P. METCALF, Consultant, formerly with the International Atomic Energy Agency (IAEA), Austria, now with BBM Consulting e. U., Austria and B. BATANDJIEVA, Consultant, formerly with the International Atomic Energy Agency (IAEA), Austria

DOI: 10.1533/9780857097446.1.73

Abstract: This chapter presents the key factors and current status of the development of international safety standards and recommendations on safe remediation and radioactive waste management. It highlights the international legally binding instruments, safety fundamentals, safety requirements and guides, with specific emphasis on pre-disposal and disposal of radioactive waste, as well as transport.

Key words: safety, standards, pre-disposal, disposal, radioactive waste, transport, remediation.

3.1 Introduction

This section is a general introduction to RAW management planning and implementation. The objective is to provide a basic orientation with inputs as to what should be considered during waste processing planning and selection of the proper waste processing technological sequences. More detailed technical and technological information can be found in other chapters of this book, dedicated to waste processing technologies.

2.2 References

1. IAEA Radioactive Waste Management Status and Trends — periodical overview of international status and trends in radioactive waste management, IAEA/ WMDB/ST/, IAEA, Vienna, available at http://newmdb. iaea. org/

2. IAEA (1994) Classification of Radioactive Waste, Safety Series No. 111-G-1.1, IAEA, Vienna.

3. IAEA (2009) Classification of Radioactive Waste: General Safety Guide GSC-1, IAEA, Vienna.

4. IAEA (2004) Application of the Concepts of Exclusion, Exemption and Clear­ance, IAEA Safety Standard Series No. RS-G-1.7, IAEA, Vienna.

5. COMMISSION OF THE EUROPEAN COMMUNITIES (1993) Principles and Methods for Establishing Concentrations and Quantities (Exemption Values) below which Reporting is not Required, European Directive, RP-65, CEC, Luxembourg.

6. IAEA (2005) Categorisation of Radioactive Sources, IAEA Safety Standard Series No. RS-G-1.9 , IAEA, Vienna.

7. IAEA (2002) Management of Radioactive Waste from the Mining and Milling the Ores, IAEA Safety Standard Series No. WS. G.1.2, IAEA, Vienna.

8. A. Aloy, S. Amoravain, R. Burcl et al. (2007) Strategy and Methodology for Radioactive Waste Characterization, IAEA-TECDOC-1537, IAEA, Vienna.

9. IAEA (2005) Methods for Maintaining a Record ofWaste Packages during Waste Processing and Storage, IAEA Technical Report Series No. 434, IAEA, Vienna.

10. IAEA (2003) Radioactive Waste Management Glossary, 2003 Edition, IAEA, Vienna.

11. P Brennecke, R. Burcl, P Carter et al. (2006) Development of Specifications for Radioactive Waste Packages, IAEA-TECDOC-1515, IAEA, Vienna.

12. M. I. Ojovan (ed.) (2011) Handbook of Advanced Radioactive Waste Condition­ing Technologies, Woodhead Publishing Series in Energy: Number 12 , Wood — head, Cambridge.

3

There are two principal steps in RAW processing: treatment and condition­ing. The main role of treatment is to change the characteristics of the waste or to reduce the volume to make waste suitable for final processing by conditioning. The main role of conditioning is to incorporate or encapsulate the waste into the waste matrix, and/or package the waste in a container, where the container functions as an efficient and safe barrier for isolation of the waste from the environment. The distinction between treatment and conditioning is sometimes not clear — depending on the national waste management policy and approach, some kinds of treated waste can be considered as suitable for disposal and in other cases can be considered as needing further processing. This decision also depends, of course, on whether an ultimate disposal option is available or expected. More safe, advanced and sophisticated disposal options can potentially lower the requirements for the conditioning procedure, for example if deep geological disposal of low and intermediate level waste is considered, packaging of the waste into special containers can be acceptable instead of solidification into an encap­sulation matrix.

In some cases pre-treatment of RAW is applied to modify ‘as generated’ waste into the form suitable for further treatment. A typical example is adjustment of the chemical properties (e. g., adjustment of acidity, or destruc­tion of organic compounds in the waste) of liquid waste. Segregation of solid waste is also often considered as pre-treatment procedure.

