REMOTE DECOMMISSIONING | COVER STORY
decommissioning. “In Ukraine, some years after the accident at unit 4 of the Chornobyl NPP in April 1986, research and development activity was carried out to develop a number of robotic techniques to be used for different purposes inside the damaged facility,” she noted. “Due to high exposure doses inside and the concentration of radioactive aerosols, an approach employing robotic techniques seemed very promising, for example, for characterisation of the premises and sampling of radioactive materials. It would mitigate doses for workers involved in stabilisation of the situation at the destroyed unit and help in planning further actions.” However, it soon became clear that there were
challenges. Robots could not move due to the difficult configuration of surfaces – a lot of construction debris and no space for movement – and the extremely high exposure doses affected the electronic devices. Kilochytska added: “In cases where robotic devices stopped working or were stuck somewhere inside the unit, it was very difficult and sometime dangerous to bring them back. Some examples of these robots are still stored at Chornobyl.” Nevertheless, the use of robotic devices is now planned
for use at Fukushima in Japan. Key to the development of robots for use at Fukushima is the International Research Institute for Nuclear Decommissioning (IRID) that was created as a matter of urgency in 2013 to upgrade and develop decommissioning technology for the Fukushima Daiichi NPP. This has included development, testing and use of a range of robots for different purposes (see box). In addition, US-based Jacobs, for instance, has designed and built a robotic tool to obtain crucial information about the damaged reactor. It will collect pebble-like debris from the bottom of the containment vessel. A prototype passed extremely demanding factory acceptance and performance tests from Mitsubishi Heavy Industries (MHI), which is leading the project. It is expected that a radiation resistant version will be built for deployment. “This is a prime example of how we are combining innovative engineering and deep nuclear knowledge to help decommissioning agencies meet the challenge of transforming legacy sites into a safe end state,” said Jacobs Energy, Security & Technology Senior Vice President Karen Wiemelt. The robot had to be small enough to enter the damaged
containment vessel and pick up sand and pebbles up to 10mm in size by deploying a bucket-style retrieval device.
The exact nature of the debris is currently unknown, and examination of the retrieved debris samples will provide crucial data for the next steps in decommissioning. Trials have shown that a remote operator, guided by
images from a built-in camera, will need no more than eight minutes to insert the device into the containment vessel and retrieve debris samples, thus minimising the impact of radiation damage on the device. “The government of Japan and Tokyo Electric Power
Company (TEPCO) plan to conduct test retrieval of fuel debris from inside the unit 2 reactor of the Fukushima Daiichi NPP by the end of 2022,” Kilochytska said. “To this end, TEPCO has been working with the UK to build a robotic arm, which has already arrived in Japan. The robotic arm is currently undergoing evaluation testing, and as soon as that is completed, it will be placed in a mock-up facility for debris retrieval training. In addition, various remote-control devices are being used to monitor the situation in high- dose areas such as inside nuclear reactors.” Retrieving fuel debris is the most challenging part of
decommissioning efforts at the Fukushima Daiichi plant, according to Tadahiro Washiya of the Division of Fuel Debris Handling, Collaborative Laboratories for Advanced Decommissioning Science (CLADS) at the Japan Atomic Energy Agency. “An investigation of the damaged unit 1 [F1] was carried out by robots and remote inspection tools; however, there are many uncertainties in understanding the conditions of the fuel debris,” including its composition and mechanical properties, Washiya said. Knowledge gained from the 1986 accident at Chornobyl is
already supporting efforts at Fukushima Daiichi, said Boris Burakov of the Khlopin Radium Institute in St Peterburg, Russia, which hosted a training seminar with Japanese experts using real Chornobyl fuel debris samples in October 2019. “The results of the material study of Chornobyl samples are very important for predicting the main properties of the fuel debris at Fukushima Daiichi F1,” as the fuel debris at both sites share several similarities, Burakov said. Similarities include lava-like materials, porous fuel produced by this lava contacting water and hot particles with fuel and corium matrices.
New approaches to the use of robots With so many NPPs scheduled to close in the coming decades, the nuclear industry will need more U
www.neimagazine.com | August 2022 | 17
Above left: Mobot-h-hv special equipment that helped cleaning Chernobyl nuclear power plant Photo credit: viacheslav_petrusha/
Shutterstock.com
Above right: The Lyra robot was used to survey a 140-metre-long underfloor duct at Dounreay Photo credit: Manchester University
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
