24 Mai 2015
May 23, 2015
By HIROMI KUMAI/ Staff Writer
Inspections of containers holding contaminated water at the Fukushima No. 1 nuclear power plant found that at least 10 percent have leaks, which could trigger a hydrogen explosion.
Tokyo Electric Power Co., the plant’s operator, reported its findings at a meeting with a study group from the Nuclear Regulation Authority on May 22. 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.
Tokyo Electric Power Co. (TEPCO) revealed on May 22 that one of its containers for waste liquid remaining after the processing of contaminated water at the Fukushima No. 1 Nuclear Power Plant did not have the necessary holes in its lid for venting out gas.
A total of 305 containers are being used without having been checked for venting holes. TEPCO says it will quickly inspect all of the containers.
The containers hold sludge and other waste liquids containing radioactive materials that remain after contaminated water is put through the Advanced Liquid Processing System (ALPS). The waste produces gasses like hydrogen, so as a safety measure the Nuclear Regulation Authority had asked TEPCO to create the holes.
In early April, containers were found to be leaking radioactive waste liquids through the venting holes. Later in the month, a company in a cooperative relationship with TEPCO was inspecting the containers when it discovered the container without the venting holes. Out of the approximately 1,400 containers, 334 -- including ones that are not being used yet -- have not yet been checked for venting holes.
TEPCO has speculated that the work to create the holes was skipped over at a factory in the United States.