An Analogue Validation Study of Natural Radionuclide Migration in Crystalline Rocks using Uranium-Series Disequilibrium Studies

1985 ◽  
Vol 50 ◽  
Author(s):  
J. A. T. Smellie ◽  
A. B. MacKenzie ◽  
R. D. Scott
Keyword(s):  
Natural Radionuclide ◽  
Hydrothermal Activity ◽  
Crystalline Rock ◽  
Crystalline Rocks ◽  
Radionuclide Migration ◽  
Uranium Series ◽  
Saturated Rock ◽  
Decay Series ◽  
Uranium Migration ◽  
Natural Decay

AbstractConcentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water-conducting fractures deep in the bedrock. Radioactive disequilibria resulting from rock-water interactions were observed in two of the cores. These indicated uranium migration along distances of 40 cm or more on a timescale of 106 years in conjunction with thorium immobility under the same conditions. Fracture surface minerals showed a high affinity for radionuclide retardation and a limit of about 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock. This limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels.

Verfication of matrix diffusion by means of natural decay series disequilibria in a profile across a water-conducting fracture in granitic rock

1989 ◽  
Vol 176 ◽  
Author(s):  
W.R. Alexander ◽  
I.G. McKinley ◽  
A.B. MacKenzie ◽  
R.D. Scott
Keyword(s):  
Safety Assessment ◽  
Crystalline Rock ◽  
Assessment Model ◽  
Base Case ◽  
Matrix Diffusion ◽  
Advective Flow ◽  
Model Base ◽  
Decay Series ◽  
Main Fracture ◽  
Natural Decay

ABSTRACTData from a rock drillcore, taken perpendicular to a water-bearing fracture in crystalline rock, clearly indicate water-rock interactions in and around the fracture. Although there is evidence of microfracturing at some distance from the main fracture, and therefore potential advective flow across the entire shear zone, simple calculations indicate that transport of Ra-226 in the vicinity of the main fracture can be described simply by matrix diffusion. This is a useful simplification for safety assessment studies and the consequences to the estimated radionuclide retardation in the vicinity of the fracture are discussed with respect to the probably over-conservative assumptions made in Nagra's safety assessment model base case.

Colloid Properties in Granitic Groundwater Systems, with Emphasis on the Impact on Safety Assessment of a Radioactive Waste Repository

1992 ◽  
Vol 294 ◽  
Author(s):  
C. Degueldre
Keyword(s):  
Test Site ◽  
Hydrothermal Activity ◽  
Crystalline Rock ◽  
Radionuclide Migration ◽  
Migration Rates ◽  
The North ◽  
Groundwater Systems ◽  
Consistent Picture ◽  
Irreversible Sorption ◽  
The Impact

ABSTRACTSince colloids are present in all groundwaters, they are studied because of their potential role in the migration of relevant radionuclides in the geosphere. Colloid sampling and characterization campaigns have been carried out in the Grimsel area, Switzerland (Transitgas tunnel, Grimsel Test Site) and in the North Switzerland/Black Forest area (Menzenschwand, Bad Sickingen, Zurzach, Leuggem). On the basis of results obtained for 25 groundwaters a consistent picture is emerging. Colloids in granitic systems are basically composed of components of the aquifer materials (clay, silica). Under the hydrogeochemical conditions existing at depth in crystalline rock systems, colloid concentrations are not expected to exceed 100 ppb. However, under transient conditions when physical and/or chemical changes are occuring (e.g., hydrothermal activity), colloid generation may be enhanced. Colloid concentration of 10 ppm may be observed when the calcium concentration is low enough (<5 ppm).Whereas reversible sorption on the host rock leads to conservative predictions for radionuclide migration rates, the reverse is true for sorption onto colloids. The most conservative assumptions are therefore reversible nuclide sorption and colloid attachment on the rock and irreversible sorption on colloids.For calcium concentrations larger than 5 ppm, and sorption capacities at the nM level, their presence in granitic aquifer can be neglected in safety analyses when reversible sorption onto colloids is considered. This situation could change when sorption is followed by aggregation or incrustation processes. This study shows that for the colloid conservative size distributions found and for the granitic water conducting fissures considered, sorption-agglomeration reactions are unlikely to take place. Therefore, irreversible sorption by this mecanism is improbable.

