Thermal contact resistance and ambient temperature effects on the cooling of Mo99 plate targets inside the hot cell

In this work the simulation of heat transfer and the temperature distribution of the Low Enriched Uranium (LEU) irradiated targets, inside the nuclear research reactor hot cell, are carried out using the software package FLUENT – GAMBIT. The LEU irradiated targets are used for Molybdenum-99 production for medical purposes. The cooling of the targets requires close attention to avoid exceeding the Aluminium cladding melting or blistering limits during targets transportation. The exceeding of those limits could cause a radionuclide release from the targets, hence, an over radiation dose and clad deformation could result. These consequences could prevent the targets transportation from the hot cell to the Molybdenum-99 process cell. The targets are mainly cooled by convective air and thermal radiation inside the hot cell. In the simulation, it is assumed that the hot cell operators, by mistake, unload three target plates from the target holder and stack them on a table instead of keeping them separated. The heat transfer and temperature distribution for the targets are calculated based on that described scenario, taking into consideration the effect of contact resistance between the plates themselves and between the lower plate and the table. Also, simulations are carried out under different boundary conditions as a result of the change in the ambient conditions caused for example by the malfunction of the hot cell ventilation system. The simulation results showed that separate uploading of targets on the table keeps them far away from the blistering limit, while stacking them would expose them to blistering and melting under bad ambient conditions. The thermal contact resistance has a strong effect on LEU targets cooling; it could produce up to 50 °C temperature difference between two adjacent plates in some presented simulations.

► Heat transfers through three plates, in pile form, laid on a table were studied.
► The maximum temperature of irradiated target, during its transportation belongs to safety.
► The heat transfer simulation is carried out using FLUENT – GAMBIT software.
► The thermal contact resistance has an effect on LEU targets cooling.
► The hot cell surrounding temperature is very important parameter.