Preliminal study of micro-defect self-wastage on 2 Cr-1Mo steel nozzles for LMFBR steam generators; Studies of micro-leak sodium-water reactions (1)

Kuroha, Mitsuo; not registered; Daigo, Yoshimichi; not registered

Experimental study on self-enlargement of a micro-defect was carried out using SWAT-2 test loop in order to establish the counter-plan for the micro-water leak in the LMFBR steam generators. The leak nozzles were made of 2.25Cr-1Mo steel which will be used as the heat transfer tube in the evaporator. The sodium temperature was fixed at 480C and the initial leak rates were chosen within the range of 1.610 g/s to 2.310 g/s. Main results of the experiments are as follows: (1)The self-wastage rate S (mm/sec) is dependend on the water leak rate L(g/sec), and the relation is expressed as following equation. S = 0.0173 L (2)The post test micrographs show that the self-enlargements started from the surface of sodium side, developed toward the water side, and finally the leak rates increased suddenly. (3)It is a characteristic of the self-wastaged holes that enlarged diameters of the sodium side are several times as large as that of the water side. (4)The minimum diameters of the enlarged nozzles were measured within 0.45 mm to 1.3mm, and the enlargement ratios of nozzle diameters increased as the water leak rates decreased.