Design considerations for a microwave advanced gas reactor fuel detector

During the design of a new irradiated fuel dismantling facility at Hunterston `B´ nuclear power station, a requirement was identified for a device which would reliably detect the presence of a fuel assembly in the small gap between the top of a receptacle tube and the underside of a transfer carriage. The detector would provide an interlocking signal which would permit or inhibit the movement of the carriage which, if moved, with a fuel element partly in the tube and partly in the carriage, could result in serious damage to the fuel and possibly to the facility. A microwave detector is developed based on the use of a 41 GHz Gunn oscillator. This was fitted into a standard steel enclosure together with the other active components in the system. This enclosure was fixed to the outside wall of the facility in an area of little or no radiation and of normal room temperature. The microwave signals were fed through the metre thick steel wall of the cell to determine if the gap was obscured