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Posiva’s FISST test proceeds to concreting of end plug for demonstration tunnel

The Full Scale In Situ System Test (FISST) conducted in Posiva’s final disposal project proceeded on 3 May 2019 to the concreting phase in the construction of the end plug for the deposition tunnel.

- We are talking about the largest continuous casting operation ever in ONKALO®. Concreting work started at seven in the morning and completed at seven in the evening on the same day. Once the formwork built for the concreting of the plug is removed, the surface of the plug will be the only visible part remaining from the FISST test, explains R&D Coordinator Johanna Hansen.

The FISST test covers 50 m of tunnel, two modified final disposal canisters, bentonite buffers for two deposition holes, tunnel backfill, and instrumentation for all these.  FISST is designed to demonstrate that Posiva’s concept for final disposal can be implemented safely and according to plans.

Test executed by dozens of Posiva employees and cooperation partners

The canisters and the buffers were installed in the deposition test holes in the summer of 2018 and the backfilling of the tunnel with blocks and pellets started at the end of the summer.

Tunnel backfilling was completed in early December 2018. - After that, a filtering and sealing layer as well as pressure elements were mounted behind the plug structure. The installation of the reinforcing bars for the reinforced concrete cast inside the plug and the construction of the formwork for the plug are the last phases of the entire FISST test, and culminate in the low-pH concreting process, says Project Engineer Hannu Leino.

FISST tulpan valu 3.5.2019 - pieni-42


During 2017–2019, more than 40 Posiva employees and numerous cooperation partners have been involved in the design and execution of FISST.

Concreting is followed by a test monitoring phase which continues for several years.

Sensors installed in the demonstration tunnel have already allowed real-time monitoring of the test. The test canisters are equipped with electric heaters which heat the canisters creating conditions that correspond to the final disposal conditions.  

- We have compiled measurement data since August 2018 and nothing unexpected has occurred, says Programme Manager Pasi Rantamäki.

FISST in numbers:
- Design started in 2016
- Test components and monitoring equipment were manufactured in 2017
- Execution of test started in 2018
- Concreting of plug on 3 May 2019: amount of concrete 130 m³, casting speed 12 m³/h, a mixer truck departing from Olkiluoto concrete station every 20 min to the -420 metre level in ONKALO®.


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