ENERGY PARTITION OF A CORE MELT ACCIDENT IN A NUCLEAR POWER REACTOR (STEAM EXPLOSION, STRUCTURAL ANALYSIS)
Abstract
A broad data base was established on the energetics of single-phase and two-phase discharge into a liquid pool. The experimental setup using simulant fluids was a 1/7 scale model of the core-and-vessel configuration of a loop-type liquid metal fast breeder reactor. The condensation-driven entrainment of the pool liquid into the expanding bubble was significant. The impact pressure on the top of the containment vessel dropped significantly because of heat transfer caused by the mixing of gas and liquid resulting from the Taylor instabilities formed at the pool-cover gas interface. The discharge of the steam-water mixture into the Freon-11 pool was energetic and resulted in high impact pressures. A parametric analysis was conducted for the thermal to mechanical energy conversion of a steam explosion accident in a pressurized water reactor. This study provides the groundwork for energy partition by providing the ideal explosion energy for a broad range of initial conditions. The structural analysis of the lower plenum of the reactor pressure vessel was conducted with the finite element computer code STRAW (A Nonlinear Fluid-Structural and Thermomechanical Finite Element Program), which was coupled with fluid modeling in order to account for the rapid pressure drop during expansion. During the very early stage of expansion, a significant amount of energy was transferred from the explosion mixture to the vessel wall and to the water which did not participate in the explosion. A detailed analysis of the expansion of the explosion mixture was conducted for eleven representative cases covering a broad range of explosion energy. The expansion analysis accounted for possible mechanisms of energy release. It was found that the explosion energy was 1/7 of that calculated under ideal conditions. A calculation of the slug impact on the upper core structural plate was conducted using STRAW. Approximately 35% of the kinetic energy of the slug, that initially was directed upward, was redirected along the radial direction and was dissipated into the UCSP and the core barrel by means of strain energy.
Degree
Ph.D.
Subject Area
Nuclear physics
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