Decommissioning is a growth area with a significant number of the world’s 439 nuclear power reactors approaching retirement age. Globally, 199 power reactors have been shut down, but only 21 of which are fully decommissioned. In addition, 130 fuel cycle facilities have been decommissioned as well as about 450 research reactors. The International Atomic Energy Agency (IAEA) projects that 12-25% of the 2020 nuclear electrical generating capacity is expected to be retired by 2030.

While existing methods of decommissioning are more or less sufficient to the task, innovations are developing faster, safer, and more cost-effective ways of working. Digital technologies coupled with robots and drones provide for the significant potential to work more effectively, and at lower risk.

The IAEA decommissioning survey

In February, an IAEA survey on the global status of nuclear decommissioning found that operators and authorities in a growing number of countries prefer the immediate dismantling of retired nuclear facilities. “Previously, many programmes elected to defer dismantlement of retired facilities, but immediate dismantling is now becoming the predominant decommissioning strategy worldwide,” explained Olena Mykolaichuk, Head of the IAEA’s Decommissioning and Environmental Remediation Section.

This requirement is an added driver for the use of remote and robotic technologies given the increased activity levels found in recently operating plants compared with those that have remained in a de-fuelled and shut-down state for decades.

Emerging digital technologies coupled with increasing use of robots and drones could potentially provide for more effective project implementation and risk reduction. “The use of robotic techniques and remotely controlled techniques are being presented and discussed more and more in the decommissioning community,” Tetiana Kilochytska, a decommissioning specialist in the IAEA’s Decommissioning and Environmental Remediation Section, told NEI.

As part of the survey, the IAEA sent out a Global Decommissioning Strategy questionnaire to more than 50 countries and evaluated the responses alongside data from the IAEA’s Power Reactor Information System (PRIS), Research Reactor Data base (RRDB) and Integrated Nuclear Fuel Cycle Information System (iNFCIS). IAEA also hosted a series of technical meetings over three years that brought together dozens of experts from some 20 countries as well as the Nuclear Energy Agency of the OECD and the European Commission to share experiences and provide feedback.

Countries managing accident sites such as those in Japan are using innovative robotic technology and remote inspection tools to locate and characterise fuel debris in an effort to retrieve and dispose of this material. Technologies such as 3D modelling or building information modelling (BIM), virtual reality and remotely controlled technologies, including drones and robots, are also being applied increasingly to the decommissioning of facilities. These technologies enable more efficient collection, understanding, display and management of data, allowing different scenarios to be visualised during planning and preparation of dismantling and decontamination activities.

“Coupling BIM with GPS or location-aware Wifi networks enables the deployment of semi- or fully autonomous robotics systems and drones,” said Hannes Hanggi of the Swiss Federal Nuclear Safety Inspectorate, who helped lead the IAEA project. “They have the potential to significantly lower costs, further increase safety and enhance performance in decommissioning projects.”

Lessons from Chornobyl and Fukushima

Kilochytska told NEI how the Chornobyl and Fukushima accidents had influenced the use of robotic technology in 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, its soon became clear that there were challenges to the use of such devices. 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 10 millimetres 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 the clean-up and 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 expected similarities, Burakov said. While significant differences between the two are also anticipated, 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 professionals working in decommissioning. To attract new talent to the field, in 2020 the IAEA held a global crowdsourcing challenge that sought original concepts or project outlines from young people for advancing the decommissioning of nuclear facilities or environmental remediation of radiologically contaminated sites. Entries included characterisation toolkits, instruments for field measurements and collecting 3D radiation data, as well as robots and artificial intelligence.

A total of 26 submissions from 12 countries were received and evaluated against criteria such as the level of innovation and creativity. Of the five best entries selected by the IAEA, several relied on robotics. For example, Zeni Anggraini from the National Nuclear Energy Agency of Indonesia (BATAN) led a team that came up with a concept of a robot for mapping and monitoring of contaminated areas. “So far, measuring of contamination has been limited to a small area and was done manually,” he said. “We want to make a robot that can be used to avoid potential radiation risks to staff. The importance of radiation monitoring is a commitment to radiation safety. As a manifestation of our commitment… there needs to be a breakthrough in the method of radiation monitoring using robots to measure and visualise contamination in affected areas.

Another proposal featuring robots came from the USA. “With the nuclear industry growing, the need for new subject matter experts is in high demand. As technology increases throughout our lifetime so does the need for experts in these fields, for example robotics,” said Daniel Martin, a research assistant at the Florida International University in the USA, whose team’s proposal envisaged use of a robotic platform and artificial intelligence to aid in preventing defects before they occur in facilities to be dismantled.

Meanwhile, Erin Holland, a PhD student from the University of Bristol in the UK, led a team that submitted a characterisation toolkit to enable accelerated decommissioning activities. “Nuclear energy is a very important part of ensuring that future energy grids are low carbon, reliable and sustainable,” he said. “Nuclear robotics is a fast-growing discipline and physical demonstrations of advanced robotic systems help make nuclear decommissioning quicker and safer for human operators. We hope our work will help to improve public knowledge of and interest in nuclear energy, using advanced technologies. It is very important for cementing nuclear energy as a keystone energy technology for decades to come,” said Holland. He added: “The overall aim of this project is to make a legacy site, formerly used for uranium and thorium ore processing, safer for the civilians working there.”

