[ RadSafe ] High radiation levels detected at Fukushima grounds a month after explosions

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High radiation levels detected at Fukushima grounds a month after explosions
 
2011/04/26 
_http://www.asahi.com/english/TKY201104250130.html_ 
(http://www.asahi.com/english/TKY201104250130.html)   
Please check the latest developments in this disaster. From Toshio Jo, 
managing editor, International Division, The Asahi Shimbun. 
 
 
* * *  
High levels of radiation were detected on the grounds of the Fukushima No. 
1 nuclear power plant one month after explosions spewed radioactive 
materials, according to Tokyo Electric Power Co.  
The findings were shown in a map depicting radiation levels that TEPCO 
released for the first time on April 24.  
Radiation levels in the air around the No. 1 and No. 3 reactor buildings 
were especially high, mainly because the explosions damaged the buildings and 
spread radioactive materials.  
The air in an area to the northwest of the No. 3 reactor building had 
radiation levels of up to 70 millisieverts per hour. That building was damaged by 
explosion on March 14, three days after the Great East Japan Earthquake and 
tsunami crippled the plant.  
TEPCO first compiled the radiation level map on March 22 and has 
periodically updated it. The map is used to monitor radiation exposure of workers at 
the Fukushima plant and prepare new work plans for the plant grounds.  
Workers check radiation levels in the air every seven to 10 days or before 
any work procedure starts.  
If unusually high radiation levels are detected, further testing of rubble 
in the area is conducted to determine the cause of the high levels.  
Radiation levels as high as 130 millisieverts per hour were confirmed 
around the No. 1 and No. 3 reactor buildings in late March.  
Because radiation decreases with the passage of time, subsequent testing 
found lower levels.  
But if the level of 70 millisieverts per hour continues to the northwest of 
the No. 3 reactor building, a worker who remains in that area for four 
hours will have been exposed to more than the upper limit of 250 millisieverts 
established for individuals engaged in work at the Fukushima plant.  
Workers exposed to that total level of radiation will not be allowed to 
work in the area.  
On March 20, concrete rubble found west of the No. 3 reactor building had 
radiation levels of 900 millisieverts per hour. Even after that rubble was 
removed, radiation levels in the air measured between 10 and 30 millisieverts 
per hour.  
Another pile of rubble emitting radiation levels of 300 millisieverts per 
hour was found near the No. 3 reactor building.  
Almost all of the contaminated rubble was concrete from the No. 1 reactor 
building that was damaged in a hydrogen explosion on March 12 as well as from 
the No. 3 reactor building, hit by an explosion there on March 14.  
According to calculations by the Nuclear Safety Commission of Japan, the 
equivalent of 190,000 terabecquerels of radioactive iodine had been spewed 
from the reactor buildings by March 15. A terabecquerel is equivalent to 1 
trillion becquerels.  
That high level meant the Fukushima plant accident had already reached the 
worst level 7 on the International Nuclear and Radiological Event Scale, 
matching the assessment given to the 1986 Chernobyl nuclear disaster.  
A pipe installed to move radiation-contaminated water from the trench of 
the No. 2 reactor to a central waste processing facility was found to have 
radiation levels of 160 millisieverts per hour on its surface.  
Areas within the plant ground at a distance from the reactor buildings were 
also found to have radiation levels that exceeded 1 millisievert per hour.  
High radiation levels in the air were found even after rubble in the area 
was removed.  
The rubble, removed by remote-controlled heavy equipment, has been placed 
in 50 containers and moved to a temporary storage area within the plant 
grounds. A considerable amount of rubble remains, however.  
While TEPCO officials continue to remove the rubble to allow for easier 
work within the plant, one official said the radiation would not have a major 
effect on work because the contamination has already been figured into the 
road map for work procedures.  
(This article was written by Keisuke Katori and Hidenori Tsuboya.) 
Very truly yours, 
M.Sato
RRG: Ryokan Route Gento (Grand Mali Park)
WNY: West Noga (area) Yokohama
Environment Monitoring