An Experimental research on the effect of the axial power distribution on the critical power

軸方向出力分布の限界出力に及ぼす影響の実験的研究

Liu, W.; 呉田 昌俊   

Liu, W.; Kureta, Masatoshi

稠密格子炉心熱流動特性技術開発で対象とする炉心は二重炉心であり、軸方向の熱流束分布がステップ状に急峻に変化する特徴を有する。本技術開発において37本バンドル限界出力試験を実施し、各種パラメータが限界出力に及ぼす影響を明らかとしたが、軸方向出力分布に関しては熱的に厳しい条件を評価対象基準として固定しており個別評価はなされていなかった。このため、軸方向出力分布が限界出力に及ぼす影響を別途モデル実験で明らかにして、各種限界出力相関の適用性を評価することが必要であった。そこで、本研究では、二重炉心の三層分をモデル化した試験体を用いて、軸方向出力分布形状及び相対出力比が限界出力等に及ぼす影響を明らかにし、各種限界出力相関の二重炉心体系への適用性を評価することを目的としてモデル実験を実施した。その結果、軸方向出力分布の効果が明らかとなり、限界クオリティー限界熱流束相関法と限界クオリティー限界沸騰長相関法を相互補完的に組合せることで軸方向出力分布の影響を比較的よく相関できる見通しを得た。

R&D project to investigate thermal-hydraulic performance in the tight-lattice rod bundles for Innovative Water Reactor for Flexible Fuel Cycle (FLWR) has been progressed at Japan Atomic Energy Agency (JAEA). The basic thermal-hydraulic characteristics about the critical power and the pressure drop, under both steady and transient conditions, have been ascertained with using 37-rod tight lattice bundle. The effect of the spacer on the critical power has also been ascertained. However, as to the axial power distribution, the severest one - which is called as the basic heating case in this research - is selected in these experiments, with no considering to the change of the axial power distribution with the proceeding of the burnup. Therefore, an experimental research on the effect of the axial power distribution on the critical power is necessary. In this paper, an experimental research on the effect of the axial power distribution on the critical power is performed under the atmospheric pressure with using a circular tube, which is axially divided into 3 insulated levels and is heated separately by 3 DC power supplies. The test section is capable to simulate the power distribution in the double-humped core. Axial uniform heating condition, the upper 3 layers simulation and the center 3-layers simulation of the basic heating case are selected as the cases for the detailed evaluation. The effects of relative power ratio on the critical power, critical quality and critical boiling length under different heating conditions are ascertained for the detailed evaluation cases. With using the experimental data, existed correlating methods for the boiling transition are evaluated. As the result, a combination of the critical quality - boiling length method and the critical heat flux - critical quality method is found a good correlating to the present data with a changed axial power distribution.