The second group of workers to enter the reactor building of unit 1 since successive hydrogen explosions rocked the Fukushima Daiichi nuclear plant in March calibrated a crucial water-level gauge, Japanese regulators reported Tuesday.
Fixing gauges measuring pressure and water levels in the unit is a critical step in Tokyo Electric Power Co.’s plan to flood the reactor’s containment and bring the enclosed pressure vessel to cold shutdown status. The Asahi Shimbun newspaper also reported the workers discovered rubble inside the unit, but that water leaks or significant damage to primary equipment was not evident.
Last Thursday crews installed an air filtration system that diminished airborne radioactive contaminants in the unit to levels that allowed a crew on Sunday to enter the reactor building for the first time in nearly two months. While dose levels in some areas are still extremely high, TEPCO has said readings in most places where work on the makeshift cooling system will take place topped out at 100 millisieverts per hour. The utility also is considering removing rubble and covering highly radioactive areas with lead mats to reduce dose, according to the Asahi Shimbun.
The Nuclear and Industrial Safety Agency also reported that work began this week to shore up the spent-fuel tank of unit 4. TEPCO and government officials recently announced several measures to reinforce the plant in anticipation of aftershocks that have occurred frequently since the March 11 magnitude-9 earthquake. The plans call for 30 pillars beneath the tank to help reinforce the unit’s fire-damaged building. After that, a wall 3-to 6-feet thick is scheduled to be built around the pillars by the end of July.