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プラント動特性解析コードSuper-COPDの開発,2; もんじゅ試運転データによる自然循環解析機能の検証

Development of plant dynamics analysis code Super-COPD, 2; Validation of natural circulation analysis function by MONJU experimental data

大滝 明 

Ohtaki, Akira

自然循環による崩壊熱除去の評価に対するプラント動特性解析コードSuper-COPDの適用性を検討するため、1次/2次熱輸送系単独の場合及びそれらを組み合わせた場合を対象としたもんじゅ自然循環模擬試験の解析を実施した。1次系の解析では炉心部のモデル化及び系統の圧力損失特性を、2次系の解析ではオーバーフロー系の汲み上げの有無をパラメータにそれらの影響を検討した。1次系及び2次系の自然循環解析では、炉心部流路のモデル化とともに、自然循環力を算出する流路の軸方向高さに関する入力データが重要である。また、過渡変化の開始から自然循環状態への移行過程において、熱輸送系の自然循環流量が定格値の1$$sim$$2%と比較的少ない場合は、自然循環力の評価に対して配管部の温度成層化の影響がみられることから、成層化に対するモデル化の必要性が指摘された。自然循環移行過渡時に2次系蒸発器側流路に生じる流れ方向の順流/逆流の変化は、オーバーフロー系の考慮により再現できた。1次系2次系とを組み合わせた総合解析結果と実測データは、$$pm$$10%範囲内で一致しており、自然循環除熱特性評価に対するSuper-COPDコードの適用性及び系統全体解析モデルの妥当性が確認できた。

In this paper analyses of natural circulation simulation tests in Monju were conducted to study the applicability of a plant dynamics analysis code (Super-COPD) to the evaluation of decay heat removal by natural circulation. At first basic characteristics of both primary and secondary heat transport systems were examined by separate analyses and then integral system analyses with primary and secondary systems were conducted to confirm the whole system behavior. A modeling of the reactor core and pressure loss characteristics were selected as analysis parameters in the primary system analyses. The effect of the overflow line on natural circulation characteristics were examined in the secondary system analyses. By the separate analyses it was indicated that a precise modeling of core flow channels and input data of axial height for calculating natural circulation head were important for the evaluation of natural circulation characteristics. In addition in the case of low flow condition (about 1-2% of rated flow), the effect of thermal stratification in the horizontal pipe on natural circulation head was observed during the transition to natural circulation condition. Therefore, the need of modeling for thermal stratification in the piping system was pointed out. The switching of flow direction from forward flow to back flow observed at the evaporator side in the secondary system was successfully simulated by the consideration of the overflow line. The results of synthesis analyses with primary and secondary systems were agreed with the measured data in Monju within the accuracy of 10%. Thus it was confirmed that Super-COPD is applicable to the evaluation of decay heat removal by natural circulation.

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