A computer code, FAUST (Flow Analysis of U-tube Steam Generator), for U-tube steam generator design analysis is developed on the basis of the PWR core transient analysis code, THERMIT. The original (x,y,z) coordinates used in THERMIT are transformed into the cylindrical (r,$\theta$,z) coordinates for FAUST which are better fitted in the geometry of steam generators. In order to couple the primary side with the secondary side, a 1-dimensional sample tube heat transfer model is developed with a geometrical mapping between the primary and secondary sides. The special unitary group SU(2) is used to treat the complex geometry of the U-bend region for frictional wall force. A form loss model for tube-support plates in two-phase flow is implemented in the code. The steam dome model developed here enables us to consider the different amounts of feedwater distributed into the hot and cold sides of the downcomer. Chemical analysis of the secondary fluid in the steam generator is given here by using the gaseous mass transfer model. Measured data from the steam generator at the BUGEY 4 nuclear power plant are used for the assessment of FAUST. Predicted results for the measured parameters are in good agreement with measured data : circulation ratio within 8\% error and total power within 2\% error. Considerable liquid recirculation is found in the U-bend region as the C.E. design code CALIPSOS shows. The heavier corrosion attack in the cold leg side is predicted due to liquid recirculation. Just above the tube sheet, however, the low void fraction in this region than in the hot leg region results in higher PH, which is well coincident with measured results at the BUGEY 4 nuclear power plant.