Characteristics and maintenance requirements for the sampling pump of the stationary gaseous effluent monitor

Kobayashi, Hirohide ; not registered ; not registered; Maruo, Yoshihiro; Miyabe, Kenjiro; not registered

The stationary gaseous effluent monitor is equipment intended for continuously monitoring radioactivity in gaseous effluents released from the nuclear facilities. This monitor consists of sampling, detection and control assemblies. The sampling pump is a most integral part of the sampling assembly and required to be operated with an appropriate pressure to keep the continuous monitoring. However, in 1998, the failures of sampling pumps had successively occurred.This was due to the overload in pressure at the intake or the outlet. To prevent from the failures of sampling pumps, the overload characteristics and the mean time between failures (MTBF) were investigated. The following results were obtained. (1)The performance and tolerance tests with rapid increase of air pressure were carried out. The sampling pumps could withstand two or three times higher pressure than the regularly operating pressure during a few minutes. But, after that, the pump suddenly fell down by an over-current relay (OCR). (2)The MTBF were analyzed on the basis of the maintenance and repair records over a period from 1988 to 1998. The MTBF of a sampling pump were in the range from 7,600 to 35,500 hours. For a preventive maintenance, the consumption parts, such as a carbon blade and a bearing of rotor shaft, etc., should be replaced periodically.