disposal ends. When you factor that in, it's nowhere near as green as perceived. Furthermore, their lifespans are quite short. Wind is a relatively very low output technology and, while you can discount political arguments, some of those arguments are valid environmental concerns. Yes they kill birds, but they also change wind patterns. That energy is not completely free in the sense that (review your laws of thermodynamics) nature is expecting it to go somewhere. $\endgroup$ – Secundus Jul 13 '17 at 11:46
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    $\begingroup$ "I don't really know what makes fusion so awesome". The pie in the sky with fusion is the sheer scale of energy that is given off in a sustained fusion reaction. It is orders of magbitude more than you can get with solar and wind and, if continued, requires hydrogen as a fuel input rather than messing around with fossil fuels and everything that comes with that. $\endgroup$ – Secundus Jul 13 '17 at 11:50
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    $\begingroup$ @Brian This answer could be improved with some citations backing up the claims, such as "nuclear fusion is a long ways off" and the cost of a test reactor being >$100 million $\endgroup$ – BarbalatsDilemma Aug 2 '17 at 18:58

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