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
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.
