Risk Evaluation of Flow-Accelerated Corrosion Based on One-Dimensional FAC Code

The possibility of thousands of flow-accelerated-corrosion (FAC) zones causes long and costly inspection procedures for nuclear, as well as fossil-fuel power plants, even if the number of zones is minimized on the basis of temperature and flow velocity. In order to decrease the number of inspection zones, suitable prediction or estimation procedures for FAC occurrence should be applied, and the resulting computer programs should be tuned with as many inspection data as possible. Such coupling of the estimation and inspection procedures should allow effective and reliable preparation to be made against FAC occurrence and propagation.

This paper defines the FAC risk as the mathematical product of the possibility of the occurrence of wall thinning and its hazard scale. The possibility of the occurrence of wall thinning was designated as the time margin for pipe rupture determined by applying a one-dimensional FAC code, which could predict the wall-thinning rate with an accuracy within a factor of 2, while the hazard scale was defined as the volume of effluent steam and water from the ruptured mouth, which was enthalpy of water originally flowing in the pipe multiplied by the square of the pipe inner diameter. High FAC risk zones along entire cooling systems could be evaluated in only one-tenth or one-hundredth of the computer time as for a three-dimensional FAC code to determine the priority for inspection-order importance.