Databank

Databank

Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications


Workreport 2020-47

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Name:

Results of Monitoring at Olkiluoto in 2019, Rock Mechanics

Writer:

Haapalehto, S., Malm, M., Kaisko, O., Marila, S., Saaranen, V.

Language:

English

Page count:

117

Summary:

The rock mechanical monitoring is done at Olkiluoto in order to measure potential tectonic movements, estimate the stability of the bedrock and to implement safeguards-work. The rock mechanics monitoring programme 2019 consisted of seismic, GPS, precise levelling, and temperature measurements at Olkiluoto and seismic, displacement, temperature measurements and visual tunnel observations recorded in the final disposal facility.

Posiva runs a microseismic network in ONKALO® and its surroundings for monitoring the structures and long-term stability of the bedrock and as a part of the safeguards programme. The permanent network consisted of 18 seismic stations equipped with a total of 22 sensors in 2019. In addition, ten temporary sensors deployed for study purposes were running but excluded from the permanent network. The monitoring was operated continuously in 2019, even though individual stations suffered from short operation breaks. Altogether 466 events were located inside the seismic semi-regional area, of which 274 were explosions (ML = -1.2 … 0.8), 17 microearthquakes (ML = -2.7 … -1.7) and 170 were classified as miscellaneous or unidentified small events inside the seismic ONKALO block (ML = -2.9 … -0.3). In addition, 5 explosions (ML = 1.1 … 1.8) outside the ONKALO block but within the semi-regional area were located. Also, 4 regional earthquakes (ML = 1.3 … 2.6) were recorded. The excavation works of the final disposal facility were much quieter in 2019 compared to the previous year of observation. Also, the amount of induced seismicity was much lower compared to the previous year. The microearthquakes were of small magnitudes, and no visual observations or tremors directly related to these events were observed. Some of the microearthquakes were connected to construction operations and no natural earthquakes could be identified in the seismic ONKALO block area. Despite the very small induced microearthquakes, the rock mass has remained stable according to the seismic monitoring in 2019.

The GPS network of Olkiluoto consists of same 16 continuously operating stations as last year. Pyrekari GPS12 measurements were not performed this year. Largest gaps in the GPS data were GPS1 (>0.5 years) and GPS14 (2.5 months). The station velocities with uncertainties were estimated for each station from the daily coordinate solutions taking into account the seasonal signals and discontinuities. The relative horizontal velocity components of the stations were all below 0.2 mm/year except GPS12. The uncertainties of the horizontal velocities were on average 0.1 mm/year at 95 % confidence level. The mean (absolute values) of estimated vertical velocities was 0.7 mm/year and the uncertainties of the vertical velocities were clearly larger compared to the horizontal estimates, on average 0.6 mm/year at 95 % confidence level.

The whole Posiva levelling network was measured in 2019. Between 2018 and 2019, the height changes in the ONKALO and VLJ were small. In the comparison with the previous measurements in 2017 at the GPS station 17, some significant height changes exist between the control benchmarks of the station. When analysing longer time period, large height changes can be found in the ONKALO area, where benchmark 06220 has uplifted 3.08 mm since 2006 relative to the fixed BM 03216. On the island of Olkiluoto, GPS9A has uplifted 2.53 mm in the same time period relative to the same fixed benchmark. Between the measurements in 2017 and 2019 the difference was 0.51 mm at BM GPS9A.

The extensometers installed in the final disposal facility at 7 different measurement areas measured the displacements of the tunnels mainly continuously in 2019. Several downtimes were observed in all measurement areas. The dataset of the parking hall 1 is unreliable at the end of the year. None of the displacements exceeded 0.1 mm in the final disposal facility.

During 2019 temperature measurements were performed in two deep drillholes, in the access tunnel and in the displacement measurement areas. The results of 2019 follow the results from previous years. The seasonal change is observed in the measurements made in the tunnels. In OL-KR23 the tunnel effect is observable due to the proximity of the access tunnel.

No visual observations were recorded during 2019 because of a very low excavation activity.

Keywords:

Monitoring, rock mechanics, Olkiluoto, seismic network, microearthquake, induced seismicity, safeguards, GPS, precise levelling, extensometers, temperature measurements, rock noise

File(s):

WR 2020-47_web (pdf) (8.4 MB)


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