The authors proposed a work flow for selecting a waste management technology [2] (as shown in Fig. 28.1). Establishment of the development criteria for each tech­nology is a fundamental issue and the first step of the development.

For treatment technology, it is important to have a simple system that can be applied to a variety of wastes, and which has a volume reduction factor and is economical. In addition, the system must minimize secondary waste and address the difficulty of residual research and development (R&D) to commercialize the technol­ogy. Regarding the stability of waste forms produced by any treatment technology, a low leaching rate is required, especially for waste containing long-lived radionuclides over a certain amount. Easy identification and measurement of the radionuclides in the waste by the treatment process would also be considered an advantage.

Storage technology has many options that are either in operation or under R&D in different countries. The storage cost is an important index to use when selecting an option. If a waste generates a large quantity of heat as a result of containing a large amount of beta — and gamma-emitting nuclides such as Cs-137, the waste storage period should be considered before final disposal to reduce heat generation. If the waste has greater heat generation in disposal, the waste emplacement area must be increased to reduce the temperature of the surrounding engineered barriers or rock to less than the allowable temperature. As a consequence, disposal cost will increase. The storage period and disposal cost have a strong mutual relationship. If the storage period must be increased by more than a few hundred years to reduce heat generation for disposal, certain radionuclides such as Cs-137, whose half-life is less than several decades, would have undergone significant decay by time of disposal, which also raises the possibility of lowering the waste classification level for disposal.

Fig. 28.1 Flow chart for selection of waste management technology [2]

Disposal technology also has many options that are either in operation or under R&D in different countries. The disposal cost depends on the design of the disposal facility, the composition of the engineered barriers, and the depth of the disposal facility, which are strongly dependent on the characteristics of the radionuclides in the waste.

Table 28.2 Items for the management database of treatment technology options I. D. No.

Name of technology Description of technology Applicability to various wastes Process flow diagram Description of process flow diagram

Treatment conditions, including temperature, pressure, conditions, material balance, radionuclide balance, and decontamination factor (DF)

Chemical reagents and utilities Volume reduction ratio of waste

Characteristics of waste form, including configuration, uniaxial compression strength, vacant volume ratio, apparent density, leaching rate of radionuclides, and leaching rate of chemical components Content and status of NaCl

Status of technology; commercialization, development, fundamental research Technical issues (R&D for commercialization)

Standards to be applied References

Technology options for treatment, storage, transportation, and disposal have been proposed by domestic and international organizations. These options should be integrated and managed in a database of technology options. R&D results should also be added in the database as soon as possible. To manage the technology options, a database should be prepared and used to share information among the related organizations. The authors proposed a set of items to be managed in the database of treatment technology options (Table 28.2).

When an appropriate technology is being selected from several options, it is important to evaluate each technology option and compare them. At the end, it is also important to evaluate the combination of technologies from treatment to disposal to make the final selection of an appropriate set of these technologies and to establish a total system for specific wastes. The authors propose a set of indexes for evaluation of the combination of waste management technologies (Table 28.3). Evaluation of the total system should include the long-term safety of disposal because this is the most important issue and goal of waste management.