Boundaries between waste

It is highly desirable that a waste classification system be expressed in quantitative terms. More specifically, the intrinsic waste characteristics that define the boundaries between waste classes should be stated numerically. Qualitative definitions of waste classes, such as the definition of high-level radioactive waste discussed in Section 4.1.2.3.1, simply defer the issue of waste classification to a subsequent definition of the qualitative terms or to case-by-case determinations that typically occur after waste is generated. 

It is not NCRP s intent to recommend specific boundaries between waste classes. Rather, the examples illustrate that the recommended framework has the potential to be practical and to result in an implementable waste classification system when a variety of plausible assumptions are used. Many assumptions are made in developing the examples. NCRP endorsement or disapproval should not be construed from the use or absence of specific assumptions about exposure scenarios and allowable doses or risks. It is the responsibility of the appropriate regulatory authorities to develop and guide implementation of any waste classification system. 

The concept of a hypothetical inadvertent intruder at a nearsurface waste disposal site, including permanent occupants of a site after an assumed loss of institutional control, provides a suitable basis for defining exposure scenarios that would be used to calculate risks that arise from waste disposal and the boundaries between waste classes. For other dispositions of waste, alternative scenarios would need to be developed and evaluated. 

Numerous formal waste classification systems, or, equivalently, boundaries between classes of waste and rules for using them, have been developed over the years (see Section 4 for an extensive discussion). The bases for the boundaries also are numerous, with the following being the most common ... 

For the purpose of illustrating how the composite risk index in Equation 6.6 would be used to classify a hypothetical waste, it is helpful to simplify Equations 6.4 and 6.5. This is done by assuming that the summation over all responses (index r) has been calculated, that only one waste classification boundary represented by the index j is being considered (i.e., the boundary between exempt and low-hazard waste, based on a negligible risk, or the boundary between low-hazard and high-hazard waste, based on an acceptable risk), and that the modifying factor (F) is unity. Further, the calculated dose in the numerator of the risk index is denoted by D and the allowable dose in the denominator is denoted by L. Then, the composite risk index for all hazardous substances in the waste, expressed in the form of Equation 6.6, can be written as ... 

The boundaries between different waste classes would be quantified in terms of limits on concentrations of hazardous substances using a quantity called the risk index, which is defined in Equation 6.1. The risk index essentially is the ratio of a calculated risk that arises from waste disposal to an allowable risk (a negligible or acceptable risk) appropriate to the waste class (disposal system) of concern. The risk index is developed taking into account the two types of hazardous substances of concern substances that cause stochastic responses and have a linear, nonthreshold dose-response relationship, and substances that cause deterministic responses and have a threshold dose-response relationship. The risk index for any substance can be expressed directly in terms of risk, but it is more convenient to use dose instead, especially in the case of substances that cause determinstic responses for which risk is a nonlinear function of dose and the risk at any dose below a nominal threshold is presumed to be zero. The risk index for mixtures of substances that cause stochastic or deterministic responses are given in Equations 6.4 and 6.5, respectively, and the simple rule for combining the two to obtain a composite risk index for all hazardous substances in waste is given in Equation 6.6 or 6.7 and illustrated in Equation 6.8. The risk (dose) that arises from waste disposal in the numerator of the risk index is calculated based on assumed scenarios for exposure of hypothetical... 

The analysis for chemicals that induce deterministic effects presented in Section 7.1.7.4 and summarized in Table 7.8 indicates that lead is the most important such constituent. Furthermore, the risk index for lead of about 0.7 is only marginally below the value of unity used to define the boundary between low-hazard and high-hazard waste. Therefore, the assumption that an acceptable dose of... 

Important properties of a boundary between inside and outside can be identified in terran cells. Most importantly, the permeability of the boundary must be low enough to prevent loss of valuable metabolites, but high enough to allow the import of nutrients and the export of waste. In terran extant life, the permeability of cell boundaries is low, and transport processes are carried out by proteins embedded in the boundary. The boundary must be fluid rather than solid, to facilitate both transport and incorporation of new components during enlargement prior to cell division. Furthermore, a fluid boundary allows cells to engulf objects in their environments. This ability is important for predation in terran life. 

