쉐도잉 연습: The Magic of Thorium Nuclear Reactors - YouTube로 영어 말하기 배우기

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Thorium is a kind of miraculous element.
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Thorium is a kind of miraculous element.
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Thorium found in nature isn't fissile – the atom's nucleus won't split when it absorbs a neutron.
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And yet, if you put a chunk of this same thorium in a special nuclear reactor,
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after a while most of the thorium will be gone,
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a whole bunch of energy will have been generated,
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and you'll be left with typical byproducts of fission.
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It's as if thorium is fissile, even though it's not.
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This is the genius of thorium breeder reactors.
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Oh, and I should disclose here that this video is sponsored by Copenhagen Atomics,
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who are working to make thorium power a reality,
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but they didn't get any say in the video and didn't get to review it before posting.
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The standard oversimplified picture of a fission reactor is,
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a uranium nucleus splits apart,
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or fissions, releasing heat energy and two or three neutrons,
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and those neutrons go on to be captured by more uranium nuclei and cause them to fission,
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releasing more heat energy and more neutrons, and so on.
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The heat is used to generate electricity,
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the neutrons to maintain the fission chain reaction.
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However, the actual story is more complicated.
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When a nucleus splits, there are actually four things that can happen to the neutrons it emits.
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One, like we've already mentioned,
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they can be captured by a fissile atom like uranium-235,
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causing it to fission and release more neutrons,
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and this part has to happen on average at least once per fission to sustain the chain reaction.
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Two, neutrons can be captured by the nuclei of other atoms in the reactor,
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without causing fission, like maybe the metal case,
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or the moderator, or the control rods, or whatever.
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3 Neutrons can escape and leave the reactor entirely.
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Or 4 A neutron can be captured by an atom that's not fissile,
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and transmute it into an atom that is fissile.
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Because remember, these are atomic nuclei we're dealing with.
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Absorption of a neutron will turn uranium-238 into uranium-239,
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the number is just the total number of protons and neutrons.
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And uranium-239 can then radioactively decay into neptunium-239,
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which can then decay into plutonium-239, which is fissile.
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If the capture of a neutron transforms a non-fissile element into a fissile one,
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it's called a fertile capture.
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And fertile capture is what makes thorium useful.
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In fact, even in a normal uranium reactor,
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fertile capture accounts for over a third of the energy generated by the reactor.
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A normal nuclear reactor uses uranium-235,
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which is fissile, but naturally occurring uranium ore contains only 0.7% uranium-235.
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Almost all the rest is uranium-238,
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which is essentially non-fissile, but it is fertile.
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Even when using fuels with enriched levels of uranium-235 undergoing fission,
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there's so much non-fissile U-238 around that some of the chain reaction neutrons instead transform U-238 into plutonium-239,
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which can then fission.
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But U-235 doesn't make enough neutrons,
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and U-238 doesn't turn into plutonium easily enough
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that you can both sustain a fission chain reaction and continue to transform new fissile fuel.
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So at the end you're left with a big chunk of unfissioned but still full of radioactive waste, uranium-238.
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There's a different kind of reactor,
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called a fast breeder reactor,
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that uses plutonium as the primary fissile fuel,
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and uranium-238 as a fertile secondary source.
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This combination can both sustain the fission chain reaction and transform new fuel in a self-sustaining way.
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But fast breeder reactors are less researched,
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more expensive, and harder to run effectively.
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For now.
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This is where thorium comes in.
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The same route used in the transformation of uranium-238 to plutonium-239 can be replicated down here,
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starting instead with thorium-232.
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By adding a neutron, we get thorium-233,
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which decays to protactinium-233, which decays to uranium-233,
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which is fissile and can be used to generate energy.
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So if you load your reactor with thorium-232,
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which, remember, is not fissile,
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and you throw in some starter fissile fuel,
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then for each fission reaction,
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the number of new fissile atoms created is more than one on average,
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and the number of new atoms split is more than one on average,
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and remember those atoms give you more neutrons.
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So the transformation of thorium,
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and the fission of uranium,
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can keep going and going and going,
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until in principle, all of the thorium is gone.
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And crucially, thorium transformation can happen in a reactor that doesn't have the same challenges as a fast breeder reactor,
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and it gets rid of most of the long-lived radioactive waste.
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And thorium is more abundant than uranium,
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and doesn't need the expensive refining process to concentrate the fissile uranium-235,
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and so you can see why people get excited about thorium.
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There are, of course, challenges and downsides to making thorium reactors,
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which is why we don't have and so far have never had commercial energy generation from thorium.
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But that's fertile material for another time.
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Getting commercial power from thorium may soon be possible thanks to the work of organizations such as this video's sponsor, Copenhagen Atomics.
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Copenhagen Atomics is building compact,
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modular thorium reactors to produce cheap energy.
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Unlike traditional nuclear power stations,
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which are giant infrastructure projects,
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Copenhagen Atomics are designing a self-contained reactor unit that can fit inside a shipping container.
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The reactors are based on a design pioneered over 50 years ago that uses molten salt to carry the fuel,
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resulting in fewer lost neutrons and more complete combustion,
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so you get more energy for less waste.
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These reactors can also use plutonium waste from classic nuclear reactors as fuel,
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extracting ten times more energy out of spent nuclear fuel than the initial reactor did in the first place,
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and in doing so converting long-lived radioactive waste into short-lived radioactive waste.
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In theory, these reactors could run anything from grids to ships to moon bases.
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Check out Copenhagen Atomics website to learn more about their work.

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일상 소통을 위한 TOP 5 문구

  • 토륨은 기적의 원소입니다. (Thorium is a miraculous element.)
  • 핵 반응에서의 중성자 역할은 복잡합니다. (The role of neutrons in nuclear reactions is complicated.)
  • 비가열 원소가 가열 원소로 변할 수 있습니다. (A non-fissile element can become fissile.)
  • 핵 반응기에서 방출되는 중성자의 운명은 다양합니다. (The fate of neutrons emitted in a reactor is diverse.)
  • 우라늄-238은 비가열 원소이지만, 유용합니다. (Uranium-238 is non-fissile, but it's useful.)

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