Summary of Potential Mitigation methodologies

The technical discussions of the chemical and physical behaviour of iodine in containment presented in the previous sections of this chapter give a summary of the key processes and fectors that can influence the airborne iodine concentration during a severe accident. Based on this material, six options that could be used to limit the airborne iodine concentration are outlined below. 

There is evidence that surface coatings containing zinc metal can adsorb and retain iodine from water at a high pH (9 -10). Continued retention of the iodine requires that the water in contact with the zinc coating be maintained at a high pH. Hence, for this mitigation strategy to be effective, it must be combined with the use of pH buffer to control the pH of the water in containment. 

Paint with a high adsorption capacity for iodine 

There have been some efforts to develop paint with a high adsorption capacity for iodine. However, such paint may not help much in terms of the overall iodine sorption during an accident. The overall adsorption rate on dry surfaces under accident conditions is limited by the gas phase mass transport. Furthermore, because water films may cover surfaces, there appears to be limited scope for using surface reactions to immobilise iodine and reduce the gas phase concentrations. 

Systems designed to vent the containment atmosphere and to filter molecular iodine from the vented flow are in service and a body of research results characterizing the effectiveness of these systems also exists. Application of the research data to other systems of different design is possible in principle. Retention capability of wet scrubbers for organic iodides are not well established. 

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