Sodium-concrete Reaction Research Articles

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

Abstract 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.

Melting behavior and thermal conductivity of solid sodium-concrete reaction product

ABSTRACT This study revealed melting behavior and thermal conductivity of four samples generated by sodium-concrete reaction (SCR). We prepared the samples using two methods such as firing mixtures of sodium (Na) and grinded concrete powder, and sampling depositions after the SCR experiments. In the former, the mixing ratios were determined from the past experiment. The latter simulated the more realistic conditions such as the temperature history and the distribution of Na and concrete. The thermogravimetry-differential thermal analyzer (TG-DTA) measurement showed the temperatures of the onset of the melting (solidus temperatures) were 865–942°C, but those of the samples containing metallic Na could not be clarified. In the two more realistic samples, the compression moldings in a furnace were observed. The observation revealed the softening temperature was 800–840°C and the solidus temperature was 840–850°C, which was 10–20°C lower than the TG-DTA results. The thermodynamics calculation of FactSage 7.2 revealed the solidus temperature was caused by melting of the some components such as Na2SiO3 and/or Na4SiO4 and NaAlO2. Moreover, the thermal conductivity was λ ~ 1–3 W/m-K, which was comparable to xNa2O - (1 - x)SiO2 (x = 0.5, 0.33, and 0.25), and that at 700°C was explained by NBO/T of Equation (1).

A study on self-terminating behavior of sodium-concrete reaction (2)

ABSTRACT Fundamental experiments were carried out to investigate the self-termination behavior of sodium–concrete reaction (SCR). In the reference experiment, the reaction time was controlled to investigate the distribution change of Na and the reaction products in the pool and around the reaction front. The measured concentrations at the reaction front were 18–24 wt.% for Na, 22–18 wt.% for Si, and 4–3.4 wt.% for Al and Ca after the self-termination. From the thermodynamics calculations, stable materials at the reaction front comprised more than 90 wt.% solid products such as Na2SiO3 and no Na. Furthermore, in two sensitivity experiments with additional heating or using mortar, the concrete-ablation behavior depended strongly on the reaction at the reaction front. It was concluded that SCR termination was caused by the lack of Na at the reaction front. The distribution of Na and reaction products could be explained by a steady-state sedimentation–diffusion model. At the early stage of SCR, the reaction products were suspended as particles in the Na pool because of the high H2-generation rate. As the concrete ablation proceeds, they start settling down due to the decreased H2-generation rate, thereby allowing SCR termination.

Thermophysical Properties of Sodium-Concrete Reaction Products

Thermophysical Properties of Sodium-Concrete Reaction Products

Thermal behavior of sodium hydroxide–structural concrete composition of sodium-cooled fast reactor

Under postulated accidental condition of sodium-cooled fast reactor (SFR), liquid sodium spill into the floor may lead to fail the steel liner. Consequently, sodium–concrete reaction (SCR) comes to occur by direct contact of liquid sodium with structural concrete. Significant phenomena of SCR for safety assessment of SFR are hydrogen release, energy release by exothermic heat generation, and concrete ablation by chemical corrosion. SCR consists of two reaction stages: (1) dehydration of concrete and hydrogen release by the reaction of evolved water vapor with Na as initial stage and (2) ablation of concrete by reactions between concrete compositions and Na compounds as secondary stage. In this study, the sodium hydroxide (NaOH)–silica (SiO2) reaction as one of the possible secondary stage reactions was investigated for safety assessment of SFR. Thermal behavior of NaOH–SiO2 reaction such as reaction onset was determined using a differential scanning calorimetry (DSC). As a result of DSC measurement, it was revealed that NaOH–SiO2 reaction occurs as rapid reaction right after NaOH melting at 583 K. Therefore, it was expected that NaOH–SiO2 reaction is dominant in the time frame of secondary stage of SCR if significant amount of NaOH has been generated during the initial stage reaction. Meta sodium silicate (Na2SiO3) was detected as the major solid product of NaOH–SiO2 reaction from XRD analysis. Considering the phase diagram of NaOH–SiO2 reaction system, likely overall reaction pathway of NaOH–SiO2 reaction was discussed.

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

ABSTRACTA sodium–concrete reaction (SCR) is one of the important phenomena to cause the structural concrete ablation and the release of hydrogen (H2) 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 H2 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 H2 bubbling and Na ablated the concrete surface with the high H2 generation rate, the reaction products gradually settled down with decreasing of the H2 generation rate. Therefore, the Na concentration decreases at the reaction front with time and the SCR terminates of itself.

Experimental study and kinetic analysis on sodium oxide–silica reaction

ABSTRACTIn a sodium-cooled fast reactor (SFR), if considering hypothetical severe accidental condition such as the steel liner failure of structural concrete caused by intensive leakage of liquid sodium (Na) coolant, the liquid sodium–concrete reaction (SCR) may take place. The major consequences of SCR are hydrogen release, energy release and concrete ablation. Thus, it is important to understand the phenomenology and kinetic behavior of SCR. As a part of a series of studies on SCR, this study focused on the reaction between sodium oxide (Na2O) and silica (SiO2), which is dealt with possible formation of Na2O as the result of sodium–water reaction in the initial stage of SCR. Through thermoanalytical and X-ray diffraction measurements, it was revealed that Na2O–SiO2 reaction to form sodium orthosilicate (Na4SiO4) occurs at significantly lower temperature in comparison with Na–SiO2 reaction. The reaction is kinetically characterized as a largely overlapping multistep reaction, which is composed of at least three reaction steps. On the basis of the observations, the impact of Na2O–SiO2 reaction in the overall SCR and the significance of the conventional kinetic analysis using the Kissinger method are discussed.

