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Nuclear reactors are a good way to produce green energy as long as they are run correctly and not built in areas that are disaster prone, such as japan. In areas like that, other forms of energy production such as solar, tide generators, wind power should be used. That way if a big earthquake and/or tsunami damages these facilities there is less envioronmental impact. God help Japan if those reactors go critcal. They should have never been built there in the first place and I've heard several scientists say the same thing.
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"Critical" sounds scary, but with nuclear reactions it's not applied in the same way as it is with hospital care or whatever. In nuclear engineering that term actually describes any sustainable fission reaction that is taking place, ie a criticality event. In nuclear energy terms if something has gone critical it's actually doing what it's supposed to. However that fact is actually irrelevant as these reactors actually aren't even undergoing fission anymore, they're only in danger because of decay heat that should fully dissipate later this week. The reactors were automatically SCRAMmed as soon at their cooling systems failed by inserting the control rods and adding neutron poisons like xenon and boron, they're only still hot because of the natural decay of radioisotopes present in the vessel. It's hardly some runaway nuclear reaction, which the media generally refuses to try to understand. "####'S STILL KIND OF DANGEROUS BUT EVERYTHING WILL BE GOOD IN A FEW DAYS AS LONG AS THE OCEANS DON'T MAGICALLY DRY UP AND DEPRIVE US OF EMERGENCY COOLING WATER" isn't a headline that's going to bring in the ratings, I guess.
Since the reactors have been successfully shut down there is actually way to safely cool it via flooding with boron-impregnated seawater, which has been an emergency plan since the reactors were built (hence their location on the seafront.) They've already done it to Fukushima Daiichi reactor #1, and are in the process of doing it to #3 from what I've read. They were hesitant to use this method right away because there was no immediate danger of the reactor itself breaching, and the procedure will scrap the reactor due to contaminants from sea salt and boric acid. They held off because they were hoping to save them since their loss will be a crippling blow to regional power generation in a country trying to rebuild after a huge natural disaster, but it's not like the reactors have been teetering precariously on the edge of Fallout: New Fukushima for the past three days.
Also the media comparing the emergency in Japan to Chernobyl is ignorant fear-mongering at it's finest. Chernobyl's reactors were a design known as an RBMK, which is a graphite-moderated water-cooled reactor. Moderating neutrons and cooling the fuel with two different materials caused a dangerous design flaw, the potential for a phenomenon called "high positive-void coefficient." Here's a simple explanation of void coefficient and how it relates to reactor safety:
http://en.wikipedia.org/wiki/Void_coefficient
See, in the most common kinds of reactor design light or heavy water is used to both moderate neutrons (slow them down so they can actually split fissile atoms, because if they're going too fast they give no #### and will zip right through your fuel without the desired effect) and to cool the nuclear fuel. This means the reactor has a high
negative void coefficient and will actually shut itself down if the fuel gets too hot and a meltdown is imminent, because the water in the core will turn to steam and steam sucks as moderator. That means the if steam voids form in these types of reactors, fast neutrons won't be slowed down and therefore can't go on to properly split other atoms as would happen with liquid water present. The reactors in trouble in Japan are Boiling Water Reactors (BWRs) and use this design feature.
At Chernobyl's #4 RBMK reactor bad design combined with ill-trained operators, human errors, and willful disregard of safety protocols to produce a very fast runaway reaction (530MW to ~30GW within a few seconds) that caused a steam explosion powerful enough to toss a 2,000 metric ton containment lid off the top of the reactor. For a more detailed explanation of what happened this covers it well (
http://en.wikipedia.org/wiki/Chernob...aster#Accident) but in a nutshell, as I best understand the accident, there was a scheduled experiment with the cooling system which required the reaction rate to be lowered quite a bit. As RBMKs are very powerful reactors these "low" levels of power generation were actually still comparable to smaller reactor designs running full out, so heat generation in the core was still substantial. Due to the slow reaction time of the control/moderator rods and the decreased flow of the reactor coolant system they were having trouble adjusting and stabilizing the core, as lower power levels are were RBMKs start seeing high positive void coefficient problems. The light water in the core, while there primarily to cool the reactor, just like in BWRs do have a neutron moderation effect independent of the graphite moderator rods. As the reactor began to heat up and the coolant started to form steam voids the reaction rate dropped while the operators wanted it stabilized, so they increased graphite moderation levels to compensate (in a BWR, the heat spike would have actually killed the reaction because the only moderator would have been turned to steam.) Problem is they set the moderation rates waaaaaay too high which set off a positive feedback loop that caused the reaction to increase to around ten times the maximum safe output in seconds. That's why a BWR reactor could never turn into another Chernobyl- there's an inversely proportional relationship between moderation effectiveness and reactor core temperature.
There have been explosions in the reactor containment buildings but not only are they not due to core ruptures, but the damage caused to the containment buildings seem to be to the sheetmetal facade on top that basically exists to keep the containment vessel from being rained on/corroded by sea spray/colonized by hobos. The explosions were chemical hydrogen detonations, present in the steam purposefully vented from the reactor, and occurred between the 3rd layer of containment and the roof of the building, which wasn't meant to be a serious reactor containment structure. Now the hydrogen's presence does suggest that the reactors 1st containment system may have been damaged in some way, because the zircaloy fuel rod cladding will react with water to form hydrogen gas when it overheats. This doesn't even mean for sure that the fuel rods are exposed, as the reaction would occur on the outside of the thick cladding. Here's a GE BWR/4 reactor and containment building, showing the three containment layers (reactor vessel, concrete and steel building sarcophagus) and the roof that has been blown off (which is pretty much just sheet metal over girders like you'd see in large warehouses, factories, prefab metal buildings, etc.)
Here's a BWR reactor, showing the steel pressure vessel and rod assemblies that make up the first two containment layers:
We've been using nuclear plants to provide public utility power for over 50 years now, and there are currently 442 active nuclear plants worldwide (most operating 3-6 individual reactors.) Prior to these events there have only been three major accidents with nuclear power plants:
-The Windscale incident, from the first reactor ever used for power generation, affected ~200 people
-Three Mile Island's complete core meltdown, with average radiation within 10 miles of the plant measuring 8 millirem. That's about the same dosing as a chest x-ray, and is 1/40th of the amount of radiation you receive yearly from naturally-occurring radiation in food, rocks, cosmic background radiation, etc
-Chernobyl, a disaster that only could have happened with the RBMK reactor design used exclusively by the USSR in small numbers, which in turn never would have happened if the reactor hadn't been purposefully run outside of it's safety protocol parameters during an experiment.
Meanwhile coal plants belch radioactivity and greenhouse gases and people ignore it because they're ######ed. In Japan dozens of LP gas farms and oil refineries caught fire or exploded in the earthquake's aftermath, releasing huge quantities of uncatalyzed hydrocarbon pollution. At least one hydroelectric dam broke, wiping out a village that had been unaffected by the tsunami itself. Thousands are confirmed dead, tens of thousands more missing (and probably dead at this point) and the real story is a contained nuclear reactor that's so far known to have released less radiation than most people get through the radon in their basement? #### media sensationalism
