The Influence of the air fraction in steam on the growth of the columnar oxide and the adjacent -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

https://doi.org/10.1016/j.anucene.2017.12.017

The growth kinetics of the columnar oxide and -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 -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 -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.

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 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 -Zr(O) sublayer thickness decreases with the increasing fraction of air in steam. Microhardness, measured within the prior -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.

水蒸気と反応したジルカロイ管のX線回折; 生成物の同定

本橋 治彦; 古田 照夫

JAERI-M 8649, 28 Pages, 1980/01

JAERI-M-8649.pdf:1.06MB

軽水炉の冷却材喪失事故(LOCA)条件において被覆の破裂と水蒸気酸化によって起るジルカロイ被覆の内面酸化挙動を明らかにする目的で、滞留水蒸気あるいは水蒸気・水素混合雰囲気中でジルカロイ-4管の高温酸化を行った。そして主として被覆管表面に形成した酸化膜をX線回析法によって調べた。この結果2つの異なった酸化物が観察され、1つは単斜晶ZrOのみで形成され、他方は単斜晶と正方晶ZrOの混合物から形成されている。また酸化膜とジルカロイ金属相の界面では準安定相といわれるZrOがZrOの結晶系によらずほとんど形成されていることがわかった。水素吸収量の多いジルカロイ管では金属相中に8-ZrH.5の水素化物が析出しいていることが認められた。