The Backfill as an Engineered Barrier for Nuclear Waste Management

Nowak, E. J.

doi:10.1007/978-1-4684-3839-0_48

Cited by 12 publications

(9 citation statements)

References 2 publications

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“…A properly designed backfill should 1) retard or exclude the migration of ground water between the host rock and the waste canister system; 2) retard the migration of selected chemical species (corrosive agents and radionuclides) in the ground water; and 3) control the Eh and pH of the ground water within the wastepackage environment [1,2,3].…”

Section: Introductionmentioning

confidence: 99%

Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials

et al. 1981

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Section: Introductionmentioning

confidence: 99%

Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials

et al. 1981

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“…Estimates show that sorption retardation can delay the release of cationic species into the surrounding medium for up to lo4 years. (Nowak, 1980). Secondary clay minerals in the surrounding geological medium serve the same purpose.…”

mentioning

confidence: 98%

“…To slow this release several engineered barriers are proposed. One of these is a protective layer of bentonite-based packing surrounding the waste canister (Waste Isolation Systems Panel, 1983) whose purpose is to prolong canister life (Anderson et al, 1982) and delay the initial release of ions (Nowak, 1980). To design a waste repository, realistic predictions are needed for the physical transport rates of radionuclides through the packing and host rock.…”

mentioning

confidence: 99%

Caesium and strontium diffusion through sodium montmorillonite at elevated temperature

Jensen

Radke

1988

Journal of Soil Science

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Counter ionic migration rates of dilute Cs' and Sr2+ against sodium in a Namontmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion-exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for lo-', lo-', and M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2 x and 8.0 x cm2 s-', respectively. These values are found to be essentially independent of background ionic strength over the range to lo-' M NaCI. Experimental evidence of enhanced transport through Na-montmorillonite for the divalent cation Sr2+ is also confirmed with a surface diffusivity of 2 x cm2 s-' at 22°C and in lo-' M NaCl. D E F I N I T I O N O F S Y M B O L S =gel cross-sectional area, cm2 =tank concentration, M =initial tank concentration, M =total gel concentration, M =interstitial gel concentration, M =inlet concentration to the diffusion cell, M =outlet concentration from the diffusion cell, M =overall diffusion coefficient, (D,/r2) (1 +(I -E) KDJED,), cm2 s -l =effective diffusion coefficient, D / a , cm2 s-' =molecular diffusion coefficient, cm2 s-' =radially perfused cell overall mass transfer coefficient, cm s-' =dimensionless ion-exchange isotherm slope =absolute permeability, m2 =length of gel sample, cm =volumetric flowrate, cm3 s-' = Laplace space variable, s =time, s =time of experiment, s =fluid volume of external tank, cm3 =cell dead volume, cm3 =axial position inside gel, cm =dimensionless axial position in gel, x / L = sorption retardation coefficient, (1 + (1 -E)K/E) = 4~~a D A l V k~, =porosity =clay density, g cm-3 = tortuosity ' 53

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“…Numerical solution of the linear Equations (6) is by Galerkin finite elements with bilinear basis functions. A critical test applied to assess the accuracy of the numerical procedure was matching of the integrated net radial flux at two arbitrary radial positions.…”

Section: Theorymentioning

confidence: 99%

“…Also, once the canister is breached, the favorable ion-exchange properties of montmorillonite retard the migration of cations into the host rock [6). Further discussion of transient cation diffusion in compacted montmorillonite is found in our companion paper [4).…”

Section: Introductionmentioning

confidence: 99%

Steady Radionuclide Release Rates from a Bentonite-Protected Waste Canister

Jensen¹,

Radke²

1987

Coupled Processes Associated With Nuclear Waste Repositories

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A bentonite-based packing or engineered barrier is one ingredient of the multibarrier concept for underground storage of high-level nuclear waste. This paper investigates the possible effectiveness that such a smectiteladen barrier might have in controlling steady, solubility-limited release rates from a cylindrical waste canister.Darcy's law and the convective-diffusion equation in two dimensions are solved numerically with and without an annulus of packing material. Reduced fractional release rates quantifying the role of the packing are studied over wide ranges of ground water velocities, packing amounts, and packing permeability and effective diffusivity. Release rates are shown to be strongly dependent on the physical properties of the packing, particularly the effective diffusivity.Although the low permeability of a bentonite-rich packing negates convection next to the canister, calculated release rates of the packing-protected waste canister do not differ dramatically from the those for the unprotected canister, except at high ground water velocities. To afford more protection, consideration must be given to reducing the porosity of the packing material.

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The Backfill as an Engineered Barrier for Nuclear Waste Management

Cited by 12 publications

References 2 publications

Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials

Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials

Caesium and strontium diffusion through sodium montmorillonite at elevated temperature

Steady Radionuclide Release Rates from a Bentonite-Protected Waste Canister

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