If sand is moist, the slope of a sand pile can be higher. A sand castle can have vertical walls when it is built of moist sand in the morning, but as the afternoon wears on and the sand dries out, it cmmbles and collapses (mass wastes) until a stable slope forms. This is because the water makes the sand more cohesive. With the proper moisture content, there will be both water and air between most of the grains of sand. The boundary between the water and the air has surface tension— the same surface tension that supports water striders or pulls liquids up a capillary tube. In moist sand, surface tension holds the grains together like a weak cement. 

Oxides, especially those of silicon, aluminum, and iron, are abundant components of the earth s crust they participate in geochemical reactions and in many chemical processes in natural waters, and often occur as colloids in water and waste treatment systems. The properties of the phase boundary between a hydrous oxide surface and an electrolyte solution depend on the forces operating on ions and water molecules by the solid surface and on those of the electrolyte upon the solid surface. The presence of an electric charge on the surface of particles often is essential for their existence as colloids the electric double layer on their surface hinders the attachment of colloidal particles to each other, to other surfaces, and to filter grains. 

Transporter regulations apply only to the off-site transport of hazardous waste. They do not apply to the on-site transportation of hazardous waste within a facility s property or boundary. On-site refers to geographically contiguous properties, even if the properties are separated by a public road. Consequently, a facility may ship wastes between two properties without becoming subject to the hazardous waste transporter regulations, provided that the properties are contiguous. 

Second, generic and site-specific assessments of near-surface disposal facilities for radioactive waste have shown that allowable doses to hypothetical inadvertent intruders usually are more restrictive in determining acceptable disposals than allowable doses to individuals beyond the boundary of the disposal site. This conclusion is based on predictions that concentrations of radionuclides in the environment (e.g., ground-water) at locations beyond the site boundary usually should be far less than the concentrations at the disposal site to which an inadvertent intruder could be exposed, owing to such factors as the limited solubility of some radionuclides, the partitioning of radionuclides between liquid and solid phases, and the dilution in transport of radionuclides in water or air beyond the site boundary. More people are likely to be exposed beyond the site boundary than on the disposal site, but acceptable disposals of radioactive waste in near-surface facilities have been based on assessments of dose to individuals, rather than populations. 

By definition the first requirement of any cell, natural or artificial, is to be compartmentalized. Once a closed system has been created it is possible to develop, or evolve, mechanisms that control the concentrations of essential nutrients and waste materials within that system. This will inevitably involve a route for chemical species of different sizes and properties to move between the cell s interior and its external surroundings. There are several candidates for the cell boundary material. 

Cut strategy I allows a waste fraction between the product fractions, which can be either discarded or processed further (e.g. by recycling the waste fraction or by application of other separation steps, such as crystallization, to purify it). Due to the introduction of a waste fraction the optimization problem gains additional degrees of freedom, i.e. times for the beginning and the end of waste collection. These additional degrees of freedom, however, will not increase the complexity of the optimization, because they are pinpointed automatically by the purity demand, which serves as a boundary condition for the optimization problem. 

It will be thus necessary to introduce a hierarchical approach. Lapkin et al. [65] have proposed four vertical hierarchy levels (i) product and process, (ii) company, (iii) infrastructure and (iv) society. Each level should reflect different boundary limits and use an appropriate choice of indicators. It is proposed also that the choice of appropriate indicators depends on the speciflcs of the industry sector and even on the types of products. The indicators should reflect speciflc by-products, wastes and emissions that are characteristic of the process or the product. Of course, alimit of the approach is how to make uniform the comparison between diflferent industrial sectors. On the other hand, we have already remarked that industrial chemical production is different from other manufacture industrial sectors, because (i) it includes very different types of productions, from several thousand tons per day in refinery to kg amounts per day in fine chemical production and (ii) it is characterized by a highly integrated structure in which a large part of the products are the input for other chemical processes. 

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