Mitigation system of severe accidents for CAREM-25: modeling of system associated with the role of iodine retention

Within the CAREM-25 prototype reactor design a severe accident mitigation system was incorporated. This system is framed within Defense in Depth level 4. The functions of this system are: (a) limiting the containment hydrogen concentration, (b) external cooling of the reactor pressure vessel and (c) pressure suppression pool water alkalinization. Actions associated with these functions are intended to mitigate the radiological consequences of severe accidents as much as possible. The objective of this paper is to present a brief description of the CAREM-25 severe accident mitigation system, focus on the role of pressure suppression pool water alkalinization system. The effect of pH water sink on iodine volatility, is study using a simplified and general model. The effect of pH variation was modeled using the 'Iodine Pool Model' of MELCOR code, studying a general case. The results indicate that alkaline pH values enhance iodine retention in aqueous phase, increasing this effect if the sink is alkaline at the beginning of the accident. Actually, this MELCOR model is in validation process at Nuclear Safety Department, comparing this result with an experimental one reported in international documents. Once validation is completed, this model will allow us to simulate a complete severe accident for CAREM25 reactor, including the phenomenology of iodine in reactor containment rooms. This will be used for the Safety analysis and for licensing assessments. (author)