The Yomiuri Shimbun
Radiation levels inside the No. 1 reactor building at the Fukushima No. 1 nuclear power plant are low enough for full-scale work to begin on a new cooling system for the reactor, it was discovered Monday.
A double set of doors linking the reactor building to its adjacent turbine building was opened completely early Monday morning. Nine workers--seven from Tokyo Electric Power Co. and two from the Nuclear and Industrial Safety Agency--entered the reactor building shortly after 4 a.m.
It was the first time for workers to enter the second floor of the reactor building since a hydrogen explosion occurred at the building on March 12.
They took radiation measurements and found that levels on the second floor--where full-scale work on the new cooling system would be conducted--were 100 millisieverts per hour at maximum.
In some locations on the first floor the readings ranged between 600 millisieverts and 700 millisieverts per hour, which would quickly exceed the yearly permissible maximum exposure of 250 millisieverts. However, TEPCO officials said it is unlikely workers will have to be in those locations.
The nine workers were found to have been exposed to radiation of up to 10.56 millisieverts during their time in the reactor building, posing little threat to their health.
"If shielding and decontamination of radioactive materials is conducted properly in locations with relatively high levels of radiation, we'll be able to start building a new cooling system for the reactor," a TEPCO official said.
On Monday, a small enclosure set up inside the turbine building to cover the double set of doors was removed, as were pipes connecting the reactor building with a ventilator to filter out radioactive materials and reduce the high radiation levels inside the building.
At the place where the doors were opened--measuring about 80 centimeters wide and 2 meters high--the air in the reactor building and turbine building mixed.
As of 9 a.m. Monday, there had been no major changes in radiation readings within the premises, leading TEPCO and the agency to conclude that there was little impact on the environment.
TEPCO now plans to install and adjust equipment needed for a so-called water coffin operation, in which the reactor's containment vessel will be filled with water to stabilize the reactor, and to install pipes needed to set up a cooling system outside the building.
On Monday afternoon, TEPCO took detailed measurements of radiation levels and brought power cables inside. Starting Tuesday, it will install instruments to measure the water level and water pressure inside the containment vessel and take measures to shield and decontaminate the radioactive materials.
Securing a path toward full-scale work at the reactor building is expected to contribute greatly to the task of stabilizing the No. 1 reactor.
(May. 10, 2011)