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Journal Articles

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

Kawaguchi, Munemichi; Miyahara, Shinya; Uno, Masayoshi*

Journal of Nuclear Science and Technology, 56(6), p.513 - 520, 2019/06

This study revealed melting points and thermal conductivities of four samples generated by sodium-concrete reaction (SCR). We prepared the samples using two methods such as firing mixtures of sodium 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 melting points were 865-942$$^{circ}$$C, but those of the samples containing metallic Na couldn't 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$$^{circ}$$C and the melting point was 840-850$$^{circ}$$C, which was 10-20$$^{circ}$$C lower than the TG-DTA results. The thermodynamics calculation of FactSage 7.2 revealed the temperature of the onset of melting was caused by melting of the some components such as Na$$_{2}$$SiO$$_{3}$$ and/or Na$$_{4}$$SiO$$_{4}$$. Moreover, the thermal conductivity was $$lambda$$=1-3W/m-K, which was comparable to xNa$$_{2}$$O-1-xSiO$$_{2}$$ (x=0.5, 0.33, 0.25), and those at 700$$^{circ}$$C were explained by the equation of $$NBO/T$$.

Journal Articles

A Study on self-terminating behavior of sodium-concrete reaction, 2

Kawaguchi, Munemichi; Miyahara, Shinya; Uno, Masayoshi*

Journal of Nuclear Science and Technology, 55(8), p.874 - 884, 2018/08

 Times Cited Count:2 Percentile:16.17(Nuclear Science & Technology)

As parts of severe accident studies in sodium-cooled fast reactor, experiments were performed to investigate the termination mechanism of sodium-concrete reaction (SCR). In the experiment, the reaction time was controlled to investigate the distribution change of sodium (Na) and the reaction products in the pool and around the reaction front. In the results, the Na around the reaction front decreased from the enough amount with the reaction time. The concentrations were 18-24 wt.% for Na, and 22-18 wt.% for Si after the termination. From the thermodynamics calculations, the stable materials around the reaction front comprised more than 90 wt.% solid products such as Na$$_{2}$$SiO$$_{3}$$, and no Na. Further, 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 H$$_{2}$$-generation rate. As the concrete ablation proceeds, they start settling down due to the decreased H$$_{2}$$-generation rate, thereby allowing SCR termination. It was concluded that SCR termination was caused by the sediment of the reaction products and the lack of Na around the reaction front.

Journal Articles

Discussion about sodium-concrete reaction in presence of internal heater

Kawaguchi, Munemichi; Miyahara, Shinya; Uno, Masayoshi*

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 8 Pages, 2018/07

Sodium-concrete reaction (SCR) is one of the important phenomena during severe accidents in sodium-cooled fast reactors (SFRs) owing to the presence of large sources of hydrogen and aerosols in the containment vessel. In this study, SCR experiments with an internal heater (800$$^{circ}$$C) were performed to investigate the chemical reaction under the internal heater. Furthermore, the effects of the internal heater on the self-termination mechanism were discussed. Because the internal heater hindered the transport of Na, the moisture in the concrete, and reaction products, Na could permeate and react with the surface concrete at the periphery of the internal heater. As the SCR proceeded, the reaction products accumulated under the internal heater and disturbed the Na diffusion. Therefore, the Na concentration under the internal heater decreased relatively lower, and the concrete ablation depth under the internal heater decreased compared to that under the periphery of the internal heater. However, the Na concentration around the reaction front was about 30 wt.% despite the position of the internal heater. The Na concentration was similar to that of Na$$_2$$SiO$$_3$$, which was almost same as that in our past study. It was found that the Na concentration condition was one of the dominant parameters for the self-termination of SCR, even in the presence of the internal heater.

