抄録
Leakage of solution was found to occur from a steam jet in an acid recovery process at the Tokai reprocessing plant. To determine the cause, we retrieved the steam jet unit from the cell which held it and examined the inside. As a result, it was revealed that a corrosion defect had penetrated the inside of the structure, originating from the steam nozzle root in the suction part of the jet unit.
To ascertain why such a failure occurred, we carried out observation of the metallurgical structure of the jet unit, an analysis of the temperature distribution of the structure involving verification with a trial jet unit, and a corrosion test of the material.
Consequently, the origin of the corrosion defect was determined to be a pin hole on the material surface at the end of the steam nozzle root, where nitric acid fluid had been in contact, and the defect progressed along the structure at a temperature of about 120°C. Anisotropy of the material, possibly originating in the manufacturing process, was observed from the corrosion test.
As a result of these investigations, we have devised a new design to improve the corrosion resistance.
