Name: TEDx】TEDxYYC - カーク・ソレンセン - トリウム (【TEDx】TEDxYYC - Kirk Sorensen - Thorium)
Uploaded: 2021-01-14T04:54:50.000Z
Duration: 10 min 3 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

程度の副詞

nearly everyone in the world is part of some community whether large or small

and all of these communities have similar needs

they need air conditioning people can't function very well when

they need food to be grown or provided distributed and stored safely

they need waste products to be collected removed and processed

people in the community need to be able to get from one place to another

and a supply of energy is the basis for all of these activities

energy in the form of electricity provides light and air conditioning

energy in the form of heat keeps us warm and energy in chemical form

provides fertilizer drives farm machinery and transportation

and in the beginning of my time there in 2000 i was very interested in communities

but this is the kind of community i was thinking of

a lunar community it had all of the same needs as a community on earth would have

and we had to think about how we would provide energy for this very unique community

there's no coal on the moon there's no petroleum

there's no natural gas there's no atmosphere

and solar power has a real problem: the moon orbits the earth once a month

for two weeks the sun goes down and your solar panels don't make any energy

you want to try to store enough energy in batteries for two weeks

so nuclear energy was really the only choice

now back in 2000 i really didn't know too much about nuclear power

so i started trying to learn almost all of the nuclear power

we use on earth today uses water as the basic coolant

that has had some advantages but it has a lot of disadvantages

you have to get the water a lot hotter than you normally can

at normal pressure water will boil at 100 degrees celsius

this isn't nearly hot enough to generate electricity effectively

so water-cooled reactors have to run at much higher pressures

some water-cooled reactors run at over 70 atmospheres of pressure

and others have to run at as much as 150 atmospheres of pressure

there's no getting around this it is simply what you have to do

if you want to generate electricity using a water-cooled reactor

and this means that you have to build a water-cooled reactor as a pressure vessel

with steel walls over 20 centimeters thick if that sounds heavy that's because it is

things get a lot worse if you have an accident where you lose pressure inside the reactor

if you have liquid water at 300 degrees celsius and suddenly you depressurize it

it doesn't stay liquid for very long it flashes into steam

so water-cooled reactors are built inside of big thick concrete buildings

which are meant to hold all of the steam that would come out of the reactor

if you had an accident where you lost pressure

steam takes up about 1000 times more volume than liquid water

so the containment building ends up being very large relative to the size of the reactor

another bad thing happens if you lose pressure and your water flashes to steam

if you don't get emergency coolant to the fuel in the reactor it can overheat and melt

now the reactors we have today use uranium oxide as a fuel

it's a ceramic material similar in performance to that of the ceramics that

we use to make coffee cups or cookware or the bricks we use to line fireplaces

they are chemically stable but they're not very good at transferring heat

and soon your fueld will melt down and release the radioactive fission products within it

making solid nuclear fuel is a complicated and expensive process

and we extract less than 1% of the energy from the nuclear fuel

before it can no longer remain in the reactor

water cooled reactors have another additional challenge

they need to be near large bodies of water where the steam they generate

can be cooled and condensed otherwise they can't generate electrical power

now there's no lakes or rivers on the moon so if all this makes it sound like water-cooled reactors

aren't such a good fit for a lunar community i would tend to agree with you

you see i had the good fortune to learn about a different form of nuclear power

that doesn't have all these problems for a very simple reason: it's not based on water cooling

and it doesn't use solid fuel surprisingly it's based on salt

one day i was at a friend's office at work and i noticed this book on his shelf

fluid fueled reactors and i was interested and asked if i could borrow it

i learned about research in the United States back in the 1950s into a kind of

nuclear reactor that wasn't based on solid fuel or water cooling it didn't have the problems

of the water-cooled reactor and the reason why was pretty neat

it used a mixture of fluoride salts as a nuclear fuel

specifically the fluorides of lithium, beryllium, uranium and thorium

fluorides are remarkably chemically stable

they do not react with air and water you have to heat them to 400 degrees celsius

to get them to melt but that's actually perfect

for trying to generate power in a nuclear reactor

here's the real magic: they don't have to operate at high pressure

and that makes the biggest difference of all

this means that they don't have to be in heavy thick steel pressure vessels

they don't have to use water for coolant and there's nothing in the reactor

that's going to make a big change in density like water

so the containment building around the reactor

can be much smaller and close fitting unlike the solid fuels that can melt down

if you stop cooling them these liquid fluoride fuels are already melted

in normal operation you have a little plug here at the bottom of the reactor vessel

a piece of frozen salt that you've kept frozen

by blowing cool gas over the outside of the pipe

if there's an emergency and you lose all the power to your nuclear power plant

the frozen plug melts and the liquid fluoride fuel inside the reactor

through the line into another tank called a drain tank