Aerosol deposition in horizontal steam generator tubes in severe accident conditions

The understanding of fission product deposition in realistic steam generator conditions is needed for release estimates in PSA studies, and for the design of efficient accident management procedures. This is considered very important because primary-to-secondary leakages risk dominant sequences in many plants. Furthermore, the decay heat of the fission product deposits adds to the thermal load to the steam generator tubes also in other sequences, especially in case of cold leg leakages. This brings out the concern of induced steam generator tube ruptures in cases, where the steam generators are initially intact. The experimental data showed that the highest deposited fraction within the tubes were found in cases with lowest flow velocities. The minimum value of the deposited fraction was observed at intermediate flow velocities. With these relatively low Reynolds numbers, the results calculated with deposition models agree well with the experiments. At high Reynolds numbers, representing the defect tubes during steam generator tube rupture sequences, the deposition is dominated by turbulent impaction. According to experimental results, the deposited fraction was highly overestimated with plain deposition models. It appears that resuspension affects the deposition significantly, and it should be taken into account when estimating the deposition in the defect tubes. The experimental data obtained with the HORIZON experiments serve as a good database for aerosol deposition within the steam generator tubes at realistic severe accident conditions. The experiments also showed that the deposition models are adequate for calculating the deposition at lower flow velocities. At higher velocities, when turbulent impaction is dominating, the resuspension of deposits has to be accounted for