dragonstar57 Posted March 11, 2011 Posted March 11, 2011 (preface: i had absolutely no clue where to put this. i considered physics, Engineering and a couple others but decided to just guess and let mods move it if they want) http://www.cnn.com/2011/WORLD/asiapcf/03/11/japan.nuclear/index.html?hpt=T1 apparently a Japanese nuclear reactor's power source has been disabled by the earthquake in japan and the backup was disabled by the tsunami and now they can't cool the core what possibility of there being a meltdown (Chernobyl like melt down) or any significant release of radionuclides from the power plant?
Cap'n Refsmmat Posted March 11, 2011 Posted March 11, 2011 Another good article on it: http://www.nytimes.com/2011/03/12/world/asia/12nuclear.html?hp It sounds like they've got backup battery power keeping the core cooled, and if they can keep the backup systems working, the reactor will be safe. Apparently they have to release some slightly radioactive steam, but so long as water is being pumped in effectively, there's no reason for the core to have a meltdown.
lemur Posted March 11, 2011 Posted March 11, 2011 If it's producing steam, why doesn't that generate the power to run the pumps? Were the generators damaged by the quake?
Cap'n Refsmmat Posted March 11, 2011 Posted March 11, 2011 According to the New York Times article: A pump run by steam, designed to function in the absence of electricity, was adding water to the reactor vessel, and as that water boiled off, it was being released. Such water is usually only slightly radioactive, according to nuclear experts. As long as the fuel stays covered by water, it will remain intact, and the bulk of the radioactive materials will stay inside it. If the fuel is exposed, it could result in a meltdown at the plant. Incidentally, the Chernobyl accident occurred when they were testing a steam-powered backup system; their generators took a minute or two to kick in, so they planned to use the inertia in the steam turbines to power the pumps in the interim. Unfortunately the test was botched and the reactor went without coolant for far too long.
lemur Posted March 11, 2011 Posted March 11, 2011 Incidentally, the Chernobyl accident occurred when they were testing a steam-powered backup system; their generators took a minute or two to kick in, so they planned to use the inertia in the steam turbines to power the pumps in the interim. Unfortunately the test was botched and the reactor went without coolant for far too long. That's interesting but why isn't it just as simple as the fact that the reactor itself generates electricity so its own systems would run off that electricity? Why does a power plant need external power to run itself?
Cap'n Refsmmat Posted March 11, 2011 Posted March 11, 2011 That's interesting but why isn't it just as simple as the fact that the reactor itself generates electricity so its own systems would run off that electricity? Why does a power plant need external power to run itself? The Japanese reactors had to shut down due to equipment damage, so they're not generating electricity. The Guardian is now reporting that several other reactors have also suffered cooling equipment damage, and they've lost some control of the plants. Let's hope they get this under control quickly.
lemur Posted March 12, 2011 Posted March 12, 2011 The Japanese reactors had to shut down due to equipment damage, so they're not generating electricity. The Guardian is now reporting that several other reactors have also suffered cooling equipment damage, and they've lost some control of the plants. Let's hope they get this under control quickly. Surely they would be prepared for such a situation by having backup generators for the cooling pumps on site and ready, unless those were damaged too.
Cap'n Refsmmat Posted March 12, 2011 Posted March 12, 2011 Surely they would be prepared for such a situation by having backup generators for the cooling pumps on site and ready, unless those were damaged too. Had you read either of the news articles linked here, you'd see that the diesel generators were damaged by the tsunami.
