Methodology to assess waste management needs

The basic methodology for developing an assessment of waste management needs includes identifying current and arising waste streams, their properties, and processing methods and waste facilities infrastructure that might be needed. This methodology is applicable to both reactors and fuel cycle facilities. Figure 4 outlines the main steps in assessing waste management needs.

Consideration needs to be given to all steps of the system. Different activities in the nuclear fuel cycle will produce different types of waste, with different characteristics and requirements for further management, such as:

— Mining and milling wastes;

— Wastes from conversion, enrichment and fuel manufacturing;

— Operational wastes from NPPs;

— Spent fuel from NPPs;

— Process wastes from NPPs and from spent fuel reprocessing;

— Secondary wastes from other waste management activities (e.g. treatment of primary wastes or operation of waste management processes);

— Decommissioning waste.

All of these waste streams have to be considered in the overall assessment to develop a safe, technically sound and economical approach to waste management. In addition, a detailed plan is needed for each waste stream and for each facility in the nuclear energy system. Such a plan sets out how the waste is to be processed and managed, from generation to storage and long term disposal in a safe end state.

Enumerate assumptions and bounds for assessment

- define starting and ending points of the assessment - define constraints and limitations (e.g. waste classification

and categories)

Determine current inventories - establish existing waste inventory by source, classification category, type, location, etc.

- level of detail needs to be sufficient for purpose - establish planning scenarios (e.g. lifetime of future

operations)

- gather and collate raw data inputs from waste generators - level of details needs to be sufficient for purpose

Forecast future waste arisings

- select reference options for treating and managing the various waste streams (e.g. to determine volume reduction factors and final waste forms)

Determine appropriate waste management options

- based on forecast of future arisings and reference waste management options, calculate expected future waste inventory

Prepare forecast of resulting future waste inventories

- the future waste forecasts and the reference waste management options provide a basis for determining future waste management infrastructure needs (what needs to be built, by when and perhaps where)

Prepare plan of future waste management needs

FIG. 4. Basic methodology for assessing waste management needs.

The safe end state will vary according to the waste stream, and may include:

— Recycling and reuse of the material within a nuclear or non-nuclear facility (including a possible period of storage for decay of short lived radionuclides);

— Release to the environment as a liquid or gaseous effluent;

— Near surface disposal (that limits/excludes long lived radionuclides);

— Intermediate depth or enhanced confinement disposal;

— Geological disposal (multiple barriers, including those for highly active wastes and stable waste form);

— Disposal in mine and mill tailings facilities.

Information about the waste (e.g. classification, categorization, properties and inventory) is needed in order to identify suitable waste management processes and select optimal processing technologies.

3.2.1. Waste classification

According to IAEA Safety Standards Series No. GSG-1, Classification of Radioactive Waste [18], waste can be classified as follows:

This internationally accepted waste classification system classifies radioactive waste according to the activity and half-lives of radionuclides. This classification defines as acceptable, from the safety point of view, disposal routes (end points) for solid or solidified waste (plus liquid and gaseous wastes in the case of EW).

3.2.2. Waste categorization

Categorization of waste provides for consistent approaches to waste processing and storage/disposal.

While classifying waste solely according to its radioactivity and half-life is a reasonable approach, it has to be complemented with additional information on the waste properties relevant for activities performed in various pre-disposal waste management steps, such as the point of origin, physical state, type of processing method, properties and process options [19–22].

Point of origin

Radioactive waste is produced from a range of activities, and the waste streams vary by form, activity, physical state and so on. The sources (point of origin) of radioactive wastes considered may include: (a) the complete nuclear fuel cycle, including the refining and conversion of uranium concentrates (yellow cake), enrichment, fuel fabrication and fuel reprocessing; (b) operation of nuclear power reactors; or (c) naturally occurring radioactive materials (NORM) waste, including uranium milling and mining.

Categorization of a waste stream based on its point of origin provides valuable insights related to expected waste stream properties. This can reduce the burden associated with subsequent characterization analyses, processes, classification and disposition.

Physical state

This is perhaps the most obvious subcategory and is comprised simply of three physical states: liquid, gaseous or solid.

