The Yomiuri Shimbun
Engineers have been racing against time in a radioactive environment.
On Saturday, 279 engineers, including Tokyo Electric Power Co. employees, led the battle desperate effort to prevent a catastrophic nuclear meltdown.
Some were tasked with laying down a power line to the No. 2 reactor of TEPCO's Fukushima No. 1 nuclear power plant. These workers wore protective suits and special masks with activated charcoal filters. The also were outfitted with dosimeters, which measure radiation levels.
The workers were tasked with stretching the power line from a roll loaded on a vehicle and laying it along the ground. In addition to the driver of the vehicle, the workers included a crew assigned to remove debris from in in front of and behind the vehicle, while unloading and setting up the power line.
Radiation levels naturally rise as they get closer to the nuclear reactor. When their exposure to radiation exceeds 80 millisieverts, their dosimeters sound an alarm for the limit per shift. Teams of 20 engineers took turns conducting the task under the 80-millisievert restriction.
After the first fire at the No. 4 reactor on Tuesday, many workers were evacuated from the site, but 50 remained. These 50 then began working to lay the power line, joined by dozens of others who came to the site to contribute to the effort.
At the same time, work to cool overheating reactors at the nuclear power plant also was under way. Employees of affiliated companies such as TEPCO subsidiary Toden Kogyo Co.; Hitachi Ltd., a manufacturer of nuclear reactors; and construction firm Kajima Corp. put themselves in line for dangerous work.
The companies sought volunteers from among their workers, mainly those without wives or children.
At a press conference Friday, Hidehiko Nishiyama, a senior official of the Nuclear and Industrial Safety Agency, said, "I sincerely pray" for their safety.
In the United States on Wednesday, a news program on ABC television referred to the 50 who remained on the site as the "Fukushima 50," praising them as a group of "nameless brave men."
People who work at nuclear plants are allowed to be exposed to up to 100 millisieverts a year. But the Health, Labor and Welfare Ministry has made an exception in the present circumstances, raising the maximum limit to 250 millisieverts so the employees can continue their work at the Fukushima plant.
The highest radiation level detected inside the nuclear power plant was 400 millisieverts per hour--400 times the average annual radiation dose permitted by the government for members of the general public and four times higher than the figure believed to increase the risk of cancer.
===
Workers in protective gear
On a site contaminated by radiation like the Fukushima plant, workers usually are clad in protective suits similar to a thin raincoat made of synthetic and unwoven fabrics. The gear is light and breathable, enabling people to move easily. Because of its thinness, some people may be concerned about the gear's ability to protect wearers from hazardous material.
But the primary aim of the gear is preventing airborne radioactive material from adhering to the body or being inhaled. Although some types of highly penetrative radiation cannot be blocked, the risk can be diminished with the use of the gear. In places with high levels of radiation, protective masks with hoses enable people to breathe clean air.
Ground Self-Defense Force members who were assigned the mission of spraying water onto the Fukushima plant from helicopters and fire engines wore special GSDF protective gear designed to defend against toxic gas and biological weapons.
Some protective suits that incorporate sheets of lead and other metals have greater radiation-blocking capability but tend to be heavy, hindering the wearer's ability to work.
"The existing gear is not particularly effective in preventing radiation exposure, but it can limit it by allowing workers to conduct work quickly," a Defense Ministry official said.
Workers at the Fukushima plant are battling an invisible enemy in the form of gamma rays. This type of radiation is emitted like radio waves, penetrating paper and thin metal plates and causing diffuse damage throughout the body.
As gamma rays can be blocked only with lead or thin steel plates, ordinary suits designed to prevent radioactive materials from coming into direct contact with the body are insufficient.
Gamma rays are most likely being emitted from spent nuclear fuel rods that have been kept in the nuclear reactor's cooling pool, at which the level of water has dropped.
Gamma rays can be blocked with concrete. However, the reactor buildings have suffered heavy damage in the present crisis.
(Mar. 21, 2011)
No comments:
Post a Comment