A Study on Sodium–Concrete Reaction in Presence of Internal Heating

The sodium–concrete reaction (SCR) is an important phenomenon during severe accidents in sodium-cooled fast reactors (SFRs), as it generates large volumes of hydrogen and aerosols in the containment vessel along with structural concrete ablation. In this study, the chemical reaction beneath the internal heater (800 °C) was investigated in SCR experiments with internal heating. The experiments simulate the effects of obstacles and heating on the SCR. Especially, we focused on the concrete ablation phenomenon because the hydrogen generation is sourced from the moisture in the concrete. The effects of internal heating on the self-termination mechanism are also discussed. The internal heater on the concrete hindered the transport of sodium (Na) into the concrete. Therefore, the reaction between Na and the concrete began at the periphery of the internal heater, where the concrete ablation depth was larger than under the internal heater. The high Na pool temperature (800 °C) largely increased the Na aerosol-release rate, which was explained by Na evaporation and formed a porous reaction-product layer. The Si mass balance and image mapping by an electron-probe micro-analyzer yielded consistent porosities in the reaction-product layer (0.54–0.59). The porous reaction products suppressed the amount of Na transported into the reaction front. Regardless of the internal heater placement, the Na concentration around the reaction front was limited to around 30 wt %. The Na concentration condition was dominantly responsible for the self-termination of the internally heated SCR.

Early Stage of Solid State Interfacial Reaction between Copper and Tin

High-purity plates of Cu and Sn were diffusion bonded to clarify the early stage of the solid state interfacial reaction between Cu and Sn, focusing on the incubation time for the formation of intermetallic compounds. A clear incubation time for the formation of intermetallic compounds is observed at every temperature between 423 and 493 K. The incubation time changes depending on the annealing temperature. The interface annealed at 423 K for 3.60 ks maintains the direct interconnection between Cu and Sn being free of intermetallic compounds. The exposure of Cu surface to air affects the interfacial reaction. Annealing of the Cu/Sn interface at 493 K for 3600 s starts to form voids by using the Cu plates exposed for 8.64×104 s or longer to air. Furthermore, the reaction product layer formed by the same annealing condition becomes thinner when the Cu plates exposed for 8.64×105 s or longer to air are used.

Tunneling Cracks in Constrained Layers

A thin, brittle layer bonded between tougher substrates is susceptible to cracking under residual and applied stresses. Such a crack initiates from an equi-axed flaw, confined by the substrates, tunneling in the brittle layer. Although tunneling is a three-dimensional process, the energy release rate at the front of a steady-state tunnel can be computed using plane strain fields. Several technically important problems are analyzed, including tunnels in adhesive joints, shear fracture, and kinked tunnels in a reaction product layer. The concept is finally applied to microcracking in brittle matrix composites caused by thermal expansion mismatch.

Toughening of Intermetallics by Coated Ductile Reinforcements

The effects of reinforcement debonding and work hardening on ductile reinforcement toughening of γ-TiAl have been examined. Debonding has been varied by either the development of a brittle reaction product layer or by depositing a thin oxide coating between the reinforcement and matrix. The role of work hardening has been explored by comparing Nb reinforcements that exhibits high work hardening with solution hardened Ti-Nb alloy that exhibits negligible work hardening. It is demonstrated that a high work of rupture is encouraged by extensive debonding when the reinforcement exhibits high work hardening. Conversely, debonding is not beneficial when the reinforcement exhibits low work hardening.

Characterization of the Surface of the HLW Glass R7T7 Reacted in Salt Brines

ABSTRACTBorosilicate glasses are proposed as waste form for the final disposal of High Level Waste (HLW) in salt formations by the Federal Republic of Germany. To check the safety of this waste form the corrosion of the non-radioactive borosilicate glass R7T7 in salt brines has been studied in collaboration with the Hahn-Meitner-Institut, Berlin. Temperatures up to 190°C and S/V ratios (surface area to solution volume ratio) between 3.3 and 1000 m were applied. S/V was varied by the addition of glass powder. The results presented here concern the characterization of the surface composition of the corroded glass (corroded at 190°C in a brine containing high amounts of MgCl-, called Q brine in this paper) after removing the reaction product layer. The corrosion conditions were chosen to obtain samples typical of long term (silica saturation) corrosion. The surface composition was analyzed quantitatively by X-ray photoelectron spectroscopy (XPS) by using external standard glasses with a composition similar to R7T7. Additionally scanning electron microscopy (SEM) was employed.