蒸気発生器水ブロー系の最適運用に係わる計算

Analyses for finding the most suitable operation method of steam generator water/steam blow-down system

吉岡 直樹*; 長田 博夫*; 岸田 雅子*

not registered; not registered; Kishida, Masako*

蒸気発生器(SG)の安全性評価上重要な課題と考えられている伝熱管の過熱型破損事象に関する研究が進められている。この事象では伝熱管内の除熱効果が評価結果に大きな影響を及ぼすことから、通常運転時及び水ブロー中を含めて水蒸気系の挙動を詳細評価して、除熱条件を定めることが重要である。本作業では過熱型破損事象の評価に必要な除熱条件を定めることを目的に、主に水蒸気系の設備仕様や運転条件をパラメータにしたBLOOPHコードによる水ブロー解析、及び、反応熱を考慮した水側状態量の補正を行った。また、BLOOPHコードによる解析の妥当性を確認するため、汎用熱流動解析コードRELAP5/Mod.2)による水ブロー解析を行った。これら作業により以下の結果が得られた。(1)放出弁容量等を変更した場合のブロー特性の変化を把握できた。また、ブロー途中に伝熱管内で発生する可能性のある極低流量の継続時間を短縮する方法を見い出した。(2)放出系容量の最適設計手法を案出した。(3)過熱型破損事象の評価に必要な除熱条件を定めることが出来た。(4)同じ解析課題に対するBLOOPHとRELAP5/Mod.2の解析結果は、圧力及び流動挙動に関し、概ね一致した。このことによりBLOOPHコードによる解析の妥当性が確認された。(5)BLOOPHコードの解析精度の確認、向上のために必要な開発課題が明かとなった。

The steam generator (SG) tube rupture phenomenon due to overheating by sodium-water reaction is considered as an important issue on SG safety evaluation and has been studied intensively. At this phenomenon, the cooling effect by the water/steam flow inside the tubes plays a significant role. Therefore, it is important to define the cooling effect by analyzing the behavior of the water/steam side during normal operation and during water/steam blow-down for overheating failure evaluation. In this work, the cooling effect was analyzed by a FBR SG blow-down analysis code, BLOOPH, and was corrected by taking the generated heat from the sodium-water reaction into account. In these analyses, the capacity and the operation method of the SG blow down system were treated as parameters. In order to confirm validity of the BLOOPH code, a similar analysis was carried out for the reference case by the thermal-hydraulic analysis code, RELAP5/Mod.2, that has been used widely for analyses of the LOCA phenomena of LWRs. The following results have been obtained by this work. (1)The effect of the capacity of the SG blow-down system on the SG blow-down characteristics has been well understood. A method has been found for reducing the time duration of the small flow rate which might occur inside the tubes during the blow-down. (2)A methodology has been established to design the most optimum SG blow-down system. (3)Analyses have been perfomed to define the cooling conditions needed for overheating failure evaluation. (4)The results by the code BLOOPH and RELAP5 have shown a reasonably good agreement regarding the water/steam pressure and the hydraulic behavior during the blow-down for the reference blow-down system. The validity of the BLOOPH code has been confirmed. (5)Research and development items have been clarified to improve the BLOOPH code in future.