DETERMINATION OF CHEMICAL ACTIVITIES OF FE, CR, NI AND MN IN STAINLESS-STEEL-316 BY KNUDSEN EFFUSION CELL MASS-SPECTROMETRY

Cold-worked austenitic stainless steel of the type AISI 316 is being u sed as the cladding and wrapper materials in fast reactor fuel pins. K nowledge of the thermodynamic activities of the steel constituents is necessary to predict the possibility of fuel-cladding, coolant-claddin g or fission product-cladding chemical reactions. The thermodynamic ac tivities of Fe, Cr, Ni and Mn for stainless steel 316 were determined by measuring their partial pressures in the temperature range 1293-212 0 K, using Knudsen effusion cell mass spectrometry. High purity Ag was used as an internal calibrant. The chemical activities of Fe (a(Fe)), Cr (a(Cr)), Ni (a(Ni)) and Mn (a(Mn)) were evaluated using literature data for the vapour pressures of pure metals. log a(Fe)+/-0.18=-1.586 +2074/T (T=1293-1872 K) log a(Cr)+/-0.30=-2.350+2612/T (T=1293-2120 K) log a(Ni)+/-0.20=-2.140+1794/T (T=1468-1974 K) log a(Mn)+/-0.23=-2.04 1-5478/T (T=1302-1894 K)