Key Point: The overriding principle is defence in depth — multiple independent barriers and controls are employed so that no single failure can lead to a significant release or exposure.
Remote operation and shielding:
- The most active sections of the plant are operated entirely remotely.
- Heavy concrete and steel shielding protects workers from the intense radiation fields in the hot cells.
- Criticality accidents in reprocessing facilities are less likely to produce fatalities than in front-end processing because the high activity of fission products means that heavy shielding is already in place.
Design for reliability:
- Key mechanical plant is located outside the hot cells where possible.
- The most active sections are duplicated to allow continued operation during maintenance.
- Pumps, flanges, and valves are avoided where possible, with flow being under gravity.
- Equipment is designed to be maintenance-free as far as possible.
Criticality control:
- Favourable geometry vessels (thin cylinders and annular tanks) prevent the accumulation of critical masses.
- Batch control limits the quantity of fissile material in any one process step.
- Neutron poisons (such as gadolinium nitrate) are added to active solutions.
- Careful monitoring and accountancy for movements of fissile liquors.
Liquid and gaseous discharge controls:
- Multiple waste treatment systems (SIXEP, EARP, salt evaporators) treat liquid effluents before discharge.
- Off-gas scrubbing, condensation, electrostatic precipitation, and HEPA filtration.
- Continuous environmental monitoring.
Contamination control:
- Containment barriers (glove boxes, sealed cells).
- Ventilation systems maintaining negative pressure cascades.
- Regular monitoring and decontamination procedures.