Simulation of ATWS transients with APROS

The paper describes simulation of the Loviisa nuclear power plant ATWS-transients with APROS (Advanced Process Simulator) using several new or improved models. These include one-dimensional core model, boron transport model in the primary circuit, improved pressuriser model, new turbine model, new condenser model and improved calculation of low pressure nodes. The APROS results are compared both with the Loviisa Training Simulator results and with the results of SMATRA code. The results indicate that at present APROS is capable of simulating the Loviisa ATWS-type transients. The results also indicate that the new or improved models have fulfilled their task