核燃料再処理用機器の予防保全に向けたステンレス鋼の沸騰硝酸中での腐食の統計的検討

Statistical approach on corrosion of stainless steel in boiling nitric acid for prevention maintenance of nuclear fuel reprocessing plant

上野 文義  ; 山本 正弘 ; 加藤 千明   

Ueno, Fumiyoshi; Yamamoto, Masahiro; Kato, Chiaki

極低炭素304ステンレス鋼の沸騰硝酸溶液中での腐食について統計的な手法により解析した。蒸発缶の大型モックアップ試験装置を用いて伝熱管の腐食試験を行い、試験後の伝熱管の肉厚と粒界侵食深さを測定し、正規分布やグンベル分布を用いて統計解析した。その結果、伝熱管は均一に腐食すること、肉厚の減少量は粒界侵食深さよりも大きいことがわかった。この結果は、伝熱管の超音波による肉厚測定が沸騰硝酸溶液中のステンレス鋼に生じる粒界侵食を考慮した腐食に対する予防保全に適用できることを意味する。

Corrosion of ultra-low carbon type 304 stainless steel in boiling nitric acid solution was analyzed by statistical approach. A large scale mock-up of an evaporator was introduced to perform corrosion test of heat exchanger tubes, and change in loss of wall thickness and intergranular penetration depths of the tubes during test duration was measured and analyzed statistically applying normal distribution and Gumbel distribution. As the results, it was considered that tube wall was corroded uniformly and maximum value of loss of thickness was not exceeded by maximum depth of intergranular penetration. This conclusion means that tube wall thickness measurement can be applied to prevention maintenance against corrosion with intergranular penetration of stainless steel in boiling nitric acid solution.