An ultrasonic measurement system and its robotic deployment into vessels for the combined assessment of debris condition and water leakage

Lead Research Organisation: University of Bristol
Department Name: Mechanical Engineering


The decommissioning of the Fukushima Dai-ichi Nuclear Power Site (1F) is a high priority for Japan and there are lessons to be learned for decommissioning across the globe. The current situation is that the reactor is flooded with water and the location and distribution of the fuel debris is unknown. A specially designed robot has gained entry to the containment vessel, however, access is severely restricted. This project will investigate the potential of an ultrasonic measurement system and its robotic deployment to assess the conditions within the flooded regions of the primary containment vessel and reactor pressure vessel. Ultrasonic measurements are particularly attractive in this application as they can overcome the problems associated with poor visibility in the water in addition to which the sensors are small and insensitive to radioactivity. We propose the development of three ultrasonic measurement systems integrated into a compact package suitable for robotic deployment. The first two sensor systems will measure flow on a large-scale (meters) and on a smaller-scale (centimetres). This will enable the location and quantification of leakage points. These are known to exist as water is currently being continuously pumped into the reactor. In addition ultrasonic sensor arrays will be developed to image the interior of the vessels and locate and quantify the fuel debris. Attempts will also be made to image inside the debris to discover its structural integrity. This information will ultimately feed into attempts to safely remove the debris. These measurement systems will be built and integrated into a robotic platform and tested on a laboratory-based replica. The project will combine expertise on ultrasonic flow measurement and robotics from Japan with expertise on ultrasonic imaging from the UK. The research will lay the foundation for the decommissioning of the Fukushima Dai-ichi 1F reactor and provide valuable new techniques and expertise for decommissioning activities in the UK and around the world.

Planned Impact

The most direct beneficiaries will be companies working on the decommissioning of Fukushima Dai-ichi (e.g. TEPCO and Hitachi). We will work closely with these companies to ensure that our research is relevant to this specific challenge. The research will also impact on a wider range of companies in the nuclear sector, both those involved in decommissioning and in long-term storage of radioactive waste. Here, there is a common requirement to obtain detailed information about the state of the radioactive material within a harsh environment and typically with limited access. As detailed in our Pathways to Impact, we will actively seek to engage this wider community throughout the project.
The Tokyo Institute of Technology already have good links with both the key companies and the University of Bristol group have recently established good links with Hitachi through a direct funded project. The Bristol group have also collaborated with a range of UK nuclear industry and are linked to others through the UK Research Centre in NDE (RCNDE). The RCNDE network includes eight companies or organisations relevant to the UK nuclear sector (i.e. Hitachi, Rolls-Royce, EDF, National Nuclear Laboratories (NNL), Nuclear Decommissioning Authority (NDA) and the Office for Nuclear Regulation (ONR) as well as Rolls-Royce and BAE Systems). Early on in the project all of the above will be made aware of the project and its objectives through face-to-face meetings and through presentations and meetings at RCNDE networking events.

As the project progresses, we will organise two workshops, one in the UK and one in Japan. We will invite relevant industry and academia to these workshops and have requested funds to facilitate this. The main aim of these workshops will be to disseminate the progress, receive feedback and start the planning process for future projects.

Throughout the project the collaborators will publish their findings in relevant conferences (e.g. Annual Review of Progress in Quantitative NDE and International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components) and journals (e.g. NDT&E Int, Ultrasonics, J. Acoust. Soc. Am., IEEE Trans. Ultrason. Ferroelect. Freq. Contr., Proc. Roy. Soc.). Note that conferences in this field are well attended by representatives of the nuclear industry as well as academics working in this area.

The subject of this proposal (nuclear safety) is of major interest to the general public both in the UK and in Japan. Indeed, the general public are one of the key beneficiaries of this research through improved nuclear safety which is currently high on the political agenda in the UK where nuclear new build is imminent. We will enthusiastically engage in an on-going dialogue with the public about our work. Early in the project we will establish dedicated web pages that describe our research aims and objectives. In collaboration with the University of Bristol's Centre for Public Engagement we will develop engaging material such as YouTube videos to highlight research progress and to demystify some of the science behind our work. As well as this web-based activity we will develop an interactive exhibit to be shown at a suitable science festival (e.g. the British Science Festival organised by the British Science Association). We will also aim to write articles for the popular press (Prof. Drinkwater has an excellent record in this regard) and to seek opportunities to present the work to a wider audience (e.g. science cafes and Schools).


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Description Development of an ultrasonic imaging system to map out the interior of the fuel debris in the damaged Fukushima reactors. We have shown that compact ultrasonic arrays can be used to obtain accurate maps of the surface profile of simulated debris. We have collaborated with Tokyo Tech to develop am ultrasonic measurement system that combined high resolution imaging with Doppler flow measurement. This has been tested experimentally on a lab scale.
Exploitation Route We are working closely with Hitachi and Tokyo Tech. The aim is to deploy an ultrasonic measurements system in the Fukushima reactor. This is part of stage 1 of the reactor decommissioning process. Stage 1 is simply to properly assess the condition of the damaged reactors.
Sectors Energy

Description Our work has been discussed in detail with Hitachi, who are responsible for the decommissioning of 2 out of 4 of the damaged reactors at Fukushima. This is part of a long term project to deploy a range of measurement technology into the damaged reactors. In 2022 ultrasonics was deployed on a submersible robot to examine the damaged Fukushima reactor unit 1 ( Specifically it was used to measure the "height of deposits and examine objects underneath them in order to estimate debris height and distribution". This aspect was as shown in our work and the resulting publications.
First Year Of Impact 2022
Sector Energy
Description Tokyo Tech 
Organisation Tokyo University of Technology
Country Japan 
Sector Academic/University 
PI Contribution Worked together on a Joint project in which we are exploring way to map out condition and location of the fuel debris in the damaged Fukushima reactors in Japan.
Collaborator Contribution They are experts in ultrasonic flow monitoring.
Impact 3 visits to various nuclear power plants to better understand the challenge. Joint papers.
Start Year 2016