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論文

The Effect of nitride formation on the oxidation kinetics of Zry-4 fuel cladding under steam-air atmospheres at 1273-1573 K

Negyesi, M.; 天谷 政樹

Journal of Nuclear Materials, 524, p.263 - 277, 2019/10

The study deals with the oxidation behavior of fuel cladding under mixed steam-air atmospheres. Oxidation tests of Zry-4 were carried out at temperatures of 1273-1573 K. Post-test weight gain measurement along with metallographic examination were conducted to study separately the kinetics of the region where nitrides formed and the nitride-free region. The weight gain coming from the nitride-free region was estimated employing one-dimensional finite difference oxygen diffusion model and measured thicknesses of the metallic part of the oxidized specimen, the columnar oxide and the oxygen stabilized $$alpha$$-Zr(O) as well as the fraction of the columnar oxide at the oxide/metal interface. Consequently, the weight gain related to the nitride formation has been assessed.

論文

Effect of experimental setting and surface roughness on oxidation behavior of Zry-4 in steam at 1273 K

Negyesi, M.; 天谷 政樹

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05

This work deals with oxidation behavior of Zry-4 fuel cladding exposed to steam at 1273 K. The condition corresponds to LOCA. The effect of the specimen surface roughness and experimental setting on the oxidation behavior was investigated by employing two experimental techniques for oxidation tests and metallographic analysis along with hydrogen pick-up measurement. Slower heating rate under steam flow led to significantly slower oxidation rate during the subsequent isothermal exposure. As a consequence, the breakaway was delayed substantially. The effect of the specimen surface roughness on the oxidation behavior seemed to be rather minor under the investigated conditions. On the other hand, hydrogen uptake was found to be substantially affected by both the specimen surface roughness and the tested experimental setting.

論文

The Influence of the air fraction in steam on the growth of the columnar oxide and the adjacent $$alpha$$-Zr(O) layer on Zry-4 fuel cladding at 1273 and 1473 K

Negyesi, M.; 天谷 政樹

Annals of Nuclear Energy, 114, p.52 - 65, 2018/04

 被引用回数:1 パーセンタイル:38.14(Nuclear Science & Technology)

The growth kinetics of the columnar oxide and $$alpha$$-Zr(O) layers of Zry-4 under mixed steam-air conditions at temperatures of 1273 and 1473 K were investigated in this study be means of post-test metallographic measurements. The hydrogen uptake was also determined by the inert gas fusion technique. The kinetics of the columnar oxide layer obeyed a parabolic law for all air fractions at both temperatures. The kinetics of $$alpha$$-Zr(O) layer appeared to deviate slightly from the parabolic law. The parabolic oxidation rate constant of the columnar oxide increased with increasing air fraction, whereas the parabolic oxidation rate constant of $$alpha$$-Zr(O) layer seemed to be independent of the air fraction. Mixed steam-air conditions appeared to enhance hydrogen absorption substantially, especially after the columnar oxide lost its protectiveness.

論文

Oxidation kinetics of Zry-4 fuel cladding in mixed steam-air atmospheres at temperatures of 1273 - 1473 K

Negyesi, M.; 天谷 政樹

Journal of Nuclear Science and Technology, 54(10), p.1143 - 1155, 2017/10

 被引用回数:2 パーセンタイル:42.02(Nuclear Science & Technology)

This paper deals with the oxidation behavior of Zry-4 nuclear fuel cladding tubes in mixed steam_air atmospheres at temperatures of 1273 and 1473 K. The main goal is to study the oxidation kinetics of Zry-4 fuel cladding in dependence on the air fraction in steam in the range from 0 up to 100%. The purpose of this study is to provide experimental data suitable for an oxidation correlation applicable for thermomechanical analysis codes of nuclear power reactor under severe accidents. The influence of the air addition in steam on parameters of Zry-4 kinetic equation has been quantified using the results of weight gain measurements. At 1273 K, both pre-transient and post-transient regimes were treated. The results of weight gain measurements showed a strong dependence of the Zry-4 oxidation kinetics on the air fraction in steam, especially at 1473 and at 1273 K in the post-transient regime.

論文

High temperature oxidation of Zry-4 in oxygen-nitrogen atmospheres

Negyesi, M.; 天谷 政樹

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 10 Pages, 2017/07

Zry-4 fuel cladding tubes were exposed in mixtures of oxygen and nitrogen at temperatures of 800-1380 $$^{circ}$$C. The influence of various flow rates of oxygen and nitrogen as well as specimen height on the weight gain was examined. The overall weight gain was substantially affected by both the applied flow rates and the height of specimens. The oxidation kinetics in air was assessed based on the results of weight gain measurements. A transition in the kinetics was observed at 800 and 1000 $$^{circ}$$C. The kinetics in the post-transient regimes was rather accelerated than linear. The equation proposed in this study for air condition was in good agreement with the Leistikow-Berg correlation and the Baker-Just correlation. Prior $$beta$$-phase shrinked when the oxide scale along with the $$alpha$$-Zr(O) layer progressed. Eventually, both the specimen plastic strain and maximum load decreased due to the shrinkage and increasing embrittlement of the prior $$beta$$-phase.

