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Oxidation kinetics of low-Sn Zircaloy-4 at the temperature range from 773 to 1573 K

773$$sim$$1573Kにおける低スズ・ジルカロイ-4の酸化速度

永瀬 文久; 大友 隆; 上塚 寛

Nagase, Fumihisa; Otomo, Takashi; Uetsuka, Hiroshi

さまざまな冷却材喪失事故条件に適用できる酸化速度式を評価するため、773$$sim$$1573Kという広い温度範囲において低スズ・ジルカロイ-4被覆管の等温酸化試験を行った。1273$$sim$$1573Kでは調べた時間範囲について、773~1253Kでは900sまでの時間範囲について、酸化は2乗則に従った。一方、1253K以下での長時間酸化は、3乗則でよりよく表されることが明らかになった。重量増加に関し2乗則あるいは3乗則定数を評価し、それらの温度依存性を表すアレニウスタイプの式を求めた。3乗則から2乗則への変化及び酸化速度定数の温度依存性に見られる不連続性は、ZrO$$_{2}$$の相変態によるものであることが示された。

Isothermal oxidation tests in flowing steam were performed on low-Sn Zircaloy-4 cladding tubes over the wide temperature range from 773 to 1573 K in order to obtain oxidation kinetics applicable to various loss-of-coolant accident conditions of LWRs. The oxidation generally obeys a parabolic rate law for the examined time range up to 3600s at temperatures from 1273 K to 1573K, and for a limited time range up to 900s from 773 to 1253 K. A cubic rate law is preferable for evaluating the longer-term oxidation at 1253 K and below. The parabolic rate law constant and the cubic rate law constant for measured weight gain were evaluated at every examined temperature, and Arrhenius-type equations were determined in order to describe the temperature dependence of the rate constants. It was indicated that the change of the oxidation kinetics from the cubic to the parabolic rate and the discontinuities in the temperature dependence of the rate constants are caused by the monoclinic/tetragonal phase transformation of ZrO$$_{2}$$.

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パーセンタイル:4.96

分野:Nuclear Science & Technology

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