Control and interlocking of ventilation system at Advanced Fuel Fabrication Facility, BARC, Tarapur using microprocessor based programmable logic controllers (Paper No. 5.4)

A nuclear fuel fabrication facility has been set up by BARC at Tarapur. These fuel elements being radioactive emit nuclear radiation which is hazardous to human beings. Therefore these fuel elements during fabrication stage are handled in totally enclosed transparent boxes known as glove boxes. To prevent leakage from these glove boxes the once through ventilation system at fuel fabrication facility has been designed and interlocked such that air flow is always from surrounding atmosphere to laboratory rooms to glove boxes. This is achieved by maintaining negative air pressure in laboratory rooms and still higher negative pressure in glove boxes. Some interlocking logics have been defined to achieve these interlocks by operating a combination of specified number of main exhaust blowers, glove exhaust blowers and supply blowers. This interlocking has been done on electrical side and being very complicated, programmable logic controllers have been used instead of electromagnetic relays for building the blocks of interlocking scheme. With PLC, once the system is hard wired, any change in logic can be easily effected by reprogramming the system. In this paper the commissioning experience, teething troubles faced, remedial measures taken and modifications carried out are discussed. (author)