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Comment by dmitrybrant | Hacker News Reader

I'm not sure where people are getting this terminology of "unlimited" energy from fusion. Nothing in the universe is unlimited. The earth's supply of deuterium and/or tritium is not unlimited.

It's also not infinitely "clean" energy. A fusion reactor is not a black box that is built once and never again maintained or rebuilt, or doesn't use any consumable components besides fuel.

We already have the technology that gives us nearly clean energy, namely nuclear (fission) reactors. If we truly want to reduce CO2, we should be ramping up nuclear power, as a bridge to switching to renewables in the long term. If only nuclear power wasn't so politically... radioactive.

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Please, don’t act like nuclear fusion is a simple iteration of nuclear fission. It’s a fundamentally different process.

Fusion would provide (much) more energy, use (much) less radioactive inputs, and produce (much) less radioactive outputs. Fusion is significantly safer. In a failure mode the fusion reaction will lose containment and die out like a fire without oxygen. Fission rods will continue to produce heat & radiation in a failure mode, and all failure modes of a fission power plant need to account for this.

I’m actually pro fission, because the risks of fission are lower than the risks of coal, oil, and natural gas. Yes, the article was hyperbolic. However, you’re under-hyping the advancement of fusion. When fusion comes it will be politically palpable globally, cleaner than fission, and it will reduce the cost of energy significantly.

The actual reactive core is safer, it cannot meltdown, but we don't know much about the support systems just yet. With all that energy running through the magnets, the pressures involved in the contemplated energy collection system, there is a potential for catastrophic failure modes. A steam explosion isn't nuclear bomb but can still kill. Fusion is safer than fission but I wouldn't yet call it safer than solar panels.

Depends how you're measuring risk. Microdeaths per megawatt-year?

The thing about a fusion plant is that there likely won't be that many people on site. Failure modes for the most part ought to look like conventional explosions, which we largely know how to mitigate where they're likely.

What worries me, with the sequence of plants, starting with ITER and DEMO, is that because of the scaling laws that seem to be involved, we're heading towards very few gigantic generators, where they're each responsible for such a large proportion of the power supply that we couldn't cope with any one of them going offline. The immediate power loss itself could be responsible for loss of life.

> fission rods will continue to produce heat & radiation in failure mode

Not all fission designs require solid fuel rods, e.g. LFTR, which coincidentally has a failure mode that is much safer than solid fuel fission reactors.

>> this terminology of "unlimited" energy from fusion.

All language exists in context. This isn't a math prof talking of 1/0-type infinity. This is a practical infinity, ie so much energy that we cannot contemplate how we would run out. With literal oceans of hydrogen at our feet, and more landing on earth daily in the form of comets/asteroids, speaking of infinities is understandable.

Deuterium is measured in parts-per-million in the universe at large. Lithium is parts per billion, and in theory you can feed hydrogen into a white dwarf and harvest lithium from the novas. For a Kardashev III civilization just harvesting existing deuterium and lithium this is at least 1MJ/kg of specific energy over all the matter in the galaxy (if I did my math right). Not quite unlimited, but roughly as if 10% of the galaxy was made of hydrocarbon fuel.

The same place that fossil fuel advocates get "unlimited" for fossil fuels.

They just mean "a lot"

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