In addition to the above-mentioned classification of RAW based on its properties, technologists often use their own ‘technological classification’ of the waste. It is based on waste stream characteristics in combination with available technologies for their processing. Sometimes, a technological clas­sification allows ‘as generated’ waste streams to be merged according to typical waste characteristics and this provides for more efficient processing. A technological classification of waste is very individual, specific almost for each type of nuclear facility. However, any technological classification should obey the basic rule — to be consonant with waste package specifica­tions and WAC.

Considering the types, properties and volume of generated waste and taking into account the available waste processing technologies, waste processing organizations should prepare complex waste management plans to assure management that all kinds of waste and all waste streams are handled in a safe and sound manner with one goal — to produce waste pack­ages acceptable for ultimate disposal or long-term storage, i. e. compliant with WAC for disposal or long-term storage.

The main decision-making parameters in waste processing technology selection are activity concentration and aggregate state. With regard to aggregate state, two principal categories of RAW are generated at nuclear facilities: liquid waste and solid waste. While the composition (chemical and radiochemical) and properties of liquid waste depends more on the type of reactor, the composition and properties of solid wastes do not depend sub­stantially on the reactor type. Both primary waste streams are pre-treated and treated directly at the generator’s site and the volume of treated liquid waste is usually lower than the volume of solid waste. Another, smaller volume, waste category is spent ion exchange resins and other filtration materials, sometimes admixed with radioactive sludge and/or sediments from liquid waste storage tanks. These resin, filtration materials and sludge/ sediments are much more difficult to process. However, they are sometimes considered in the liquid waste category because of the high content of water and slurry. In some countries they are declared as a separate ‘wet waste’ category.

The principal scheme of aqueous liquid radioactive waste management is presented in Fig. 2.1, taken from Ref. [12]. Various types of aqueous liquid RAW are generated at various nuclear facilities. However, the processes by which they are managed is very uniform. Low and intermediate level waste streams are processed in three basic steps:

1. Pre-treatment (if necessary) is applied to adjust the waste properties according to its expected treatment and conditioning. In practice, adjust­ment of acidity is most commonly used.

2. Treatment is applied to reduce the volume of ‘as generated’ waste for further conditioning. There are two principal approaches: more com­monly concentration of primary waste usually by evaporation and less commonly separation of radionuclide contamination either by ion exchange or advanced ultrafiltration techniques. In the first case, the treatment results in a relatively small volume of waste concentrate with high salinity. In the second case, radionuclides are concentrated in a special ion exchange column or in the filtration material. In both cases, liquid concentrate, or spent filtration materials and filters are further addressed for final conditioning. Bulk condensate from evaporation or filtrate from ion exchange or filtration procedure can be, after proper control, reused or even cleared for discharge.

3.

Conditioning of liquid waste concentrates is the process of their incor­poration into a selected matrix. The resulting waste form is loaded into a proper container. Cement and bitumen are commonly used matrices; polymer, geopolymer and some other matrices are less frequently encountered. Recently, also cold crucible vitrification has been consid­ered for concentrate conditioning, resulting in an excellent waste form. Selection of the container usually depends on the waste form properties, the national waste management policy, the selected disposal option and the waste acceptance requirements.

The principal scheme of solid RAW management is presented in Fig. 2.2, taken from Ref. [12]. The composition and properties of ‘as generated’ solid radioactive waste are substantially more variable than liquid waste. There­fore also the technologies used for processing solid waste are more variable and should be tailored according to the individual requirements and expec­tations of the waste generator. Similar to liquid waste, low and intermediate level solid waste streams are processed in three basic steps:

1. Pre-treatment comprises mostly sorting and segregation of the waste according to waste characteristics and the expected processing

technologies. An extremely important feature of the pre-treatment step is a chance to segregate non-active waste from the bulk waste and con­tribute in this way to the minimization of waste generation. The poten­tial for reduction of solid waste generation is considerably higher than that of liquid waste. Given the present state of technology, the best results in volume minimization can be achieved with a combination of thermal treatment (pyrolysis) and compaction technology. Therefore, the most common approach is to segregate the waste into combustible and non-combustible categories and the non-combustible category is further segregated into compactable and non-compactable waste. Metal­lic waste represents a special category of solid waste and its processing is a separate issue. Decontamination is often used as a pre-treatment or treatment procedure in this case.

