Analysis on non uniform flow in steam generator during steady state natural circulation cooling

定常自然循環冷却時の蒸気発生器における非一様流動の解析

Susyadi; 与能本 泰介 

Susyadi; Yonomoto, Taisuke

ROSA/LSTF実験で観測された蒸気発生器(SG)U字管群での非一様流動に着目しPWRにおける定常自然循環を検討した。RELAP5/MOD3コードを用いた解析では、SG挙動を、一次系を1本、又は、5本、又は、9本の平行流路で表し、実験に基づく境界条件を使用するSGモデルを用いて解析した。その結果、5ないし9本の平行流路を用いる場合、逆流,流入と排水,二相成層のような重要な非一様流動現象や、実験と同様な安定な出口流動を再現できることがわかった。しかし二次系への伝熱量は最大15%過小評価された。さらに、特に低圧条件において注意深く入口流量を設定する場合のみ安定な自然循環挙動が得られるなど、定常状態を確立するための問題が見いだされた。

Steady-state natural circulation (NC) in the PWR was investigated focusing on non uniform flow among steam generator (SG) U-tubes observed in the ROSA/LSTF experiments. In the analysis using the RELAP5/MOD3 code, the SG behavior was analyzed using the partial SG model with one, five, or nine parallel flow paths in the primary side and boundary conditions based on the experiments. The results showed that simulations using the model with five or nine tubes were capable to capture important non uniform phenomena such as reverse flow, fill and dump and stagnant vertical stratification, and the stable SG outlet flow as observed in the experiments. Heat transfer rates to the secondary side were, however, underpredicted by up to 15%. Furthermore, difficulties were found in establishing the steady state condition especially for the low pressure analysis: only when the inlet flow rate was carefully imposed, stable NC behavior was obtained.