Survey Device (Shape-changing Robot) Deployed to Inspect Interior of Primary Containment Vessel (PCV)
(April 20, 2015)

On April 10 and between April 15 and 20, 2015, surveys of the 1st floor of the Fukushima Daiichi Nuclear Power Station Unit 1 Primary Containment Vessel (PCV) using two shape-changing robots developed by IRID member company Hitachi-GE Nuclear Energy were conducted (‘B1 survey’). These surveys marked the first time that robots have ventured into the damaged PCV.

Many modifications and improvements were made by the development team to enable the robots to withstand the high-radiation environment, and the surveys demonstrated the fruits of the repeated training sessions undertaken by personnel involved in their deployment and operation.

The first robot stopped working on the initial day of surveying after becoming stuck in a gap on the floor surface. However, the survey up to that point and the investigation by the second robot over a six-day period produced successful results and provided vital information; they are considered as a huge first step in a long-term decommissioning effort that may take 30 to 40 years.

The main investigation findings are as follows:

1. With the B2 survey* to be conducted at the basement of the container vessel in the next survey phase, this initial survey confirmed that there are no obstacles present around the opening connecting the first floor to the basement
2. As far as can be ascertained from video footage, no significant damage to existing fixtures (air conditioning units, PLR pipe, pedestal outer wall, etc.) was found, and it was confirmed that there was no large difference with original design plans. In considering scenarios for future decommissioning work, this finding is of vital importance.
3. During the survey, radiation levels inside the Fukushima Daiichi Unit 1 PCV were below 10 Sieverts per hour (Sv/h). The robot’s on-board camera is able to withstand levels of up to 1000 Sv, so this finding shows that the robot will be resistant to radiation for use for around four days.

*B2 Survey: This survey will involve the robot being lowered to the bottom of the containment vessel (basement), where it is thought that fuel has melted down to, and investigating the distribution of fuel debris using video, etc. Based on the information regarding the inside of the containment vessel obtained in the B1 survey, further improvements to the robot will be made and it is planned that the next phase of surveying will commence at the end of 2015.

In accordance with standard procedure, the robots used in this initial survey were not forcibly retrieved. After confirming everything was safe, the first robot was left where it was; the second robot was maneuvered to a location where it lies in a stable position where it will not hinder any future surveys or operations.

Still photographs and video footage obtained during the survey of the PCV are shown below.

Photos/video taken by survey robots

• [Photos] Click image to enlarge.
• [Videos] Click “Download video” to download MP4 file.