Innovative solutions are being developed in six main areas to protect operators during decommissioning and to minimise the overall costs and the volumes of waste produced. By Harvey Farr, Gérard Laurent and Christine Georges
France has been very active in developing nuclear technology and currently derives about 75% of its electricity from nuclear power. In addition, about 17% of France’s electricity is from recycled nuclear fuel. Reactors and fuel products and services are also a major export.
France currently has nine sites being decommissioned.
The French Alternative Energies and Atomic Energy Commission (CEA) is both the operator of important nuclear facilities across the nuclear cycle and responsible for major new build and decontamination/decommissioning projects, as well a research and development group with a dynamic policy of technology transfer.
The position of CEA in D&D is important because of the number and diversity of facilities under decommissioning, some with high levels of contamination. Innovative solutions are being developed in six main areas to protect operators, to reduce the overall costs and minimise the volumes of waste generated during decommissioning projects.
1. IT methods and tools
Certified tools and methods have to be developed to evaluate dismantling forecasts. These tools are also available to estimate future dismantling costs for a facility before its construction or to compare dismantling scenarios in order to optimise costs, scheduling, integrated doses, and amounts of waste generated.
Electricite de France and CEA are aggressively exploring and developing wireless network capabilities.
RFID tags can be positioned on a worker’s badge or on a waste container that is being monitored. They can be accessed by software on a tablet and can:
- verify that the initial condition of equipment and components is correct for commencing work;
- verify that an employee has the required qualifications;
- verify that an instrument being used is correctly calibrated;
- identify samples and automatically provide measurement results;
- provide real-time knowledge of coordinates X, Y, Z and T via the GPS (to within 10cm, inside and outside).
Data transmitted via the cloud to the external systems (wells, reservoirs, pipes, cathodic protection, etc.) are linked to the coordinating GPS. Permanent links to the wireless control platform provide improved management of employee safety and better control of the work on the systems.
In order to ensure traceability and to harmonise data provided by D&D programmes and to optimise waste management scenarios, a network of interconnected operational IT tools is welcome for waste and transportation management.
2. Facility characterisation
Characterisation of the radiological and physical condition of facilities to be decommissioned is key to providing the right data to minimise hazards, to predict waste quantities, and can save time and money.
A major challenge in this field is to minimise destructive analysis in order to reduce doses received by workers and to relieve congested site laboratories.
New in situ techniques have been developed to map facilities and soil, to localise hot spots, to identify radionuclides, to estimate radioactivity, and to minimise the number of samples required or conduct radiochemical analyses simultaneously. These techniques are already used in France. Some, like geostatistics, have been commercialised while others are at prototype scale, on the way to industrialisation (e.g. gamma and neutron imaging, alpha camera or auto-radiography for beta emitters, and LIBS technology).
3. Waste measurement
Optimisation and validation of the waste characterisation strategy is needed. This involves:
- drawing up objectives for radiological, physical and elementary waste characterisation;
- choosing equipment and scenarios to implement for waste retrieval;
- optimisation of characterisation procedures;
- high-performance modelling and simulation tools to enable equipment and scenarios to be optimised.
Design and qualification of customised characterisation devices is also necessary to avoid destructive analysis, or to meet changes in regulatory requirements. These systems could also be developed from prototypes to industrial scale or by adapting existing systems.
New tools have been developed for decontamination and decommissioning purposes, including robots, tele-operated equipment, cutting processes and software to validate and optimise scenarios.
For 20 years, project managers dreamed of getting 3D cartographies from in situ investigations and using them to conceivedecommissioning scenarios. All the technological components are now available and ready to be linked from data collection up to training of operators.
Operators have also learnt to choose devices suitable for use in chemical and radiological conditions by nuclearization of ‘off-the-shelf systems’ or by designing innovative systems for computer-assisted tele-operation actions, as well as carriers. MAESTRO developed by CEA and commercialised by Cybernetix is an example of a remote handling arm designed for use in high-radiation areas. It can be adapted for use on various types of carrier: a crane, a telescopic mast, a remote controlled machine, etc. Progress has to be made in order to qualify remote devices to even higher levels of radiation.
In order to improve cutting yields while limiting aerosols and waste generated, powered laser processes were developed. Laser heads had to be designed for cutting in air with air-cooling to prevent water leakage and for cutting under water.
Various platforms and tools have also been developed to optimise and qualify new equipment. These have included:
- Test and demonstration platforms for cold qualification;
- 3D simulation software and virtual reality in an immersive room to compare alternative scenarios, qualify remotely-controlled equipment, or ensure that equipment will be accepted by safety authorities;
- 3D simulation and doses calculation software, used in an immersive situation to choose the best way to operate with minimum dose integration;
- Pilot job sites for qualification under real conditions.
Technologies for decontamination of solids were developed and adapted to many geometrical configurations, and to a wide range of materials and types of contamination. These include self-drying coating gels, topping gels for the treatment of contaminated small items, laser ablation, viscous foams or active solutions, float foams or supercritical fluids.
Several chemical mediums and suitable techniques were studied for implementation on pilot or industrial sites in order to decrease radiological and chemical releases.
6. Waste treatment/conditioning
Treatments for complex radioactive waste were developed to enhance the efficiency of decontamination, to minimise the volumes of secondary waste, to protect the operators and to minimise the overall costs.
Innovative solutions continue to be developed with processes involving chemical, electrochemical, hydrometallurgical, pyro-chemical as well as thermal techniques.
Progress in liquid waste decontamination techniques is mainly based on two complementary approaches: process development and reagents and/or materials development.
The two main processes used for liquid waste treatment are filtration, including conventional processes (microfiltration, nanofiltration or reverse osmosis) and more advanced processes (such as photocatalysis coupled with microfiltration, filtration coupled to biological adsorbent); andsolid phase adsorption on a fixed bed, or fluidized bed, including co-precipitation processes.
Modelling of these processes is also of great interest to help improve them and move them from laboratory scale to pilot scale and then industrial scale. The materials and reagents used in liquid waste treatment processes are designed to control their chemical composition, morphology and microstructure, to improve their efficiency and to optimise final waste management.
Several processes have been developed for the treatment of solid or liquid organic radioactive waste, including incineration and mineralisation of organic liquids by hydrothermal oxidation or by plasma incineration.
A process for incineration of radioactive solvents containing chlorine or Fluor by plasma under water is being industrialised in France. The use of plasma under water should simplify dust treatment and prevent corrosion of the facility.
Historically, when it comes to waste conditioning the two major fields of development have been cementation and vitrification. Cementation with mineral geopolymers for encapsulation of magnesium and vitrification ‘in can melting’ for high-level waste, have been carried out in France.
Optimised cement-based matrices allowing radiolytic production of dihydrogen to be reduced are also under development. This would enable increased loading of intermediate-level waste, and thus a reduction in the number of cemented waste packages.
Exciting new technologies are emerging in nuclear and non-nuclear sectors. The next step is to adapt and develop applicable technologies and integrate them for use in decommissioning. This will require industry consensus, collaboration, and focus. Broad-spectrum initiatives are necessary to lay the groundwork and fully realise the capabilities of theme specific initiatives such as autonomous equipment, high-energy lasers, long-term monitoring, and more powerful data collection and processing capabilities. These capabilities must then be paired with better project management and interpretation tools such as paperless work controls, geostatistics and digital spatial models. Developing such platforms now will greatly assist in deploying and testing the next generation of robotics and autonomous equipment and other evolving technologies safely and integrating them into active decommissioning projects.
About the authors
Christine George is Head of the R&D for D&D programme at the French CEA