論文

Oxidation behavior of Zry-4 in steam-air mixtures at high temperature

Negyesi, M.; 天谷 政樹

Proceedings of Annual Topical Meeting on LWR Fuels with Enhanced Safety and Performance (TopFuel 2016) (USB Flash Drive), p.1065 - 1074, 2016/09

This study dealt with oxidation behavior of Zry-4 nuclear fuel cladding under a severe nuclear reactor accident scenario. Influence of the reaction extent on cladding mechanical properties was also treated. Zry-4 fuel cladding segments were exposed to steam atmosphere containing different amount of air in composition ranging from 0 to 100 vol.%. Exposure times covered both pre- and post-breakaway regimes. Metallographic observations along with microhardness testing were carried out to study the effect of air fraction on the material microstructure. Hydrogen pick-up was measured and residual mechanical properties were assessed employing Ring Compression Tests. The results show that the addition of air in steam can lead to more than 300% increase of weight gain in case of $$sim$$ 50% or higher air fraction after the exposure of 60 min., namely, "late post-breakaway regime". Approximately three times thicker oxide scales were observed in such cases, indicating that most of the weight gain was due to the oxide layer increase. Nitride phase was preferentially observed close to the interface between oxide and metal layers. The $$alpha$$-Zr(O) sublayer thickness decreases with the increasing fraction of air in steam. Microhardness, measured within the prior $$beta$$-phase region, slightly depends on the air fraction. Hydrogen uptake, on the other hand, depends strongly on the air fraction in steam. In the case of shorter exposure times, the effect of air addition in steam was suppressed. Eventually, specimen plastic strains drastically reduced in the late post-breakaway regime.

口頭

Oxidation and embrittlement behaviors of Zry-4 cladding in air-containing atmospheres at high temperatures

Negyesi, M.

no journal, , 

The presentation deals with oxidation behavior of Zry-4 alloy during severe accidents of LWR. Zry-4 fuel cladding was exposed in steam-air mixtures at temperatures of 1000-1200 $$^{circ}$$C. Specimen weight gain was measured, metallographic observations were carried out, hydrogen uptake was determined and ring compression tests were conducted. The oxidation kinetics of Zry-4 was significantly affected by the air fraction in steam at 1000 $$^{circ}$$C in the post-transient regime and at 1200 $$^{circ}$$C. The effect of air fraction was diminished at 1000 $$^{circ}$$C in the pre-transient regime. Metallographic examination revealed severe oxide layer cracking and nitride formation. Substantial hydrogen pick-ups were measured, especially at 1000 $$^{circ}$$C after 60 min, strongly depending on the air fraction. They probably led to the significant decrease in plastic strain at 1000 $$^{circ}$$C after 60 min. The effect of air fraction on plastic strain has been hardly observed at 1200 $$^{circ}$$C.

口頭

Oxidation and embrittlement behaviors of Zry-4 cladding in steam-air mixtures at high temperatures

Negyesi, M.

no journal, , 

The presentation deals with oxidation behavior of Zry-4 fuel cladding during severe accidents of LWR. Zry-4 fuel cladding was exposed in steam-air mixtures at temperatures of 1273-1473 K. Specimen weight gain was measured, metallographic observations were carried out, hydrogen uptake was determined and ring compression tests were conducted. It was found out that the oxidation behavior of Zry-4 may be affected significantly by the experimental setting. Higher air fraction in steam accelerated the oxidation kinetics substantially. The kinetics of the oxide and $$alpha$$-Zr(O) layers have been also assessed. Substantial hydrogen pick-ups were measured, strongly depending on the air fraction. As a consequence, the mechanical properties deteriorated significantly.

口頭

Study on breakaway oxidation of Zry-4 fuel cladding

Negyesi, M.

no journal, , 

This study deals with high-temperature steam oxidation behavior of Zry-4 fuel cladding. The experimental conditions correspond to the loss of coolant accident (LOCA) of LWRs. Oxidation tests were carried out at 1273 K employing two experimental techniques. The effect of the heat-up conditions on the subsequent isothermal oxidation rate were investigated. Furthermore, the effect of specimen surface roughness on the oxidation behavior was treated. The oxidation rate during the isothermal exposure was substantially suppressed at higher degrees of oxidation upon the heat-up. Consequently, the well-known "breakaway" effect, which results in accelerated oxidation rate, was found to be significantly delayed. The effect of the surface roughness on the oxidation behavior appeared to be rather minor under the test conditions of this study. The effect of the degree of oxidation upon the heat-up showed to be crucial and needs to be further addressed when evaluating the "breakaway" effect.

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