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Radiation Leak Found at Fukushima

Posted by feww on April 2, 2011

Japan Nuclear Disaster Update – Apr 2

Radiation near Reactor 2 in Fukushima NPP measures 1,000 millisieverts per hour

TEPCO, operator of the crippled Fukushima NPP, has found radioactive water leaking into the sea from a cracked concrete duct near Reactor 2, NHK said.

A TEPCO employee points to the inlet of a cracked concrete duct containing power cables near Reactor 2 at Fukushima Daiichi Nuclear Power Plant where contaminated water,  emitting radiation at 1,000 millisieverts per hour, is  leaking into the sea, April 2, 2011. Source: TEPCO

“With radiation levels rising in the seawater near the plant, we have been trying to confirm the reason why, and in that context, this could be one source,” said deputy head of Japan’s Nuclear and Industrial Safety Agency (NISA).

“There could be other similar cracks in the area, and we must find them as quickly as possible.”  Mr Nishiyama added.

TEPCO  is planning to pour concrete into the duct in an attempt to stop the leak, a company spokesman was quoted as saying.

The US Energy Secretary, Steven Chu, estimated on Friday that about 70% of one reactor core and 30% of another were severely damaged. However, these figures have not been confirmed by TEPCO.

What is a lethal dose of radiation from a single Exposure?

Studies of the 1945 atomic bombing at Hiroshima and Nagasaki show that 100 percent of victims whose bodies were exposed to 600,000 millirems (6,000 mSv) died from radiation. About 50 percent of victims who received  450,000 millirems (4,500 mSv) of radiation also died.

(Note: Rem is a unit of ionizing radiation equal to the amount that produces the same damage to humans as one roentgen of high-voltage x-rays.  Source: MIT)

1 rem = 10 mSv  (1 Sv = 100 rem)

Background Radiation in millirems per year (mrem/yr)

  • Average background radiation (US):  300
  • Higher altitudes (eg. Denver): 400

“Safe Levels” of Radiation (U.S.)

Limits above natural background radiation levels (average 300 millirems per year) and medical radiation:

  • Occupation Limit: Maximum of 5,000  (the limit for a worker using radiation)
  • Average Natural Background: 300

[Note: Lifetime cumulative exposure should be limited to a person’s age multiplied by 1,000 millirems, e.g., a 70-year-old person, 70,000 millirems.]


  • Max single dose for an adult: 3,000
  • Annual total dose: 5,000

Under 18

  • Max single dose for a person aged under 18 years: 300 millirems (whole body equivalent)
  • Annual total exposure: 500

Fetal Exposure

  • Maximum limit for fetal exposure during gestation period:  50 millirems per month above background levels


  • Single Chest X-ray (the whole body equivalent): 2 millirem

Air Travel

  • Coast-to-coast US round trip flight: 12 millirems

Megaquake and Tsunami Death Toll

The latest figures released by the authorities put the number of dead at about  12,000 with 16,000 people still listed as missing.

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