Corrosion behavior of the cladding tube(AISI Type-316SS) for FBR in high temperature sodium (II); Effeet of quality of cladding tube and temperature gradient in sodium

Kano, Shigeki; not registered; Namekawa, Masaru; Nakasuji, Takashi; Atsumo, Hideo

In relation to the experimental estimation of corrosion behavior of AISI Type-316SS fuel cladding tube in high temperature flowing sodium, we clarified the relationship for sodium corrosion as a function of oxygen concentration in the preceding report.. The present study has been carried out to establish the dependence of corrosion behavior on the quality of cladding tube and the temperature gradient in sodium. Two kinds of the second fabrication tubes for JOYO (S-II and K-II) and three kinds of tubes to be used for JOYO MK-I core (S-III, K-III and C) have been exposured in flowing sodium of 425C through 660C for 5000 hours. The results obtained are as follows: (1) The corrosion behavior in sodium is depend on the quality (differenee of chemical conpositions and refining) of cladding tube. S-III tube shows the greatest corrosion rate of all cladding tubes tested. The cavity which has been observated in the vicinity of the surface in contact with 650C sodium distributes over the whole thickness of S-III tube. The $alpha phase has been detected on the surface of S-II and S-III tubes but not on C tube. (2) The profile of corrosion rate along sodium flow under the continuous rise of sodium temperature shows the unique shape. It is different from the test result at the isothermal region in the vicinity of the outlet of heat exchanger. (3) The beginning temperatures of decarburization and denitrization have been obtained under the continuous rise of sodium temperature. The beginning temperature of decarburization is depend on the heat of cladding tube, while that of denitrization is depend on the initial nitrogen content of cladding tube. (4) The dependence of short-term tensile strength and hardness on the exposure temperature has been investigated at ambient temperature. S-III and K-III tubes show the high level (the higher the temperature rises, the greater the strength and the hardness become), while C tube shows the ...