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The Effect of oxidation-and-quenching process during a LOCA on the behavior of the oxidation and embrittlement of Zircaloy-4 cladding under reheating transients

LOCA時の酸化および急冷が再昇温時のジルカロイ4被覆管の酸化/脆化挙動に与える影響

三輪 英紀; 天谷 政樹

Miwa, Hideki; Amaya, Masaki

冷却材喪失事故時の高温酸化や急冷却が、長期炉心冷却機能喪失時の酸化・脆化挙動に与える影響を確認するために、急冷後再昇温を模擬した温度推移条件で両面酸化試験、リング圧縮試験およびクエンチ試験を実施した。未照射ジルカロイ-4被覆管の試料を水蒸気流中で1173Kから1473Kの温度で酸化し、その後に室温の冷却水にて急冷した。再昇温試験はこの試料を用いて水蒸気流中で1173Kから1473Kの温度で実施した。特定の急冷後再昇温の条件では酸化膜成長や重量増加の低減が見られた。しかしながら、急冷後再昇温を含む温度推移が被覆管脆化に与える影響は顕著でなかった。急冷後再昇温を含む温度推移条件下での被覆管の脆化挙動はBaker-Justの式を用いて算出したECRで評価できることが分かった。

Two-sided oxidation tests, ring compression tests and semi-integral quench tests on Zircaloy-4 cladding specimens were conducted under the temperature transient conditions simulating a post-quench reheat transient in order to evaluate the effect of high temperature oxidation and quenching during a LOCA on the behavior of the oxidation and embrittlement of the cladding under a loss of long-term-core-cooling condition. Test specimens prepared from non-irradiated Zircaloy-4 cladding tube were oxidized at a temperature between 1173 and 1473 K in steam flow and quenched by soaking the specimen in room temperature water. By using the test specimens, re-heating tests were performed in steam flow at a temperature between 1173 and 1473 K. The suppression of oxide layer growth and weight gain was observed under certain reheating-after-quenching conditions. Nevertheless, it seemed that the temperature transients including quenching-and-reheating process did not significantly affect the embrittlement of cladding. It was found that the embrittlement behavior of cladding during the temperature transients including quenching-and-reheating process could be dealt with on the basis of the ECR based on Baker-Just correlation.

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