Club409
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I can't tell you how many people I've heard talking about the radiation coming here to California and the protective measures we should be taking here.
why you can't stop playing angry birds
neat quote from the article: "the total number of hours consumed by Angry Birds players world-wide is roughly 200 million minutes a DAY which translates into 1.2 billion hours a year. To compare all person-hours spent creating and updating Wikipedia totals about 100 million hours over the entire life span of Wikipedia"
Also question for Steven that I have not been able to find an answer for anywhere: They said the main pumps went offline due to loss of grid power. But if the reactor is still producing enough heat that they must vent pressure to keep it from rupturing the containment why isn't that pressure driving the turbine and generating their own power to run the pumps?
oh and yall most likely already have seen this but xkcd made a nice radiation dose chart
Good call on the dose chart I saw that and forgot to post.
Now for the question about electricity from the turbine.
Short Answer: In those particular reactors the water passing through the turbine is radioactive and when the reactor is shut down a valve shuts off water flowing to the turbine to attempt to control the spread of that radioactive water.
Long Answer: The reactors at Fukushima are boiling water reactors (BWRs) as opposed to pressurized water reactors (PWRs). In a BWR the coolant (water) passes through the core gets heated up and turns to steam which passes through the turbine to generate electricity. In a PWR the coolant is pressurized to a level where it won't boil and after passing through the core it is passed through a heat exchanger which heats up water in a secondary coolant loop that goes to the turbine. See here for a visual comparison. BWRs are more efficient because they don't have the extra heat exchanger. However the water passing through the core contains bits of metal that have flaked off of pipes and when they pass through the core they're bombarded with neutrons that cause those metals to become highly radioactive. In a BWR that radioactive water is also traveling through the turbine. When a BWR is SCRAMed valves are closed that prevent water/steam from passing into the turbine as a safety mechanism to contain radioactivity. In a PWR the residual decay heat could theoretically continue to drive the turbine and produce electricity but I'm not sure if they are actually designed to do that in practice. I believe the pumps are still usually powered by offsite power 1st diesel generators 2nd and batteries 3rd.
Have you guys been hearing about how Thorium-based power systems would have prevented all of this trouble?
Steven if that radioactive steam is passing through under normal operations why is it a concern once it has been shutdown? Wouldn't it be far better to continue circulating and generating power for the pumps to cool the fuel than to risk a meltdown?
B you mean like so?
you can change this to be about thorium reactors. there's always a constant stream of people touting thorium reactors as fixing every possible aspect of existing nuclear reactors as if nobody ever thought of it before. as long as you ignore all of the downsides its clearly the ideal solution. India (apparently China also) is persuing a thorium cycle because they're sitting on basically an endless supply of thorium but not very much uranium.
oh oh what about the IFR?
I'm rapidly approaching (more likely well past) the limits of my expertise here (my work focuses on the reactor core itself what happens to the water after it leaves containment is not my concern) but I will do my best take everything with a grain of salt.
About the radioactive steam the materials generally have very short half lives (a few minutes) so that if no freshly radioactive material leaves the core then people can enter the area to perform work within a few hours. As long as water is circulating from the core its highly dangerous for people to be in a relatively large area surrounding the reactor making it difficult to assess damage or make repairs.
The use of decay heat to generate electricity is sort of chicken or the egg situation. Once the reactor is shut down it stops producing electricity. In order to resume producing electricity you would have to restore circulation through the turbine which requires pumps which require electricity. So basically I think to use self-produced electricity it would have to keep generating throughout the entire incident once its down its down for good.
Finally there are likely some practical issues. I believe the electrical lines/connections to the pumps were severely damaged by the earthquake so even if electricity were being produced it might not have been possible to make the pumps operational. Also I have almost no knowledge of turbines but I know they're usually designed to operate at a given power level and steam quality so a reactor producing 1% of its original heat might not equate to a turbine producing 1% (or any) of its original output.
Hopefully the true reason is contained somewhere in there.
There are actually a lot of reactor designs out there that are `superior' to existing operating reactors (higher efficiency less waste and passively safe). The problem is that it's difficult to convince a utility company to spend tens of billions of dollars on a design that's untested when there are designs very close to what they've been operating for 4+ decades that are cheaper.