Description of some damages to the Nigata Nuclear plant in 2007 - Courtesy TEPCO

The earthquake at Nigata, Japan in 2007 was 6.9 on the Richter scale. The one that hit Fukushima was 8.9.(The Richter scale is Logarithmic!!!) See the damages caused by the Nigata earthquake...


"Displacement of the ducts connected to the main exhaust stack (units 1 to 5)'. Courtesy of The Tokyo Electric Power Company, Inc


Courtesy of The Tokyo Electric Power Company, Inc
"Leakage of water containing a trace of radioactivity into the sea via the non-controlled area of unit 6.
The seismic motion caused the overflow of water from the spent fuel pools in units 1 to 7. At unit 6, the overflowed water leaked into the non-controlled area via the electric cable conduit of the refueling machine and flowed into the sump. It was confirmed that water in the drainage sump had been discharged into the sea by the sump pump when the water level increased. (Refer to the figure below".)



Courtesy of The Tokyo Electric Power Company, Inc


Courtesy of The Tokyo Electric Power Company, Inc
Iodine and radioactive particulate materials were detected at the main exhaust stack of unit 7.
"When the earthquake occurred, unit 7 was automatically shut down. However, it was confirmed that since the gland steam ventilator continued to operate for a while, the steam sealing the shaft was exhausted, and subsequently radioactive steam left in the turbine had flowed out to through the gland steam ventilator. (This event was reported on July 16th.)
During normal operation, the turbine shaft is covered with the gland steam (containing no radioactive material) so that the steam containing radioactive materials sent from the reactor to the turbine does not flow out from the turbine through the gland steam ventilator.
Impact to the Environment
The radioactivity of radioactive iodine and radioactive particulate materials released to the environment through the main exhaust stack was about 4 × 108 becquerels and 2 × 106 becquerels, respectively. The dose by this radioactivity was 2 × 10-7 millisieverts, an equivalent to about one 10 millionth of the dose (2.4 millisieverts) an average person is exposed to from natural sources annually.
No radioactive material has been detected since the gland steam ventilator was stopped on July 19th".
For more details visit the TEPCO site in this link