Fuel coolant interaction results in the fuel pins melting facility(PMF)

The experimental work related to FCI at PNC has been concentrated to molten UO2-dropping test. The primary objectives of the fuel pin-melting facility test are to obtain the detailed experimental results on the FCI under transient overpower and loss of flow conditions, to observe the movement of fuel before and after the failure of a pin by X-ray cinematography, to simulate the fuel behavior in the pin-pile test, and others. In the experimental apparatus, the UO2 pellets clad in SUS 304 tubes are melted by direct electrical heating in a liquid sodium column, and the molten UO2 coming out of the cladding tubes interacts with the surrounding sodium. The variation of electrical voltage and current, temperature, pressure and the movement of the sodium column are measured. The results of four capsule tests are presented in this paper, two for the open type test section and two for the closed type. Although the fuel motion and the FCI in the closed test section appeared to be different from those in the open test section, more experimental data are required to come to a conclusion. The best heating condition for UO2 pellets in the FCI study with the pin-melting facility was able to be established. Further development will be continued for providing thermocouples in UO2 pellets, increasing the stack length of pellets, visualizing the movement of fuel, and forwarding the loop test. (Kako, I.)