Corrosion behavior of the cladding tube (AISI Type-316 SS) for FBR in high temperature sodium (III); Effect of quality of cladding tube in high velocity sodium and estimation of corrosion rate

Kano, Shigeki; Maruyama, Akira*; not registered; not registered; Kawai, Masashi; Namekawa, Masaru; Nakasuji, Takashi

A series of tests have been conducted in relation to experimental estimation of corrosion behavior of AlSI Type-316 fuel cladding tube in high temperature flowing sodium. A present study relates to establish the difference of corrosion behavior between qualities of fuel cladding tubes. A kind of the second fabrication tube for JOYO (S-II) and two kinds of tubes used for JOYO MK-I core S-III and K-III) have been exposed to 650C sodium at a flow velocity of 3 m/sec for 5000 hrs. Also, corrosion data up to date at the Sodium Technology Section have been arranged by test variables to obtain basic information for design criterion relating to sodium corrosion of domestic fuel cladding tubes. The results obtained are as follows: (1)Corrosion behavior in sodium depended on qualities of fuel cladding tubes. The S-III tube showed the greatest corrosion rate among fuel cladding tubes tested. (2)Alpha phase, sigma phase and carbide disappearance layer were observed in the surface vicinity of sodium contact. However, sigma phase existed in bulk thickness of the S-III tube. (3)Carbon and nitrogen transferred to sodium from all fuel cladding tubes, but boron didn't. Denitrization content depended on initial nitrogen content in the tube. Decarburization content was nearly constant and didn't depend on initial carbon content in the tube. (4)It was clarified that corrosion data obtained at the Sodium Technology Section stood comparison with foreign data. A rate of thickness change was 3.5 m/year (max. variation: 25%) at JOYO design conditions (sodium temperature: 650C, cold trap temperature: 150C, Reynolds number: 55,000 and L/D: zero). (5)A literature survey showed that active carbon content in sodium was 0.1 ppm through 0.2 ppm, which was one of rate controlling factors in carbon transfer.