Application of time-dependent growing mesh for crud growth simulation in single rod scale

Abstract

CRUD-induced power shift (CIPS) is one of the reasons of the Axial Offset-Anomaly (AOA) which reduces the operation safety margin. The CIPS results from local boron hide-out in a corrosion-related unidentified deposit (CRUD) layer. In addition, due to the low conductivity of CRUD layer, the temperature peak is occurred when non-uniform CRUD layer, named as CRUD-induced local corrosion (CILC). The increased and imbalanced temperature distribution of cladding surface can threaten the integrity of the fuel cladding. The objective of this study is to develop multi-physics simulation code for predicting the CRUD thickness distribution in full-core scale. The development is conducted by coupling with physics-oriented 1-D based external codes which calculate thermal-hydraulic and chemical variables. Furthermore, by using time-dependent growing mesh, the computational simulation can predict gradually growing computing domain in CRUD layer and be coupled with heat-transfer calculation. To achieve full core scale parallel computing method is conducted using message passing interface (MPI) method to decrease computational load. Prediction of CRUD growth is conducted with several inputs such as power, turbulent kinetic energy (TKE), particulate concentration and wick-boiling heat flux. The concentration of the particulate, nickel ferrite (NiFe2O4), is received from CRUD source term model based on water chemistry conditions of primary system. The wick boiling heat flux was derived from CRUD heat transfer & chemistry model which calculate heat transfer and pore-fill kinetics of CRUD layer. Average heat flux and inlet temperature of the coolant are set to 1,000 kW/m2 and 556.76 K, respectively. The distribution of axial relative power and TKE are extracted from reference study which developed coupling with multi-physics framework. The computing domain for the fuel rods is segmented with 400 axial nodes which have the height of 1 cm. The results of calculation shows that the maximum CRUD thickness of approximately 80 μm was calculated for 500 EFPD through axial direction. The calculation result was validated using thickness data of CRUD deposition experiment.