Migration of radionuclides through sorbing media analytical solutions--II

This report presents analytical solutions, and the results of such solutions, for the migration of radionuclides in geologic media. Volume 1 contains analytical solutions for one-dimensional equilibrium transport in infinite media and multilayered media. One-dimensional non-equilibrium transport solutions are also included. Volume 2 contains analytical solutions for transport in a one-dimensional field flow with transverse dispersion as well as transport in multi-dimensional flow. A finite element solution of the transport of radionuclides through porous media is discussed. (DMC

Nuclide migration from areal sources into a fracture

This document shows analytic solutions to the problem of hydrogeologic transport of radionuclides released from finite areal sources into a planar fracture. It illustrates the solutions through numerical and graphical displays of the spatial and temporal distribution of the radionuclides as a result of advection in the fracture, transverse dispersion and surface sorption, as well as diffusion into and sorption in the rock matrix. The numerical illustrations indicate that sufficient distances away from the sources equivalent single sources give acceptable approximations. 2 refs., 3 figs

Transient and steady-state radionuclide transport through penetrations in nuclear waste containers

In this paper we analyze the transport of radionuclides through penetrations in nuclear waste containers. Penetrations may result from corrosion or cracks and may occur in the original container material, in degraded or corroded material, or in deposits of corrosion products. We do not consider how these penetrations occur or the characteristics of expected penetrations in waste containers. We are concerned only with the analytical formulation and solutions of equations to predict rates of mass transfer through penetrations of specified size and geometry. Expressions for the diffusive mass transfer rates through apertures are presented. We present numerical illustrations for steady-state mass-transfer rates through a circular hole, including concentration isopleths. The results are extended to multiple holes, including a criterion for hole spacing wherein superposition of single-hole solutions can be used. Results illustrated for holes in thin-walled containers show that significant mass transfer can occur even if a small fraction of the container area is perforated. We also illustrate the case of holes facing a water gap, instead of being in intimate contact with porous rock. In this case the radionuclide flux from many small holes approaches that from a bare waste cylinder

Gas flow in and out of a nuclear waste container

We analyze the flow of gases out of and into a high-level-waste container in the unsaturated tuff of Yucca Mountain. Containers are expected to fail eventually by localized cracks and penetrations. Even though the penetrations may be small, argon gas initially in the hot container can leak out. As the waste package cools, the pressure inside the container can become less than atmospheric, and air can leak in. {sup 14}C released from the hot fuel-cladding surface can leak out of penetrations, and air inleakage can mobilize additional {sup 14}C and other volatile radioactive species as it oxidizes the fuel cladding and the spent fuel. In an earlier paper we studied the gas flow through container penetrations occurring at the time of emplacement. Here we analyze the flow of gas for various penetration sizes occurring at 300 years. 3 refs., 2 figs

Waste-package release rates for site suitability studies

Performance-assessment calculations in support of the site- suitability effort for the Yucca Mountain Project will address radionuclide transport arising from various disruptive scenarios. Here we present release rates of radionuclides from individual waste packages for scenarios involving various postulated forms of water intrusion, including increased infiltration rate as well as rock immediately surrounding an individual waste package becoming saturated with ground water. We examine: (1) effect of increased water infiltration rate on release rates; increases in radionuclide release rates resulting from water filling the annulus between the waste container and the surrounding rock, as well as water saturating the pores and fractures in the rock surrounding the waste package; (3) the effect of flow in fractures in the saturated rock on release rate; and (4) release of radionuclides to the mountain surface resulting from an exploratory borehole shaft intersecting a waste package. The radionuclides considered are Tc-99; I-129; Cs-135; Np- 237; Pu-239,240,242; and Am-241,243. Release rates are calculated for both the wet-drip bathtub and the wet-continuous water-contact modes, as described in the Working Group 2 report, applying equations as published by Sadeghi, et al., [1990] and as extended in the present report

Mathematical models for diffusive mass transfer from waste package container with multiple perforations

A robust engineered barrier system (EBS) is employed in the current design concept for the potential high-level nuclear waste repository at Yucca Mountain, Nevada, US. The primary component of the EBS is a multi-barrier waste package container. Simplifying the geometry of the cylindrical waste package container and the underlying invert into the equivalent spherical configuration, mathematical models are developed for steady-state and transient diffusive releases from the failed waste container with multiple perforations (or pit penetrations) at the boundary of the invert. Using the models the steady-state and transient diffusive release behaviors form the failed waste container are studied. The analyses show that the number of perforations, the size of perforation, the container wall thickness, the geometry of the waste container and invert, and the adsorption of radionuclide in the invert are the important parameters that control the diffusive release rate. It is emphasized that the failed (or perforated) waste package container can still perform as a potentially important barrier (or diffusion barrier) to radionuclide release

Dissolution/precipitation of a two-member chain at a dissolving waste matrix

When the matrix of a nuclear waste in porous rock dissolves in ground water, other species in the waste are also released. Some species, such as the actinides and rare-earths, are of such low solubility that they may precipitate as soon as they are dissolved, depending on the rate of matrix dissolution, their concentration in the waste solid, their solubilities, and the ground water transport rate. We have previously studied the solubility-limited dissolution of single species as controlled by the rate of advective mass transfer from the waste surface. When the waste constituents include low-solubility members of a decay chain, the radioactive decay daughter can form a precipitate at the waste surface or in the rock away from the waste surface. Here we present a simplified analysis of the precipitate formation and dissolution of species in a two-member decay chain. For this purpose it is assumed that flowing ground water becomes saturated with the chemical species of the nuclides as it flows past the waste, resulting in a constant rate of solubility-limited dissolution of the waste matrix. Assuming congruent release of other waste constituents from the solid, the time-dependent amounts of precipitates of the first and second member of the decay chain at the waste surface can be calculated. Numerical illustrations for the /sup 234/U..-->../sup 230/Th chain from spent fuel are given in this paper. Full derivations are given elsewhere. 6 refs., 3 figs., 1 tab

A review of near-field mass transfer in geologic disposal systems

In this report we summarize the analyses of the time-dependent mass transfer of radionuclides from a waste solid into surrounding porous or fractured media that have been developed at the University of California, Berkeley. For each analysis we describe the conceptual model, we present the governing equations and the resulting analytic solutions, and we illustrate the results. Designers of geologic disposal systems for solid waste must predict the long-term time-dependent rate of dissolution of toxic contaminants in ground water, to provide the source term for predicting the later transport of these contaminants to the environment. Mass-transfer analysis is being used to predict rates of dissolution and release of radioactive constituents in future repositories for high-level radioactive waste, and it has been applied to predict the life of a copper container for high-level radioactive waste. Mechanistic analysis of mass-transfer is based on well-established theory of diffusive-convective transport. Its application requires experimental measurement of well-defined parameters such as porosity, solubility, diffusion coefficient, and pore velocity. Our first analysis assumed a waste solid in direct contact with porous rock. Subsequently we analyzed the more realistic situations of backfill between the waste and rock, rock with discrete fractures as well as pores, and the effects of waste constituents of high solubility. Those dealing with specifically with mass transfer in the near field are presented here. In order to have a consistent set of notation within this review, some of the notation here is different than in the reports cited. 71 refs., 47 figs., 7 tabs

Release rates from waste packages in a salt repository

In this report we present estimates of radionuclide release rates from waste packages into salt. This conservative and bounding analysis shows that release rates from waste packages in salt are well below the US Nuclear Regulatory Commission's performance objectives for the engineered barrier system. 2 refs., 2 figs