Enumerate assumptions and bounds for assessment

- define starting and ending points of the assessment - define constraints and limitations (e.g. waste classification

and categories)

Determine current inventories - establish existing waste inventory by source, classification category, type, location, etc.

- level of detail needs to be sufficient for purpose - establish planning scenarios (e.g. lifetime of future

operations)

- gather and collate raw data inputs from waste generators - level of details needs to be sufficient for purpose

Forecast future waste arisings

- select reference options for treating and managing the various waste streams (e.g. to determine volume reduction factors and final waste forms)

Determine appropriate waste management options

- based on forecast of future arisings and reference waste management options, calculate expected future waste inventory

Prepare forecast of resulting future waste inventories

- the future waste forecasts and the reference waste management options provide a basis for determining future waste management infrastructure needs (what needs to be built, by when and perhaps where)

Prepare plan of future waste management needs

FIG. 4. Basic methodology for assessing waste management needs.

Types of processing method

This subcategory is particularly useful in identifying potential treatment and conditioning technologies. In fact, waste type names are often established by the processing methods. In the case of waste to be disposed of, the waste type often relates to a portion of a repository, such as unstable or stable wastes. Examples of waste types include:

— Physical waste types (categorized for processing options based on the physical state of the waste);

— Process waste types (categorized for a known process);

— Disposal waste types.

3.2.3. Waste properties

Knowledge of waste properties assists in determining the optimal choice of process or technology that is necessary for:

— Pretreatment and treatment of primary waste;

— Conditioning for storage;

— Interim storage;

— Conditioning for disposal;

— Packaging for transport or disposal;

— Direct disposal;

— Discharge to the environment;

— Clearance.

The properties of unconditioned waste (raw, pretreated and treated) and conditioned waste (waste forms and waste packages) that need to be taken into account during the waste management process are outlined below.

Unconditioned waste properties

The three groups of unconditioned waste properties (radiological, physical–chemical and biological) are:

— Group 1 (radiological properties):

● Total activity and activity concentration;

● Radionuclide composition (type of radiation, half-life);

● Fissile mass and criticality potential;

● Thermal power;

● Surface dose rate;

● Type of contamination (fixed, non-fixed);

● Origin of the activity (contamination or activation).

— Group 2 (physical properties and chemical properties):

● Physical state;

● Volume, mass and dimensions of waste items;

● Density;

● Volatility;

● Chemical composition;

● Combustibility and thermal resistance;

● Chemical compatibility;

● Ignitability, pyrophoricity;

● Gas generation;

● Acidity/alkalinity (pH);

● Toxicity.

— Group 3 (biological properties):

● Putrescibility;

● Infectious/pathogenic.

Properties of waste forms and waste packages

The two groups of conditioned waste properties (radiological and physical–chemical) that provide the bases for acceptance criteria for waste storage or disposal are:

— Group 1 (radiological properties):

● Total activity;

● Radionuclide composition;

● Surface dose rate;

● Surface contamination;

● Thermal power;

● Radiation stability;

● Fissile content.

— Group 2 (physical and chemical properties):

● Mass and weight;

● Structural and dimensional stability;

● Permeability and porosity;

● Density;

● Voidage;

● Mechanical strength/load resistance;

● Impact resistance;

● Homogeneity;

● Chemical stability (leachability);

● Chemical composition;

● Corrosivity;

● Explosiveness;

● Gas generation;

● Toxicity;

● Thermal stability;

● Fire resistance.

3.2.4. Waste inventory

A waste inventory summarizes the knowledge of waste generators, waste processors and waste disposal operators about current or forecasted waste streams. It includes information about classification, categorization, and properties of individually defined waste streams, as well as the timescale and dynamic of waste production.

This information is needed to manage different waste streams; determine the necessary technologies, processes or resources; and establish the timing needed to develop an adequate infrastructure. On the other hand, some information cannot be obtained at the design stage since it needs to take into account the operating experiences related to maintenance, upsets and outages, and decommissioning practices for reactors and nuclear fuel cycle (NFC) facilities.