A robotic survey of the unit 2 reactor building at the Fukushima Daiichi site in mid-June measured radiation levels directly over the fifth floor reactor well, and found extremely high levels.

Measured levels ranged from 415-530 mSv/hr directly adjacent to the well, and 783-880 mSv/hr directly over it. Even near the open spent fuel pool, photographed by the mobile robot ‘Quince’, levels ranged between 80-173 mSv/hr. The temperature and humidity over the reactor well was 20.5°C – although it is ventilated by the opening from the blow-out panel – and humidity is 75.3%. Radiation measured on lower floors was much less: 10-23 mSv/hr on the third floor, and 11-22 mSv/hr on the fourth floor.

In units 2 and 3, the rooms surrounding the torus have been discovered to be flooded with approximately 5m of water, without an obvious source, or obvious damage.

An attempt has been made to use infrared photography to determine the height of the water inside the torus at unit 2. Although workers determined that the temperature inside the torus was 38°C, warmer than in the torus room (35°C), the height of the water could not be ascertained using this method.

A steel-framed cover was installed in mid-June over the unit 4 spent fuel pool. The steel cover, like the first cover installed in 2011 but made of plastic floats, is intended to protect the pool from debris. Operator Tepco has been demolishing the upper walls and roof of the unit 4 reactor building, which were damaged by an explosion in March 2011, to prepare the building for a temporary cover. The new cover will be able to protect the pool from rubble weighing up to 1.5 tons.