[en] This is the first of three articles on the development of standards for geologic disposal of radioactive waste presented in this issue of Radioactive Waste Management and Environmental Restoration. Knowledge of how entire disposal systems will function is needed before they can be regulated effectively. This article describes the operation of terrestrial and subseabed geologic repositories, and presents an evaluation procedure that can be used to supply information needed to develop standards and regulations, evaluate repository concepts, and compute design requirements of specific repository systems. The attenuation factor method of evaluation was developed based on spatial and temporal dispersion, retardation, and dilution processes. This method computes the reduction of risk potential made by each component of the system. Mathematical models for deterministic and probabilistic analyses along with several examples are given. Uses and limitations of the method are discussed. Although the attenuation factor method was developed for the disposal of radioactive waste, it can be adapted to the disposal of nonradioactive hazardous wastes. The second article presents the functional requirements of geologic repositories, defines the functions and hierarchy of repository standards, and suggests procedures for developing the standards. The third article develops original standards for nuclear waste disposal processes not covered by the existing regulations, such as subseabed disposal, and evaluates proposed alternatives to modify the existing nuclear waste disposal standards for terrestrial repositories. (author) 7 figs., 2 tabs., 19 refs

[en] The role of microorganisms in transformation and absorption of metals in the environment is examined in this article. Understanding the metabolic processes by which microorganisms interact with toxic metals is paramount for any bioremediation process dealing with restoration of toxic waste site. Bacteria, fungi, and yeast that displayed resistance to lead, mercury, or chromium were isolated from the environment. Cotolerance studies revealed that many of these organisms could grow in high concentrations of several different toxic elements. Transformation of chromium, mercury, and lead was displayed by means of the isolated bacterial strains. Data regarding the activities of these organisms can provide a basis for use of metal/tolerant organisms in bioremediation of toxic wastes containing mercury, chromium, and lead. (author) 1 fig., 7 tabs., 28 refs

[en] This article focuses on developing a robot control system capable of meeting hazardous waste handling application requirements, and presents as a solution an adaptive strategy for controlling the mechanical impedance of kinematically redundant manipulators. The proposed controller is capable of accurate end-effector impedance control and effective redundancy utilization, does not require knowledge of the complex robot dynamic model or parameter values for the robot or the environment, and is implemented without calculation of the robot inverse transformation. Computer simulation results are given for a four degree of freedom redundant robot under adaptive impedance control. These results indicate that the proposed controller is capable of successfully performing important tasks in robotic waste handling applications. (author) 3 figs., 39 refs

[en] The cleanup of hazardous nuclear and chemical wastes is a major environmental problem. Some of the material is so toxic that handling it will require the use of remotely/controlled robots. Operators of the robots will be situated remotely from the waste and will need a user interface for controlling the robot within its environment. The remote robot will have a variety of sensors in addition to the usual video feedback. The three dimensional data from these multiple sensors must be displayable in an integrated way on the two dimensional user interface. This project has investigated the design of a user interface for tele/robotic systems. We have developed a number of three dimensional visualization tools for use with standard user interface toolkits. (author) 6 figs., 7 refs

[en] The objective of this research was to characterize biologically produced materials for the recovery of toxic heavy metals from contaminated groundwaters. Specifically, components of the cells of the organism Datura innoxia (angel's trumpet) were investigated. Several approaches to understanding the interactions involved in the binding process have been employed. These methods range from the phenomenological to the fundamental. Measurement of the binding capacity of cadmium ions onto both the free Datura innoxia cells and immobilized cells has been undertaken. Immobilization of the cell material was observed to result in a significant increase in the amount of cadmium ion bound to the material. A methodology which will provide both the binding coefficient and the binding capacity of the metal ion has been developed. This is based on adsorption isotherms. A methodology for the rapid characterization of the binding of a metal pollutant with minimal generation of waste has been investigated. This methodology utilizes peak-shape analysis of transient signals resulting from the introduction of a small volume (<0.50 mL) of the metal-containing solution. Using europium as a probe species, it has been fluorometrically determined that at least two separate types of active binding sites exist on the cell walls of Datura innoxia. Specifically, these binding sites have been determined to be sulfate functionalities (pH≤3) and single and dual carboxylate containing sites (pH≤4). (author) 4 figs., 1 tab., 4 refs