2. Treatment steps are applied to reduce the waste volume. Combustible waste can be thermally treated by pyrolysis with follow-up conditioning of ash by incorporation into a matrix or by supercompaction. In some countries there are objections to the application of the high temperature thermal treatment resulting in generation of exhaust gases. In this case, compaction or medium temperature thermal destruction in the absence
of air (steam reforming) are the only applicable options for volume reduction of solid waste. However, steam reforming is still not com­monly used in RAW management. There are two principal options for compaction of the radioactive waste: low pressure in drum compaction and, more favourable for operational waste, high pressure compaction (supercompaction), when the whole drum filled with waste is com­pacted. Pellets are obtained in this conditioning step and can be placed into a container and/or encapsulated in a proper matrix.

3. Conditioning of solid waste is in principle immobilization of treated waste into a proper matrix, most commonly cement grout. Ash from a high temperature thermal treatment facility is either directly cemented in a container, or first compacted and the pellets from the compactor are encapsulated (grout or another matrix) into a proper container. Non-compactable waste is adjusted and sorted by size and usually encapsulated (e. g., grouted) in a proper container. In some cases, non — compactable waste is packed into drums and the filled drums are then loaded into special containers (e. g., reinforced concrete containers) and the void space is filled with cement grout. In all the above-mentioned cases, cement grout can be prepared with liquid radioactive waste to provide better utilization of container space.

Each waste processing technology uses specific types of containers for accommodation of waste forms. The most common container worldwide is the standard 200 L metallic drum, made from various types of steel (in general carbon steel and/or stainless steel) with consideration of various corrosion protection measures. Waste packages made of 200 L drums are commonly accepted for final disposal. However, in some countries there is a requirement to place 200 L drums with conditioned waste into special reinforced concrete containers and fill the void space by cement grout or another appropriate filling material. Since reinforced concrete containers themselves provide a 300-year leak-tightness guarantee, such an approach can be considered as an important contribution to the long-term safety of waste disposal. This is of special importance in densely populated countries, where disposal facilities are located close to settled sites.

Spent ion exchange resins and sludge, sometimes generated during waste evaporation or formed as sediment at the bottom of storage tanks, are a special waste category, which usually causes some processing problems. Direct incorporation of the resins/sludges/sediments into most common cement matrices requires a special procedure and modifications of the cement matrix which sometimes leads to a waste form with insufficient mechanical and durability properties. There are some other options: appli­cation of another matrix, compatible with the organic structure of spent resins (e. g., polymers or geopolymers), high temperature pyrolysis, medium temperature destruction (steam reforming), etc. Another option is to pack spent resins and sludge into special high integrity containers and consider their long-term storage or disposal in underground repositories or deep geological formations.

As has been demonstrated in this section, the selection of the individual steps and technological sequences involved in RAW processing is a serious problem with many various aspects to be considered. Each waste stream requires an individual approach and an individual selection of the proper waste encapsulation matrix, waste form and waste container. In this chapter, therefore, only general considerations have been presented that should be taken into account in the waste management planning process.

The waste package as a final product of RAW processing, prepared and ready for long-term storage, or disposal, consists of two components: the waste form and the waste container. In some cases there are also additional barriers or shielding used to increase the safety features of the waste package. The waste package should be prepared in a form corresponding to the requirements for handling, transport, storage and disposal.

A wasteform is defined as ‘radioactive waste after treatment and condi­tioning, usually in solid form, prior to its packaging into the waste con­tainer’. A waste container is defined as ‘the vessel into which the waste form is placed for future handling, storage and disposal’. The waste container fulfils the role of a protective barrier and shielding tool. The waste container should guarantee the tightness for the entire period of storage and/or dis­posal of the waste.

To ensure the long-term safety of waste disposal, WAC should be devel­oped based on a safety assessment of the considered disposal options and should be approved by the relevant authorities. Waste acceptance require­ments (criteria) are by definition quantitative or qualitative criteria for processed RAW to be accepted by an operator of a repository for disposal, or by an operator of a storage facility for storage. WAC are specified by the relevant authorities, or proposed by an operator and approved by the rel­evant authorities. Waste acceptance requirements might include, for example, restrictions on the activity concentration, or the total activity of particular radionuclides (or types of radionuclide) in the waste, or require­ments concerning the waste form or waste package [10]. In the past, the term waste acceptance criteria was only applied and used in the context of waste disposal. Later on, the approach to specify WAC has been extended also to some other steps of the waste life cycle — in particular, for transport and storage. In general, WAC can be specified for any foreseen waste man­agement operation and handling. WAC can prescribe and cover various waste package features and properties, such as: [2]

• requirements for waste container (e. g., design features, mechanical sta­bility, thermal resistance and also some additional features — shielding, corrosion protection, etc.);

• limitations for activity — permissible activities of individual radionu­clides, total activity, activity of selected critical radionuclides;

• radiological safety parameters — surface dose rates, surface contamination.

