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Japan Nuclear Disaster Update – March 31

Posted by feww on March 31, 2011

UPDATED at 13:00UTC

Japan Should Consider Extending Radiation Evacuation Zone: IAEA

Radiation at Iitate village, 40 km (25 mile) NW of the crippled Fukushima NPP, exceeded safety limits

Radiation levels within the 40-km radius of Fukushima NPP has exceeded safety limits, the International Atomic Energy Agency (IAEA) said.

They have recorded 20 megabecquerels per square meter (20,000,000 Bq/m²) at the village, which is twice the agency’s evacuation criteria, NHK reported.

Two radioactive elements, iodine-131 and cesium-137, had caused the contamination, the report said.

[Note: One becquerel (Bq) represents one nucleus decay per second in a given quantity of radioactive material. 1 GBq = 0.0270 Curie (Ci). Curie is an older unit of radioactivity equal to the decay of 1 gram of radium-226.   1 Ci = 3.7 x 10^10 decays per second.]

“[IAEA has advised Japanese government to] carefully assess the situation on the basis of this report,” Japan’s Chief Cabinet Secretary Yukio Edano said at a daily news briefing earlier today.

“At the moment, we have no reason to think that the radiation will have an effect on people’s health. We need to closely monitor the situation and see if the radiation is consistently high,” Edano said.

“I don’t think that this is something of a nature which immediately requires such action.”

“But the fact that the level of radiation is high in the soil is inevitably pointing to the possibility that the accumulation over the long term may affect human health,” he added. “Therefore, we will continue monitoring the level of radiation with heightened vigilance and we intend to take action if necessary.”

Meanwhile,  radioactive iodine levels found in seawater about 330 meters south of the stricken plant’s water outlet has climbed by 4,385 times the legal limit, Japan’s nuclear and industrial safety agency (NISA) said. The latest reading is the highest level recorded since radiation first leaked from the plant following the Tohoku 9.0 Megaquake and tsunami, which struck the region on March 11.

The previous high for radioactive iodine found in seawater near Fukushima was reported yesterday at 3,355 times the legal limit.

Radiation at Iitate village

Dangerous radiation levels of about 10 microsieverts per hour have been recorded at Iitate village, according to Greenpeace, which has urging the Japanese government  to “stop choosing politics over science.”

“It is clearly not safe for people to remain in Iitate, especially children and pregnant women,” Greenpeace said.

Iodine 131 is believed to have caused the high incidence of thyroid cancer among children living near the Chernobyl plant when the 1986 nuclear disaster occurred.

Significant Aftershocks

Another significant aftershock measuring 6.2  struck the region about 114 km (71 miles) SE of  Morioka, and 126 km NE of Sendai, USGA/EQHP reported.

The quake was epicentered at 38.954°N, 142.017°E  and struck at a depth of about 39.6 km at 04:15:30 PM local time, EQ report said.


EQ Location Map. USGS/EHP

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.]

Adults

  • 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

Medical

  • 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  11,420, with 16,370 people still listed as missing.

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