No abstract

A sodium-concrete reaction (SCR) is one of the important phenomena to cause the structural concrete ablation and the release of hydrogen (H 2) gas in the sodium (Na) leak accident. In this study, the long-time SCR test had been carried out to investigate the self-termination mechanism under the condition to keep the temperature of Na on the concrete more than the reaction threshold temperature during 24 hours. The test results showed the SCR terminated by itself even if enough amount of Na remained on the concrete. In addition, quantitative data were collected on the SCR terminating behavior such as the temperature, the concrete ablation depth, the H 2 generation behavior and the concentration profiles of Na, silicon (Si), aluminum (Al) and calcium (Ca) in the reaction products after the test. In the concentration profiles, the calculation by the sedimentation diffusion model of the steady state was comparable with the experimental results. Though the reaction products were suspended by H 2 bubbling and Na ablated the concrete surface with the high H 2 generation rate, the reaction products gradually settled down with decreasing of the H 2 generation rate. Therefore, the Na concentration decreases at the reaction front with time and the SCR terminates of itself.

This study developed phase-field method (PFM) technique in oxide melt system by using a new mobility coefficient (L). The crystal growth rates (v 0) obtained by the PFM calculation with the constant L were comparable to the thermodynamic driving force in normal growth model. The temperature dependence of the L was determined from the experimental crystal growth rates and the v 0. Using the determined L, the crystal growth rates (v) in alkali disilicate glasses, Li 2 O2SiO 2 , Na 2 O2SiO 2 and K 2 O2SiO 2 were simulated. The temperature dependence of the v was qualitatively and quantitatively so similar that the PFM calculation results demonstrated the validity of the L. Especially, the v obtained by the PFM calculation appeared the rapid increase just below the thermodynamic melting point (T m) and the steep peak at around T m 100K. Additionally, as the temperature decreased, the v apparently approached zero ms ¹1 , which is limited by the L representing the interface jump process. Furthermore, we implemented the PFM calculation for the variation of the parameter B in the L. As the B increased from zero to two, the peak of the v became steeper and the peak temperature of the v shifted to the high temperature side. The parameters A and B in the L increased exponentially and decreased linearly as the atomic number of the alkali metal increased due to the ionic potential, respectively. This calculation revealed that the A and B in the L were close and reasonable for each other.