Analysis of Tracer Movement in Single Fracture in Granite Core (INTRAVAL Case 2).

Abstract

This paper presents an analysis of INTRAVAL (An International Project to Study Validation of Geosphere Transport Models) test case 2, which is based on laboratory experiments on the tracer movement in a single fracture in granite cores. We have applied two kinds of mathematical models for simulations of tracer experiments; a constant aperture model that aperture of fracture is constant in the fracture plane and a variable aperture channel model that apertures of fracture are varied with a given probability distribution. Calculated breakthrough curves of non-sorbing and sorbing tracers were compared with experimental ones. Analysis of non-sorbing tracer shows that fracture flow velocities do not have linear relationship to injection flow rates, it may be explained by the variable aperture model taking into account of the stagnant water in the fracture. Those of sorbing tracers show that calibrated matrix retardations of the constant aperture model are approximately two times larger than the variable aperture model. This feature indicates that the variable aperture model gives longer travel time of nuclide than the constant aperture model if the retardations are same, and channeling is important phenomenon in safety evaluations of waste disposal.