Analysis of CABRI-BI1 Loss of Flow Experiment based on ISAA-Na

[Background]: Sodium boiling is a critical transient phenomenon prior to severe accidents in sodium-cooled fast reactors. Accurate prediction of the two-phase state and thermodynamic parameters of the coolant during sodium boiling is essential for sodium-cooled fast reactors accident analysis. [Purpose]: This paper aims to develop a core thermal-hydraulic model for the sodium-cooled fast reactor integrated analysis program ISAA-Na, based on the multi-bubble liquid slug assumption. [Methods]: The ISAA-Na code was used to simulate and analyze the loss-of-flow experiment CABRI-BI1 (Cœur à Haut Bûrnup Irradiation). [Results]: Comparison with experimental data shows that ISAA-Na provides more accurate predictions of coolant temperature and pressure prior to boiling compared to other codes such as SAS4A, ASTEC-Na, and SIMMER. However, after the onset of boiling, overestimations of bubble growth rate and two-phase interface movement were observed due to the lack of fuel melting and cladding failure models. [Conclusions]: Overall, the application of the multi-bubble liquid slug boiling model in ISAA-Na for the analysis of the CABRI-BI1 experiment is deemed reasonable and reliable.

[背景]：钠沸腾是钠冷快堆严重事故前的关键瞬态现象。准确预测钠沸腾过程中冷却剂的两相状态与热力学参数，对钠冷快堆事故分析至关重要。[研究目的]：本文基于多气泡液塞假设（multi-bubble liquid slug assumption），旨在为钠冷快堆整体分析程序ISAA-Na开发堆芯热工水力模型（core thermal-hydraulic model）。[研究方法]：采用ISAA-Na程序对失流实验（loss-of-flow experiment）CABRI-BI1（Cœur à Haut Bûrnup Irradiation，高燃耗堆芯辐照实验）开展模拟与分析。[研究结果]：与实验数据对比结果显示，相较于SAS4A、ASTEC-Na及SIMMER等程序，ISAA-Na对沸腾前冷却剂温度与压力的预测更为准确。但在沸腾发生后，由于未纳入燃料熔化（fuel melting）与包壳失效（cladding failure）模型，该程序对气泡生长速率（bubble growth rate）及两相界面运动（two-phase interface movement）存在高估现象。[研究结论]：总体而言，将多气泡液塞沸腾模型应用于ISAA-Na程序以分析CABRI-BI1实验，被认定为合理且可靠。