Prediction of waste performance in a geologic repository

Conference · Sun Jan 01 04:00:00 EST 1984 · Mater. Res. Soc. Symp. Proc.; (United States)

OSTI ID:5904101

Chambre, P L; Pigford, T H

The rate of dissolution of low-solubility species from waste forms in a geologic repository can be calculated from a theoretical analysis of the time-dependent rate of mass transfer by diffusion and convection into the groundwater surrounding the waste, assuming a concentration at the waste-form surface equal to the solubility of the radioelement. The predicted steady-state dissolution rates are considerably below those observed in laboratory leaching experiments with borosilicate glass and with other waste forms, indicating that the solid-liquid chemical reaction rates measured in the laboratory experiments are greater than the rates of diffusive-convective mass transfer in the concentration boundary layer surrounding the waste form in a geologic repository. The steady-state mass transfer rate can be increased, and the time to reach steady state decreased, by sufficiently short half lives of the dissolving species. The mass-transfer theory has been extended to include the effect of time-dependent solubilities, diffusion coefficients, and retardation coefficients, which provides a means of calculating the time-dependent dissolution of low-solubility species from waste exposed to groundwater during the period of repository heating. The transient and steady-state diffusion of radionuclides through a finite backfill layer separating a finite waste solid and porous rock has been analyzed, including the effects of radioactive decay. The results show that the break-through time and rate of radionuclide release depend on properties of the backfill and surrounding rock and on the waste form dimensions. Peak far-field concentrations of more soluble radionuclides such as cesium-135, with suitably long radionuclide transport times and sufficiently large axial dispersion, are shown to be insensitive to dissolution rate. Equivalent phenomena occur in fracture-flow radionuclide transport. 36 references, 16 figures, 2 tables.

• Research Organization: Univ. of California, Berkeley
• OSTI ID: 5904101
• Report Number(s): CONF-831174-
• Conference Information: Journal Name: Mater. Res. Soc. Symp. Proc.; (United States) Journal Volume: 26
• Country of Publication: United States
• Language: English

Related Subjects

052002* -- Nuclear Fuels-- Waste Disposal & Storage
053000 -- Nuclear Fuels-- Environmental Aspects
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
520301 -- Environment
Aquatic-- Radioactive Materials Monitoring & Transport-- Water-- (1987)
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
ALKALI METAL ISOTOPES
BACKFILLING
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BOROSILICATE GLASS
CESIUM 135
CESIUM ISOTOPES
CONVECTION
DIFFUSION
ENERGY TRANSFER
ENVIRONMENTAL TRANSPORT
GLASS
GROUND WATER
HEAT TRANSFER
HYDROGEN COMPOUNDS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MANAGEMENT
MASS TRANSFER
MINUTES LIVING RADIOISOTOPES
NUCLEI
ODD-EVEN NUCLEI
OXYGEN COMPOUNDS
RADIOACTIVE WASTE DISPOSAL
RADIOISOTOPES
RADIONUCLIDE MIGRATION
SOLUBILITY
TIME DEPENDENCE
WASTE DISPOSAL
WASTE MANAGEMENT
WASTE-ROCK INTERACTIONS
WATER
YEARS LIVING RADIOISOTOPES