Study on eutectic melting behavior of control rod materials in core disruptive accidents of sodium-cooled fast reactors; Project overview and progress until JFY2022

Yamano, Hidemasa; Takai, Toshihide; Emura, Yuki; Fukuyama, Hiroyuki*; Nishi, Tsuyoshi*; Morita, Koji*; Nakamura, Kinya*; Pellegrini, M.*

Nihon Kikai Gakkai 2023-Nendo Nenji Taikai Koen Rombunshu (Internet), 5 Pages, 2023/09

A research project has been conducting thermophysical property measurement of a eutectic melt, eutectic melting reaction and relocation experiments, eutectic reaction mechanism investigation, and physical model development on the eutectic melting reaction for reactor application analysis in order to simulate the eutectic melting reaction and relocation behavior of boron carbide as a control rod material and stainless steel during a core disruptive accident in an advanced sodium-cooled fast reactor designed in Japan. This paper describes the project overview and progress until JFY2022.

Experimental study on reaction behavior between control rod material and molten stainless steel for core disruptive accidents of sodium-cooled fast reactors

Emura, Yuki; Kamiyama, Kenji; Yamano, Hidemasa

Dai-26-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2022/07

https://doi.org/10.1299/jsmepes.2022.26.A224

no abstracts in English

Effects of potential on the electrical conductivity of a solution within a crevice of stainless steel in high-temperature water

Soma, Yasutaka; Komatsu, Atsushi; Ueno, Fumiyoshi

Corrosion, 78(6), p.503 - 515, 2022/06

https://doi.org/10.5006/3187

The effects of electrochemical potential (ECP) on water chemistry within a crevice are of critical importance for understanding stress corrosion cracking (SCC) of Fe-Cr-Ni alloys in high temperature water. In this study, the effects of ECP on the electrical conductivity of a solution within a Type-316L stainless steel crevice () have been studied in 288C and 8 MPa water containing 10 ppb Cl as major anionic species. In situ measurements of in a rectangular crevice with a gap of 15 m and a depth of 23 mm have been conducted using small sensors installed at different crevice depths. An increase in ECP from -0.49 V (vs. standard hydrogen electrode) to -0.12 V resulted in an increase in from 12 Scm to 160 Scm at a distance of 21 mm from the crevice mouth. The increase in reached a maximum at about 0.15 V (about 300 Scm) and then tended to decrease with increasing potential. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. It is considered that Cl is the major anionic species transported into the crevice at relatively low potentials, and that increases monotonically with increasing ECP. On the other hand, when ECP exceeds around 0 V, a sufficient amount of HCrO generated by transpassive dissolution also transported into the gap. Since this chemical species is highly oxidizing, unlike Cl, it is assumed that it reacts with metal cations to oxidize and precipitate them, thereby lowering conductivity.

Viscosity measurements of Molten casting steels for high temperature using an oscillating crucible viscometer

Takatsuka, Yuriko*; Matsumoto, Saori*; Nishi, Tsuyoshi*; Ota, Hiromichi*; Hori, Ayumi*; Hayashi, Kiichiro*; Yamano, Hidemasa

Jikken Rikigaku, 22(2), p.117 - 119, 2022/06

https://doi.org/10.11395/jjsem.22.117

This study clarified the effect of the viscosities of molten casting steels for high temperature by measuring them using the oscillating crucible method. The casting steels for high temperature samples used for viscosity measurements contained 0, 10, 20, 30, 40, and 50 mass% Ni. Viscosities were evaluated using Roscoe's equation and measured in the temperature range of 1693-1803 K.

Electrochemical behavior of Fe-Cr-Ni alloys in simulated crevice condition in high temperature water

Soma, Yasutaka; Kato, Chiaki

Zairyo To Kankyo 2022 Koenshu (CD-ROM), p.219 - 220, 2022/05

It is important to understand the electrochemical properties of stainless steel in environment created within crevice of stainless steel in high temperature water (crevice environment). This is because acidification and concentration of impurity ions occur in the crevice environment and this is common inside the stress corrosion crack. In this study, we reproduced the crevice environment in bulk scale and investigated mainly the effect of Cr concentration on the electrochemical properties of Fe-Cr-Ni alloys. Polarization curves of Fe-20Ni-xCr (x=16.4, 23, 26) were measured in water with a temperature of 288C, a Cl concentration of 210 mol/dm, a pH value of about 4.5, and a dissolved hydrogen concentration of 10 ppb. The peak currents of active dissolution (at -400 mV) and passive current density (at -50 mV) for specimens with Cr concentrations x = 16.4, 23, and 26% were approximately 13.8, 15.9, 10.0 Acm, and 18.4, 8.5, 8.5 Acm, respectively. Although the current values of x=26 were slightly lower in both cases, it was concluded that there was no clear dependence of the polarization curve on Cr concentration in this environment.

