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Titel |
Preliminary results on variations of radon concentration associated with rock deformation in a uranium mine |
VerfasserIn |
Massimo Verdoya, Massimo Bochiolo, Paolo Chiozzi, Vincenzo Pasquale, Egidio Armadillo, Daniele Rizzello, Enrico Chiaberto |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250079574
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Zusammenfassung |
Time–series of radon concentration and environmental parameters were recently
recorded in a uranium mine gallery, located in the Maritime Alps (NW Italy). The
mine was bored in metarhyolites and porphyric schists mainly composed by quartz,
feldspar, sericite and fluorite. U–bearing minerals are generally concentrated in veins
heterogeneously spaced and made of crystals of metaautunite and metatorbernite.
Radon air concentration monitoring was performed with an ionization chamber
which was placed at the bottom of the gallery. Hourly mean values of temperature,
pressure, and relative humidity were also measured. External data of atmospheric
temperature, pressure and rainfall were also available from a meteorological station
located nearby, at a similar altitude of the mine. The analysis of the time series
recorded showed variation of radon concentration, of large amplitude, exhibiting
daily and half–daily periods, which do not seem correlated with meteorological
records. Searching for the origin of radon concentration changes and monitoring
their amplitude as a function of time can provide important clues on the complex
emanation process. During this process, radon reaches the air– and water–filled
interstices by recoil and diffusion, where its migration is directed towards lower
concentration regions, following the local gradient. The radon emanation from
the rock matrix could also be controlled by stress changes acting on the rate of
migration of radon into fissures, and fractures. This may yield emanation boosts due
to rock extension and the consequent crack broadening, and emanation decrease
when joints between cracks close. Thus, besides interaction and mass transfer with
the external atmospheric environment, one possible explanation for the periodic
changes in radon concentrations in the investigated mine, could be the variation of
rock deformation related to lunar–solar tides. The large variation of concentration
could be also due to the fact that the mine is located next to the Ligurian Sea coast.
When the sea tides change the water level at the shore, this might produce additional
pressure which increases the deformations (sea loading). This paper presents the
preliminary results of an experiment, which is in progress in the uranium mine.
During the experiment, several geophysical parameters are monitored together
with radon concentration. After appropriate insulation in order to prevent radon
escape through normal atmospheric circulation, the gallery was equipped with three
radon detectors, four passive dosimeters, an array of unpolarisable electrodes for
measurements of self-potential variations and a microgravimeter for monitoring of the
tidal effect. We expect that changes in the mechanical state can be accompanied by
changes in the electric potential. Since the latter variation can be related also to
changes in the natural magnetic field, measurements with a three components fluxgate
magnetometer are also being carried out. The recorded signals will be analysed
according to standard procedures, such as spectral analysis and cross-correlation, aimed
at discriminating the periodic components and the governing physical processes. |
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