Hospital Neutron Irradiator Thermal Hydraulics Numerical Simulation

The thermal-hydraulic numerical study plays an important role in reactor design. In this paper, the thermal-hydraulic behaviors in the reactor core in hospital neutron irradiator is investigated . Because of the complexities of constructions in hospital neutron irradiator and the natural circulation, the advanced numerical method is used for the detailed study by the computational fluid dynamics program generally used in the world.The unstructured grids are used in the region of the inside of the reactor core and the structure grids are used in the region of the outside of the reactor core for the quality of the grids and decrease of the number of grids. The standard turbulence model and the wall function approach are adopted.The computational method is established by the comparison of the experiment and the calculation of the temperature difference between the inlet and the outlet of the core and the temperature on the surface of the fuel elements.The established computational method is used in hospital neutron irradiator for different power levels. The detailed fluid velocity and temperature fields in the core and the temperature of the fuel elements are calculated. The maximum power for the onset of the boiling is also predicted.The effects of the leading barrel and the outlet-extending barrel are evaluated. After the sensitivity calculations, an appropriate height of the leading barrel is proposed. However, the outlet-extending barrel does not have an appreciable impact on the natural circulation.The calculation gives the temperature distribution and flow behavior at the outlet of the core, which provide an important basis for the establishment of the outlet temperature in the reactor.The calculation indicates that the influences of the heating and conduction in the beryllium reflector, aluminium and graphite components, and the ununiform heating of the fuel elements are negligible to the temperature difference between the inlet and the outlet in the core. The present computation provides the support for the thermal-hydraulic design of hospital neutron irradiator.