jackson33 Posted March 12, 2011 Posted March 12, 2011 It's now up to five reactors, two different locations. They have 50 others think ten different locations and there should be some around to back up those out of control. The US is flying in some back up systems, so they may not have been adequately prepared. Two however are 45 YO...said to be antiquated. http://www.japannuclear.com/nuclearpower/program/location.html
Mr Skeptic Posted March 12, 2011 Posted March 12, 2011 That's interesting but why isn't it just as simple as the fact that the reactor itself generates electricity so its own systems would run off that electricity? Why does a power plant need external power to run itself? The reactor generates heat only. The heat is used to boil water and run a turbine, same as in a coal plant. I assume the main turbines are too big to be powered by the steam now that the reactor has been shut down, or maybe damaged by the 8.9 magnitude quake or tsunami. Janie Eudy told CNN that her 52-year-old husband, Joe, was working at the plant and was injured by falling and shattering glass when the quake struck. As he and others were planning to evacuate, at their managers' orders, the tsunami waves struck and washed buildings from the nearby town past the plant. Ouchie! 1
swansont Posted March 12, 2011 Posted March 12, 2011 (edited) (preface: i had absolutely no clue where to put this. i considered physics, Engineering and a couple others but decided to just guess and let mods move it if they want) http://www.cnn.com/2011/WORLD/asiapcf/03/11/japan.nuclear/index.html?hpt=T1 apparently a Japanese nuclear reactor's power source has been disabled by the earthquake in japan and the backup was disabled by the tsunami and now they can't cool the core what possibility of there being a meltdown (Chernobyl like melt down) or any significant release of radionuclides from the power plant? Basically a zero chance of there being a Chernobyl-like meltdown. Different reactor type, different situation. Chernobyl occurred immediately while the reactor was in the act of shutting down, so it was still critical. The reactor went prompt critical and this resulted in a steam explosion, with the graphite moderator catching on fire, which then melted the fuel elements. A boiling water or pressurized water reactor that doesn't have any graphite doesn't have this issue, and these reactors have shut down. The core will produce about 7% of rated power and that will slowly get smaller as the radioactive fission products decay. edit: the situation is a lot closer to Three Mile Island than Chernobyl edit2: quickie blog post with some more details http://blogs.scienceforums.net/swansont/archives/8132 Edited March 12, 2011 by swansont added link 1
Blahah Posted March 12, 2011 Posted March 12, 2011 (edited) Western news is a bit slow, but there was a press conference a short while ago on Japanese television. Basically there is no chance of any major radiation leak event, and the explosion was caused by a hydrogen leak which exploded. The momentary rise in radiation near the perimeter was caused by the release of slightly irradiated steam, and the radiation level has now dropped down to 70.5 microsieverts. The reactor is completely undamaged. It is a light water reactor which relies on the presence of water as the coolant and neutron moderator for the reaction to continue, so when they released the coolant water and steam, the nuclear reaction slowed down. They are now reintroducing sea water to cool the reaction as it stops. Edited March 12, 2011 by Blahah
swansont Posted March 12, 2011 Posted March 12, 2011 Western news is a bit slow, but there was a press conference a short while ago on Japanese television. Basically there is no chance of any major radiation leak event, and the explosion was caused by a hydrogen leak which exploded. The momentary rise in radiation near the perimeter was caused by the release of slightly irradiated steam, and the radiation level has now dropped down to 70.5 microsieverts. The reactor is completely undamaged. It is a light water reactor which relies on the presence of water as the coolant and neutron moderator for the reaction to continue, so when they released the coolant water and steam, the nuclear reaction slowed down. They are now reintroducing sea water to cool the reaction as it stops. I had read they've detected Cesium, which implies there was some core damage. That's not a product you'd normally see in the coolant
Cap'n Refsmmat Posted March 12, 2011 Posted March 12, 2011 Indeed: Fuel rods at the reactor may be melting after radioactive cesium material left by atomic fission was detected near the site, Nuclear and Industrial Safety Agency spokesman Yuji Kakizaki said by phone. http://www.smh.com.au/environment/meltdown-fear-after-nuclear-plant-blast-20110312-1bsf4.html That doesn't sound good.