[en] Efforts are being made to devise technologies and treatment systems to remediate contaminated soil-on site without generating significant wastes for off-site disposal. Heap leaching, a technique used extensively in the mining industry, has been investigated as a method for remediation of hazardous chemical contamination of the vadose zone. In the mining industry, metal-bearing ore is excavated and mounded on a pad. The metals are removed by passing a special leaching solution through the ore. In this study, the removal of chromium(VI) from the New Mexico soils (sand, sandy loam, and clay) using heap leaching was evaluated at a column scale. The heap leaching study demonstrated greater than 99% removal of Cr(VI) from all three soils using tap water as the leaching agent. (author) 13 figs., 5 tabs., 21 refs

[en] ²³⁷Np Moessbauer-effect studies of glassified (3 wt%) Np, in a glass labeled as SON 68 18 17 L1C2A2T1 is reported. This glass was designed by the CEA-Marcoule (France) and is used in France for glassification of radioactive materials, especially fission products and actinides like Np, Pu and Am, for waste disposal. It is shown for the first time that the Lamb-Moessbauer factor (f) can give insight into the binding forces and the motional degrees of freedom of the bound actinide in a glass. We conclude that in the SON glass there exist two types of glassified Np. Both types show strong binding of the Np in the glass matrix. However, the first type (labeled as site 1 in the Moessbauer spectra) is much stronger bound to the glass matrix. (author) 2 figs., 1 tab., 9 refs

[en] At the present time, two different approaches are taken in defining acceptable near-surface disposals of uranium in low-level radioactive waste. For civilian waste, the waste classification system developed by the Nuclear Regulatory Commission (NRC) in 10 CFR Part 61 does not include limits on concentrations of uranium. Therefore, in principle, uranium in any concentrations is generally acceptable for near-surface disposal, provided the performance objective for protection of off-site members of the public is met. For defense waste, Order 5820.2A of the Department of Energy (DOE) includes dose limits for protection of inadvertent intruders, principally a limit on effective dose equivalent of 100 mrem per year for continuous exposures, rather than limits on concentrations of radionuclides as in the NRC's waste classification system. Since the DOE Order does not specify a time limit for protecting inadvertent intruders, the eventual buildup of uranium decay products could result in doses to inadvertent intruders in excess of 100 mrem per year for concentrations of uranium comparable to the average background concentration in surface soil of about 1 pCi/g. Therefore, near-surface disposal of uranium at DOE low-level waste disposal sites essentially could be precluded. As an alternative to the current NRC and DOE approaches, this paper discusses analyses which suggest a concentration limit for uranium of at least 0.2-2 nCi/g, depending on the isotopic composition, would provide reasonable protection of inadvertent intruders. However, such a concentration limit can be supported only with some or all of the following conditions: (1) protection of inadvertent intruders were required only for 10⁴ years after disposal; (2) doses to inadvertent intruders from exposure to radon were excluded: and (3) concentrations of uranium in disposal facilities were significantly reduced over long time periods by mobilization and transport into the environment. The first two conditions would require changes in current DOE regulatory policies. (author) 2 tabs., 21 refs

[en] Sorption of strontium on an amorphous ferrihydrite has been studied under a proceeding of its crystallization to goethite. Sorption fraction of strontium decreased from approximately 100% to 60% during the crystallization. A sequential extraction technique was applied to study a degree of binding of strontium on the amorphous ferrihydrite and the crystalline goethite. Its result suggested that most of strontium sorbed on the iron(III) compounds was reversible form, but some amount of strontium once sorbed on the amorphous ferrihydrite was transferred into an irreversible form on the crystalline goethite during the crystallization. The model calculation was carried out to study the redistribution behavior of strontium during the crystallization. From this calculation, it is likely that strontium sorbed on the amorphous ferrihydrite was trapped into the crystalline goethite when the amorphous ferrihydrite was once dissolved to be crystallized to goethite. (author) 9 figs., 3 tabs., 20 refs

[en] The problem of groundwater pollution by leaking underground storage tanks became evident in the 1970s. A recent U.S. Environmental Protection Agency (EPA) survey showed that 35% of the underground storage tanks in the U.S. leak or are not liquid tight. Benzene, toluene and xylenes are highly toxic and mobile compounds present in fossil fuels. These compounds can be easily removed by adsorption using chemically modified zeolites. Cationic exchange of natural zeolites with quaternary amines, for instance, greatly enhances the capacity of zeolites to remove some heavy elements and single/ring aromatic compounds, in particular benzene, toluene and xylenes (the BTX group). Removing hexavalent chromium by adsorption onto zeolites is significantly improved by the tailoring process. The considerable affinity of natural zeolites to remove lead is not altered by the tailoring process. (author) 8 figs., 1 tab., 26 refs