Aerosol deposition in a horizontal VVER-440 steam generator

During a severe reactor accident, leakages from the reactor coolant system out of the containment may lead to significant releases of fission products into the environment. In primary-to-secondary leakages there is a possibility for relatively large environmental releases. The leak location in the steam generator plays an important role in the flow pattern of the defect steam generator as part of the leakage takes place through the intact tubes. The flow velocities in the intact tubes are much less than those in the defect tubes, and different deposition mechanisms are significant in these flow regimes. Furthermore, resuspension reduces the deposited fraction of the fission products at high flow velocities. The paper presents the total retention of aerosols in the steam generator primary side as function of leak location. The flow distribution between defect tubes and groups of intact tubes having different lengths is evaluated by assuming the same pressure loss for each route from the hot collector to the leak location. In the retention, different aerosol particle sizes are considered, as well as different amounts of defect tubes. It seems that a very high deposited fraction of aerosols will not occur in any flow conditions in the horizontal steam generator of VVER-440 reactor despite the large horizontal surface area within the tubes.