Tepco released documents on Friday detailing in depth the analysis of the stored HIC (high impact container) containers at the disaster site. Radioactive water had been found puddling up in the lip of the plastic and steel containers a few months ago. The end result is that the highly radioactive sludge in the containers is generating hydrogen gas. The sludge in these containers can be as high as 3 Sv/hour – 9 Sv.hour just for a single type of isotope. Container W6 was found to have concentrations high enough to cause an explosion of it encountered a spark or flame.
It said no radioactive water was found to have escaped outside the concrete structures that encase the containers.
According to TEPCO, there were about 1,300 such containers at the plant as of May 20.
They store waste water from the ALPS (advanced liquid processing system) equipment that removes radioactive substances from contaminated water.
The containers, which are made of polyethylene, are 1.8 meters high and have diameters of 1.5 meters.
The first leak was discovered in a lid on April 2.
TEPCO began inspecting others to see if they had similar problems. Of the 278 it had examined by May 20, it found 26 had some sort of leak or were bleeding from their lids.
The operator said the leaks and bleeding were likely caused by hydrogen and other types of gases that resulted from the water’s exposure to high levels of radiation.
Such gases appear to have accumulated in sediment at the bottom of the containers, expanding the volume of the liquid.
An NRA official said the accumulating hydrogen poses a potential danger.
“If the concentration level is high, a spark caused by static electricity could cause a container to explode,” the official said.
Although all the lids of the containers were supposed to be fitted with pressure-release valves to allow gasses to escape, TEPCO’s survey found that one did not have the mechanism.
Further review of the delivery records for the containers showed there may be as many as 333 that are also defective, a TEPCO official said.
NHK : http://www3.nhk.or.jp/nhkworld/english/news/20150522_27.html
Asahi Shimbun : http://ajw.asahi.com/article/0311disaster/fukushima/AJ201505230059
Fukuleaks : http://www.fukuleaks.org/web/?p=14772