significantly larger amount of energy that is deposited, albeit in a much more localised volume ( radiation is assumed to be deposited fairly evenly over the waste package).

2.7.2.2. Chemical data

Masses of materials If no production data exist, material masses can be determined from the examination of the process or, in the case of decommissioning wastes, the plant design. It is particularly important to identify organic materials (cellulose, plastics, rubbers, etc.), complexing agents (EDTA, Prussian blue, etc.) and gas-producing materials (e.g., aluminium, zinc, etc).

Organic materials have the potential to either directly, or following degradation, form complexing agents that can increase the mobility of otherwise insoluble or retarded (e.g., sorbed on geological media) radionuclides in a repository. Therefore, it is important not only to know how much is present, but also which type. For example, cellulose-contain- ing materials have been identified as having the potential to produce complexing agents and, as such, it is important to have good knowledge of which wastes contain these types of materials.

Non-radiolytic gas production, i.e., that arising from microbiological or chemical degradation of materials, is also important in a repository. If too much gas is produced, this can lead to disruption of the repository, possibly leading to an increased migration of certain radionuclides (especially the more volatile radionuclides such as 14C).

Elemental compositions of materials For radionuclide solubility calculations, it is necessary to know how much of any particular element is available, and in what form.

Classification of materials into chemical groups Different materials have different repository properties and, for the purposes of an efficient safety analysis, it is therefore necessary to simplify repository modelling. This can be achieved by grouping the materials into various categories, e.g., highand low-molecular weight organics, concrete and cements, metals, electropositive metals, etc.

2.7.2.3. Physical data

Container description For engineering (repository design) purposes, it is necessary to describe all relevant features of the container (materials, dimensions, weight, etc.). Further, in certain instances, the container is relied on to play a role as a barrier to the release of radionuclides in a repository (as opposed to its general function of allowing safe handling during disposal operations – see Chapters 3, 5–7), e.g., in the case of vitrified HLW, the container, or overpack, is considered to ensure a minimum period of containment before any ingress of water is possible. In these cases, the properties of the container are considered in the safety assessment (see also Chapter 6).

Total mass and volumes These data are required for engineering, repository planning, etc.

Production statistics It is important that an inventory contains information concerning the waste already produced, but also estimates of how much waste will arise in the future and when. This can be based, for existing waste types, on previous production or can be derived from waste arisings studies.

This information is used not only for repository planning but can, in connection with a decay program, derive more realistic radionuclide inventories, i.e., an arising radionuclide inventory which includes calculations of radionuclide decay can reduce the total