CITYBLOGGER..PENAFIAN Laman ini tidak bertanggungjawab atas hasil penulisan yang dipetik dari sumbe

Did'nt the Taliban get its start when America provided it with funding to fight the Soviets? Do we not ever learn from past mistakes?ever hear of the northern alliance, or massoud, the lion of panjshir (assassinated on 9/10)...In a nuclear plant shut down, the fuel control rods are inserted into the fuel bundle. The CEDM's (control element drive mechanisms) do that and the stops the fission in the reactor. The reactor cooling pumps keep running to remove the heat. There are "giant" heat exchangers to remove the heat from the primary system which is closed loop that is radio active. Somewhere during this process they pump in boriated (boron) water which inhibits the nuclear reaction and slowly the temperature is lowered to less then boiling temparture. Apparently they were shut down or in process of doing do when all hell broke loose and they lost the ability get it cool.When the earthquake hit, the reactors were automatically shut down (ie control rods inserted), which stopped the nuclear (fission) reactions. As the article indicates, stopping the nuclear reactions does not instantly eliminate the heat. Think of it like your car: you just drove it for 4 hours, stopped and turned it off. The engine is no longer running, however, the engine, radiator, exhaust, etc are still extremely hot. Unlike your car, which cools down solely by heat exchange with the air after it's turned off, a nuclear reactor still requires water to be circulated to cool it down. This is because of the normal heat level. A car engine is typically kept about 195 degrees F (water boils at 212 degrees F). Depending on the type reactor (boiling water or pressurized water), a nuclear reactor runs at temperatures of about 550 degrees F to 700 degrees F when water is present (pressure is used to increase the boiling temperature of water).

After the earthquake, everything was fine at the plants until the tsunami hit and knocked out all the electrical power including the emergency diesel generators the plants were running on. Since the pumps that keep the water circulating to remove residual heat run on electricity, they shut down. When that happened, the residual heat was enough to turn the water into steam. As more water turns to steam, the water level drops, and with no pumps to add more water, eventually the fuel rods are uncovered and exposed to air. The fuel rods are still so hot that uncovering them results in a significant increase in temperature (think of your car engine with little water in the radiator). The fuel rods can become so hot (approximately 4000 degrees F) that the outer casings begin to melt and you have 'meltdown'.

The hydrogen problem is related as a byproduct of the overheating problem. When the core overheats due to loss of coolant, the temperature gets high enough (700 to 1000 degrees F) to break water down into its individual elements (hydrogen and oxygen). Since there is twice as many hydrogen atoms as oxygen (H2O), the buildup of hydrogen occurs at a faster rate than the buildup of oxygen and hydrogen is an explosive gas. The hydrogen forms an explosive bubble inside the reactor vessel, which can result in an explosion, since you also have heat and oxygen present, so there are provisions to bleed the hydrogen out of the reactor vessel and into the building that houses the reactor vessel. Normally, the bleed off is at a slow rate and doesn't pose a problem, however as the temperature increases, the bleed off rate accelerates. Similar to a house with a small gas leak, eventually there is enough buildup of gas that a heat source causes an explosion. Once the explosion occurs, any further release of hydrogen will be dissipated by the air (just like a natural gas leak with the windows and doors open.) Nuclear plants don't have the ability to open windows and doors, since normally the air is filtered and monitored before any is released, so they were walking a fine line. Bleed off too much hydrogen too fast and cause an explosion in the building or don't bleed it off enough fast enough and cause a worse meltdown or explosion in the reactor. Like a tightrope walker, they lost their balance in two of the units and explosions occurred.

Additional units may experience explosions; however, that's not necessarily a bad thing under the circumstances. The more important thing is to keep the reactor vessels intact to minimize the amount of radiation released. If they have to sacrifice more buildings to keep the reactor vessels intact, they will. After the explosions, there is a measurable amount of radiation released as more hydrogen is bleed from the reactor, although the amount is minimal compared to the alternative. As a precaution they evacuated the area near the plants and monitor the radiation release. No cover-up or conspiracy.