Lumped parameter, state variable dynamic models for U-tube recirculation type nuclear steam generators

A number of lumped parameter dynamic models were developed for a vertical U-tube recirculation steam generator (UTSG) of the type used in most pressurized water reactor nuclear steam supply systems. The models ranged in complexity from a simplified model (Model A) with only three lumps to represent the primary fluid (reactor coolant), tube metal, and the secondary fluid to a detailed model (Model D) with fourteen lumps and a moving boundary between the subcooled and boiling sections of the heat exchange region. The models are linear and are in the state variable form which is convenient for using standard general purpose computer codes for time or frequency domain analysis. The adequacy of the models was tested in several ways. The calculated response from the models was studied for physical plausibility. The adequacy of the analytical work was tested by comparing results from progressively more detailed models. The detailed model response was compared with the results of other UTSG dynamic models and with test results obtained at the H.B. Robinson (739 MWe PWR) plant. All of the checks on model validity demonstrated the adequacy of the lumped parameter approach for the simulation of the dynamic response of a UTSG for normal operating transients involving small deviations from the steady state conditions