Calculating flux to predict future cave radon concentrations

0466615 - ÚSMH 2017 RIV GB eng J - Článek v odborném periodiku
Rowberry, Matthew David - Martí, Xavier - Frontera, C. - Van De Wiel, M.J. - Briestenský, Miloš
Calculating flux to predict future cave radon concentrations.
Journal of Environmental Radioactivity. Roč. 157, JUN (2016), 16-26. ISSN 0265-931X. E-ISSN 1879-1700
Grant CEP: GA MŠMT LM2010008
Institucionální podpora: RVO:67985891 ; RVO:68378271
Klíčová slova: cave radon concentration * cave radon flux * cave ventilation * radioactive decay * fault slip * numerical modelling
Kód oboru RIV: DC - Seismologie, vulkanologie a struktura Země; BG - Jaderná, atomová a mol. fyzika, urychlovače (FZU-D)
Impakt faktor: 2.310, rok: 2016

Cave radon concentration measurements reflect the outcome of a perpetual competition which pitches flux against ventilation and radioactive decay. The mass balance equations used to model changes in radon concentration through time routinely treat flux as a constant. This mathematical simplification is acceptable as a first order approximation despite the fact that it sidesteps an intrinsic geological problem: the majority of radon entering a cavity is exhaled as a result of advection along crustal discontinuities whose motions are inhomogeneous in both time and space. In this paper the dynamic nature of flux is investigated and the results are used to predict cave radon concentration for successive iterations. The first part of our numerical modelling procedure focuses on calculating cave air flow velocity while the second part isolates flux in a mass balance equation to simulate real time dependence among the variables. It is then possible to use this information to deliver an expression for computing cave radon concentration for successive iterations. The dynamic variables in the numerical model are represented by the outer temperature, the inner temperature, and the radon concentration while the static variables are represented by the radioactive decay constant and a range of parameters related to geometry of the cavity. Input data were recorded at Driny Cave in the Little Carpathians Mountains of western Slovakia. Here the cave passages have developed along splays of the NE-SW striking Smolenice Fault and a series of transverse faults striking NW-SE. Independent experimental observations of fault slip are provided by three permanently installed mechanical extensometers. Our numerical modelling has revealed four important flux anomalies between January 2010 and August 2011. Each of these flux anomalies was preceded by conspicuous fault slip anomalies.
Trvalý link: http://hdl.handle.net/11104/0264885