Inventory and solubility of fission products in molten lead to quantify source term in lead-cooled fast reactors

We have investigated the dissolution and retention of several metallic fission products and iodine in lead coolant under conditions relevant to accident scenarios in lead-cooled fast reactors (LFRs). First, the inventory of these fission products was calculated under some possible LFR operating conditions using a numerical model at various reactor operation times ranging from 6 months to 2 years. Secondly, low concentrations (1 to 2 wt%) of these fission products were dissolved in molten lead and the measured solubilities compared to the calculated reactor inventory, with the exception of iodine and niobium, which volatilized and did not digest, respectively. Finally, the transient dissolution behavior of certain selected fission products was examined and shown to take place on the timescale of hours. The findings of this study have bearings on the modeling of LFR accident scenarios and the overall safety analysis of this class of reactors. In addition, the results suggest that the behavior of molybdenum in molten lead at temperatures in excess of 800 C is more complex than has previously been supposed and merits future study.