Study on Total Instantaneous Blockage Accident for CEFR

Chinese Experimental Fast Reactor (CEFR) is under construction in China. It is essential to investigate core disruptive accidents (CDAs) for the evaluation of CEFR’s safety characteristic. Accident of total instantaneous blockage in single assembly scale had already been modeled and analyzed. The degradation scenario had been calculated by a fluid-dynamics analysis code for liquid-metal fast reactors (LMFRs). For further investigation of accident process and influence to the near bundles, the seven assembly scale were then simulated and calculated. Total instantaneous blockage was assumed to occur in the center assembly under normal operating conditions and consequences to neighboring assemblies were studied. The result shows that the key events such as sodium boiling, clad melting, fuel particles relocation, hexcan failure and melt discharge into neighboring six assemblies symmetrically were adequately simulated. All the key events appeared in the same sequence as the single assembly simulation, while hexcan failure occurred later than that of single assembly simulation. The reason for the different timing may be the boundary condition assumption can influence the heat removal from the blocked assembly. The seven-assembly scale model can reduce the boundary condition’s uncertainties and help to give a better understanding and prediction of hypothetical accident scenario in subassembly blockage accidents for CEFR.