The No. 4 reactor of the stricken Fukushima No. 1 nuclear power plant, where workers are removing spent nuclear fuel, is still a gutted shell and conditions there remain extremely hazardous.
The No. 4 reactor of the stricken Fukushima No. 1 nuclear power plant, where workers are removing spent nuclear fuel, is still a gutted shell and conditions there remain extremely hazardous.
The damage is extensive, with mangled debris seemingly everywhere.
A team of reporters from The Asahi Shimbun visited the site on Jan. 29.
Unlike the No. 1 to No. 3 reactors at the Fukushima facility, the No. 4 reactor did not experience a meltdown after the 2011 Great East Japan Earthquake and tsunami.
The No. 4 reactor has seen the most decommissioning work of those four reactors as radiation levels there are much lower than in the other reactors.
This is because it was undergoing regular inspection when the disaster struck. Even so, an explosion occurred at the No. 4 reactor building around 6 a.m. on March 15, 2011. It was caused by hydrogen that had entered through piping from the No. 3 reactor, where a meltdown had occurred.
The explosion damaged the cooling equipment for the spent nuclear fuel storage pool, leading to global fears that the fuel would become exposed once the coolant had dried up.
Climbing a narrow temporary staircase, the Asahi team reached the fourth floor of the No. 4 reactor building. While part of the wall was blown away by the explosion, a canopy that has since been installed kept the site in darkness. A flashlight shined on the destroyed wall to reveal its exposed steel framework. Rusted machinery parts and shattered measurement equipment lay buried in the debris.
The radiation level--0.03 millisievert per hour--was about half the level announced a year earlier.
In the area immediately above the explosion site, work began in November to remove fuel assemblies from the storage pool on the other side of the wall. A canopy and crane have been installed, giving a sense of how the site looked prior to the 2011 nuclear accident.
In the basement of the reactor building, a working pathway has been set up around the doughnut-shaped suppression chamber. Its bright paint has dulled, and in places has cracked and fallen off.
Water was visible about two to three meters below the pathway. The water is believed to have entered the reactor building when the site was deluged by tsunami triggered by the Great East Japan Earthquake.
In the neighboring No. 3 reactor, work continues to remove debris from the upper part of the reactor building. Robots are being used in the decontamination work because of the high radiation levels.
In the absence of knowledge about the state of the melted fuel in the No. 1 to No. 3 reactors, no decision has yet been made on how to remove that fuel. In the best-case scenario, plans call for work to begin removing the melted fuel from the No. 1 and No. 2 reactors from fiscal 2020.
Another major problem is the volume of water contaminated by radiation being stored on the plant site. Tokyo Electric Power Co., operator of the facility, said that around 400 tons of contaminated water continues to be generated daily. The accumulated total comes to 507,000 tons.
Problems with the ALPS (advanced liquid processing system) have delayed work to remove radioactive materials from the contaminated water.
In August 2013, 300 tons of highly radioactive water was found to have leaked from the storage tanks.
Due to concern about additional leaks, TEPCO has increased its patrol of the storage sites.
The H2 North area in the compound contains 17 tanks, each with a diameter of 12 meters or so.
Shortly before noon on the day of the reporters’ visit, a team of three workers wearing protective gear inspected the tanks to measure and record radiation levels. The workers checked the connecting parts of the approximately 11-meter-tall tanks for leaks. They also inspected the barrier surrounding the tanks to prevent contaminated water from flowing outside the area. The valves and connecting parts of the barrier were scrutinized for leaks.
A number of pipes through which contaminated water flowed lay on the ground. Overhead was a network of equipment that had been installed after the discovery that contaminated water had leaked. There were cables for the water meter that was installed in November 2013 as well as pipes to remove rainwater from the top of the tanks.
All the equipment meant attention had to be paid when walking in order to avoid tripping and falling.
The 900 or so tanks on the plant site are inspected four times a day by 10 three-person teams. Each team walks for at least four kilometers on each inspection trip, which can take between two to two-and-a-half hours.
Yuichi Okamura, the deputy head of the water treatment equipment department, said: "We believe it is inconceivable that contaminated water will suddenly squirt out. Because we have strengthened the patrol methods, we can discover and deal with problems more quickly."
Another problem exists underneath the embankment on the eastern side of the plant site. Radioactive materials have been found to be spreading under that embankment. Contaminated water in the underground trench may still be leaking into the ground.
Preparatory work began Jan. 29 to remove the contaminated water from the trench. The project involves constructing an underground wall of frozen soil to block water from leaking from the reactor buildings. Workers were opening holes in order to pump up the contaminated water that lies in the trench 5.5 meters underground.
The Asahi team spent about five hours at the Fukushima plant site. The level of radiation exposure was 0.09 millisievert, which is about one-tenth the annual exposure limit for the general population.
(This article was written by Shunsuke Kimura and Hisashi Hattori, a senior staff writer.)