31 Décembre 2014
December 31, 2014
By MIKI AOKI/ Staff Writer
Tokyo Electric Power Co. diluted a dust suppressant that rendered it ineffective and allowed the spread of radioactive materials that contaminated 12 workers at the Fukushima No. 1 nuclear plant in summer 2013, officials said.
The suppressant is supposed to prevent radioactive dust from getting into the air and spreading.
However, TEPCO not only diluted the suppressant to levels well below the manufacturers’ recommended standard, but it also did not use the suppressant on a daily basis when removing rubble at the stricken nuclear plant.
The sloppy use of the dust suppressant continued for about a year.
“As a result, the effectiveness of the suppressant decreased and likely led to the spewing of radioactive materials in the summer of 2013,” an official with the Secretariat of the Nuclear Regulation Authority said.
The NRA Secretariat issued administrative guidance to TEPCO, instructing the utility to use the suppressant in a safe manner.
According to an official with a dust suppressant manufacturer, the product is an alkaline liquid that solidifies after a few hours. It is mainly used to prevent the spread of asbestos.
The company recommends that when removing asbestos, the dust suppressant should be used as is or diluted in 10 parts water. It should also be sprayed daily throughout the removal process.
According to TEPCO officials, when workers were removing rubble from the No. 4 reactor at the Fukushima No. 1 plant, the dust suppressant was sprayed on the day before work and right before the removal of the rubble. The suppressant was either undiluted or diluted in 10 parts water.
However, from August 2012, when rubble removal began at the No. 3 reactor, the suppressant was diluted in 100 parts water, and it was used only once every several days or even once every several weeks, the officials said.
In summer 2013, when the spread of radioactive dust came to light, the suppressant had been used at the No. 3 reactor only twice, in mid-June and on Aug. 13.
“Dilution in 100 parts water produces the same result as using only water,” said an official at a dust suppressant manufacturer. “Because work should, in principle, only be conducted when the dust has been moistened with the suppressant, not using the suppressant for several days will naturally lead to the spewing of radioactive dust.”
In fact, on Aug. 12 and 19, 2013, when rubble was being removed, alarms went off at the Fukushima No. 1 plant because the spread of radioactive dust raised the radiation levels there. Twelve workers were confirmed to have been contaminated by radioactive materials.
On Aug. 19, the volume of radioactive materials released was 6,700 times normal levels, according to an estimate made by the NRA Secretariat.
On one occasion, airborne radiation levels increased at a location 3 kilometers from the Fukushima No. 1 plant.
TEPCO officials admitted that was likely caused by the spewing of radioactive dust after the improper spraying of the dust suppressant.
“When the dust suppressant was mixed in the nuclear fuel storage pool, the level of alkalinity increased, and there were concerns about the effect on equipment,” a TEPCO official said. “While we were aware there was no problem with the effectiveness of the suppressant, our actions in the end were insufficient.”
The utility returned to using suppressant diluted in 10 parts water from October 2013, and the liquid was sprayed daily before and after work to remove rubble.
TEPCO did conduct an experiment to find out if dust solidified when the suppressant was diluted by 100 parts water, but no tests were done on the duration of that effect.
“The thinking toward safety management was extremely sloppy,” said Hiroyuki Mori, a professor of public policy at Ritsumeikan University who has conducted studies on the spread of asbestos at disaster-stricken areas. “The work should have been conducted while thinking foremost about the safety of the workers and local residents.”
An official with the NRA Secretariat’s office dealing with the accident at the Fukushima No. 1 plant said: “Initially, we did not check the concentration of the dust suppressant or the frequency with which it was used. We have since strengthened monitoring.”