Effect of temperature on escape behavior of Cl ion concentrated in metal crevices

Soma, Yasutaka; Kato, Chiaki

Dai-68-Kai Zairyo To Kankyo Toronkai Koenshu (CD-ROM), p.205 - 206, 2021/10

This study investigates the effect of temperature on dissipation behavior of Cl ion within the crevice of stainless steel. Concentration of Cl ion was evaluated by conductivity measured by using sensors installed at crevice specimen. At 50 and 80 C, Cl ions within the crevice of PEEK and Pt dissipated in accordance with concentration diffusion. On the contrary, dissipation speed of Cl ions inside the Type-304L stainless steel were much lower than those anticipated by simple concentration diffusion. This behavior attribute to the anodic dissolution of stainless steel inside the crevice, therefore, to quantitatively understand the effect of temperature on the dissipation behavior, it is necessary to know the anodic dissolution rate and occurrence of localized corrosion. Numerical analysis taking the effect of concentration diffusion and migration into account is also needed.

Decrease in pitting corrosion resistance of extra-high-purity type 316 stainless-steel by Cu in NaCl

Aoyama, Takahito; Ogawa, Hiroaki; Kato, Chiaki; Ueno, Fumiyoshi

Metals, 11(3), p.511_1 - 511_13, 2021/03

https://doi.org/10.3390/met11030511

The effect of Cu in bulk solution on pitting corrosion resistance of extra high purity type 316 stainless steel was investigated. Pitting occurred in 0.1 M NaCl-1 mM CuCl whereas pitting was not initiated in 0.1 M NaCl. Although deposition of Cu on the surface occurred regardless of potential region in 0.1 M NaCl-1 mM CuCl, Cu in bulk solution had no influence on the passive film formation. The decrease in pitting corrosion resistance in 0.1 M NaCl-1 mM CuCl resulted from the deposited Cu or Cu compound and continuous supply of Cu on the surface.

Study on eutectic melting behavior of control rod materials in core disruptive accidents of sodium-cooled fast reactors, 4; Effect of BC addition on viscosity of austenitic stainless steel in liquid state

Ota, Hiromichi*; Kokubo, Hiroki*; Nishi, Tsuyoshi*; Yamano, Hidemasa

Proceedings of International Nuclear Fuel Cycle Conference / Light Water Reactor Fuel Performance Conference (Global/Top Fuel 2019) (USB Flash Drive), p.858 - 860, 2019/09

A viscosity measurement apparatus has been developed. It is known that the measurement of the viscosity of molten alloy at elevated temperatures is difficult due to the difficulty of handling for low viscosity fluids such as the stainless steel (SS)+BC alloy. In this study, the viscosities of the molten nickel (Ni) and stainless steel (SS) were measured by the oscillating crucible method to confirm the performance of the viscosity measurement apparatus as a first step. This method is suitable for high temperature molten alloys. A crucible containing molten metal is suspended, and a rotational oscillation is given to the crucible electromagnetically. The oscillation was damped by the friction of molten metal. The viscosity is determined from the period of oscillation and the logarithmic decrement. The crucible was connected to a mirror block and an inertia disk made of aluminum, and whole of them was suspended by a wire made of platinum-13% rhodium alloy. A laser light is irradiated to the mirror. The reflection light is detected by the photo-detectors, and then, the logarithmic decrement of molten metal is determined. The viscosities of molten nickel and SS melts were measured up to 1823 K. In these results, the measured viscosity values of molten Ni and SS were close to those of the literature values of molten Ni and SS. By the equipment, the viscosity of molten SS+BC alloys are measured. The BC concentration dependence of the viscosity of molten SS+BC alloys is to be clarified.

Plastic anisotropy and deformation-induced phase transformation of additive manufactured stainless steel

Chae, H.*; Huang, E.-W.*; Jain, J.*; Wang, H.*; Woo, W.*; Chen, S.-W.*; Harjo, S.; Kawasaki, Takuro; Lee, S. Y.*

Materials Science & Engineering A, 762, p.138065_1 - 138065_10, 2019/08

https://doi.org/10.1016/j.msea.2019.138065

Empirical equations for tensile properties and stress-strain curves of neutron irradiated stainless steels in LWR conditions

Fukuya, Koji*; Fujii, Katsuhiko*; Chimi, Yasuhiro; Hata, Kuniki

Proceedings of 19th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors (Internet), p.523 - 531, 2019/08

For structural integrity assessment on reactor internals of light water reactors, empirical equations of tensile properties as a function of neutron dose, and trend curves of stress-strain relations of neutron-irradiated austenitic stainless steels was proposed by fitting to recently developed database. The data in the database were obtained from reports of national projects in Japan and open literature, which was summarized in the form of data sheets. The empirical equations for tensile properties were formulated by using a saturation-type formulae. The equations were for CW 316 and SA 304/316 stainless steels in the temperature range of 280-350C and the dose range up to 80 dpa. Stress-strain relation curves were reproduced based on the Swift model. Obtained calculated results by the empirical equations and stress-strain relations were reasonably well fitted to experimental data. The effects of composition and cold-working, etc. on tensile properties were discussed.