Journal Articles

Thermophysical properties of sodium-concrete reaction products

Kawaguchi, Munemichi; Miyahara, Shinya; Uno, Masayoshi*

Netsu Sokutei, 45(1), p.2 - 8, 2018/01

Liquid sodium (Na) has been used as the coolant of fast reactors for the various merits, such as the high thermal conductivity. On the other hand, it is postulated that a steel liner may fail and lead to a sodium-concrete reaction (SCR) during the Na-leak accident. Because of concrete ablation and release of hydrogen gas due to the chemical reactions between Na and concrete components, the SCR is one of the important phenomena in the Na-leak accident. In the study, fundamental experiments related to the SCR were performed using Na and concrete powder. Here, the used concrete powder is milled siliceous concrete which is usually used as the structural concrete in Japanese nuclear power plants. The obvious temperature changes at 3 temperature regions were observed for the reaction process such as Na-melt, NaOH-SiO$$_{2}$$ and Na-H$$_{2}$$O-SiO$$_{2}$$ reaction, which occurred around 100, 300 and 500$$^{circ}$$C, respectively. Especially, the violent reaction around 500$$^{circ}$$C caused the temperature peak to $$836 sim 853^{circ}$$C, and the reaction heat of $$0.15 sim 0.23$$ kW/g was estimated under the Na-concrete mixing ratio such as $$gammaapprox 0.32$$. The main components of the reaction products was identified as Na$$_{2}$$SiO$$_{3}$$ with X-ray diffraction technique. Moreover, the measured thermophysical properties such as melting point, density, specific heat, thermal conductivity and viscosity were similar to those of $$x$$Na$$_{2}$$O-$$(1-x)$$SiO$$_{2}$$ ($$xleq 0.5$$).

Journal Articles

A Study on self-terminating behavior of sodium-concrete reaction

Kawaguchi, Munemichi; Doi, Daisuke; Seino, Hiroshi; Miyahara, Shinya

Journal of Nuclear Science and Technology, 53(12), p.2098 - 2107, 2016/12

 Times Cited Count:3 Percentile:42.29(Nuclear Science & Technology)

A sodium concrete reaction (SCR) is one of the important phenomena to cause the structural concrete ablation and the release of H$$_2$$ gas in the case of sever accident of sodium cooled fast reactors. In this study, the long-time SCR test had been carried out to investigate the self-termination mechanism. The results showed the SCR terminated even if the enough amount of Na remained on the concrete. The quantitative data were collected on the SCR terminating such as temperature and H$$_2$$ generation. The reaction products, which became the small solids in liquid Na were transferred with slurry state by generated H$$_2$$ bubbles. Though the Na transfers actively and ablated the concrete surface with the high H$$_2$$ generation rate, the mass exchange coefficient defined as $$E_p$$ decreased and the reaction products settled gradually with decreasing the H$$_2$$ generation rate. Therefore, the Na concentration decreased at the reaction front and resulted in the SCR terminating naturally.

Journal Articles

Development of fast reactor containment safety analysis code, CONTAIN-LMR, 3; Improvement of sodium-concrete reaction model

Kawaguchi, Munemichi; Doi, Daisuke; Seino, Hiroshi; Miyahara, Shinya

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

CONTAIN-LMR code is an integrated analysis tool to predict the consequence of severe accident in a liquid metal fast reactor. A sodium-concrete reaction is one of the most important phenomena, and Sodium-Limestone Concrete Ablation Model (SLAM) has been installed into the original CONTAIN code. The SLAM treats chemical reaction kinetics between the sodium and the concrete compositions mechanistically, the application is limited to the limestone concrete. In order to apply SLAM to the siliceous concrete which is an ordinary structural concrete in Japan, the chemical reaction kinetics model has been improved. The improved model was validated to analyze a series of sodium-concrete experiments which were conducted in Japan Atomic Energy Agency. It has been found that relatively good agreement between calculation and experimental results is obtained and the CONTAIN-LMR code has been validated with regard to the sodium-concrete reaction phenomena.

Journal Articles

Development of fast reactor containment safety analysis code, CONTAIN-LMR, 5; Improvement of debris-concrete interaction model

Seino, Hiroshi; Kawaguchi, Munemichi; Izumi, Keitaro*

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05

As a part of development of CONTAIN-LMR, CORCON and VANESA models for calculating the debris-concrete interaction (MCCI) have been improved taking into account the influence of soudium-pool existence. In this study, the following LMFR specific models in the code have been developed and improved: (1) chemical reaction in sodium pool, (2) aerosol decontamination in sodium pool, and (3) heat conduction in concrete. These models have been also confirmed and validated with experimental results. As a result, improved CORCON and VANESA can represent the MCCI behavior reasonably well. Further improvement and validation of CONTAIN-LMR will be continued in order to apply to the ex-vessel accident progression of LMFRs.

