A study on self-terminating behavior of sodium–concrete reaction

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.

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

“…d 0 , t 0 , and k are fitting parameters defining the maximum concrete ablation depth, the start time, and the time constant, respectively, and d is the concrete ablation depth at the current time t. From the approximation curve in I-8M experiment, d 0 was determined as 0.09 m. This value almost matched the final concrete ablation depth obtained in a long-term SCR experiment [13]. In the 0.6 mhigh concrete block (used in the III-1M experiment), the maximum concrete ablation depth was 0.18 m. These results confirm that in the absence of heating, the maximum concrete ablation depth strongly depends on the height of the concrete block.…”

“…However, the concrete ablation depth saturated at 0.1 m in both tests, because the internal heater hindered the Na transfer into the concrete and the reaction area decreased. Previous papers [6,8,13,16] reported a decrease in concrete ablation depth with decreasing reaction area. Na permeated not only the depth of the cylinder, but also the horizontal direction (H ¼ 0 to À0.07 m), because the reaction heat was measured below the internal heater in Fig.…”

“…The siliceous concrete blocks used in this experiment typify the typical structural concrete in Japanese nuclear facilities. Table 1 lists the components and characteristics of the siliceous concrete block specified in previous works [7,13]. The concrete types and sizes were unchanged from past experiments [6,7,13].…”

“…Table 1 lists the components and characteristics of the siliceous concrete block specified in previous works [7,13]. The concrete types and sizes were unchanged from past experiments [6,7,13]. Before storage in air for approximately 1 year, the concrete blocks were embedded with 12 and 22 thermocouples at various heights from the center (R ¼ 0 m) and from an eccentric position (R ¼ 0.07 m).…”

“…For safety assessment of Na leak accidents, researchers have investigated the self-terminating behavior of SCR [6,13] and measured the thermophysical properties of SCR products [14]. The SCR self-terminates when sedimentation of the SCR products blocks the Na from entering the reaction front [6].…”