Conclusionįission is efficient at human scale, but uncontrollable at planetary scale (if you had a fissile pile the size of a planet, good luck making a power plant out of that). That's not even taking into account the thermal losses in the lasers themselves, which are some of the most powerful ever built, or all the energy spent running cooling pumps and other essential equipment. ![]() NIF, which uses lasers to trigger fusion, only converts about 10% of the laser energy into potential fusion. That's roughly a medium-sized power plant that could normally power a decent-sized city, just to warm up a single fusion reactor. ITER, one of the oldest and most mature fusion reactors, takes about half a gigawatt to operate. But as others have noted, sustaining a fusion reaction is even harder than starting one. If they could produce more energy than they consume, then once started, they would be self-sustaining. In reality, only a fraction of that turns into fusion reactions, so we don't get a whole lot of fusion out of each attempt.įusion reactors require a tremendous amount of energy just to operate. If we could get all that energy to turn into fusion reactions, we would be golden. Simply heating up a fuel pellet to 1 million degrees isn't very useful. Doty is referring to with the square/cube scaling. And since the fusion targets tend to be very small, it is extremely difficult to get all that input energy to drive fusion, rather than just heating up your target. If you don't have 10 Jupiters of gravity to do that work for you, then the energy needs to come from somewhere else: lasers, plasma, really powerful hammers, etc. ![]() Unfortunately, the flip side is that to achieve fusion, you need to inject a lot of energy into a fairly small space. Chemistry itself would become relatively unstable. Even a rocket launch might permanently change the exhaust products. Imagine if a car crash concentrated enough energy to transmute elements. If it were easy, then a lot of elements would not be stable. If fission bombs weren't practical, we would almost certainly not have any fusion weapons of any kind right now. If we compare the masses of these natural reactors, it's clear that fission is at least 6 orders of magnitude easier than fusion (and probably closer to 9-12.just too lazy to do the math).Īs others have pointed out, the only reason fusion bombs even exist is because we can use fission reactions to compress the fusion products. However, the smallest natural fusion reactor is probably the brown dwarf, which has a mass at least 10x Jupiter's. Natural fission reactors exist on earth, at a small scale, and low energy. Unmoderated fission on a very short timescale (known as prompt criticality) is how the World War II-era atomic bombs worked. Please note that the loss of ability to moderate nuclear fission was the cause of various high-profile nuclear accidents ( e.g. In contrast, nuclear fission can be controlled (known as a moderated fission reaction), and this energy can be captured and re-distributed as electrical power. The entire multi-stage explosive reaction happens on the order of microseconds. This Wikipedia page lists various methods currently being developed.Ī thermonuclear weapon does indeed use nuclear fusion - at these very high temperatures - but the fusion reaction (secondary stage) only happens because a fission reaction (primary stage) precedes it to set up the conditions needed for fusion. This is where the current research & development is happening. To successfully capture the energy of nucluear fusion, we need to control the fusion process and sustain it for a much longer time. The Sun can achieve fusion with "only" $1.5 \times 10^7 K$ because of its sheer bulk and intense pressure at the core. ![]() The conditions needed for nuclear fusion here on Earth involve extremely high temperature - on the order of $10^8$ K. ![]() The key difficulty in fusion power is sustaining a controlled nuclear fusion reaction.
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