The Thermal Hydraulics of High-Pressure Molten Fuel Ejection

Abstract of the technical paper/presentation presented at:
OECD/NEA/CSNI Specialists Meeting on Transient Thermal Hydraulics in Water Cooled Nuclear Reactors
December 13-17, 2021

Prepared by: Thambiayah Nitheanandan
Canadian Nuclear Safety Commission

Abstract

The underwater expulsion of vapour, gas, and molten material, or a combination thereof, is of great practical interest in several industrial applications to predict behaviour and estimate consequences. While many experimental and analytical studies have improved our understanding, more variations in the applications and challenges have emerged and require more probing studies.

The dynamics of bubbles formed underwater during the rupture of a submerged and pressurized tube containing molten fuel and gaseous by-products were investigated. When a pressurized tube ruptures underwater and produces a vapour bubble around the tube, the Rayleigh-Taylor instability distorts the bubble interface with time. On top of this instability of the interface, the expansion and collapse of the bubble create additional bubble distortion. The experimental data confirms that interface instability plays a significant role in the dissipation of thermal and inertial energy stored in the molten metal and the pressurized gases ejected from the dynamic rupture of the pressurized tube. The unique characteristic of the temporal history of the bubble is explained through a separate effect gas-bubble-encapsulated molten metal particle test.

This paper aims to provide the thermal-hydraulic similarities among some submerged pipe-burst experiments using various pipe sizes and fluids. Experimental results are compared, and the differences between an inertial and thermal pressurized pipe rupture underwater are discussed. An important observation is that the peak pressures reached in the inertial rupture, i.e. non-corium tests, were higher than the peaks measured in the thermal rupture, i.e. corium tests. An analytical study confirmed this experimental observation. In that study, the inertial rupture of the pressure tube was more energetic than the thermal rupture of the pressure tube.

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