There are usually several other requirements, developed and specified based on the safety assessment of risks of the planned operations (trans­port, storage, disposal, etc.) with prepared waste packages. A more detailed description of this subject can be found in Chapter 3.

WAC are site-specific, but not container-specific. They are developed based on a safety assessment of the design and implementation of the waste disposal or waste storage facility and eventually waste transport tools. WAC are general criteria, usually not specified for particular waste containers and/or waste packages. Therefore they are not simply applicable in every­day technological practice.

To overcome the above limitations of WAC, the general waste acceptance requirements are usually transformed into detailed waste package specifica­tions (WPS). WPS should be developed and individually implemented for each type of RAW package and should reflect specific characteristics of the waste package. WPS are therefore waste package (and also waste con­tainer) specific and they are normally substantially more detailed than WAC. They shall be a consistent part of the QA/QC system applied by the waste package producer. Application of WPS allows simple control and verification of waste packages for both the waste producer as well as the waste disposal facility operator. Compliance of waste packages with WPS is considered a guarantee of compliance of said waste package with the WAC for a particular waste lifetime step. More details and guideline for development of WPS can be found in Ref. [11].

Waste acceptance criteria for disposal can normally be developed based on the safety assessment of an available, already constructed, or intended waste disposal facility. In any case, a clear idea of the waste disposal option should be available. However, many countries are in the situation where processing of RAW is unavoidable and the decision regarding a disposal facility is still deferred. In such cases, there are two principal options on how to proceed with waste processing to avoid future complications with acceptance of waste packages at the disposal site:

• Develop and apply generic WAC, based on international experience, approaches, and analogy with similar nuclear programmes. In this manner, a sufficiently conservative approach shall be taken and it shall be demonstrated that a national waste management policy and vision of future disposal options had been considered. These criteria can then be used for development of waste package specifications for available waste management technologies and waste packages already in use.

• Develop and apply only waste package specifications for particular waste streams and waste processing technologies, based on a detailed analysis of potential disposal options. A sufficiently conservative approach and margins in critical parameters shall be applied to avoid future problems with acceptance of waste packages for disposal.

The main objective of RAW processing is to avoid any potential negative impact of the processed RAW on the population and environment for a sufficiently long time, necessary for the decay of the major fraction of radio­nuclides contained in the waste. This target is normally achieved by:

• selection and application of proper waste processing technology, assur­ing production of waste packages, corresponding to WAC;

• implementation of safe and proven long-term storage or disposal of waste packages, providing for high safety and reliability.

It is clear that long-term storage and/or permanent disposal are key issues. There is a lot of flexibility in selection and implementation of waste processing technologies; however, there is almost no chance to modify a waste package once it is already made: the waste package can either be accepted for storage and/or disposal or not. And ‘not’ in this context always means many problems, which are sometimes very dif­ficult to solve.

Therefore any consideration of waste handling and processing activities should start with the end product — from detailed analyses and evaluation of available disposal conditions and requirements. The waste manager, the planned waste processing steps, should always consider the ‘end-point’ of the waste life cycle — disposal — and propose an integrated sequence of linked steps, following waste management policy, aimed at the production of waste packages compliant with WAC. Properly designed sequences of waste processing steps should provide for a systematic step-by-step increase of safety features related to the processed waste and, at the same time, minimization of waste volume. All parties involved in the waste manage­ment shall assume responsibilities to assure that only acceptable risks are taken.

Such a logical and preferably optimized strategy, which includes a complex set of technical and administrative measures, must be used in the planning and implementation of a RAW management programme as a whole from waste generation to disposal. The strategy must be such that the interactions between the various stages are taken into account so that decisions made at one stage do not preclude certain alternatives at a subsequent stage: this is usually called the ‘integrated approach’ to RAW management [10].

