The recent hoopla got me digging into this subject. Turns out we've all been ruthlessly flim-flammed about fusion for decades. Here are the biggest "energy utopia" bogosities and why they're irreducibly not true.
1) The National Ignition Facility "breakthrough" returned 150% of the energy input required to "ignite" the burn.
This is only true when pure mathematical energy values for energy in and energy out are calculated for a tiny envelope directly around the target, which was bombarded with 2 mega-Joules (MJ) of laser energy and returned 3 MJ-- but "pumping up" those lasers for the discharge ate FOUR HUNDRED MJ of grid electricity, so the return on that energy was 0.75 percent. Never mind the energy input at the power plant where the grid electricity came from. Never mind conversion losses for changing the 3 MJ output back into electricity. Never mind the energy needed to create the fuel pellet or any exotic environment, e.g. high vacuum or extreme pressure or inert gas, inside the ignition chamber.
2) the fuel for this "energy utopia" will be hydrogen from sea water, of which we have a multi-billion-year supply.
This is a fantasy based on hydrogen's natural isotopes, protium and deuterium. Hydrogen has three isotopes of interest: protium (one electron orbiting one naked proton), deuterium (one electron orbiting a proton plus a neutron), and tritium (one electron orbiting one proton and two neutrons). As always with nuclear energy, isotopes are all-important.
natural, readily available hydrogen is 99.98 percent protium. While this isotope is fused deep inside stars, essentially forming deuterium, this only happens at fantastic i.e. non-feasible pressures, temperatures, and timescales. Many "aneutronic" fusion schemes are being floated but no one floats fusion of pure protium because no one is irresponsible enough to explicitly pretend it's possible (they only implicitly pretend). As you go up through these isotopes by mass, energy inputs drop and outputs increase, with tritium being the holy grail of feasible fusion, returning 22 times more energy than deuterium from a relatively "do-able" input. Most of this energy is in the form of "fast" radiated neutrons.
The fuel used for the recent "breakthrough" was 1:1 deuterium/tritium, a blend that promises to be our only viable fusion fuel for many decades, possibly forever.
So while deuterium can be derived from seawater (one deuterium atom per 6,410 hydrogen atoms), tritium does not exist in nature at all. The current supply is synthesized inside conventional nuclear reactors at a cost of $100,000.00 per gram. The pro-fusion wonks theorize that tritium can be synthesized en masse inside fusion reactors (by neutron bombardment of lithium-6, yet another problem) but until it's actually done no one really knows that. So the real "limiting nutrient" of fusion isn't deuterium in seawater at all, but how much lithium-6 we can extract and refine from the earth's crust. Only 7.5% of natural lithium is isotope 6, which no one is sure can be separated.
3) nuclear fusion is "clean," i.e. will produce negligible nuclear waste.
Again, this is a fantasy based on fusion of protium or deuterium. The first problem is tritium, which is radioactive (a beta emitter) with a half-life of 12.3 years. Scientists report that tritium is "slippery" stuff that's extremely hard to contain, and upon escape into the environment it immediately reacts with oxygen to form tritiated water, which is considered extremely dangerous. Once inside your body, tritiated water can cause fatal radiation sickness, cancer, birth defects, every other calamity radiation is known for.
So before we even get to the fusion part, the fuel alone presents an unprecedented radiological hazard.
Then there's fusion itself. As stated before, most of the energy output from deuterium-tritium fuel is in the form of free neutrons. The larger reactor can be shielded from much of this neutron flux, but 100% shielding is probably not possible, and any material (including shielding) that's bombarded with neutrons will absorb said neutrons into its atomic nuclei, becoming incredibly nasty high-level nuclear waste. So much for "clean." If you recall the cobalt "doomsday" bomb postulated decades ago, that idea was based on "salting" fusion bombs with cobalt, which upon detonation would absorb neutrons becoming cobalt-60, a radionuclide vastly worse than those of "mundane" fission fall-out (strontium-90, cesium-137, iodine-131). That's a taste of what we're looking at here.
A much more detailed article about all this, written by a retired atomic scientist who went rogue against the prevailing propaganda.
In other words, all current pro-fusion hoopla is basically Reddy Kilowatt II.
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