CEFLASH-4AS: a computer program for the reactor blowdown analysis of the small break loss-of-coolant accident. [PWR]

The document describes modifications to the CEFLASH-4AS computer code which provide for a more realistic description of the small break LOCA, particularly for break areas less than 0.2 ft/sup 2/. The model changes include: (1) a steam generator heat transfer model which considers heat transfer in the steam region; (2) a new variable drift velocity model; (3) an improved inner vessel geometry model; and (4) an option to prohibit the return to nucleate boiling during blowdown. In addition to these modeling changes, several general improvements have been made to the code. These include: (1) an optimization of the transient equations integration scheme; (2) generalized data input and (3) an improved plot package. These improvements result in a decrease in computer running time and an increase in user convenience. They do not affect any of the transient responses calculated by the code.