Analysis of in-pile operation and modeling of tritium transport in lead-lithium irradiation experiments Libretto 4/1, 4/2 and 5

In the framework of the European R and D for the Helium Cooled Lead Lithium (HCLL) test blanket concept for ITER, NRG has designed three new Libretto irradiation experiments. Two experiments, Libretto 4/1 and 4/2, have been irradiated in HFR for 730 Full Power Days. The objective was to monitor on line the in-pile tritium production and permeation through Eurofer in contact with lead lithium eutectic. The irradiation of Libretto 4/1 and 4/2 has been conducted at 550 oC and 350 deg. C, respectively. Libretto 5 experiment has been irradiated for 520 Full Power Days in the temperature range of 300-500 deg. C with the objective to study tritium behavior in a lead lithium eutectic. The operation of the Libretto experiments included in-pile variations of hydrogen concentration in the purge gas and temperature transients. The irradiation of all three Libretto experiments has finished in 2009 and this work reports the analysis of the in-pile data. To analyze the data a model of tritium transport in lead lithium has been developed. The model incorporates two transport mechanisms: bulk diffusion and via rising tritium-helium bubbles. It was demonstrated that the bubble transport mechanism is much faster and in better agreement with the tritium residence times measured in the Libretto experiments.