Aqueous Phase Diffusion in Crystalline Rock

1981 ◽  
Vol 11 ◽  
Author(s):  
M.H. Bradbury ◽  
D. Lever ◽  
D. Kinsey
Keyword(s):  
Radioactive Waste ◽  
Aqueous Phase ◽  
Water Movement ◽  
Degradation Products ◽  
Crystalline Rock ◽  
Crystalline Rocks ◽  
Radionuclide Transport ◽  
Fracture Networks ◽  
Phase Diffusion ◽  
Main Factors

One of the options being considered for the disposal of radioactive waste is deep burial in crystalline rocks such as granite. It is generally recognised that in such rocks groundwater flows mainly through the fracture networks so that these will be the “highways” for the return of radionuclides to the biosphere. The main factors retarding the radionuclide transport have been considered to be the slow water movement in the fissures over the long distances involved together with sorption both in man-made barriers surrounding the waste, and onto rock surfaces and degradation products in the fissures.

scholarly journals Re-Evaluating the Age of Deep Biosphere Fossils in the Lockne Impact Structure

Geosciences ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 202 ◽  
Author(s):  
Mikael Tillberg ◽  
Magnus Ivarsson ◽  
Henrik Drake ◽  
Martin J. Whitehouse ◽  
Ellen Kooijman ◽  
...  
Keyword(s):  
Hydrothermal Activity ◽  
Crystalline Rock ◽  
Hydrothermal Systems ◽  
Fungal Colonization ◽  
Precambrian Basement ◽  
Impact Event ◽  
Deep Biosphere ◽  
Microbial Ecosystems ◽  
The Impact

Impact-generated hydrothermal systems have been suggested as favourable environments for deep microbial ecosystems on Earth, and possibly beyond. Fossil evidence from a handful of impact craters worldwide have been used to support this notion. However, as always with mineralized remains of microorganisms in crystalline rock, certain time constraints with respect to the ecosystems and their subsequent fossilization are difficult to obtain. Here we re-evaluate previously described fungal fossils from the Lockne crater (458 Ma), Sweden. Based on in-situ Rb/Sr dating of secondary calcite-albite-feldspar (356.6 ± 6.7 Ma) we conclude that the fungal colonization took place at least 100 Myr after the impact event, thus long after the impact-induced hydrothermal activity ceased. We also present microscale stable isotope data of 13C-enriched calcite suggesting the presence of methanogens contemporary with the fungi. Thus, the Lockne fungi fossils are not, as previously thought, related to the impact event, but nevertheless have colonized fractures that may have been formed or were reactivated by the impact. Instead, the Lockne fossils show similar features as recent findings of ancient microbial remains elsewhere in the fractured Swedish Precambrian basement and may thus represent a more general feature in this scarcely explored habitat than previously known.

Episodic Subseafloor Hydrothermal Activity Within the Eastern Manus Back-Arc Basin Determined by Uranium-Series Disequilibrium in Barite

2014 ◽  
Vol 109 (8) ◽  
pp. 2227-2242 ◽  
Author(s):  
S. M. Johns ◽  
R. G. Ditchburn ◽  
B. J. Barry ◽  
C. J. Yeats
Keyword(s):  
Hydrothermal Activity ◽  
Uranium Series ◽  
Back Arc

Radioactive ingrowth in a natural decay series. A demonstration

1990 ◽  
Vol 67 (5) ◽  
pp. 374
Author(s):  
K. Murray Matthews ◽  
Rachael M. Larkin
Keyword(s):  
Decay Series ◽  
Natural Decay
Sign in / Sign up

Export Citation Format

Share Document