In this paper predicted results obtained with the POLCA-T code are compared to measurement data from an all recirculation pump trip test made at the Nuclear Power Plant Olkiluoto 1 during its commissioning in 1978. Olkiluoto 1 is one of three nuclear power plants owned by the electrical power company Teollisuuden Voima OY in Finland. The prediction is based on a best estimate reactor analysis code that incorporates a full 3D model of a reactor core into a system model. The use of a coupled code provides a means to simulate interactions between the reactor core and the plant dynamics to increase the understanding of different events and its impact on the core behaviour. The following conclusions are made based on the simulations with POLCA-T of the Olkiluoto 1 commissioning test of tripping all recirculation pumps: • POLCA-T predicts the event accurately, the flow coast down and the power decay is in good agreement with measured data. • 3D effects in channel flow can not be observed. The observed effects support the current use of a 1D approach since this is conservative with respect to power and the evaluation of Operating Limit Critical Power Ratio, (OLMCPR). This conclusion is also supported by measurement data.

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