Detecting a small area failed fuel element with a moving-piece precipitator

A new kind of electrostatic precipitator that can detect the gaseous fission products released from failed fuel elements is introduced. The negative electrode of the precipiating chamber is a piece of metal plate. A step-motor drives the electrode which passes through in turn the precipitating and measuring positions. The results of tests show that for this precipitator, the measured background is small; the ratio of signal to background is rather high; its perfomance is preferable to those precipitators which have the static precipitaing electrodes, e.g. a sintered stainless steel porous plate or a miniature counter. In addiation, it is particularly useful for detecting failure in PWR fuel element with a small hole