ACTIVIDAD AGRÍCOLA

The first step in the decommissioning process is the development of a decommissioning plan. This plan sets out the necessary sequence of administrative and technical actions leading to the eventual removal of some or all of the regulatory controls applied to the facility during its operation. The plan also sets out the necessary policies and procedures, which typically include the following:

(a) A health and safety policy, with allocation of roles and responsibilities;

(b) An outline procedure for dismantling the installation, with flowsheet and timeline;

FIG. 57. A deteriorating phosphoric acid plant awaiting dismantling.

(c) Procedures for the flushing of process lines, the cleaning of vessels and the categorization of wastes as hazardous, radioactive or mixed;

(d) Standard operating procedures for contractors and third parties, with training and certification requirements as appropriate;

(e) A methodology for the treatment, transport and disposal of scale, other radioactive material and radioactively contaminated equipment, including the necessary documentation;

(f) Contingency arrangements.

The decommissioning plan is based on a comprehensive radiological survey that identifies the location of radioactive material and the resulting exposure levels over the whole site, including peripheral areas used for activities such as transport, cleaning, repair and maintenance. The activity concentrations of radionuclides in environmental media such as water, soil and crops may have to be measured in areas surrounding the site to determine any contamination via airborne dust or entry into water courses. In addition, the survey needs to identify the radiological situation that will prevail during the decommissioning process itself as a result of the presence of radioactive material and contaminated equipment associated with decontamination and waste management activities.

FIG. 58. A wet process plant at Gela, Italy, during decontamination and dismantling.

The decommissioning plan incorporates a detailed description of the facility, including a history of operations at the site compiled from official records and, where appopriate and feasible, from worker interviews. A detailed knowledge of these aspects helps to ensure not only that the radiological objectives of the decommissioning process are achieved but also that the scale and cost of the decommissioning process do not extend beyond what is really necessary. The following historical aspects are typically documented:

(a) All known industrial activities carried out on the site since the land was first occupied and developed;

(b) The process steps in which radioactive material was handled, the locations of the pipes, pumps, valves, tanks and storage areas involved, and the activity concentrations of the materials concerned;

(c) As full a description as possible of plant modifications and changes of ownership;

(d) Known leakages, spillages and movement of radioactive material, including transfers from storage for onward transport and transfers to impoundment areas.

The plan addressses each aspect of the decommissioning process in a level of detail commensurate with the degree of radiological hazard. As a plant undergoing decommissioning is likely to have been in operation for a long time, often with imperfect documentation and record keeping, it can prove difficult to anticipate exactly the location, nature and extent of radioactive deposits and soil contamination that have accumulated over the years of routine plant operation.

For this and other reasons, the plan may have to be adjusted in response to unforeseen events as the decommissioning process proceeds.

The decommissioning plan quantifies the likely environmental impacts of the decommissioning process and the risks (both radiological and non-radiological) to workers engaged in the decommissioning work and to members of the public. In this regard, the following process materials are typical of those that have to be considered:

(a) Acids used in the various production processes;

(b) Ammonia;

(c) Hydrogen sulphide that might be present in sulphur storages;

(d) Scale, sludge residues and other materials in which radionuclides, such as radium, and heavy metals, such as arsenic, cadmium, chromium, lead, mercury and selenium, may accumulate.

The adoption of postulated ‘scenarios’ can be useful in the planning of a decommissioning process, especially if there are major gaps in the known history of the plant. The scenario concept permits a ‘what if’ approach to the determination of hazards and risks that may be present at the site. It also facilitates future planning, including the consideration of possible future uses of the site and the likely exposure implications.

The compilation of the necessary risk assessments and other documentation is facilitated by having a comprehensive checklist of all types of equipment on the site, which may typically include:

(a) Reactor vessels, such as the attack tank and defluorination reactor;

(b) Storage tanks;

(c) Buffer tanks for spilled acids;

(d) Evaporators;

(e) Scrubbers;

(f) Pumps, valves and steel pipes, including rubber linings where used;

(g) Stainless steel frames, transport reels and rubber belts from belt filters;

(h) Seal tanks and table filters;

(i) Filter cloths and bag filters;

(j) Metal filter pans;

(k) Machine frames and other metal structures;

(l) Carbon stones and bricks from the reactor lining;

(m) Other bricks and ceramic floor tiles;

(n) Drains, gutters and drain wells.

The decommissioning plan sets out the training and safety procedures to be used, including the keeping of records of the training provided. The responsibility for radiation protection training is generally assigned to a designated radiation protection officer. The training of on-site personnel is of particular significance since few, if any, of these individuals are likely to have had prior experience of working in such an environment. The procedures are usually designed to ensure that work experience is formally documented in order to support a systematic learning process and to ensure that best practices developed during the course of the work are passed on to other decommissioning operations in the future.