Journal Articles

Reactive wetting by liquid sodium on thin Au plating

Kawaguchi, Munemichi; Hamada, Hirotsugu

Journal of Nuclear Science and Technology, 51(2), p.201 - 207, 2014/02

 Percentile:100(Nuclear Science & Technology)

The behavior of sodium wetting is investigated for the practical use of the under sodium viewer (USV), in which the modeling of the reactive and non-reactive wetting for the metallic-plated steels by liquid sodium are performed to simulate the behavior of sodium wetting. Simulation results of the non-reactive wetting showed a good agreement with the Tanner's law. For the simulation of reactive wetting, the model of fluid flow induced by the interfacial reaction was incorporated into that of the non-reactive wetting. The simulation results of the reactive wetting, such as the behavior of precursor liquid film and the central droplet, showed a good agreement with the sodium wetting experiments using thin Au plating at 250$$^{circ}$$C. In reactive wetting simulation, it is important that the gradient of reaction energy at the interface appeared on the new interface around the triple junction, and that the fluid flow was induced.

Journal Articles

Reactive wetting of metallic plated steels by liquid sodium

Kawaguchi, Munemichi; Tagawa, Akihiro; Miyahara, Shinya

Journal of Nuclear Science and Technology, 48(4), p.499 - 503, 2011/04

The sodium wetting experiments were performed to investigate the reactive wetting of metallic plating materials by liquid sodium at 250 $$^{circ}$$C for the ultrasonic sensor of the under-sodium viewer. SUS304 stainless steel specimens were electrolytically plated with four metallic materials (Nickel, Palladium, Gold and Indium) which have different solubility in sodium, and the spreading velocity of sodium droplets on the metallic plated specimens was measured. It was confirmed that the spreading velocity increased as the solubility increased, and the constant $$alpha$$ on the spreading velocity on the plated specimens was unique for the plating materials and was proportional to the logarithm of the solubility of the plating materials. Furthermore, it is considered possible to select plating materials based on solubility from the result of this study.

Oral presentation

Development of core damage evaluation technology (Level 2 PSA) for fast reactors, 13; Development of analytical code for ex-vessel phenomena; Improvement of sodium-concrete reaction model

Seino, Hiroshi; Ishikawa, Hiroyasu; Ohno, Shuji; Kawaguchi, Munemichi; Isozaki, Mikio; Miyahara, Shinya

no journal, , 

As a part of development of the core damage evaluation technology (level 2 PSA), validation studies were carried out to improve the analytical accuracy for the sodium-concrete reaction model in CONTAIN/LMR.

Oral presentation

Study of the impurity effect on wetting property by liquid sodium

Kawaguchi, Munemichi; Hamada, Hirotsugu

no journal, , 

In the practical use of the under sodium viewer (USV), it is important subject that wetting property of USV sensor by liquid sodium (Na). Though wetting property is decided by surface tension, a very small amount of metallic particle may dissolve in Na in reactor. We report the results of study of dissolved metallic impurity effect on Na surface tension.

Oral presentation

Wetting of metallic plated stainless steels by liquid metal sodium

Kawaguchi, Munemichi; Hamada, Hirotsugu

no journal, , 

Since liquid sodium is used as a coolant of sodium-cooled fast breeder reactors, the optical visual inspection in the inner of the reactor is difficult. Then, Japan Atomic Energy Agency has developed the under sodium viewer (USV) for the purpose of visually inspecting, and it is important to understand the wetting mechanism between the liquid sodium and USV sensor surface. In order to improve the wettability, Au plating is used in the surface of USV sensor at the present. In this study, some various plating specimens including Au plating were manufactured, and their wettability by liquid sodium were measured experimentally. In the result, we confirmed that solubility of the plating is important parameter for the plating processing on the sodium wetting.

