The protection and safeguarding of the environment today is of primary importance. Nuclear power agencies are taking significant additional measures to introduce and adopt innovative monitoring techniques in respect of waste storage.
The Swedish Nuclear Fuel and Waste Management Company (SKB) in collaboration with HydroResearch Sam Johansson AB, Uppsala University and Silixa Ltd have introduced Silixa’s distributed fiber optic sensing systems to evaluate its monitoring capabilities of conditions in the sub-surface and deliver feedback to engineers to assist with the design and construction processes of a new waste storage facility. The system is currently being evaluated together with existing technologies in an effort to expand the monitoring capabilities not only during construction but also through the operational life of the repository.
The main scope of this feasibility trial, which is the first of its kind, is to compare technologies for seismic monitoring and to map and characterize the geological formation, which is achieved using active and passive seismic techniques.
During the first survey, geophones and different cable constructions were installed in a monitoring borehole to an initial depth of 200 m. Additionally the borehole was instrumented with a heat active optical fibre cable to allow characterisation of the thermal conductivity along the entire depth using active distributed temperature sensing. Preliminary tests have produced encouraging results using both the intelligent Distributed Acoustic Sensor (iDAS™) and Carina® Sensing System, as well as the ULTIMA™ DTS, distributed temperature sensor.
Distributed sensing systems offer an unprecedented opportunity for applications in the environmental sector, where the processes are on scales from centimetres to kilometres. Distributed fibre optic monitoring offers fine spatial resolution and the ability to easily repeat measurements to create a temporal profile. This can be delivered for large areas, long lengths and at locations where conventional transducers are not applicable or cost effective.
Temperature sensing has been proven to be the technique of choice for numerous environmental applications, such as soil moisture monitoring, groundwater-surface water interactions in streams, fractured rock characterisation and flow dynamics into boreholes.
Distributed acoustic sensing has been used in many seismic acquisitions to date, encompassing vertical seismic profiles (VSP), in both flowing and non-flowing oil wells, CO2 storage wells and surface seismic surveys.
Both techniques have been deployed in geophysical monitoring applications.
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