Robot use in the field

Sellafield, the UK’s largest nuclear site and the focus of its nuclear-decommissioning efforts, is making increasing use of robots. Spot the robot dog made its debut on the Sellafield site in October 2021 with three days of successful trials and a shift within an active area. Sellafield’s remediation teams are leading Spot’s deployment for Sellafield Ltd, working with Cumbria-based engineering consultant Createc, the UK Atomic Energy Authority (UKAEA) and its US manufacturers Boston Dynamics.

Valuable information was collected through laser scanning and gamma radiation imaging using a system provided by Createc. The robot completed its work wearing a suit specially designed and manufactured at the UKAEA which protected it from any radioactive contamination.

Chris Hope, remediation capability development manager, Sellafield Ltd said: “This was a really challenging task – we deployed Spot into a complex, cluttered, highly contaminated area with a mission to capture information. The quality of the data we captured is fantastic and will help us with our decommissioning and waste planning.”

He added: “Until now, this type of survey has relied on our operators manually deploying equipment in hazardous environments wearing full protective equipment. This proves that Spot can help us take humans away from harm. This allows us to free up our workers to deliver other value-adding work. The protective suit did its job too – the robot was monitored and cleared by our health physics team, and was able to leave the Sellafield site.”

Elsewhere in the UK, this year saw Dounreay Site Restoration Ltd (DSRL) begin working with the Robotics and Artificial Intelligence in Nuclear (RAIN) Hub to develop a second-generation robot called Lyra. It includes a package of surveying measures including LIDAR, multiple angle cameras, radiation probes and the ability to take swabs using the manipulator arm.

The Lyra robot was used to survey a 140-metre-long underfloor duct at Dounreay. (Credit: Manchester University)

In February, the robot completed a survey of a 140-metre-long underfloor duct which runs under the central corridor between laboratories, providing useful information that will help decommissioning.

“Now the characterisation survey is complete we have built up a very comprehensive picture of the duct, which will help us make informed decisions on how the duct should be decommissioned,” said DSRL Project Manager Jason Simpson.

OC Robotics flexible snake-arm robot has been deployed to help decommission the Dragon reactor at Winfrith in the UK using its high-powered cutting laser. Passing through a narrow hole in the 3 metre-thick concrete around the core, it sliced through a 400mm diameter Purge Gas Pre-Cooler (PGPC) vessel attached to the reactor core.

One end of the vessel joined to the core in the high radiation area behind the concrete shielding and several steel plates, while the other end extended outside the shielding.

Developed by OC Robotics and TWI with R&D funding from the NDA, LaserSnake allowed the work to be carried out inside the existing radiation shielding of the reactor, saving time and money.

Magnox Senior Project Manager, Andy Philps said: “We believe this is the first time that laser-cutting technology has been deployed directly on the core of a nuclear reactor.”

Meanwhile, in 2021 Russia’s Special Design and Technological Bureau of Applied Robotics (SKTB PR) developed a robotic complex for dismantling the graphite stack of carbon-graphite reactors.

It consists of a mobile robot, a remote control and a magazine with a special cutting tool which makes it possible to remotely undertake dismantling work.

“This development removes the need for the presence of people in the zone with increased radiation. The operator remotely controls the robot, and with the help of the video system, which is part of the complex, directs the work. The robot manipulator is capable of lifting and carrying up to 100 kg, which is sufficient to extract the graphite blocks,” said Gennady Dyogtev, General Director of SEZ Technopolis Moscow.

The same year, Framatome confirmed the operation of robotic systems for handling and sorting high-dose waste components, paving the way for increasing automation.

The Virtual Remote Robotics (VIRERO) project focused on automating robot control systems for waste handling in partnership with the Institute for Factory Automation and Production Systems (FAPS) of the Friedrich-Alexander-Universität, Erlangen-Nürnberg (FAU), and Aachen Institute for Nuclear Training GmbH (AiNT).

The VIRERO project, funded by the German Federal Ministry of Education and Research, develops technologies for dismantling and sorting high-dose operational wastes, post-conditioning of packaged radioactive waste, and radiological sorting for handling, storage and disposal. The VIRERO project is expected to be completed by the end of 2023.

According to Kilochytska, for the time being, many remotely-controlled devices can be used for characterisation of surfaces (walls and floors) during the decommissioning of facilities, for dismantling different structures, systems and components that may be radioactively contaminated or activated. “Moreover, robotic techniques such as drones can investigate the radiological situation and measure levels of contamination inside the premises and rooms,” she told NEI. “In this way, doses to workers can be avoided and time and money needed for conducting these actions, for example, characterisation or dismantling, can be decreased. Together with 3D modelling this makes it possible to create a full picture of a particular room or facility, making planning of further activities easier, taking into account dose rates and levels of contamination.”

She noted some important points for the future use of robotic techniques. “First, it is necessary to assess real needs and potential benefits, taking into account a particular plan for decommissioning a particular facility. Usually, development of such techniques requires significant investment. In addition, the further use of devices requires maintenance costs to support operation and repairs, as needed, such as a qualified staff to do this.” She added that there may also be an issue with decontamination of such devices to make possible regular use. “All this should be considered in advance before any decision is taken about developing or buying devices.”

It is clear that robotics and other digital tools are playing an increasingly important role in advancing nuclear decommissioning projects, not only by enabling experts to characterise environments and decommissioning challenges but also by improving their execution. As Mikhail Chudakov, IAEA Deputy Director General and Head of the Department of Nuclear Energy, said: “Innovative digital technologies can provide crucial insights for the planning and implementation of decommissioning projects. They can provide support in decommissioning situations that are difficult or dangerous for human workers and can help ensure that projects are executed safely and effectively”.

This article first appeared in Nuclear Engineering International magazine.