Monitoring System Design of Underground Repository for Radioactive Wastes – In Situ Demonstrator

Abstract

Abstract-This paper describes the qualification of sensors envisioned for Cigéo, the planned deep disposal center for French radioactive waste. More precisely, it describes an in situ demonstrator, similar with the system planned to monitor intermediate level long lived radioactive wastes cells. These cells would be a tunnel, located 490 m deep, with 9 m in diameter, with concrete liners realized in three steps.The demonstrator was instrumented in 2011 in the Andra's Underground Research Laboratory. The instruments provide useful information on sensors' adaptability to the environment; robustness and technology comparisons (accordance and discrepancies). As an example, accordance between localized sensors and distributed measurements for strains, by optical fiber sensors and vibrating wire extensometers and temperatures, by optical fiber sensors and platinum probe, was verified.After 3 years more than 95% of sensors still provide measurements and show no drift over time.

France’s State of the Art Distributed Optical Fibre Sensors Qualified for the Monitoring of the French Underground Repository for High Level and Intermediate Level Long Lived Radioactive Wastes

“…In GCR gallery, after 6 years more than 95% of the sensors still provide measurements, without any drift. What is more, strain measurements obtained in concrete liners with optical sensing cables are very in good accordance with collocated reference sensors, namely VWE [ 19 , 24 ]. In GER gallery, for FOS placed in the poured concrete layer, survival rate is 100%, after more than 1.5 year and good accordance is also obtained [ 25 ] (cf.…”

“…Obtained performances were reported in [ 19 , 24 , 25 ]. Specific one-site implementation difficulties were detailed in [ 49 ].…”

“…Similar comparative tests can be also performed for concrete and metallic structure monitoring [18,19]. The selected cables present advantages and drawbacks regarding handling (flexible and easy to install) and durability (metallic reinforced cable).…”

“…Electricité de France (EDF, the French Electricity Company) and Andra have selected and tested several sensing cables, for soil monitoring, as illustrated in Figure 4 [ 17 ]. Similar comparative tests can be also performed for concrete and metallic structure monitoring [ 18 , 19 ]. The selected cables present advantages and drawbacks regarding handling (flexible and easy to install) and durability (metallic reinforced cable).…”

Effects of gamma radiation on perfluorinated polymer optical fibers

“…Optical fibers can act also as a sensing element for various external parameters. Fiber-based systems have been exploited for strain [2], temperature [3] or humidity [4] sensing in radiation environments. Various fiber sensing schemes are being investigated, including distributed Rayleigh [3,5], Raman [6] or Brillouin [7] scattering techniques and fiber Bragg gratings or interferometric sensors [8,9].…”