Application of process control system in a semi-industrial scale LLW incinerator

Abstract The semi-industrial scale incinerator for low-level radioactive waste, designed and built by the Italian Electricity Board (ENEL), in cooperation with the Milan Polytechnic and the engineering company SINCOS, has been tested by treating about 3,000 kg of inactive and active, organic IX-resins. The plant was designed for largely automated operation, carried out during both normal and emergency shutdown conditions by means of control and synoptic boards placed outside the plant room. The most important operations can also be performed manually either through the control board or acting directly on the plant. The plant is equipped with process control instrumentation, which transmits its signals to a PLC (Programmable Logic Controller) installed in the control board. If a controlled parameter oversteps its predetermined range, two occurrences may take place. If the parameter is connected with the operation of a redundant component, the PLC actuates the stand-by component. If the overstepping of a process variable depends on the breakdown of an unduplicated component or on a service blackout, the PLC starts a sequence of interventions leading the plant into safe conditions. During the incineration campaigns the process control system intervened many times because of failures of the 380-V power supply and lack of the service compressed air and service water. In all cases the control system operated correctly, quickly restoring the normal operating conditions as soon as the normal service conditions were recovered.