Fukushima Dai-ichi (#1) Nuclear Reactor

Key Facts

For the most complete information, check out the IAEA: www.iaea.org (Add 9 hours to UTC to get Japan time).

  • The power plant is 240 km north of Tokyo.
  • An area of 20 km around the power plant has been evacuated. Since the explosion of the #4 reactor. Some towns further outside this zone are now being evacuated based on radiation readings on the ground.


  • There are 6 reactors at the Dai-ichi Power Plant, each numbered 1-6. The #1, #3 and #4 reactors at Dai-ichi have suffered hydrogen explosions that partially or completely knocked off the outermost concrete shell (#1 went on 3/12, #3 on 3/14, #4 on 1/15). According to reports, none of these containment units have been damaged.
  • The #2 reactor suffered an explosion in the suppression pool on 3/15. 


  • Fukushima Dai-ni (#2) Nuclear Power Plant is 11.5 km to the south of Dai-ichi. A 10 km radius has been evacuated around Dai-ni. This is essentially contained within the evacuation radius for Dai-ichi.
International Nuclear Event Scale (INES)  
7 Major Accident (Chernobyl, Fukushima)
6 Serious Accident
5 Accident with Wider Consequences (Three Mile Island)
4 Accident with Local Consequences
3 Serious Incident
2 Incident
1 Anomaly
0 Deviation (No safety significance)



How much is a microSievert? 1 Sv = 100 rem, so 1 uSv = 100 urem (u  means 0.000001). Sometimes reports will refer to milliSieverts (mSv). This is a factor of 1000 higher: 1 mSv = 1000 uSv. The following is a partial reproduction of a chart that has been used on Japanese TV:

Radiation Exposure (in microSieverts, uSv)
50  X-ray exam
100-200  Flight from Tokyo to New York
2,400  Natural exposure in one year

I've also seen it reported that 1,000 uSv is the natural exposure for one year, while the NCRP (National Council on Radiation Protection and Measurements) in the US sets it at 620 mrem, or 6,200 uSv. Not sure why the US number is so much higher. The NCRP also says an X-ray exam is 40 mrem, or 400 uSv. Their dosage calculator is here: www.epa.gov/radiation