HTGR Knowledge Base

Conference Article: Operating experience of gas bearing helium circulators in HTGR development facility

Shimomura, H.; Kawaji, S.; Fujisaki, K.; Ihizuka, T. (Japan Atomic Energy Research Inst., Tokai, Ibaraki. Tokai Research Establishment)

Abstract

The large scale helium gas test facility (HENDEL) has been constructed and operated since March 1982 at the Japan Atomic Energy Research Institute to develop HTGR components. The five electric driven gas circulators with dynamic gas bearings are used to circulate the helium gas of 4MPa and 400 deg. C in loops for their compactness, gas tightness, easy maintenance and free from gas contamination. All of these circulators are variable speed types of 3,000 to 12,000 rpm and have the same gas bearings and electric motors. The four machines among them are equipped with centrifugal impeller and one other machine has regenerative type, and the weight of both type rotors are nearly the same. After the troubles and repairing, both type of circulators were tested and the vibration characteristics were measured as preventing maintenance. From the test and measurements of the circulators, it was presumed that the first trouble on regenerative type was caused from excess unbalance force by falling off of a small pin from the rotating part and the second severe trouble on it was caused by the whipping in gas bearing. The static load on tilting pads indicated close relations to occurrence of the whirling through the measurements. It is recognized that fine balancing of the rotors and delicate clearance adjustment of the bearings are very important for the rotor stability and that the mechanism should be designed and machined so precise as to be adjustable. As the gas bearing would be damaged in an instantaneously short time, the monitoring technique for it should be so fast and predictive as to prevent serious damage. Through the tests, the vibration spectrum monitoring method seems to be predictive and useful for early detection of the shaft instability. It will be concluded that the gas bearing machine is an excellent system in its design philosophy, however, it also needs highly precise machining and delicate maintenance technique.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Specialists' meeting on gas-cooled reactor coolant circulator and blower technology. San Diego, CA (USA). 30 Nov - 2 Dec 1987
International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors
IWGGCR--17, pp:148-156