Documentation

Dismantling and demolition will be facilitated if technical records are available [29]. Therefore, after a facility is commissioned, a records retention system needs to be established to provide the following [69]:

— Details of design and construction;

— Details of operating history;

— Details of modifications to the plant and maintenance experience.

An extensive amount of information is generated during the design, construction, operation and shutdown of a large nuclear facility [15, 42]. Some of these data could be extremely valuable in planning and executing the decommissioning of the facility. However, as a large percentage of the information is not pertinent, the primary tasks at the design and construction stages are to select the information required for decommissioning and to find a suitable, cost effective method of storing it so that it will be available when required.

A database for this purpose must contain an accurate and detailed description of the facility so that the most effective ways of removing equipment and structures can be determined. Ideally it will include items such as:

— Details of design and construction of the facility, including records of:

• Construction material specifications and analyses;

• Construction prints and as built drawings of the plant, and lists of these items;

• Photographs taken during construction and installation;

• Pre-operation environmental and radiological data;

• Any data from a national database that are particularly relevant to the particular facility;

— Details of the operating history of the facility, including records of:

• Fuel failures and fuel accounting, if applicable;

• Incidents leading to spillage or inadvertent release of radioactive material;

• Unusual occurrences during operation that might affect the decommis-sioning procedure;

• Radiation and contamination survey data, particularly for plant areas that are rarely accessed or are especially difficult to access;

• Releases that could potentially affect groundwater;

• Radioactive inventory;

• Details of decontamination carried out during operation and plant maintenance;

• Details of radioactive/toxic waste stored;

— Details of modifications to the plant and maintenance experience including records of:

• Updated as built drawings and photographs, including details of the materials used;

• Special repair or maintenance activities and techniques (e.g. effective temporary shielding arrangements or techniques for the removal of large components);

• Details of the design, material composition, and history and location of all temporary experiments and devices;

• Information and drawings of specialized procedures and equipment used during maintenance that could be of value during decommissioning.

It is advisable that documentation systems be designed to ensure long term maintainability and readability.

A site specific database for a particular facility could save money and time during decommissioning. The concern is that creating and maintaining such a large database for decommissioning purposes alone probably would not be cost effective. The database that is used during the construction and operational phases could later be downgraded to eliminate data that are not relevant to decommissioning. Such a database would need to be designed to ensure intact data storage for long periods of time, perhaps for a long as a hundred years. It is imperative that at least two separate physical locations be established to maintain the documentation over these long periods of time to ensure that the backup information is not lost through events such as fires.

If computer databases are used to store information for long periods of time, the systems associated with these databases will require frequent updating to ensure compatibility with current computer operating systems.

Data retrieval procedures will also require updating. Computer databases should be backed up by hard copies of the data to ensure data availability and retrievability.

Generic data outlining techniques or experience from previous decom-missioning or decontamination may be stored in national or international databases, which can be then accessed by computer. One type of generic data that is not currently in such databases but that could eventually be of assistance in planning and costing future decommissioning operations is unit cost factors.

These factors are used to describe the decommissioning process by breaking it down into elementary activities such as removing pumps and cutting pipes.

Experimental irradiation of specimens of selected materials (coupons) used in the construction of the facility may also assist in comparing the measured data with the calculated activation levels to provide better estimates of the final radioactive inventory. Therefore, such coupons should be obtained during construction and preserved for future experimental use.

Pre-operational environmental data are often unavailable for existing facilities [70]. Analysis of information from background locations (unaffected by past or current facility operations) and information provided by the charac-terization survey regarding the current state of the natural environment and the extent of contamination will help in the understanding of pre-operational environmental conditions. This will allow identification of changes to the environment arising from operations and waste management practices.

However, it is important that the area to be used as a reference to establish background conditions be environmentally similar to the site, since environ-mental conditions can vary over even short distances. Characterization and baseline surveys use the same measurement and sample analysis techniques as those applied to the environmental media. Characterization surveys require that soil sampling be conducted at greater depths to assess contaminant leaching into the subsoil, and it is necessary to sample waste materials. The use of a non-uniform distribution of monitoring wells may be needed on the site, as well as off the site, to track possible existing contaminant groundwater plumes.

Similar requirements need to be considered for characterization surveys of buildings or selected materials.

The owners, designers, builders and operators are responsible for ensuring that all data are available to the decommissioner in a readily usable form, even if dismantling is not to begin until a much later date. The designers and owners need to establish a suitable database, which is to be maintained by the builders and operators. The data management system must ensure that:

— All relevant documents impacted by any modification are identified and updated, remain consistent with the plant specific design requirements and accurately reflect the modified plant configuration;

— All changes to the design over the lifetime of the plant are based on the actual status of the plant, as reflected in the current plant documentation;

— The modified plant configuration conforms fully to the conditions and supporting documentation of the operating licence.

It is recognized that the knowledge of operational and research staff is beneficial for decommissioning, particularly during the transition from operation to decommissioning [3]. A lack of action or unjustifiable delays in this transition are a serious concern, particularly owing to the ageing of

operational staff in many facilities with research reactors. Mechanisms need to be in place to expedite the transition from operation to decommissioning, and to include the establishment of a comprehensive set of decommissioning records. Nevertheless, planning for decommissioning and for the plant final end state requires the development and maintenance of significant professional decommissioning expertise. Such expertise is specific to decommissioning and different from the experience base required during plant operation. Training or retraining of decommissioning operators is another important consideration, particularly for deferred decommissioning.