Out of pile tritium release behaviour and microscopic investigation of lithium metatitanate irradiated in the High Flux Reactor in Petten

摘要

The irradiation experiment EXOTIC 9/1 is the latest in a series of EXOTICs that has been irradiated in the high flux reactor in Petten and studies tritium release and inventory in ceramic pebbles containing lithium, which are key properties for the fusion fuel cycle. New production routes of pebbles are developed, leading to different thermomechanical and tritium release properties. The pebbles, produced by an extrusion-spheroidisation-sintering process at CEA in 2004, differ in porosity and density from the Li_2TiO_3 ceramics tested in the previous EXOTIC 8 programme. The pebbles have a diameter in the range from 0.6 to 0.8 mm, a high density (93% TD) and an open porosity of 1.7%. The pebbles mainly differ in enrichment (7.5% and 30% ~6 Li-enrichment).During irradiation of 300 Full Power Days in the HFR in Petten, the temperature in EXOTIC 9/1 was varied between 340 and 580℃ The final irradiation (EOL) temperature is 480℃ and the average total ~6Li burn-up is 3%. The total measured activity from tritium during irradiation is 220.42Ci.After the completion of the irradiation, the out of pile release behaviour was studied by temperature programmed desorption (TPD). More specifically, the remaining tritium inventory in the pebbles and the activation energy of different release mechanisms were studied. The TPD was carried out for Li_2TiO_3 samples with 7.5% (natural) and 30% (enriched)~6Li-abundance and revealed very different curves, indicating that the materials have different release mechanisms. Dissolving the irradiated samples in hydrogen peroxide indicates that no tritium is left in the pebbles after TPD. Results from optical microscopy show it is likely that more intense bubble formation has taken place in the enriched samples, compared to the natural samples.