Detecting small sealing defects in nuclear fuel rods - by reducing surrounding pressure and measuring escape of helium using mass spectrometer isolated from vacuum pumps

摘要

Very small defects in the sealing of nuclear fuel rods are detected by placing the rods in an enclosure in which the pressure is reduced to 10-3 torr and which communicates with the measuring cell of a mass spectrometer. The fuel rods are pressurised with helium to >=1 torr and the rate of escape of helium from the casings of the rods is measured by the spectrometer. The enclosure is isolated from all pumping appts. for the duration of the measurement. The pressure is pref. rduced to 10-4 toor before isolation from the pumping appts. The method is used for testing fuel rods, e.g. during mfr. The response of the spectrometer is accelerated and thus the measurement time is reduced. Disturbances to the measurements due to accidental overpressures are avoided. The sensitivity of measurement is increased permitting smaller leaks to be measured and hence smaller defects to be detected.