Wireless monitoring system for spent nuclear fuel repositories

Project summary

Monitoring systems are used to measure parameters, such as temperature, pressure, humidity, radiation and movement, in deep geological repositories for nuclear waste. These systems traditionally rely on wired instrumentation. To ensure the safe sealing of the repository and avoid compromising the integrity of the engineered barriers, this instrumentation must be eventually removed. Amphos 21, in collaboration with ENRESA (the Spanish organisation responsible for managing nuclear waste), has developed a wireless monitoring system that can remain in place when the repository is closed, enabling continued monitoring afterwards.

The background

A global consensus recognises deep geological repositories (DGR) as the safest long-term solution for managing spent nuclear fuel and other long-lived radioactive wastes. Implementing a DGR requires solutions that meet both technical and societal expectations. Repository monitoring has the potential to support the implementation of safety strategies and to provide transparent information on performance, which contributes to reducing concern and building confidence in repository performance among the different stakeholders.

Through a long-term collaborative project on nuclear waste management, supported by ENRESA, Amphos 21 has developed a WDT system that can connect to conventional measurement instrumentation, supply power, collect data and transmit them wirelessly through radio waves. The system is built around transmitter nodes (connected to the sensors) and receiver nodes that capture the transmitted data.

Multidisciplinary approach/strategy

The project was a long–standing collaborative effort that began with the MoDeRn project (2009–2013, Euratom FP7 programme) and continued through the Modern2020 project (2014–2018). Both European projects involved several key international actors interested in solving the same problem: how to efficiently monitor and supervise the future DGRs. Since 2024, the development is ongoing and is supported by ENRESA through the WT-E project at the Mont Terri international underground research laboratory in Switzerland.

The challenges

In order to maintain the integrity of the DGR’s engineered barrier system, the data communication system must be wireless (WDT) when closure is initiated. The system needs to be intended for use in underground environments and capable of operating with the measurement instrumentation commonly used to monitor the main geotechnical parameters relevant to the operation of the DGR. The system must collect underground data for transmission to the surface. The WDT must address signal attenuation caused by solid surrounding media and increasing water content within the engineered barrier system over time, while providing the necessary long-term power supply.

The solutions

The WDT system developed is based on a short-range transmitter designed to accommodate up to ten geotechnical sensors of different types and capable of transmitting data to a receiver at distances of up to 30–40 m using a 90–cm–diameter antenna, under conditions such as those expected in future deep geological storage. Using larger diameter antennas, known as long-range, the information can be re-transmitted up to 400 m. Key to the development are the frequency used, the modulation and the energy management.

The impact

A combined system of short-range transmitters, with a concentrator based on a long-range receiver–transmitter can meet the wireless monitoring requirements of future repositories. New potential improvements to the system have been identified: providing an alternative power supply to the batteries, enhancing software to provide more information from the transmitters, such as signal strength and battery condition, implementing an ionising radiation shield, including the option of connecting vibrating wire sensors and developing a multi-hopping arrangement. These improvements will be implemented in the future, but the current base can already address industrial application.

The new wireless data transmission monitoring system will provide valuable data from future DGRs, improving both safety and public confidence. While designed for long-term nuclear waste storage, the system is also suitable for monitoring a wide range of underground environments, such as mines, tunnels, caverns, utility networks and buried storage facilities for medium and low-level waste or industrial materials.