Radon and variable rock stress

Radon variations in an underground galleryPumping Storage Facility, SEO, L-Vianden

Francis Massen, Physics Lab, Lycée Classique DiekirchAntoine Kies, LPR, Université du Luxembourg

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basin 1

basin 2

Upper basins 1 & 2

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Construction : 1959 to 1964Maximum used volume of basins : 6.8 million m3

Maximum water level change : 16 m ~ 1.6 atFlow during power generation : 432.5 m3/sMean daily power generation time: 4.25hMean daily pumping time: 7.25h

www.seo.lu

SEO main figures:

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Water outlets

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B1_stat2 B1_stat1 B1_stat3B2_stat1 B2_stat2

Location of stations

galleries

B2_stat3( in use since July04)

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Geology

basin1

basin2

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Fractures and fillings (J. Bintz, 1964)

Voids were filled with concreteduring construction work!

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Interior of gallery

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Boreholes

1m concrete

40cm rock

~16cm diameter

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21Nov02 – 13Dec02, 4 stations [100uRoe/h ~1uSv/h ~100 Bq/m3 EER]Difference in radon signal between basin1 and basin2

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May02

Possible anticorrelation with atmospheric pressure …. large voids in underground?

Basin1, station1: influence of atmospheric pressure variations

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Basin2 stat1: radon and water level (station1, 21Nov02-13Dec02)

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Basin2 stat2: radon and water level (station2, 02 – 30 Apr.04)

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Basin2: stations 1,2,3 : 04Aug-27Sep 2004Vanishing signal….

stat1

stat2

stat3

190m

245m

approx.direction offissures

24h

why?

Autocorrelation of radon

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Gravitational effects

stat1stat2stat3

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Water level modulates existing radon background

Emptying basin 2: radon regains background level in ~24h

24 hours

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21Nov02 - 13 Dec02Time lag between radon and water level: Basin2, station1

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21Nov02 - 13 Dec02

Time lag between radon and water level: Basin2, station2

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Is the delay between radon and water level ~ constant?…. YES!

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More time lags between radon and water level:

from…to days B2stat1 B2stat2 B2stat3

21Nov02-05Feb03 77 93 24612-18Jun03 7 36 26302-30Apr04 29 109 27804Aug-27Sep04 55 205 240 (300)______________________________________________________

? ?

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Relation between radon concentration and water level: B2 stat1

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Better fit: parabolic

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Relation between radon concentration and water level: B2 stat2

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Explication?

stat1

stat2

stat3

B1_stat3

Stations 1 and 2 lie in a fissuresystem with one dominatingorientation preferentialmigration path for radon strong water level dependance

Fissure system is random: no dominant migration path no water level dependance

Basin 1

Basin 2

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RM80 Aware counter

“Pancake” Geiger tube (,,)

Sensor driven by serial or parallelport of (notebook) computer

Sensor is not waterproof: usually will be sealed in PET bag with calcium chloride CaCl2 as desiccant.

Many humidity related problems!

Price: ~319 US$www.aw-el.com

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Calibration of RM80

Calibration was done in-situ , (in gallery with no ventilation)comparing readings of a RM80 and a Alphaguard:

borehole

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RM80 and Radim sensor (borehole B2 stat2)

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Computer problems

1. Protection against humidity: never shut down!2. Protection against fine dust: seal floppy drive by tape; install Laplink in case of floppy malfunction3. Use only notebooks: power outage protection!4. Save backlight tubes: shut off screen5. Use surge protectors (many lightning impacts!)6. Combat computer clock drift: RIGHTIME software

7. Use only old equipment!

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Software

Very large data files ( > 150000 lines): use DADiSP

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DADiSP www.dadisp.com

Price: 1995 US$

Same as full version,limited in numberof windows and datasize

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Merci de votre attention…

antoine.kies@uni.lu francis.massen@education.luetclaude.boes@bigfoot.com

http://meteo.lcd.lu/papers/http://www.speleo.lu