Robot Measures Huge Radiation Levels at Fukushima Daiichi Nuclear Plant
By Kimberly Arsenault
Contributor, EDM Digest
In what was the world's worst nuclear disaster since 1986 at Chernobyl in Ukraine, the Fukushima Daiichi nuclear plant owned by Tokyo Electric Power Co. Holdings (TEPCO) had a triple meltdown following a 9.0 magnitude earthquake and tsunami in March 2011. Nearly six years after the nuclear disaster, a robot has finally been able to access a location near the reactor 2 core in order to measure its current radiation levels.
The measurement recorded a jaw-dropping 530 sieverts of radiation per hour. For comparison, an acceptable level of radiation exposure for an individual should not annually exceed 5 rem, or roentgen-equivalent (in) man. It takes 100 rem to equal 1 sievert of radiation and experts note that exposure to 4 sieverts of radiation will kill 1 in 2 people, while just 1 sievert can lead to cataracts, hair loss, and possibly infertility.
With radiation levels this high, the robot, built to withstand up to 1,000 sieverts of radiation exposure, only has about two hours of working time before it will be rendered inoperable at the current 530 sievert level recorded.
Scientists did caution, however, that the radiation reading taken near the reactor 2 core is an estimate based on radiation generated electronic noise in the camera, an estimation method that has a margin of error of around 30 percent.
Black Mass Deposit
In addition to obtaining a reading on the approximate level of radiation, the robot also found about a 3-foot-wide hole in the metal grate under the pressure vessel, along with a black mass deposit on the grating. The black mass deposit may be melted fuel, and if so, it would be the first fuel to be found after the meltdowns. However, because of the hole in the grating, there is concern that the investigation could be delayed due to the likely need to find another route for the robot to use to gain access the interior and the containment vessel.
What's more concerning is how Japan will move forward in the decommissioning process of the three nuclear reactors at Fukushima Daiichi with such high radiation level readings nearly six years after the disaster. The nuclear fuel needs to be removed and with radiation levels this high, attempting to contain and remove the fuel becomes a major challenge. TEPCO had hoped to begin removing the fuel by 2021, but these findings might alter the decommissioning schedule significantly according to one former research scientist from the Japan Atomic Energy Research Institute. Readings have yet to be taken on reactors 1 and 3, but plans to begin probing reactor 1 are being finalized.
Death Toll and Evacuations
The earthquake and subsequent tsunami caused the deaths of more than 15,800 people with a reported 2,500 people still missing. Another almost half a million or 448,000 people were eventually evacuated due to the nuclear plant disaster. The meltdown of the nuclear plant originally caused the evacuation of anyone within 2km of the facility, which was changed just 3o minutes later to 3km. In just seven hours, the new evacuation zone was moved to 10km, and another three hours later, to 20km. At the time, a total of 390,000 people were evacuated or ordered to remain indoors and a 20km exclusion zone still exists around the nuclear plant.
2011 Japan Earthquake Facts
The earthquake was so strong that it shifted the earth on its axis, caused about 250 miles of Japan's coastline to drop about 2 feet, moved Honshu, Japan's main island 8 feet eastward, and broke icebergs off the Sulzberger Ice Shelf in Antarctica. In the year following the earthquake, Japan also had more than 5,000 aftershocks, the largest of which was a 7.9 earthquake.
Fukushima: A Triple Disaster
The 9.0 earthquake struck off the northeastern coast of Japan at 2:46 p.m. on March 11, 2011, causing reactors 1, 2, and 3 at the Fukushima Daiichi nuclear power plant to shut down automatically because maximum tolerances for these reactors were exceeded. Cooling cooling sources also failed due to the earthquake. As a final power backup, 13 generators were located in the basement of the nuclear plant and were able to act as a power source to ensure the cooling of the reactors.
50 minutes later, seven tsunamis generated by the earthquake struck the facility, including an estimated 45 foot high tsunami, swamping the nuclear plant and flooding the basement. This rendered all but one of the generators operational with nowhere near the required power necessary to ensure the reactors were being sufficiently cooled.
A nuclear meltdown appeared imminent, and the Unit 1 reactor exploded on March 12, Unit 3 on March 14, and Unit 2 on March 15. On March 15, a fire also broke out in Unit 4, releasing radiation into the atmosphere. Although it seemed that pumping the water into Unit 2 was meeting with some success, a leak was discovered inside its core, which had been allowing radiation to seep out for days - most of into the water.