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| Titel |
Predictive model for reducing radon risk in scheduling visits in an underground quarry |
| VerfasserIn |
J.-C. Sabroux, J. Wassermann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030666
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| Zusammenfassung |
| Radon volumic activity has been monitored almost continuously for more than five years in
the atmosphere of an abandoned underground quarry located in the north of France. The
quarry is used as a test bench for studies of the subsidence risk, and is subject consequently to
regular visits by scientific teams. Despite its geological setting – chalk marl covered by an
impervious layer of clay and alluvial deposits – suggesting a low radium content of the source
rock, the radon background level in the atmosphere of the quarry is not less than 12
000 Bq.m-3. The floor of the quarry is 20 m below the flat ground surface and the
height of the galleries is no more than 2 m, portions of the rock being left in place as
pillars to support the roof. The horizontal extension of the qarry is at least 100 000
m2.
Notwithstanding a very weak natural ventilation, due to a single vertical access pit for the
whole quarry, the radon volumic activity is affected by seasonal variations, with anomalous
high levels reaching 30 000 Bq.m-3 for several days or weeks during winter, an unexpected
pattern for an horizontal subterranean cavity. Such high levels prohibit long visits in the
quarry, all the more so as equilibrium factor in the underground atmosphere in consistently of
the order of 0.7.
Spectral decomposition of the radon time series, and correlations with meteorological
parameters enabled to propose a mechanism explaining the conspicuous radon variations and
allowing to predict the radon surges for scheduling visits accordingly. |
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