The millisievert (mSv) is a measure of the absorption of radiation by the human body.
Released on April 24, 2011, the map released shows the high levels of radiation throughout the site--including the 300 mSv from debris near the No. 3 nuclear reactor which had its outer building badly damaged after a hydrogen explosion back in March.
In the map - image above - it denotes radiation levels at some 230 areas in the facility - with the number of millisieverts per hour denoting where it is the most dangerous to work.
"It will take more than six months to remove all the debris from the site. Data included in the survey map were taken into consideration when the timetable [for stabilizing the reactors] was compiled," states a TEPCO spokesperson.
According to TEPCO handout, radiation levels were not above 100 mSv anywhere at the plant as of April 23, 2011. But, levels of more than 10 mSv were detected in the air at more than 30 locations around the Nos. 1 to 4 reactors.
- Debris was cleared from an area to the east of the No. 3 reactor April 21, 2011, after levels of 900 mSv per hour were detected. Later readings showed levels had fallen to 10 - 30 mSv per hour;
- Apparently, levels from 40 - 70 mSv per hour detected in the air at some places were due to diffused radiation from the hydrogen explosions;
- Near a concrete pump where TEPCO workers are pouring water into a pool holding spent nuclear fuel rods inside the building housing Reactor the No. 3, radiation levels were between 20 - 30 mSv per hour;
- A debris-strewn area to the north of Reactor No. 1 reactor tested 40 mSv per hour in the air, as did an area to the west of the reactor;
- The surface of a hose that carries radioactive water from beneath Reactor No. 2's trench to the complex's central waste treatment facility had radiation levels from 75 - 86 mSv per hour;
- Near the waste treatment facility, readings from the hose surface were 160 mSv per hour. TEPCO said it could not explain why the level there was so high. The water inside the hose at any one time contains more than 1,000 mSv per hour of radiation.
What the heck is a millisievert?
The millisievert (mSv) is a measure of the absorption of radiation by the human body.
The average person is exposed to 2.4 mSv a year through a variety of sources like x-rays, cosmic rays, radon, granite, tobacco - in fact, if you lived in a high elevation place, you are receiving more millisieverts of radiation than those at sea-level - because of the thinner atmosphere which is a blocker.
There is a rumour that the U.S. Capitol Building made up of a stone containing uranium emits more than enough radiation to shut down a nuclear power plant. I said rumour now.
Other examples of exposure include:
- Chest x-ray: .04 mSv single dose;
- Cosmic rays: .24 mSv per year;
- Smoking 1.5 packs a day: 13 mSv per year;
- Flight crew working the New York-Tokyo route: 9 mSv per year;
- Living near Chernobyl when it melted down in 1986: 450 mSv cumulative over several days.
There is a 50 percent chance of death within a month if you are exposed to a single dose of 5,000 mSv. Obviously, you double your percentage if you double the exposure: near-certain death within a month after a single dose 10,000 mSv of radiation.
Now... what does this all mean? Well, Japan's Chief Cabinet Secretary Edano Yukio (surname first) did state over a month ago that the radiation levels at Dai-ichi were hitting 400 mSv per hour - which is 20 times the annual exposure for a typical nuclear-industry worker or uranium miner. That would be bad - but keep in mind that this is very close to the nuclear radioactive sources (within metres or less)... people within the evacuated zone were getting a constant dose that was only going to add up.
Somewhere my cigarette is glowing,
Andrew Joseph
The photo image directly above will give you a better idea of some of the general layout of the facility.
