POURING OF 100-KG-SCALE MOLTEN UO2 INTO SODIUM

Two experiments known as T1 and T2 are performed in the test section TERMOS of the FARO facility. Quantities of the order of 100 kg of molten pure UO2 approximately 3000-degrees-C are poured into 130 kg of sodium at 400-degrees-C and 0.1 MPa contained in a 0.28-m-diam test tube over a height of 2.5 m. The tests show a melt delivery rate twice as high in T2 as in T1. Becasue of the large scale of the experiment, the tests reveal new features concerning this type of interaction. Particularly, fuel/coolant interaction (FCI) occurs that induces stepwise penetration and dispersion of the melt, and a limitation of the melt quantity that could penetrate into the sodium. Sodium pressure peaks up to 6.0 MPa and pressurizations of the 0.150-m3 gas phase blanket up to 0.8 MPa are recorded. These FCIs are interpreted as vapor explosions in nearly saturated sodium. Quantities of 60 kg for T1 and 45 kg for T2 of UO2 fragments are collected in the debris catcher located at the bottom of the test tube. A debris bed structure resulting from this type of interaction is identified and characterized. Porosity is almost constant all over the bed height while permeability increases by a factor of 30 when going from the top to the bottom of the bed.