Experimental investigation on characteristics of Multiple-Loops coupled natural circulation system

The passive safety design is advantageous because it simplifies the system and brings higher safety features. Passive residual heat removal system (PRHRS) is one of the most important passive safety systems, which is designed to cool down the reactor during accidental conditions. For floating nuclear power platforms, seawater could be utilized as the final heat sink of PRHRS through multiple-loops coupled natural circulation. To study the operating characteristics and thermal hydraulic behavior of multiple-loops coupled natural circulation system, the Natural Circulation Mechanism Experimental System (NCMES) has been constructed. The station blackout accident (SBO) scenario is simulated in NCMES, which leads to the stopping of circulation pump and operation of PRHRS. Based on the experimental data, an analysis was carried out using the thermal hydraulic system code RELAP5, aiming to validate applicability and accuracy, as well as predict the operating characteristics of the experiment facility. The comprehensive analysis of experimental and calculated results shows that when it comes to the SBO scenario, the releasing residual heat and sensible heat of fluid can be removed to seawater through triple-loops coupled natural circulation; the calculated results fit the experimental data quite well and the RELAP5 code is applicable to predict operating characteristics of multiple-loops coupled natural circulation and PRHRS. As a result of self-adaptive characteristic of natural circulation, with the heating power decreasing, the response rate of natural circulation flow rate and fluid temperature is slow.