Fukushima NPP: “There must be a large leak”

High levels of radiation detected near Fukushima Reactor 1

Water level in Reactor 1 reactor vessel has dropped 5 meters below operating level

TEPCO technicians at Fukushima Nuclear Plant discovered earlier today that water level in the Reactor 1 pressure vessel had dropped 5 meters below the designated operating level, or  more than one meter below the base of the uranium fuel rods, indicating a large volume of water was leaking into the containment building.

NRC schematic drawing of Containment Building and Basic Internals

“There must be a large leak,” Junichi Matsumoto, a senior manager at TEPCO told a news conference.

“The fuel pellets likely melted and fell, and in the process may have damaged […] the pressure vessel itself and created a hole.”

Fukushima prefecture officials have revealed that the radiation level rose to 1,015 mircrosieverts per hour on Saturday, NHK reported.

“One hour of exposure to this amount of radiation is equivalent to the permissible amount of radiation an ordinary person receives in one year. It is about twice the level that requires power companies to notify the government of an emergency situation.” Said the report.

[Note:  Single radiation dose of 2,000 millisieverts (200,000 millirems) and above causes serious illness. See also exposure list below.]

TEPCO raised the alarm, after noticing that the water in the pressure vessel had not risen despite pumping in 150 tons of of water daily to cool the reactor core.

The technicians  have pumped a total of about 10,400 tonnes of water into the reactor so far, a report said.

TEPCO says temperatures at the bottom of the containment building are between 100 and 120 degrees Celsius, suggesting that the damaged fuel rods have melted and fallen through the reactor vessel and into the bottom of the reactor building, where they are being cooled down for now.

Probability of a Nuclear Disaster by Country

The following probability figures are calculated by FIRE-EARTH on April 8, 2011

• Japan (880)³
• United States (865)
• Taiwan (850)
• Belgium, China, France, Finland, India,  South Korea, United Kingdom, Ukraine, Russia, Slovakia, Czech Republic, Armenia, Slovenia, Croatia, Romania,  Hungary, Bulgaria, Spain,  Pakistan, Argentina, Brazil, Mexico,  South Africa, Canada (810)
• Germany, Sweden, Netherlands (800)
• Switzerland  (750)

Notes:

1. The list represents a snapshot of events at the time of calculating the probabilities. Any forecast posted  here is subject to numerous variable factors.
2. Figures in the bracket represent the probability of an incident occurring out of 1,000; the forecast duration is valid for the next 50  months.
3. Probability includes a significant worsening of Fukushima nuclear disaster, and future quakes forecast for Japan.
4. A nuclear incident is defined as a level 5 (Accident With Wider Consequences), or worse, on the International Nuclear and Radiological Event Scale (INES). See below.
5. Safety issues considered in compiling these lists include the age, number of units and capacity of nuclear reactors in each country/state, previous incidents, probability of damage from human-enhanced natural disasters, e.g., earthquakes, tsunamis, volcanic activity, hurricanes, tornadoes, storms, wildfires, flooding… ]
6. The  Blog’s knowledge concerning the extent to which the factors described in (3) might worsen during the forecast period greatly influences the forecast.

Half-life of some radioactive elements

[NOTE: Half-life is the time taken for a radioactive substance to decay by half.]

• Cesium-134 ~ 2  years
• Cesium-137 ~ 30 years
• Iodine-131 ~ 8 days
• Plutonium-239 ~ 24,200 years

• Ruthenium-103 ~ 39 days [Ruthenium is a fission product of uranium-235.]
• Ruthenium-106 ~ 374 days
• Strontium-90 ~ 28.85 years  [Strontium-90 is a product of nuclear fission and is found in large amounts in spent nuclear fuel and in radioactive waste from nuclear reactors.]

• Uranium-234 ~  246,000 years
• Uranium-235 ~ 703.8  million years
• Uranium-238  ~ 4.468 billion years

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  12,000 with 16,000 people still listed as missing.

Related News

• Japan is shutting down 35 of its 54 reactors by late May

Related Links

• Japan Earthquakes, Disasters: Recent History and FIRE-EARTH Forecasts
• News Links 
• WARNING: JPTRMT1