Nuclear Reactors vs. Nuclear Weapons - Free Educational videos for Students in K-12

Nuclear Reactors vs. Nuclear Weapons - By MITK12Videos

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00:0-1	a nuclear reactor and a nuclear weapon are about as
00:02	similar as a hamster and an alligator . They're both
00:05	made of cells , but one is clearly more dangerous
00:07	than the other thing in common between nuclear weapons and
00:16	nuclear reactors is they're both powered by fissile isotopes like
00:19	uranium to 35 or plutonium 2 39 . Fissile isotopes
00:23	are special elements that break apart when neutrons hit them
00:26	. When this happens , they release more neutrons and
00:28	little atoms we call fission products which carry off a
00:31	lot of energy and nuclear reactors . This energy is
00:34	released over a long period of time , whereas in
00:36	weapons it's released all at once instantaneously . So fissile
00:40	isotopes are the key ingredients in both nuclear reactors and
00:44	nuclear weapons , but that's where the similarity stops the
00:47	difference . One of the many differences is that a
00:49	nuclear weapon is almost pure fizzle material . It's about
00:54	90% of the fissile isotopes . Either uranium to 35
00:57	or plutonium 239 . Whereas reactor fuel is only about
01:01	five and just getting a bunch of uranium and plutonium
01:04	together doesn't make a weapon . If you lit a
01:06	block of uranium 2 35 on fire , it would
01:09	burn chemically . There'd be a fire just like if
01:11	you let any other flammable material on fire , but
01:14	it would not be a nuclear explosion , you actually
01:16	have to compress it so much that you get the
01:19	items to slam together much denser than they'd normally be
01:22	. So a nuclear weapon . There's usually some sort
01:25	of a core of uranium plutonium in pieces and around
01:29	that is a bunch of explosive that smashes them into
01:31	each other and around that is some sort of a
01:33	shell that contains the explosion until it gets big enough
01:36	. These are exceedingly difficult to make if you took
01:40	millions of sticks of dynamite and put them around the
01:42	sphere of uranium and blew them all up at the
01:44	exact same time , the force would not be large
01:47	enough to compact the uranium to make a weapon .
01:49	If you got the right kind of explosive and surrounded
01:52	this fear of uranium with the explosive and got it
01:54	all to go off at the same time , it
01:56	still wouldn't make a weapon if you took a whole
01:58	bunch of bricks of uranium and put them all together
02:01	and then drove a tanker full of gas next to
02:03	it and had a whole bunch of high explosive blowing
02:05	up all around it . If you had enough uranium
02:08	to go supercritical , it would very , very briefly
02:12	, you would get a quick pulse of neutrons at
02:14	which point everything would heat up and blow apart and
02:17	once all the uranium in different pieces too far away
02:20	than reaction stops without the proper physics and design ,
02:23	which has taken countries like ours years to do .
02:26	The best you could do is a Michael Bay style
02:28	explosion . But you couldn't actually get a nuclear explosion
02:32	. I've just described what took the Manhattan project about
02:35	five years to do and tens of thousands of absolutely
02:38	brilliant scientists , some of whom won the Nobel prize
02:41	in order to use the MIT reactor fuel to make
02:44	a weapon . Yeah , that would be difficult .
02:46	That's the definition of easier said than done . Not
02:49	only would you have to figure out how to put
02:51	the weapon together , but you have to physically get
02:53	to the reactor's fuel and that's basically impossible . The
02:56	building is about four ft thick of rebar enforced concrete
03:01	. That's actually been simulated to take a loaded plane
03:04	crash . Because that's one of the safety criteria for
03:07	reactors in this country , you have to be able
03:09	to fly a plane into it and it shouldn't break
03:11	apart . That doesn't even count the security inside the
03:14	building , let alone the swat teams that would swarm
03:16	the place . If anyone even tried to break in
03:18	. But let's say the terrorists got past all of
03:20	that , then they still have to get to the
03:22	fuel itself , which is normally kept behind a lot
03:25	of shielding to keep it safe so we can work
03:27	with it . So if they took away the lead
03:29	, the concrete and the steel shielding , they'd be
03:31	faced with the fuel itself , which is so radioactive
03:34	that it would kill them on contact . Even if
03:36	somebody were to steal enough material to make a weapon
03:39	, you can't just put it together and have a
03:41	weapon . It doesn't work . There's so much other
03:43	stuff in the fuel . Most light water reactor fuels
03:46	in this country are made of uranium dioxide . You
03:49	put oxygen in the way of those uranium atoms doesn't
03:51	work anymore . It works as fuel , but not
03:54	as a weapon , reactor fuels only about 5% uranium
03:57	2 35 . And there's other structural materials , there's
04:00	steel holding the thing up , there's water surrounding it
04:03	, there , zirconium alloys holding the fuel pins of
04:06	fuel rods in . There's all this other stuff that
04:08	would have to be chemically separated . Another difference between
04:11	reactors and weapons is the way the chain reaction is
04:14	controlled . A reactor is a tightly controlled chain reaction
04:18	with negative feedback . So if anything goes wrong ,
04:20	the reaction stops . A nuclear bomb is an uncontrolled
04:24	chain reaction designed to get as hot as possible ,
04:27	as fast as possible . So when you hear the
04:29	word chain reaction , you might automatically think of something
04:33	that's out of control , but it's actually really hard
04:36	to keep a reactor going . So let's say you
04:38	had a certain number of uranium 2 35 atoms every
04:42	time one of those uranium atom splits apart it gives
04:46	off two or three neutrons which could cause another uranium
04:50	atom to split apart . But not everyone does .
04:53	Some of them leak out of the reactor and get
04:55	absorbed by the shielding . Some of them get absorbed
04:57	by other materials in the reactor and some of them
05:00	can get even captured by uranium 2 35 without inducing
05:04	fission . As the fission reaction proceeds more and more
05:08	, other stuff builds up . And that other stuff
05:10	which we call the fission products absorb some of those
05:13	neutrons away and make them unavailable to keep the chain
05:16	reaction going . Also , when a fission reaction heats
05:19	up , it causes the atoms to spread out ,
05:21	making it harder for some of those neutrons to hit
05:23	other fuel items and keep the reaction going . In
05:26	addition to that , there is control rods , there
05:28	are materials that are really , really good at absorbing
05:31	neutrons like boron , daphne , um or gadolinium ,
05:34	and you can simply stick those down into the reactor
05:37	to absorb away the neutrons and shut down the chain
05:39	reaction . The same sorts of reactions are happening in
05:43	a nuclear power plants and a nuclear bomb , but
05:45	in a nuclear bomb , they're happening quintillion of times
05:48	faster and it's all over in a split second .
05:50	The whole nuclear part of the explosion takes less than
05:52	a second . And in a nuclear power plant ,
05:55	you're releasing that same energy over years or decades in
05:59	a controlled way that we can harness .

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