The final objective of waste processing is to transform ‘as generated’ waste to the form suitable for final disposal, providing for high safety and avoiding any significant burden to the environment and population. Several tech­nologies have been developed and implemented to process various types of waste and waste streams. All of them are generally aimed at reducing the original waste volume and providing sufficiently stable and durable waste forms, suitable for long-term storage and ultimate disposal.

Basically two approaches can be applied for the reduction of ‘as gener­ated’ waste volumes:

1. Removal (concentration) of radionuclide contamination from the waste and processing of the small volume of concentrate as higher (intermedi­ate) level radioactive waste. After removal of radioactive material from the waste, the bulk of the original waste volume can be managed as non-radioactive (cleared from regulatory control) or very low radioac­tive material at common conventional landfills, or discharged to water reservoirs (sea, river). Significant reduction of liquid waste volume can be achieved in this way. However, some complications should be expected in relation to handling and further processing of the waste concentrate as intermediate level waste.

2. Reduction of volume of ‘as generated’ waste (e. g., by evaporation of liquid waste or thermal treatment/pyrolysis of solid waste) for further conditioning into a waste form suitable for disposal. The waste matrix in this case represents the bulk of the processed waste volume and, therefore, more space is required in the storage or disposal facility.

Selection of a waste processing route and a decision on its implementation is a complicated process, where technical, economic, safety and other aspects as well as level of industrial development, size of nuclear industry, availabil­ity and type of waste disposal options available in a country should be considered and evaluated. Typical examples of different approaches to waste storage and disposal, leading to different waste processing approaches are, on one hand, the Netherlands, where controlled long-term (100 years) storage of processed waste in special surface storage facility is implemented, while, on the other hand, Germany, where deep geological disposal is the only considered option for all kinds of waste. This latter approach could benefit from higher flexibility in selection of waste processing tech­nologies. And the third, classic example is the case of several European countries, operating near-surface repositories for disposal of processed low and intermediate level waste, where strict WAC requirements must be obeyed.

During its processing, radioactive waste is converted from an ‘as generated’ state to a processed waste form and placed in a container to form a final waste package for storage and disposal. A principal condition for accept­ance of waste packages for disposal is full compliance with the disposal site WAC, in other words, to demonstrate that chemical, radiochemical, biologi­cal, mechanical and other parameters of the waste form are in accordance with the required values. The waste parameters can change during handling and processing, and to ensure compliance of a waste package with a WAC, a system for generating and maintaining records should be established in order to save and track all relevant information. It is worth registering not only the waste parameters but also the technological parameters of the processing facilities. A record-keeping system should define the data, which should be collected and stored at each step of the waste life cycle and for each waste stream. A reliable selection system should be imple­mented not only to avoid collecting too much information, but, also to assure the long-term availability of all significant and potentially needed data. Record-keeping systems for the pre-disposal period of the waste life cycle should ideally be coordinated and interconnected with the record­keeping system for the disposal facility. However, a reasonable data reduc­tion approach should be applied for transfer of the information. More detailed information for the identification of requirements and establish­ment of record-keeping systems can be found in Ref. [9].

Knowledge of physical parameters of solid ‘as generated’ RAW is impor­tant for some processing technologies, like compaction and pyrolysis. The requirement for the content and level of information should come from the facility operator and a methodology to determine the parameters shall be tailored accordingly.

Information on the physical and mechanical parameters of processed waste is substantially more important. Demonstration of key mechanical parameters of a waste form and the entire waste package is usually required by the WAC. This requirement comes from the projected long-term durabil­ity of the waste form (in particular for solidified liquid waste) and also from the design and arrangement of waste packages in the disposal facility, where placement of waste packages in several layers is commonly used. The last requirement is usually solved by use of verified and approved waste con­tainers, providing for sufficient mechanical stability for the entire waste package. Mechanical parameters of the waste form are controlled in the waste producer facility using samples taken during waste processing — the scope of control and methodologies should be developed according to the requirements of the WAC and the expectations/requirements of the disposal site operator.

