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Title: Radionuclide transport in brackish water through chalk fractures

Journal Article · · Water Research
ORCiD logo [1];  [2];  [3];  [4];  [4];  [1]
  1. Ben Gurion Univ. of the Negev, Midreshet Ben Gurion (Israel)
  2. Geological Survey of Israel, Jerusalem (Israel)
  3. Nuclear Research Center of the Negev, Beersheva (Israel); Ben Gurion Univ. of the Negev, Beersheva (Israel)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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Mobility of radionuclides originating from geological repositories in the subsurface has been shown to be facilitated by clay colloids. In brackish water, however, colloids may flocculate and act to immobilize radionuclides associated with them. Furthermore, little research has been conducted on radionuclide interactions with carbonate rocks. In this work, the impact of bentonite colloid presence on the transport of a cocktail of U(VI), Cs, Ce and Re through fractured chalk was investigated. Flow-through experiments were conducted with and without bentonite colloids, present as a mixture of bentonite and Ni-altered montmorillonite colloids. Ce was used as an analogue for reactive actinides in the (III) and (VI) redox states, and Re was considered an analogue for Tc. Filtered brackish groundwater (ionic strength = 170 mM) pumped from a fractured chalk aquitard in the northern Negev Desert of Israel, was used as a solution matrix. Rhenium transport was identical to that of the conservative tracer, uranine. The sorption coefficient (Kd) of U(VI), Cs and Re, calculated from batch experiments with crushed chalk, proved to be a good predictor of mass recovery in transport experiments conducted without bentonite colloids. A meaningful Kd value for Ce could not be calculated due to its precipitation as a Ce-carbonate colloids. Transport of both U(VI) and Cs was indifferent to the presence of bentonite colloids. However, the addition of bentonite in the injection solution effectively immobilized Ce, decreasing its recovery from 17-41% to 0.8–1.4%. This indicates that radionuclides which interact with clay colloids that undergo flocculation and deposition may effectively be immobilized in brackish aquifers. Lastly, the results of this study have implications for the prediction of potential mobility of radionuclides in safety assessments for future geological repositories to be located in fractured carbonate rocks in general and in brackish groundwater in particular.

Research Organization:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1558866
Report Number(s):
LLNL-JRNL-782342; 977718
Journal Information:
Water Research, Vol. 163, Issue C; ISSN 0043-1354
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 6 works
Citation information provided by
Web of Science

Figures / Tables (15)

Table 1(p. 26)table Table 1
Table 2(p. 26)table Table 2
Table 3(p. 27)table Table 3
Table 4(p. 27)table Table 4
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Figure 2(p. 31)figure Figure 2
Figure 3(p. 32)figure Figure 3
Figure 4(p. 33)figure Figure 4
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Figure S1(p. 39)figure Figure S1
Figure S2(p. 40)figure Figure S2
Figure S3(p. 40)figure Figure S3
Figure S4(p. 41)figure Figure S4
Figure S5(p. 41)figure Figure S5

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Related Subjects

54 ENVIRONMENTAL SCIENCES
Bentonite colloids
Radionuclides
Ionic strength
Carbonate rock
Fracture flow