Stability of natural circulation flows of FBR. Stability of the primary loops flow

By using an experimental apparatus with water in which the primary cooling circuit of a demonstration FBR (DFBR) in Japan was roughly simulated by three inverse-U shape piping loops, a hot plenum and a cold one, stability of natural circulation flows in primary loops has been experimentally evaluated. The following were clarified as a result of the present study. 1) A strong buoyancy head arises in the core over a natural circulation operation of the DFBR. So far as a driving force of the primary flow induced by the head being secured, natural circulations in the primary loops were found to be so much stable and resistant to disturbances. Flow instability is hard to occur in the natural circulation of the DFBR under an expected condition. 2) If the buoyancy head was excessively decreased by some design modification, considerable raise of the cooling capacity of direct heat exchangers etc., oscillatory or unstable flows might occur as were observed in the study. (author)