Estimation of uranium migration parameters in sandstone aquifers

Малов, А. И.

doi:10.1016/j.jenvrad.2015.11.006

Cited by 21 publications

(25 citation statements)

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“…What is obtained is: t 1 = 0.9 Ma, which should roughly correspond to the period of a sharp cold snap in the region and filling of the paleo-valley by clay material [30][31][32][33]. The duration of the subsequent removal of hydrogenic uranium from the NDD slopes can be estimated from the equation [14]:…”

Section: Resultsmentioning

confidence: 93%

“…Evidence that recoil atoms are not transferred into water alone but carry away a certain amount of 238 U atoms explains why AR t under reducing conditions usually does not exceed 10-20. This is possible if 1000-2000 238 U atoms are transferred into the water with each recoil-atom 234 Th [14].…”

Section: Resultsmentioning

confidence: 99%

“…Consequently C 8 W = (2.6 − 1.2) = 1.4 ppm; M s -solid mass to fluid unit volume ratio = 9.2; C 8 R is average concentration of U in solid phase for a time t: C 8 R = (U 0 + 238 U): 2 = (2.6 + 1.2): 2 = 1.9 ppm; R d -dissolution rate for U; R:p = 24; and average R d :p = 3.6 × 10 −6 a −1 [14]. We get: t 2 = 0.5 Ma.…”

Section: Resultsmentioning

confidence: 99%

“…Water temperature, pH, Eh, DO, alkalinity, total dissolved solids (TDS), Fe concentrations, U concentrations (C 8 W ), 234 U/ 238 U activity ratio (AR t ), 14 C, δ 13 C were determined in groundwater, as described by Malov [14]. U content ( 238 U), 234 U/ 238 U activity ratio, Fe content in rock samples were determined, as described by Malov et al [15].…”

Section: Methodsmentioning

confidence: 99%

“…Further, a mass-balance model [14,17] was used to estimate the 234 U-238 U residence time of groundwater in an aquifer under oxidizing conditions for U.…”

Section: Methodsmentioning

confidence: 99%

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Evolution of Uranium Isotopic Compositions of the Groundwater and Rock in a Sandy-Clayey Aquifer

Малов

2017

Water

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Uranium isotopes have been used as mechanistic or time scale tracers of natural processes. This paper describes the occurrence and redistribution of U in the Vendian aquifer of a paleo-valley in NW Russia. Forty-four rock samples were collected from nine boreholes with depths up to 160 m, and 25 groundwater samples were collected from 23 boreholes with depths up to 300 m. The U, Fe concentration, and 234 U/ 238 U activity ratio were determined in the samples. Estimations were made of the 14 C and 234 U-238 U residence time of groundwater in the aquifer. It has been established that the processes of chemical weathering of Vendian deposits led to the formation of a strong oxidation zone, developed above 250 m.b.s.l. The inverse correlation between the concentrations of uranium and iron is a result of removal of U from paleo-valley slopes in oxidizing conditions, accumulation of U at the bottom of the paleo-valley in reducing conditions, and accumulation of Fe on the slopes and removal from the bottom of the paleo-valley. Almost all U on the slopes has been replaced by a newly formed hydrogenic U with a higher 234 U/ 238 U activity ratio. After, dissolution and desorption of hydrogenic U occurred from the slopes during periods with no glaciations and marine transgressions. Elevated concentrations of U are preserved in reduced lenses at the paleo-valley bottom. In these areas, the most dangerous aspect is the flow of groundwater from the underlying horizons, since during the operation of water supply wells it can lead to the creation of local zones of oxidizing conditions in the perforated screens zone and the transition of uranium into solution. For groundwater under oxidizing conditions, an increase in the concentration of uranium is characteristic of an increase in the residence time (age) of water in the aquifer. Also, the 234 U/ 238 U activity ratio increases with increasing radioactivity of groundwater. Therefore, the most rational approach is to use groundwater for drinking water supply from the slopes of the Northern Dvina basin.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Further, a mass-balance model [14,17] was used to estimate the 234 U-238 U residence time of groundwater in an aquifer under oxidizing conditions for U.…”

Section: Methodsmentioning

confidence: 99%

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