The design, and the temperature reached in the sample holders, guarantees that the Na remains liquid during operation to improve the heating transfer and avoiding solid formation (too cold working temperature) or sodium boiling (too hot working temperature). The temperature above and just below the Na surface will be monitored by six dedicated thermocouples. In order to prevent oxidation of the Na, the plenum of the 1st containment is filled with high-purity He at 0.1MPa, sealed after final assembly and kept closed during in-pile operation (no gas circulation in the 1st containment). The heat generated by fission and gamma absorption in the materials will be radially dissipated through the Na bath, the structural materials and the gas gaps by conduction and radiation to the downstream primary coolant of the TRIO wet channel.
