Tracer tests in a fractured rock and their first passage time mathematical models

Technical Report · Thu Aug 01 04:00:00 EDT 1996

OSTI ID:505533

Becker, M W ^[1]

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1. Texas Univ., Austin, TX (United States)

Many countries are contemplating the placement of high-level radioactive waste in massive fractured rock. Although these environments may be the safest place for disposal, they are unfortunately one of the most difficult to model from a contaminant transport perspective. Two groundwater tracer tests were conducted in the saturated zone of a fractured granite under approximately radially convergent (weak-dipole) hydraulic conditions. Carboxylate-modified latex (CML) microspheres and solute tracers (fluorescein, deuterium, and bromide) were used concurrently during these tests. It was anticipated that the solute tracers would diffuse into the rock matrix and other hydraulically stagnant features, whereas the colloidal tracers would not. Comparison of the solute and microsphere tracer breakthrough was therefore expected to lend information about matrix diffusion. Solute tracers behaved in a generally similar manner in both tests, even though the separation distance between the wells differed by a factor of 4. It is thought that the microspheres settled significantly during transport. This casts considerable doubt on the results of their interpretation. It does appear however, that the microspheres moved more quickly through the formation and experienced less matrix diffusion. Breakthrough behavior is interpreted using mathematical models based upon first passage time theory. These models predict transport in formations where equilibrium sorption, matrix diffusion, and Stokes settling are of interest. A new formulation allows for the calculation of first passage time transport to a pumped well under radially convergent conditions. Mathematical solutions are performed in Laplace space with subsequent numerical transformation to the time domain.

• Research Organization: Texas Univ., Austin, TX (United States); Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE Office of Civilian Radioactive Waste Management, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 505533
• Report Number(s): LA-SUB--96-112
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
FRACTURED RESERVOIRS
GROUND WATER
HIGH-LEVEL RADIOACTIVE WASTES
MATHEMATICAL MODELS
RADIOACTIVE WASTE DISPOSAL
RADIONUCLIDE MIGRATION
TRACER TECHNIQUES