Tokyo Electric Power Co. on Sunday released air from a reactor building at its crippled Fukushima No. 1 power plant, possibly allowing low-level radioactive substances to escape into the environment.
Tepco said that it opened the doors of reactor 2 at 8:50 p.m. to lower the humidity inside so people can work there. The utility claimed the move would not harm the environment.
The humidity in the damaged unit is nearly 100 percent, which is hampering efforts to bring the stricken plant under control. The utility plans to open the doors slowly and gradually in an operation that will last until around 4 a.m. Monday to avoid stirring up dust containing toxic materials.
After the venting, Tepco will start injecting nitrogen into the reactor to prevent a hydrogen explosion, and also adjust measuring equipment, it said.
A week ago, Tepco said it began filtered venting of the No. 2 reactor building to lower radiation levels to the point where workers can go inside. The high radioactivity and humidity have prevented workers from checking gauges and pipes, hampering efforts to cool the reactor.
Meanwhile, a piece of highly radioactive equipment that was removed from a separate reactor before the disaster and stored under water may be emitting radiation air after becoming partly exposed, Tepco said Sunday.
Although radiation levels are not unusually high around unit 4, which had been suspended for regular inspections when the March 11 tsunami knocked out its cooling systems, the equipment in question is not specifically monitored and requires radiation precautions be taken when work is required at the site.
Reactor 4 was not loaded with fuel when the quake hit, but it did have spent fuel rods cooling in a storage pool above it. But since the pool can’t be automatically cooled anymore, the still-hot rods are causing evaporation, which is drying up an adjacent pit. That pit contains a shroud that was used to adjust the flow of water inside the building. The 7.6-meter-deep pit contains just 2.5 meters of water, Tepco said, indicating that the hot part of the shroud, which was originally 6.8 meters high but was cut to fit in the pit, may be exposed to air.