Nuclear Chem Class #4

1. Nuclear Chem Class #4 A short review problem; and then,How does a nuclear power plant make electricity? What happened in Japan after the tsunami?

2. You dig up an old wooden box from under your garage and find a metal box inside. Inside this metal box is a bottle marked 64.0 grams of strontium-90. When you mass this metal (under the care of a nuclear chemist), you find it only has mass of 0.500 grams. The rest of it is gone?! First, write the nuclear decay reaction for Sr-90. Was this a natural transmutation or an artificial one? What did the other 63.5 grams of this strontium become? How long ago did this box get buried in your dirt?

3. You dig up an old wooden box from under your garage and find a metal box inside. Inside this metal box is a bottle marked 64.0 grams of strontium-90. When you mass this metal (under the care of a nuclear chemist), you find it only has mass of 0.500 grams. The rest of it is gone?! First, write the nuclear decay reaction for Sr-90. Was this a natural transmutation or an artificial one? Natural, we didn’t do anything to assist this to happen. What did the other 63.5 grams of this strontium become? Yttrium-39. 9038 0-1 9039 Sr e + Y

4. How old is the box assuming it really had 64.0 grams once, and you measured the left over correctly? (backwards to go back in time) Mass (g) Half lives 64.0 32.0 16.0 8.0 4.0 2.0 1.0 0.500 7 6 5 4 3 2 1 0 7 half lives X 28.1 years = 195 years ago! 2011 – 195 = 1816 (that was a very good year!)

5. Everybody, that was easy! Now, for some good stuff… How does a nuclear power plant make electricity? To make it sound really easy, the nuclear fission reaction which is the splitting of a big atom into smaller ones, that keeps going and keeps getting bigger and keeps giving off lots of heat makes water boil into steam. This steam is forced through pipes at high pressure, which is directed to turn a generator round and round. The movement of the generator (Iots of wire + magnets) makes an electric current. This electric current is sold to you by companies like NYSEG. They often have to transmit this current from the plants (far away), and they have to moderate it (too much power at once and you’ll melt all your wires). They also have to be sure it comes all the time and doesn’t stop. It’s tricky to be a power company.

6. And the outside the containment dome part. Don’t mix these up. There is the “inside” the containment dome part.

7. The containment dome is (hopefully) strong enough to keep the radiation in, and everything else out. Inside the reactor vessel is where the fission reaction happens. Uranium 235 is bombed with neutrons and the chain reaction starts.

8. This reaction should start a nuclear explosion, a chain reaction leads quickly to a massive energy release because of the small but measurable mass defect. Because of E=mc2, this mass loss should cause a huge explosion, but it doesn’t. Inside the vessel are control rods, that control the reaction. They are able to be pushed in or out of the reactor. They absorb neutrons, which slows down or moderates the reaction. It keeps it hot, but not too hot. Often they are cadmium or silver or indium metals.

9. The water in the pink pipes gets super heated, and the heat transfers to the water in the blue steam generator. The steam it makes is pumped to the turbines which spin and make a current.

10. Hopefully this water in red stays in the pipes and never escapes. It’s touching the nuclear material and gets rather radioactive itself. All the radiation is supposed to stay inside the containment dome. The water in the turbine area cools down from steam back into water, to be reheated into steam again by more heat from the reactor. This water should stay un-radioactive if all goes well.

11. STEAM Cool water, from the really big lake, or from an ocean comes in here to help cool the water down. This water absorbs the excess heat from the turbine steam so it can be recycled. The environmental water is heated and then run through the cooling tower to disperse the heat as steam to the air. Lots more heat is pumped back to the ocean/lake nearby.

12. If all goes well, the only pollution put back into the environment is excess heat. Since fish don’t vote, and warm water makes fish grow bigger and faster, lots of people like this affect. Of course, sometimes big mistakes happen. In Japan, the tsunami knocked out the electricity to pump water through the reactor, and to pushthe control rods back in to the core. The back up water pumps also failed because the tsunami knocked out the general electric supply and backup electric supply. When that happened the core got hotter and hotter. And hotter and hotter still. And things start to melt down, which is bad.

13. And when the reactor core melts because it’s too hot, the radioactive materials escape to the air and water. This is as bad as anything you could imagine. It causes panic, it makes big areas uninhabitable for long periods of time, it’s invisible – you don’t start to die until it’s too late to save yourself, and it lasts for a very long time.

14. In the US, not one death can be attributed to nuclear power generation. So far it’s been a pretty good run of safety, except for Three Mile Island in Pennsylvania. There, in 1979, the reactor almost melted down, and we almost had our own Japan like problem. Luckily the control rods were somehow pushed back into the core in time to slow down the overheating. Years later, cameras showed that the core nearly melted down. Nearly means 2 things. First it means that we almost had a disaster of epic proportions. Or, it means that science is smart enough to protect us from any difficulties with nuclear power. This is where the ethics and the pros and cons of nuclear power come into play. How can you feel safe and how can you get safe, cheap electricity to run your world? ?

15. One other problem with nuclear plants is that even when they run perfectly safe for long periods of time, the waste products are dangerous. Some wastes are radioactive (emit dangerous radiation) for weeks, or months, or years. Some wastes like plutonium-239 can last millions of years. MILLIONS of years is really a long time to safely put this stuff. Where should we put it? How should we get it there? On a train through your town? What about a plane flying over your heads? Or by truck, no accidents are allowed. No terrorists can attack it and spread it out. No lost packages, or else.

16. Right now, the general plan is to store in underwater at nuclear plants, while we figure out what else to do with it. In Japan this is not working well, as the water boils away if not kept cool.