A few comments:
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Testing of this nuclear safety feature in April of 1986 turned into this deadly disaster as established procedures were not followed and in the minutes leading up to the accident, emergency warnings were ignored and mistakes were made. There also proved to be several flaws within the design of the Soviet RBMK nuclear reactor and in its construction.
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According to the testimony of Anatoly Dyatlov, all the instruments read normal just six seconds prior to the explosion. Instrumentation was probably inadequate here, as it's considered likely that there was a "hot spot" that formed in the lower half of the reactor which went undetected.
The RBMK reactor was known to be less stable at low power levels than at high power, and it was originally instructed that they perform the test at about 60% power. However, due to electricity demand they were forbidden to shut down the reactor for several hours after when the test was supposed to start, which caused Xenon to build up (which is a strong poison). The reaction rate tanked, and they removed a bunch of control rods to try and get it back up, finally deciding to run the test at much lower power than anticipated (~14% iirc).
Again according to Dyatlov, the test completed successfully and the control rods were being reinserted to shut the reactor down after completion. The control rods, however, were tipped with graphite which moderated the reaction and when first inserted actually *increased* the reaction rate. (A fault which was first discovered in an incident at the Ignalina plant).
Canadian simulations suggest that the control rods were actually able to successfully deactivate the top half of the reactor, but there was still enough material in the lower half that it was able to operate essentially independantly from the top half.
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Worth noting is that none of the reactors at Chernobyl had a containment building, which is effectively an airtight shield made of steel and concrete that covers the nuclear reactor and presents radiation from escaping into the atmosphere.
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The RBMK was a very tall reactor, especially factoring in the fuel cranes on the top, and they didn't consider it practical to add even more to the height by adding a heavy containment to the top. They did, however, have a fairly robust accident localisation system (ALS) for the bottom half of the reactor (a lot of good that did).
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(Sweden was reportedly the first country to notice the increase in airborne radiation)
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Yep - the Forsmark power plant registered somethat higher radiation levels at their detectors and shut themselves down for inspection thinking that they might have had a leak. They didn't find one.
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The sarcophagus did help in preventing greater amounts of radioactive material from escaping into the atmosphere, but it's fallen into a state of disrepair with cracks appearing along the roof and the entire structure is considered unstable and being at a risk of collapse.
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The sarcophagus is built upon the existing structure of the reactor 4 building, which is considered unsound as one of the major supports was severely bent in the explosion. Simulations suggest that a tremor of 7 or above on the Richter scale (which happen in the area about once every 30 years or so) could cause the thing to collapse.
04-07-2010, 12:00 AM
Touring Chernobyl In 2010
Linear Mode
