高速炉蒸気発生器におけるナトリウム-水反応時の水側伝熱特性

Characteristics of heat transfer inside tube during sodium-water reaction in FBR steam generator

栗原 成計 ; 大島 宏之; 門出 政則*

Kurihara, Akikazu; Ohshima, Hiroyuki; Monde, Masanori*

高速炉蒸気発生器では、伝熱管損傷による水漏えいでナトリウムと水とが化学反応を起こし伝熱管損傷範囲が拡大する可能性がある(ナトリウム-水反応)。ナトリウム-水反応時の高精度予測には伝熱管内部の伝熱特性を理解することが重要であるため、純水を、内部圧力11.213.4MPa,初期サブクール水温度200C,質量流束45.73630kg/(ms)の条件で流し、高周波誘導加熱装置による急速加熱試験を実施した。実験では試験体加熱部の3断面で周方向の異なる2か所において伝熱管壁の温度変化を測定し、逆解法を用いて急速加熱時の内表面熱流束及び温度を評価した。実測した外表面熱流束と逆問題による評価値を比べ、20%以内の精度で評価できることを確認した。内表面の伝熱特性は質量流量の影響を強く受け、内表面では加熱時に核沸騰から遷移-膜沸騰へ推移し、加熱制御時に核沸騰へ戻ることを確認した。遷移沸騰域では沸騰曲線で左回りのサイクルが現れており、核沸騰と膜沸騰が時間変化に対して空間的に共存した状態となっている。併せて、高温ラプチャに適用できる伝熱相関式を確認した。

Sodium reacts chemically with water in the case of the unexpected tube failure of a steam generator (SG) in a fast breeder reactor (FBR). It is integral in order to predict the event with high accuracy to understand the characteristics of heat transfer inside a tube in detail during the tube failure (sodium-water reaction). Experiments were performed using purified water under the following conditions; initial pressure of 11.2-13.4 MPa, initial water temperature of 200 C and water mass flux of 45.7-3630 kg/(ms). A test tube was heated rapidly by high frequency induction current. The time averaged heat flux was estimated using an inverse solution from the measured temperatures at two points on three different locations along the tube. It was confirmed that the derived values agreed with measured heat fluxes on the outer surface within 20% accuracy. It was found that the characteristics of the heat transfer strongly depended on the flow rate. The heat transfer on the wall changed from nucleate boiling to transient-film boiling during increasing the heat flux and returned to the nucleate boiling during decreasing the heat input. A counterclockwise cycle always appeared in the transition boiling region, where the nucleate and film boiling coexisted and the area ratio of these varied with time. The adequacy of heat transfer correlations to evaluate tube overheating were confirmed.