So last term in Physics we covered Nuclear Physics, which my friends would know is something I'm somewhat kinda really interested in. Nukes are pretty cool, the ones that generate electricity, I mean. When anyone talks about nuclear technology or uranium, people immediately begin thinking about the atom bomb or big accidents like Chernobyl, Three Mile Island or the more recent, Fukushima. Unfortunately, nuclear power gets a bit of a bad rap in the media at large because of these glaring sores in its history, making it incredibly difficult and frustrating for new developments in nuclear technology to get much traction with politicians (who have the money) or the general public (who tell the people with money what to do). Given my recent experience at a nuclear material research lab, and having talked about nuclear things in Physics class, I thought it'd be apt to make a post about nuclear reactors and how they work.
So there are two major misconceptions I want to clear right off the bat:
1. Nuclear power is complicated
2. Nuclear power plants are unsafe pollution spreading machines of death
I think it's important for people understand that these two ideas are blatantly false, particularly the latter. Before we start talking about nuclear power, and why it's awesome, and why everyone should stop bad-mouthing it, I should probably explain how exactly a nuclear power plant works.
The way power is generated from nuclear reactions is, honestly, not that complicated. The engineering and technicalities may be, sure (cough, CRUD resistant materials, cough), but the concepts are surprisingly simple (refer to SuperSimpleTM diagram below).
So above, is the most simple diagram I could possibly find of a Pressurized Water Reactor (PWR). And here's the four step SuperSimpleTM explanation from yours' truly.
1. The core of the reactor generates heat through nuclear fission reactions (atoms splitting make heat)
2. This heats the pressurized coolant loop (which is high pressure water)
3. Heat is transferred to a steam generator which boils water, making steam
4. Steam blows on a turbine, generating electricity like Ye Olde Times
That's...pretty much it. There are some technicalities involved but for a layperson, that's the gist of it. But wait, you ask, how does nuclear fission generate heat? Well... nuclear fission isn't a terribly complicated idea either. Let's get another SuperSimpleTM diagram from google!
Okay so what's going on here? Well a neutron is just a neutrally charged atomic particle. This particle is shot at an atom of uranium-235, an unstable version of uranium. The thing with uranium is that it's so heavy, and bogged down with all these neutrons in its nucleus (core of an atom) that it really wants to split apart. Shooting just one more neutron at it makes it burst apart, causing the wonderful reaction known as fission. As it splits apart it creates several products: smaller atoms which are other elements, more neutrons (that go on to break apart other uranium atoms) and energy, in the form of heat!
Mind you, the only real difference between a nuclear reactor and an atom bomb is that reactors control the rate of this reaction, whereas in a bomb, the resulting neutrons go on to split more uranium atoms in a chain reaction, like a domino effect. That's why we have control rods! Control rods are made of boron, a neutron absorbing material, which essentially allow the reactor to control how much fission-ing is happening. In the unlikely event of an accident, control rods can drop down in less than a second and completely stop the reaction completely.
(But how? More on control rods for those curious).
This leads me to my second point: nuclear reactors are actually really damn safe. So here's a funny statistic:
100 people die per terrawatt hour (TWh) from coal power plants (industrial accidents, CO2 poisoning etc...).
0.04 people die per TWh with nuclear power.
More people (10x) die from installing solar panels on roofs.
"But, but...radiation! Nuclear power plants can explode! Nuclear waste!"
Let me address these common responses one at a time.
Spooky Green Glow aka. Radiation
Radiation is extremely well studied and controllable. Scientists have known about radiation since the early 1900s, and it's not some scary, mysterious deadly thing. Here is a quote from a former nuclear power plant worker:
Lots of people ... don't understand radiation, and it sounds scary. Radiation is easy to deal with. You have detectors to tell you how much you're receiving, limits on your exposure, safe practices. Typical workers receive approximately the same amount of radiation from the plant they work at as they do from standard background radiation we all receive.
Oh yeah, funny thing about radiation - it's literally everywhere. Radiation is seeping through your body right now, and not necessarily from all our crazy modern technology either. This radiation is from space! You get a higher dose of radiation on an aeroplane (because it is higher up in the atmosphere and less shielded than on the ground) than in a nuclear power plant. Don't worry though, it's pretty much harmless. Life has evolved to deal with radiation over millions of years, in fact some scientists believe it plays a crucial role in evolution!
When Things Go Boom
Okay, so the big three accidents in nuclear power everyone knows about are Chernobyl, Three Mile Island and Fukushima. Chernobyl and Three Mile Island were both results of human error. In Chernobyl, an operating crew were doing some tests and turned off the safety measures in order to do so. Queue "accident". In Three Mile Island, workers forgot to open a valve as part of the emergency feed pump. 42 hours later, queue "accident". And Fukushima...there was an earthquake and a tsunami. You can google any of these you want to read up on it. The only limiting factor of older generation reactors, despite having incredibly well designed safety systems, is human error. Mind you, new generations of molten salt reactors don't even have the capability of meltdown.
Okay, so this is probably one of the biggest supposed "issues" that people have with nuclear power. What do we do with all that radioactive waste? Isn't in harmful to the environment? And what about those big plumes of smoke coming out of nuclear power plants....okay just hold up a sec. Those big, iconic towers that many nuclear power plants have are cooling tower, and the "smoke" that is coming out is literally steam. No really, and it's not radioactive either. Scroll back up to that diagram of the pressurized water reactor. The pressurized water loop (red) is used to heat up a separate water loop (blue) through physical contact that makes it turn into steam.
The water being boiled is not radioactive.
But what about the actual nuclear waste? Well this is an issue, and perhaps the one gripe of older generation reactors is that they do produce nuclear waste that several lifetimes to break down. However it isn't all bad news. High-level waste - depleted uranium- can be easily reprocessed to be used as fuel in reactors. Even better, new generations of modified thorium reactors can directly use highly radioactive "waste" as fuel, completely defeating the problem of conventional reactors.
Also here's an interesting statistic: a typical 1000MWe light water reactor will produce about 27 tonnes of high level (dangerous-ish) waste per year. Compare this to a coal power plant of the same scale, which produces 400,000 tonnes of ash which goes straight into the atmosphere.
Oh, and that 27 tonnes of scary waste? It can be reprocessed in the same reactor (without any of that fancy new generation hipster thorium reactors) and the waste product of that is only about 3 cubic meters of glass. Literally, glass. Yep.
So yeah, nuclear power is pretty cool.
Mind you, all this is just the old generation tech. Wait till you hear about those nifty thorium molten salt reactors I mentioned...