Kinetic study on liquid sodium–silica reaction for safety assessment of sodium-cooled fast reactor

In this study, the kinetic behavior of the sodium (Na)–silica (SiO2) reaction was investigated for an assessment method of reactivity/stability of siliceous concrete against the sodium–concrete reaction (SCR) by postulating a severe accidental condition in the sodium-cooled fast reactor (SFR). The reaction behavior was tracked using a differential scanning calorimetry (DSC) equipped with a videoscope for viewing the changes in the sample during the reaction. The reaction was characterized as a partially overlapping multistep process controlled by physico-geometrical reaction scheme. The kinetic behavior in view of the change in the temperature at the maximum reaction rate with heating rate was analyzed using the simplified Kissinger method and the approximated Ozawa method. Further by separating the kinetic data for the overall reaction into five component reaction stages, the kinetic information for the second and third reaction stages was extracted. By comparing the kinetic results, it was revealed that the kinetic results determined from the kinetic data at the maximum reaction rate can be interpreted as is for the major reaction stage (the third reaction stage) controlled by an autocatalytic reaction. In addition, the second reaction stage was characterized as a possible premonitory process for the major reaction stage. Through the comprehensive interpretation of the kinetic results, significance of the kinetic analysis for the Na–SiO2 reaction using DSC for the reactivity/stability evaluation against SCR and for the safety assessment of SFR is discussed.

ナトリウム-コンクリート反応機構に関する研究:-ナトリウム-シリカ反応に関する熱分析試験-

ナトリウム-コンクリート反応機構に関する研究:-ナトリウム-シリカ反応に関する熱分析試験-

Experimental Study on Sodium-Concrete Reaction Mechanism in Sodium-Cooled Fast Reactor

Experimental Study on Sodium-Concrete Reaction Mechanism in Sodium-Cooled Fast Reactor

E204 ナトリウム冷却高速炉におけるナトリウムーコンクリート反応機構に関する実験的研究(OS8 軽水路・新型炉・原子力安全(4))

E204 ナトリウム冷却高速炉におけるナトリウムーコンクリート反応機構に関する実験的研究(OS8 軽水路・新型炉・原子力安全(4))

ナトリウム燃焼実験と火災事故例の概観および安全防護への考察

Summaries are described on the sodium combustion experiments conducted by HEDL (F1, F2, F4, F5), KfK, Cadarashe (IGNA 402 & 2002, IGNA 3602 & 3604), the former PNC, etc. The sodium fires of Almeria Solar Plant and ILONA Test Facility are taken up as the examples of large-scale accidents. Fast breeder reactor (FBR) safety considerations are discussed, with attentions paid to the integrity of steel liner and sodium-concrete reaction, in relation to the secondary sodium leakage of MONJU. The author suggests that injection of nitrogen gas is an effective measure against sodium fires, suppressing the temperature rises, chemical reactions and also surely excluding a hydrogen explosion in case of sodium-concrete reaction.

Sodium Aerosol Release Rate and Nonvolatile Fission Product Retention Factor during a Sodium-Concrete Reaction

A series of tests is conducted to study the mechanical release behavior of sodium aerosols containing nonvolatile fission products during a sodium-concrete reaction in which release behavior due to hydrodynamic breakup of the hydrogen bubble is predominant at the sodium pool surface.In the tests, nonradioactive materials, namely, strontium oxide, europium oxide, and ruthenium particles, whose sizes range from a few microns to several tens of microns, are used as nonvolatile fission product simulants.The following results are obtained: 1. The sodium aerosol release rate during the sodium-concrete reaction is larger than that of natural evaporation. The difference, however, becomes smaller with increasing sodium temperature: nearly ten times smaller at 400°C and three times at 700°C.2. The retention factors for the nonvolatile materials in the sodium pool increase to the range of 0.5 to 104 with an increase in the sodium temperature from 400 to 700°C.

Containment Response to Postulated Core Meltdown Accidents in the Fast Flux Test Facility

An assessment is made of the containment margin available in the Fast Flux Test Facility to mitigate the consequences of a postulated failure of in-vessel post-accident heat removal following a hypothetical core disruptive accident. The consequences of a number of assumed meltdown configurations (both in-vessel and ex-vessel) are assessed using the CACECO (CAvity, CEll, COntainment) containment analysis computer code together with currently available melt front penetration models. The sensitivity of the accident scenarios to a number of crucial assumptions is established by scoping studies. It is concluded from both the in-vessel and ex-vessel analyses that sodium vapor combustion is a major source of reactor containment building (RCB) pressurization. The conditions (a combination of sodiumconcrete reaction, pool size, and decay heat level) that most rapidly bring the sodium to boiling, together with those that enhance mass transfer of sodium vapor to the RCB, are the ones that most significantly affect the pressure response.