Oral presentation

Simulation of reactive wetting by liquid metal sodium on gold plating

Kawaguchi, Munemichi; Hamada, Hirotsugu

no journal, , 

Gold plating is used in the sensor of under sodium viewer (USV) to improve the sodium wetting. In this study, modeling and simulation of reactive wetting including interfacial reactivity between liquid sodium and gold plating were performed. As the result, simulations have good agreement with experiments.

Oral presentation

Study on sodium-concrete reaction

Kawaguchi, Munemichi; Doi, Daisuke; Masuyama, Daisuke; Seino, Hiroshi; Konishi, Kensuke; Miyahara, Shinya

no journal, , 

As the purpose of investigation on terminating mechanism of Na-concrete reaction, the long-time test in which Na continued to be heated than threshold temperature was conducted. Under the condition that enough amount of Na existed and continued to be heated, we confirmed that the reaction stopped.

Oral presentation

Development of estimation technology for availability of measure for failure of containment vessel in sodium cooled fast reactor, 3; Corium/sodium-concrete interaction behavior

Kawaguchi, Munemichi; Uno, Masayoshi*; Konishi, Kensuke; Yamamoto, Ikuo*; Miyahara, Shinya*

no journal, , 

We started a project on "Development of Estimation Technology for Availability of Measure for Failure of Containment Vessel in Sodium Cooled Fast Reactor" as a program for R&D for nuclear system, development of basic technology for safety. We planed to develop an evaluation method based on experiments of hydrogen generation and concrete ablation in sodium-concrete reaction. This report shows the plan and a part of the sodium test.

Oral presentation

Development of fast reactor containment safety analysis code, CONTAIN-LMR, 3; Development and validation of debris-related analysis models

Seino, Hiroshi; Kawaguchi, Munemichi; Izumi, Keitaro*

no journal, , 

The CONTAIN-LMR code has been developed in the Japan Atomic Energy Agency to evaluate ex-vessel severe accident progression in a liquid metal fast reactor. As a part of several studies in JAEA, this paper mainly describes a state of the art of a debris-concrete interaction model.

Oral presentation

Development of estimation technology for availability of measure for failure of containment vessel in sodium cooled fast reactor, 1; Outline

Uno, Masayoshi*; Ohno, Shuji; Kawaguchi, Munemichi; Doi, Daisuke; Tsukimori, Kazuyuki

no journal, , 

no abstracts in English

Oral presentation

A Study on a microscopic state of Na-concrete reaction products

Kawaguchi, Munemichi*; Miyahara, Shinya; Uno, Masayoshi*

no journal, , 

Though the steel liner is set up to prevent Na contacting with the concrete in the case of Na leakage in the Na-cooled fast reactor, it is important to grasp the Na-concrete reaction mechanism. The past studies have focused on the thermal, concrete ablation and hydrogen release behaviors. Also the natural termination of this reaction was confirmed experimentally; it was pointed out that the sedimentation of the reaction products was one of the terminating causes. This paper is reported on a discussion such as thermodynamics calculations of the reaction products, related with the Na-concrete reaction terminating study.

Oral presentation

Development of estimation technology for availability of measure for failure of containment vessel in sodium cooled fast reactor, 7; Calculation of sodium-concrete reaction with phase-field method

Kawaguchi, Munemichi; Miyahara, Shinya; Uno, Masayoshi*

no journal, , 

A calculation on a sodium-concrete reaction behavior was carried out using the phase field method. As part of a study on the reaction terminating mechanism, the calculation results will be presented.

Oral presentation

Development of estimation technology for availability of measure for failure of containment vessel in sodium cooled fast reactor, 8; Estimation of phase equilibrium state of fuel debris under sodium by thermodynamic calculation

Yamamoto, Ikuo*; Uno, Masayoshi*; Miyahara, Shinya; Kawaguchi, Munemichi

no journal, , 

An estimation technology and reaction model on phase equilibrium state of fuel debris under sodium using thermodynamics calculation has been developed. In this study, the reaction products were calculated in sodium uranate system by thermodynamics calculation using Thermo-Calc.

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