Robots investigate inside units 1 and 3

1 June 2012

A monitoring room at Fukushima Daiichi unit 3 has been found to have high levels of radiation, although a visual inspection did not find any evidence of machinery damage. The examination of the unit 3 travelling in-core probe, or TIP, room was planned to be carried out by robot, but its damaged door, which had been blown off its hinges, blocked the robot's access. A worker performed the visual inspection from the doorway instead. Radiation levels were found to be elevated (about 50 mSv/hr), about 10-20 times higher than at unit 2 (that survey data was originally released in March).

In other news, a robot called Packbot has begun a systematic survey of radiation in the unit 1 ground floor using two dosimeters (mounted at heights of 50mm and 1500mm above the floor) and gamma cameras (which compare the radiation field to a photographic image). The gamma cameras were mounted on an inclinable mount that also rotates around the vertical axis. Surveys were taken every 3m. The gamma cameras were inclined at 10, 50 and 90 degrees, and were swivelled around. The data will be used to create a continuous 3D contamination map. The survey is limited to accessible parts of the unit 1 ground floor, which excludes northern and southern regions, which are blocked, respectively, by gas processing equipment and shields that cannot be moved.

Dose rates measured were generally around 5 mSv/hr. Measurements in similar areas taken in late 2011 were higher, suggesting that the radiological contamination is decreasing. Further human-based surveys of dust and core wall boring will begin later.




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