Caskey, G.R. Jr.
Tensile tests of Tenelon (U.S. Steel), a nitrogen-strengthened iron-base alloy containing 18% chromium and 15% manganese, demonsterated that cleavage fracture can occur in some austenitic steels and is promoted by the presence of hydrogen. Tensile failure of Tenelon at 78 0 K occurred with no detectable necking at low strain levels. The fracture surface contained cleavage facets that lay along coherent twin boundaries oriented transversely to the tensile axis. Charging gaseous hydrogen at 679 MPa pressure and 650 0 K had no significant effect on the mechanical behavior or fracture mode at 78 0 K, but raised the ductile-to-brittle transition temperature from less than 200 0 K to about 250 0 K
Caskey, G.R. Jr.
Internal hydrogen embrittlement may be viewed as an extreme form of environmental embrittlement that arises following prolonged exposure to a source of hydrogen. Smooth bar tensile specimens of three stainless steels saturated with deuterium (approximately 200 mol D 2 /m 3 ) were pulled to failure in air at 200 to 400 0 K or in liquid nitrogen at 78 0 K. In Type 304L stainless steel and Tenelon ductility losses are a maximum around 200 to 273 0 K; Type 310 stainless steel is not embrittled at this hydrogen concentration. A distinct change in fracture mode accompanies hydrogen embrittlement, with fracture proceeding along coherent boundaries of pre-existing annealing twins. This fracture path is observed in Tenelon at 78 0 K even when hydrogen is absent. There is also a change in fracture appearance in specimens with no prior exposure to hydrogen if they are pulled to failure in high-pressure hydrogen. The fracture path is not identifiable, however. Magnetic response measurements and changes in the stress-strain curves show that hydrogen suppresses formation of strain-induced α'-martensite at 198 0 K in both Type 304L stainless steel and Tenelon, but there is little effect in Type 304L stainless at 273 0 K
Bezdecny, J.A.; Vance, K.M.; Henderson, D.L.
The purpose of the Los Alamos National Laboratory Accelerator Transmutation of (Nuclear) Waste (ATW) project is the substantial reduction in volume of long-lived high-level radioactive waste of the US in a safe and energy-efficient manner. An evaluation of the ATW concept has four aspects: material balance, energy balance, performance, and cost. An evaluation of the material balance compares the amount of long-lived high-level waste transmuted with the amount and type, of waste created in the process. One component of the material balance is the activation of structural materials over the lifetime of the transmutation reactor. A preliminary radioactivity and radioactive mass balance analysis has been performed on four structure regions of the reaction chamber: the tungsten target, the lead annulus, six tubing materials carrying the actinide slurry, and five reaction vessel structural materials. The amount of radioactive material remaining after a 100-yr cooling period for the base-case ATW was found to be 338 kg of radionuclides. The bulk of this material (313 kg) was generated in the zirconium-niobium (Zr-Nb) actinide tubing material. Replacement of the Zr-Nb tubing material with one of the alternative tubing materials analyzed would significantly reduce the short- and long-term radioactive mass produced. The alternative vessel material Al-6061 alloys, Tenelon, HT-9, and 2 1/4 Cr-1 Mo and the alternative actinide tubing materials Al-6061 alloy, carbon-carbon matrix, silicon carbide, and Ti-6 Al-4 V qualify for shallow land burial. Alternative disposal options for the base-case structural material Type 304L stainless steel and the actinide tubing material Zr-Nb will need to be considered as neither qualifies for shallow land burial