Monday, March 14, 2011

Explanation of nuclear power plant problems...

I have a friend from church who is a nuclear physicist and has explained the issues going on in Japan right now in dumby terms for me. Here is it...

Regarding the tsunami: there wasn't really any tsunami here in Tokai-mura. The bad tsunami pictures that you have been seeing on the news are from a lot farther north, over 100 miles away. So, no problems here, except for the inconveniences of no water yet in many places. But most places have electricity and gas services restored.
Regarding the Fukushima nuclear power plant problems: Yes, there are problems. No, it is not at all dangerous for me or other people here in Ibaraki Prefecture. Tokai-mura is over 100 km (60 miles) away from the Fukushima II power plant. The evacuation zone is only 20 km around the power plant. The reason it is only 20 km is because people who live farther away than 20 km are not in danger
Actually, 20 km is probably overkill, but the authorities want to be cautious and plan ahead for contingencies that may never happen. Yes, this morning, Prime Minister Naoto Kan said that the people between 20 and 30 km should stay indoors today, because of some increased emissions of radioactive particles from the reactors. OK, but even they don't need to evacuate. And I'm over 100 km away. So, no problem for me.
Now it's time for fun facts about nuclear reactors and radiological safety: (1) The reactors are now shut down, and they have been since immediately after the earthquake. There is no nuclear chain reaction going on. What's happening now is the residual heat caused by the natural radioactive decay of the radioactive elements that have been produced inside the reactor while it was running.
This amount is about 7% of full power at the time of shutdown, and then it decreases quickly (like only about 1% of full power after about an hour). {These values are from "Introduction to Nuclear Engineering", 3rd ed., by John Lamarsh and Anthony Baratta.} But even though it is relatively small, you still have to get rid of this heat. If you let it build up, then the temperature inside the reactor slowly climbs up.
At the limit, the temperature will get so hot that it will cause some of the metal inside the reactor to melt. This is what is called a "melt down." But it doesn't necessarily mean a large release of radioactive particles. For example, at the Three Mile Island #2 reactor accident in Pennsylvania in 1979, part of the nuclear fuel did melt. So, to this day, the utility company cannot run that nuclear reactor. But it still runs the #1 reactor next door.
‎(2) When a nuclear reactor shuts down, normally some diesel generators next to the plant turn on and provide electricity to run pumps to pump cooling water through the nuclear reactor to remove the heat from the radioactive decay. This can take place for awhile. I forget how long, and I can't find it quickly in my book, but I want to say it is about 2 or 3 days or so.
At Fukushima, the tsunami damaged these diesel generators, so that they couldn't pump in the water. That is what has caused the problems now. So, they couldn't use the diesel generators to pump the water into the shut-down nuclear reactors. Eventually, though, they did figure out a way to get water into the reactors; I haven't yet heard how, but they did.
There are a couple of problems now (A) high pressure and (B) buildup of hydrogen gas.
‎(A) High pressure is easy to understand. The reactor is acting like a tea kettle. If you boil water in a tea kettle, it whistles, because the pressure inside has increased. The same thing is going on in the reactor, except that the utility company doesn't want it to whistle at all, because the steam is slightly radioactive.
It's not very radioactive; it's not enough to cause big problems for people. But they try to limit the amount of radiation to the public as much as possible. That's one of the reasons why they evacuated up to 20 km away. They eventually decided that the pressure was too high, and they'd rather let it "whistle" than blow up. But since nobody was around, it wasn't such a big deal.
B) The hydrogen gas is a little more complicated. Basically, the problem is that the insides of the nuclear reactors were already really hot by the time that they got the water inside. When the water hit the hot metal inside the reactor, it not only made steam, but some of the water molecules actually split into hydrogen and oxygen. (Remember, the chemical formula for water is H2O?) The radioactivity inside the nuclear reactor also facilitated this splitting of the water molecules. Then, the hydrogen gas--because it is a light gas--bubbled to the top of the nuclear reactor and then seeped out. (This is not so hard for hydrogen. The molecules of hydrogen are super small, so they can diffuse out through flanged pipe joints and stuff like that.)
Now, around the entire nuclear reactor is another thick, concrete shell. This concrete building is called the containment vessel. Its purpose is described by its name--it contains anything that might leak out of the nuclear reactor, such as in this case. So, the hydrogen that leaked out of the reactor built up in the top of the containment vessel. Well, inside the containment vessel is air, of course. When enough hydrogen had built up, it ignited and exploded with the oxygen from that air. This is what has happened at two or three (I can't remember now) of the Fukushima reactors.So, when you saw the video of a big puff of dust from the reactor, that was probably the lid of the containment vessel popping off. The dust was probably concrete. So, that's not so good, because now the containment vessel has a hole in the top. On the plus side, now no more hydrogen can build up in it, right? Also, remember--the nuclear reactor itself (which is inside the containment vessel) is still intact. So, the guts are all still inside, holding together. I heard this morning that there was another explosion at the Fukushima #2 reactor that damaged the suppression pool at the bottom of the reactor. I'm not sure what caused that (neither is anyone else), so we'll have to keep an eye on the news and see what's going on. On the other hand, the utility company has been able to get cooling water into the nuclear reactors--sometimes more, sometimes less, but now always at least some cooling water. And, remember that the heat in the nuclear reactors now is just the heat from the radioactive decay. So, the point is that this crisis is short-lived. There is only a limited amount of heat that needs to be cooled away, and it gets cooler and cooler with each passing hour. I would guess that yesterday or today was/is the worst of it, and probably everything will be fine by the end of the week. As long as they keep putting some cooling water in there, it's more a matter of how messed up the equipment is after this is all over than about any catastrophe.
In other words, does the insurance agency "total" this car, or can it go to the autobody shop?
The numbers that I heard this AM were 3 to 5 microsieverts (per hour) of radiation in the air around here. That's higher than normal, but it's not anything to get up in arms about. When you smoke, you get 80000 microsieverts per year. If you fly a lot (like airplane pilots and flight attendants), you get 1600 microsieverts per year. So, if you decide to fly back to the US to wait this out and then fly again to return to Japan, you might get about the same amount of radiation as if you just sit cool here. And it's a lot less expensive to just chill here. ‎(This radiation is from the cosmic radiation from outer space, which is more when you are up at 30000 feet than when you are safely at sea level here in Japan.)
Another unreasonable response: Staying inside and not going to the store to buy stuff for dinner tonight.
A reasonable response: Postpone your soccer or golf game until Saturday. Play video games today. Besides, it's cloudy, windy, and cold today--not good soccer or golf weather.

It's super long I realize but really helpful in understanding!!!


  1. Chelsea,

    My brother and I were both born in Japan and our family spent happy years in Tokai Mura in the 60's. Naturally our thoughts are with you and are glad that the immediate disasters seem to have missed Tokai but obviously hope that the situation in Japan becomes stable and that all residents can look forward to some lasting hope.

    Kind regards

    Dominic Arnold

  2. Praying for you here in east Tennessee- thanks for the explanation because it's confusing here as well. we love you!!!!