Last Thursday, I attended a presentation by Dr. Ed Cecil, Colorado School of Mines Professor, which covered the basic science behind nuclear reactor meltdowns. I thought it would be interesting to attend a short presentation about a subject I already understand in order to see how Dr. Cecil would portray the complex information of nuclear physics and engineering to an audience of non-nuclear junkies and do it in less than an hour.
He started off with the simple idea of a nuclear power plant..."it works just like any other power plant setup" that is it contains a steam generator that spins a turbine for power. Everyone can get that...right?
He explained to the audience that from the binding energies one can determine that the average fission process gives off 200 MeV's of energy and that by using that number we can calculate that we only need 10 kg of uranium to supply a 1 GW reactor for 6 months (AWESOME). Cecil accidentally stumbled onto the "iron death of the universe" but he quickly recovered himself.
Well that's all great and dandy, but most importantly Cecil discussed the problems with nuclear power and how to interpret "radiation". Two topics I feel that the public today knows only enough to be dangerous about. On the first point, a downfall of nuclear power is the decay products left over from the process. Below is one of Cecil's slides listing the radioactive by products.
Q. So what are the radioactive by products of nuclear fission?
A. Lots and lots:
•Isotope Half-life Fraction per fission
•137Cs, 137Xe,… 30 yr, 8 min,… 6.2%
•90Sr, 90Rb,…. 28 years, 4 min,.. 5.8%
•144Ce,….. 284 days,… 5.5%
•95Zr,… 64 days, 6.5%
•etc. etc. etc
•131I,… 8 days,… 2.9%
• Total = 200%
It's because of those elements with half lives of 30ish years that we have to come up with ways of safely storing the waste. (i.e. the shorter half life elements will eventually decay away...but it takes 30 years for some of them)
Another great topic that Cecil discussed was how to interpret radiation. People have become afraid of the word radiation...and I don't blame them. But you have to realize that radiation must be quantitatively described in order to know if it is really dangerous or not. In our world today we have background radiation of up to 0.1 rem/ yr. Bananas alone give off about .0001 rem/yr...should we all be running away from bananas? No. For example, the max dose for industry (nuclear submarine workers or nuclear plant workers) is approximately 10 rem/yr. Therefore, before the public goes off and reads articles about how high the radiation levels are somewhere...they need to educate themselves on what exactly is a "high" number. It was just the other day in my nuclear energy class when we read an article about Fukushima. The article had a quote in there about how "tiny amounts of radiation were leaking..." so what exactly does "tiny" mean. Who knows.
One last thing that I would like to bring up that Dr. Cecil discussed was just a small historical fact. There are a lot of people out there that bring up Chernobyl whenever nuclear power is discussed. Well, yes everyone knows that Chernobyl was a sad day, but there are quite a few of us that don't understand that there was something different about Chernobyl than with every other nuclear reactor in the world. Chernobyl was designed to operate at a criticality above one. Everybody but Russia seemed to realize that this was a bad idea...Russia was warned repeatedly but still went ahead with plans and built the reactor. That design failed just like everyone knew it would.
Bravo Dr. Cecil, what a daunting task to try to explain most of how a nuclear reactor works and about radiation in less than an hour. The talk was a bit jargony but we were all engineers in there so... I hope those 40 some people all went home armed with accurate knowledge about nuclear energy.
I'm sorry I missed this talk! It looked great, and Ed is always fun to hear.
ReplyDeleteSome of the material you present above is still quite technical, for the layperson, and a lot of the confusion over radiation (IMHO) stems from the varying units of measurement, which even NSEs sometimes struggle to keep track of and convert. So a lot of the news from Japan has been in SVs, but you use REMs above. Just saying it's a lot to keep track of when it's not your job to do so.
I think that the world in general is trying to gear toward using Sieverts as the standard unit radiation dose. The U.S. though for some reason still wants to tend toward using rems. I also think that the max worker dose in the U.S. is 5 rem/year, but I could be mistaken. If anyone in the public was ever exposed to this dose though, there would be hell to pay! It does not look like the worker dose raises the chance for cancer statistically, but we just try to avoid exposing those into the public to such doses. I would agree in saying that it is not necessary to allow the public to be exposed to such high levels. The important thing to realize is that if someone was exposed to such a dose, it would not cause noticeable health effects. It is really the goal of the nuclear industry to protect the public. Off the top of my head, I think that the maximum dose that a plant can expose the public to is 0.2 rem/year or 2 mSv/year. This is a really low dose, but I am glad for one that the industry is expected to treat the public with such care. If only all industries were held to such safety standards.
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