Advanced Containment Experiments (ACE)

As part of the international Advanced Containment Experiments (ACE), pre-test code predictions were performed to simulate iodine behaviour in a set of experiments in the Radioiodine Test Facility (RTF). The experiments were conducted using an epoxy painted vessel, and variables included solution chemistry, initial iodine species and radiation. The codes predicted consistently low airborne iodine fractions (< 0.25 %) and significant radiation and pH effects, including adsorption onto the painted surfaces. The subsequent experiments qualitatively confirmed these effects. However, the codes differed in predicting the detailed iodine speciation, the magnitude of radiation effects, and whether surface adsorption was predominantly above or below the water level. The reasons for the differences were inconclusive because the code input was based on inconsistent assumptions about test operations and physical parameters. In a follow-up code exercise, these input assumptions were standardised so that differences in the chemistry models could be discerned better. It is concluded that the codes are well advanced, but have incomplete models to predict the effects of painted surfaces and organic materials on iodine behaviour in a radiation field. (author)