Modification of the Reflood Model in RELAP5/MOD3.1

Abstract

A few features of the reflood model in RELAP5/MOD3.1 have been modified to improve the unrealistic prediction results of the model. In the new method, the modified Zuber pool boiling critical heat flux correlation is adopted in the range of mass flux G < 150 kg/m2·s. The new criterion for reflood drop size, which is characterized by the use of We = 1.5 and a minimum drop size of 0.0007 m for p* ≤ 0.025, has been suggested based on some experimental data and the correlation derived through regression analyses of many reflood experiments. To describe the wall-to-vapor heat transfer at low pressure and low flow, the Webb-Chen correlation is utilized. The suggested method has been verified through simulations of the Lehigh University rod bundle reflood tests. A sensitivity study shows that the effect of drag coefficients is dominant in the reflood model. It is proved that current modifications result in much improved quench behavior and accurate wall and vapor temperature predictions when they are compared with those by the frozen version of RELAP5/MOD3.1.