Micro-Leak Behavior on LMFBR Monju Steam Generator Tube Materials -Studies of Micro-Leak Sodium Reaction, 3

Kuroha, Mitsuo; Shimoyama, Kazuhito 

Behavior of a micro-leak as an initiator of the leak propagation has been experimentally studied using leak nozzles made of the 2.25Cr-1Mo steel and Type 321 austenitic stainless steel which were selected as the heat transfer tube materials of the Monju steam generators. Twenty-nine micro-leak tests have been carried out in three stagnant sodium pots of the SWAT-4 test rigs installed in PNC/OEC. The main test parameters were the leak rate in the range of 10 to 10 g/sec and the sodium temperature in the range of 460 to 505C. The shapes of initial leak holes used for the tests were a circular type and a slit one. The test results showed that the self-wastage was enhanced due to both corrosion and erosion, while the self-plugging was occurred due to precipitation of the reaction products at the sodium side and the corrsion products at the steam side. Post-test examination of the self-enlarged holes revealed that the diameters of holes were in the range of 0.3 t0 0.85 mm that were insensitive to the changes in the leak rate, the material, the temperature, and the shape of the initial leak hole. The relationships among the average leak rate L, the self-wastage rate S, and the sodium temperature T was derived from the experimental data and was expressed in the form of the following equation for the above two materials. S = Exp (a + b ln L - c/T) a,b,c: constant