Waste acceptance criteria (WAC) for disposal, a principal requirement for qualification of a produced waste package, are established predominantly on the radiological parameters of waste packages. Radiological parameter control is, therefore, considered to be the main component of a RAW control system. The WAC are country-specific; however, the IAEA recom­mendations for the establishment of WAC are accepted as the basis world­wide. Besides surface dose rates, maximum permitted activity concentrations (or total activity per entire waste package) of several radionuclides is usually defined in a WAC. The list of considered radionuclides is different for each country’s WAC for disposal. Besides common and simple measur­able radionuclides (such as Cs-134, Cs-137, Sr-90, etc.), a declaration of the activity concentration of 10-40 so-called critical radionuclides for disposal (alpha emitters, biologically important radionuclides, long-lived radio­nuclides usually with half-life over 30 years, etc.), is also required in a WAC. These radionuclides are often difficult to measure. To facilitate declaration of waste package compliance with a WAC, non-destructive (mainly gamma spectrometry) as well as destructive radiochemical procedures (with radio­chemical processing of the samples) are routinely applied.

Radiological control is applied in the entire life cycle of RAW. However, analogous to chemical parameters, the main effort is put on the radiological control of ‘as generated’ (raw) waste and then on the declaration of RAW package compliance with a WAC. For radiological control of ‘as generated’ waste, carefully selected combinations of non-destructive instrumental methods and radiochemical analysis with separation and subsequent deter­mination of difficult to measure radionuclides (some fission products, transuranium elements, etc.) are applied. The information obtained is widely used in waste processing planning for each waste stream and in the estima­tion (prognosis) of final waste package parameters. Results of radiochemi­cal analysis of input waste are also used for determination of radionuclide vectors, necessary for application of scaling factor methods (see below).

Most often a non-destructive check of the entire waste package is used for a declaration of final waste package compliance with a WAC. Gamma scanning, gamma tomography and in some cases also neutron tomography, all in combination with advanced data processing, are commonly used by both waste package producer as well as by disposal facility operator. The above-mentioned techniques allow determination of the major gamma — emitting radionuclides and along with using neutron tomography deter­mines the major actinides and fissile material. In general, non-destructive determination of minor radionuclides, critical for disposal, is very compli­cated, expensive, and in some cases even impossible. Destructive determina­tion with sampling of the waste form and waste package material and subsequent laboratory radiochemical analysis is not only technically com­plicated but can cause unacceptable damage to one or more of the waste isolation barriers in the waste package. The situation is more substantial for processed liquid waste, where critical disposal radionuclides can be expected with higher probability. The way around this situation is the application of scaling factors and a nuclide vector methodology [8]. The substance of this method is simple; however, implementation is more complicated and requires special software tools. Careful and precise radiochemical analysis of homogenized waste before the start of its processing is used to establish the nuclide vectors — a mathematical relationship between the activity con­centration of major or easy-to-determine radionuclides (usually strong gamma emitters) and the activity concentrations of minor (usually difficult — to-determine) radionuclides is developed. Using nuclide vectors and thor­ough knowledge of the waste processing procedure and waste package materials, it is possible to calculate and declare activity concentrations of minor radionuclides in a waste package using measured data on the activity of the major radionuclides, obtained by non-destructive gamma scanning of the entire waste package. Such a procedure should be, of course, qualified and approved by the regulator and disposal facility operator.

Chemical parameter control is applied mostly in liquid waste streams and at the beginning of the waste life cycle. Operational control of selected technological equipment can also be incorporated in the control plan. Con­trolled parameters for each waste stream shall be carefully selected and optimized. The control plan shall be established to reflect the requirements of the technological equipment operator and to assure the quality of the final product and its compliance with the requirements for waste disposal (WAC). Information on chemical composition, acidity, salinity and other chemical and physical-chemical parameters is used in RAW process tech­nology planning, and the ‘as generated’ waste parameters can be adjusted to suit the process technology. Another objective is to manage different waste streams to optimize process conditions for available processing tech­nologies with the aim of achieving the best possible utilization of disposal facility space (‘filling’ the container) and at the same time assuring compli­ance with the WAC.

A declaration of selected biological parameters might also be required by the WAC; therefore their control shall be performed on selected waste streams (in particular in waste streams containing organic material), usually in parallel with control of chemical parameters.

Waste matrix parameters and final waste form quality control (qualifica­tion tests: chemical durability, leaching properties, long-term performance in disposal site conditions, etc.) are also a significant part of a laboratory chemical control system.