An analysis of fission product removal by BWR suppression pools during severe accidents

Aerosol fission products which can be released from the vessel of a light water reactor, during a severely degraded core accident, can be transported through the primary coolant system in mixtures of steam and hydrogen to the reactor containment. In boiling water reactors (BWR) these products must pass through a water pool designed to condense the steam in order to prevent appreciable increases in the containment pressure. It is expected that a significant amount of these fission products will be scrubbed in the pool, hence reducing the amount of radionuclide that can ultimately be released to the environment. Depending on the nature of the accident, transport to the water pool can be through spargers, quenchers, downcomers or horizontal vents. In this paper, analyses which calculate the removal of radionuclide fission products by a BWR suppression pool during hypothetical accidents are reported. The computational tool used is the Suppression Pool Retention Analysis (SUPRA) computer code. The results are shown for the differential and integral decontamination factors during the AE (large pipe break with failure of the core cooling system) and the TC (anticipated transient with failure of the reactor protection system) accident sequences. The effects of particle growth from steam condensation, particle size, distribution, flow and geometric parameters on the predicted decontamination factors (DF) are also presented as studied by simple parametric calculations