Fukushima Nuclear Disaster –On March 11, 2011, the earthquake and tsunami hit and caused the 3 reactors in Fukushima to overheat and partially melt down. The earthquake knocked out the plant’s power, and the tsunami flooded the backup generators that kept the cooling systems operational. The absorbed rods were inserted as soon as the earthquake hit to stop the nuclear reaction, but the reactors were still hot at about 550 degrees F. Heat was still generated in the fuel by the natural decay of radioactive elements. Plant engineers thus had to flood the reactors with sea water mixed with boric acid, which is efficient at absorbing neutrons. This permanently disables the reactors.
Reactor 2 – pumps sending seawater into reactor for cooling failed. Explosion in containment vessel, and radioactive steam released.
Japan has 17 nuclear plants that provide 30% of its electricity needs. The Fukushima reactors are from the 1960s, and are BWR reactors.
The Chernobyl Nuclear Disaster and Three-Mile Island are both examples of LOCA (Loss of Coolant Accident). Another possible accident is Station Black Out (SBO), where there is no electrical power to operate the pumps. This happened in Fukushima. These result in an increase in the fuel rod temperature, which may lead to a reactor meltdown since the zirconium alloy around the fuel rods becomes brittle and it may corrode.
In Japan, each nuclear reactor had 3 diesel generators. If the probability that one will fail is 1/1000. When you have 2 backups, the probability of all 3 failing will be 1/10^9.
Immediately after you insert the control rods, there is still 10% of the peak heat generation that is still being generated. The heat generation decays exponentially. So after a week you get down to only 1% of peak power.
Radiation effects – ionizing radiation has enough energy to remove electrons from atoms or molecules. Gamma rays can destroy DNA.
After hearing of all these disasters, it appears like nuclear energy is a terrible and fearsome power source..