insane_alien Posted March 12, 2011 Posted March 12, 2011 no, its not good. BUT its not as bad as it could potentially be. Quite frankly I think it is a testament to the engineering used to build the reactor that it has survived the largest earthquake in japan in recorded history, a tsunami AND a large explosion with only relatively minor breaches in containment caused by the venting of steam. kind of makes you wonder what all these people going around saying nuclear power plants are deathtraps are actually on about. for instance, if a terrorist wanted to blow up that plant, to create an explosion that size would require an amount of explosive so obvious that even the most homer simpson like security guard would be suspicious of it. I'm being optimistic about this. They've decided to flood it with seawater(writing off what remains of the plant in the process) to keep it cool and once the situation has stabilised I think they'll be quick to get a secondary containment structure in place and start decomissioning. I don't think there will be any significant release of radiation.
Blahah Posted March 12, 2011 Posted March 12, 2011 Foreign media is reporting a completely different situation from what the local news stations are saying. It's hard to tell who's making it up.
insane_alien Posted March 12, 2011 Posted March 12, 2011 we probably won't know for sure the exact chain of events until months later. There has been a major natural disaster, miscommunications and so on will be frequent not to mention the emotional side. I think we can take from the fact that the exclusion zone is sitting at only 20km is a sign that, yes, radiation has been detected but not much more is currently expected to be released.
dragonstar57 Posted March 12, 2011 Author Posted March 12, 2011 (edited) is it possibly that the reactor is damaged irreparably (will not be able to be repaired to the point of being put back on line) and how much does the Japanese infrastructure depend on this reactor? what could happen if the reactor decided safe out of the necessity of electricity ps so if the cooling system were to experiences a total failure and could not cool the reactor there could be a serious melt down? Edited March 12, 2011 by dragonstar57
Cap'n Refsmmat Posted March 12, 2011 Posted March 12, 2011 is it possibly that the reactor is damaged irreparably (will not be able to be repaired to the point of being put back on line) and how much does the Japanese infrastructure depend on this reactor? what could happen if the reactor decided safe out of the necessity of electricity This one reactor is probably not essential to Japan's power grid -- they have fifty or so, plus other conventional power-generation facilities. ps so if the cooling system were to experiences a total failure and could not cool the reactor there could be a serious melt down? Not really. The heat being generated now is from radioactive decay products, and not from nuclear chain-reactions. The heat can still melt things, but we will not see a sudden nuclear chain reaction causing a nuclear explosion, as in Chernobyl. The reactor is already shut off.
insane_alien Posted March 12, 2011 Posted March 12, 2011 This one reactor is probably not essential to Japan's power grid -- they have fifty or so, plus other conventional power-generation facilities. Also, regretably, the demand for power in Japan will have decreased until the affected areas are brought back to habitable conditions. Several large settlements currently have effectively zero power draw due to the extent of the damage.
dragonstar57 Posted March 12, 2011 Author Posted March 12, 2011 aren't there 5 reactors having problems?
insane_alien Posted March 12, 2011 Posted March 12, 2011 5 reactors shut down according to plan when the tremors were detected by the safety systems. only 1 is actually experiencing a failure. the other 4 plants will return to operating status once they have been thoroughly inspected for damage and/or repaired.
swansont Posted March 12, 2011 Posted March 12, 2011 Not really. The heat being generated now is from radioactive decay products, and not from nuclear chain-reactions. The heat can still melt things, but we will not see a sudden nuclear chain reaction causing a nuclear explosion, as in Chernobyl. The reactor is already shut off. Even in Chernobyl the explosion was not nuclear. The reactor went prompt critical which almost assuredly damaged the core, but the explosion was steam and chemical. Reactors don't have the right geometry to make them nuclear bombs. At best (or worst), they fizzle. 1
dragonstar57 Posted March 12, 2011 Author Posted March 12, 2011 will the reactors not be vital in restoring power?
swansont Posted March 12, 2011 Posted March 12, 2011 will the reactors not be vital in restoring power? They have >50 of them, as Cap'n noted, and other sources of energy.
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