A group of Diet members studying ways to build a new Japan without nuclear power plants was formed on April 26.
5,000 protest in Shibuya against nuclear power generation
Participants in an anti-nuclear demonstration walk the streets of Tokyo's Shibuya district on April 24 holding "nanohana" flowers, a symbol of the revitalization of Chernobyl following the 1986 nuclear accident. (Shingo Kuzutani)
About 5,000 citizens rallied against nuclear power in Shibuya on April 24, reflecting the increasing concerns about the energy source following the Fukushima No. 1 nuclear power plant accident.
Many of the demonstrators said they participated in a demonstration for the first time, as they urged the government to switch from nuclear power to natural and renewable energy sources.
Asked why she was participating in the rally, a 33-year-old part-time worker from Tokyo's Kita Ward, said, "I was worried nuclear plant accidents could affect my children's or grandchildren's generations."
A 42-year-old man from Tokyo's Nerima Ward added, "Through this action, I want as many people as possible to think about the issue."
Organizers of the rally planned and coordinated it mainly via the Internet. Musician Ryuichi Sakamoto was listed among the supporters of the event.
High radiation levels detected at Fukushima grounds a month after explosions
The Fukushima No. 1 nuclear power plant (Provided by Air Photo Service)
Editor's note: We will update our earthquake news as frequently as possible on AJW's Facebook page: http://www.facebook.com/AJW.Asahi. Please check the latest developments in this disaster. From Toshio Jo, managing editor, International Division, The Asahi Shimbun.
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High levels of radiation were detected on the grounds of the Fukushima No. 1 nuclear power plant one month after hydrogen 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 hydrogen 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 a hydrogen 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.)
TEPCO filling containment vessels; experts raise doubts
Tokyo Electric Power Co. started the unprecedented and potentially risky measure of allowing water to flood the containment vessels of three troubled reactors at the Fukushima No. 1 nuclear power plant, company sources said.
It is the world's first attempt to saturate the entire containment vessel with water with the aim of cooling the pressure vessels inside the containment vessels and ultimately the reactor cores themselves.
So far, TEPCO has been injecting water into the pressure vessels at the No. 1 through No. 3 reactors. Under the new plan, TEPCO will allow the water to overflow from the pressure vessels through valves and ruptured pipes until the water fills the outer containment vessels.
According to TEPCO's road map, the water levels will reach the upper end of the fuel rods within three months.
The amount of water injected into the pressure vessels is about one ton larger per hour than the amount that evaporates due to the intense heat from the fuel rods.
The water level at the No. 1 reactor has been raised to about 6 meters above the bottom of the containment vessel. That level is 3 meters below the bottom of the pressure vessel.
But TEPCO has been unable to verify the water levels at the No. 2 and No. 3 reactors, and suspect that water is leaking from the damaged containment vessels.
Industry specialists have raised doubts about the effects and safety of TEPCO's new operation.
Since the concrete-made building of the No. 1 reactor may have been weakened by the March 11 earthquake and tsunami as well as aftershocks, it might not be able to bear the weight of the water, which will reach up to 7,400 tons. TEPCO said it is re-calculating the structural strength of the building.
At the No. 2 reactor, highly radioactive water is believed to be seeping through a hole in the suppression pool, which leads into the lower part of the containment vessel.
TEPCO plans to plug that hole with adhesive cement.
The Oak Ridge National Laboratory, a top U.S. scientific research institution, reported in a study that this method can mitigate damage from nuclear incidents. Nonetheless, the U.S. study did not take into account a nuclear crisis continuing for more than one month, as has the Fukushima nuclear incident.
Keiji Miyazaki, professor emeritus of nuclear reactor engineering at Osaka University, said that filling the containment vessel with water would cool the pressure vessel from the bottom, which would likely prevent it from being destroyed by melting fuel.
However, he added that the method is not an effective way to cool the fuel rods.
Another problem will be adjusting pressure levels inside the containment vessel should the temperature and pressure again rise. The amount of gas inside the containment vessel will be substantially reduced by the injected water.
TEPCO is considering draining the water from the pressure suppression pools, cooling that water with air and seawater and then re-injecting it.
(This article was written by Ichiro Matsuo, Tatsuyuki Kobori, and Hidenori Tsuboya.)