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蒸気発生器伝熱管破損解析コードの開発(II); ナトリウム側伝熱モデルの改良

Development of tube rupture evaluation code for FBR steam generator (II); Modification of heat transfer model in sodium side

浜田 広次  ; 栗原 成計 

Hamada, Hirotsugu; Kurihara, Akikazu

蒸気発生器水リーク時の高温ラプチャ型破損に対する伝熱管の構造健全性を合理的に評価するために、ナトリウム-水反応ジェットが隣接伝熱管に及ぼす熱的な影響を検討し、新伝熱モデル等の開発と適用解析を実施した。本報で得られた主な成果を以下にまとめる。(1)反応ジェットにさらされたターゲット伝熱管における熱流束および熱伝達率の詳細評価手法を開発した。本手法を用いると、従来のモデルと比較して熱流束を現実的に評価できることを確認した。 (2)反応ジェットと伝熱管の間の伝熱特性を二相流モデルで理論的に検討し、伝熱特性に及ぼすカバーガス圧力と流体温度の影響を考慮した新伝熱モデルを開発した。本モデルにより、合理的な実験整理式およびSWAT-1R等試験データに基づく実験係数の暫定値を導出することができた。(3)高温ラプチャ解析コードTRUEに新伝熱モデル等を反映し、SWAT-3等のナトリウム-水反応試験データにより、モデルの保守性を確認した。(4)新伝熱モデルによる英国大リーク事故への適用解析では、従来の解析結果と大きく異ならないこと、すなわち、伝熱管内の減圧特性の重要性を確認できた。(5)新伝熱モデル等による「もんじゅ」蒸発器への適用解析では、従来の解析結果が十分保守的であり、現実的には累積損傷の最大値が25%程度低減できる見通しであることを確認した。

The thermal effect of sodium-water reaction jet on neighboring heat transfer tubes was examined to rationally evaluate the structural integrity of the tube for overheating rupture under a water leak in an FBR steam generator. Then, the development of new heat transfer model and the application analysis were carried out. Main results in this paper are as follows. (1)The evaluation method of heat flux and heat transfer coefficient (HTC) on the tube exposed to reaction jet was developed. By using the method, it was confirmed that the heat flux could be realistically evaluated in compatison with the previous method. (2)The HTC between reaction jet and the tube was theoretically examined in the two-phase flow model, and new heat transfer model considering the effect of fluid temperature and cover gas pressure was developed. By applying the model, a tentative experimental correlation was conservatively obtained by using SWAT-1R test data. (3)The new model was incorporated to the Tube Rupture Evaluation Code (TRUE), and the conservatism of the model was confirmed by using sodium-water reaction data such as the SWAT-3 tests. (4)In the application analysis of the PFR large leak event, there was no significant difference of calculation results between the new model and previous one; the importance of depressurization in the tube was confirmed. (5)In the application analysis of the Monju evaporator, it was confirmed that the calculation result in the previous model would be more conservative than that in the new one and that the maximum cumulative damage of 25% could be reduced in the new model.

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