Within the statutory framework that regulates the nuclear industry, there is an overriding requirement to demonstrate, through an adequate and appropriate safety case, that all hazards associated with operations on a licensed site are understood, effectively managed and controlled. The risks directly linked to the presence of radioactive material are contamination, irradiation, and criticality, and measures to limit or eliminate these are discussed below.

Containment is provided through several barriers between the radioactive material and the environment, dynamic tightness by ventilation and specific design features. Irradiation is controlled by using proper shielding (concrete, lead and lead glass). Criticality requires the use of safe geometry and redundant control.

External events and their consequences have to be taken into account: earthquakes, loss of utilities, fire and explosion.

Operations must be reliable. This is achieved through the use of maintenance — free equipment whenever possible, the duplication of units or equipment subject to failure, strict quality control, the use of specific devices for remote maintenance and a layout per design allowing direct maintenance after decontamination of equipment.

Instrumentation and control are, as well, key in a reprocessing plant. A recycling plant is equipped with several control systems to ensure the monitoring of processes and also to protect workers and the environment. This includes sampling benches for indirect sampling of an active apparatus, standard sensors (temperature, pressure, level, . . .) and nuclear sensors (activity a, yp, neutrons).

16.4.1 Containment

Contamination is produced when radioactive material escapes into the workplace or the environment. Control of contamination relies on the installation of containment systems, which generally include:

• A first static barrier that is an integral part of the equipment being used or some other envelope that is in direct contact with the radioactive material. This first barrier provides protection for the environment and the operations personnel and is designed to provide containment that is as total as possible.

• A second static barrier whose role is to limit dispersion of the radioactive material in case of a leak or breach of the first barrier. This barrier may consist of the walls of the cells or the containment building.

These static barriers are complemented by a dynamic containment system using forced draft ventilation:

• A ventilation system connected to the first static barrier keeps a depression (a negative pressure difference) between the process equipment and the cells or containment rooms.

• A ventilation system connected to the second static barrier keeps a depression between the secondary containment system and the surrounding environment (which may be a building or the open air).

These ventilation systems are designed to ensure that any flow of gas (e. g. air) is towards the areas where the level of radioactivity is highest (Fig. 16.23).

Containment system

• Ventilation

system г—Й-СТ-

Depending upon the level of radioactivity in the cells or containment areas to which they are connected, ventilation systems are characterized by the numbers, the nature and the arrangement of filters mounted on the blowing or extraction circuits.

The secondary containment system may include areas where the operations personnel have to work. It is a complementary barrier for the environment in case of failure of the first system. The areas forming the second containment are adjacent to the cells or to the containment areas; they are at a level of pressure intermediate between the cells and the external environment.