Seismic sloshing experiments of large pool-type fast breeder reactors

Abstract

This paper presents the results of seismic sloshing experiments performed on large pool-type LMFBR vessels. Two types of tests were performed. The first type of test was designed to understand the basis phenomena of sloshing (limited to linear sloshing only) and evaluate the effects of the deck-mounted components (i.e., IHXs, pumps, and UIS) on sloshing wave heights using a 1 10 - scale model (diameter 2.23 m x H 1.03 m) of the LSPB 1340 MWe pool plant. The second type of test was designed to evaluate the structural integrity of the thermal baffles of the roof-deck to withstand sloshing impulsive pressures (focused on nonlinear sloshing), using a two-dimensional 1 3 - scale model (L 8 m × W 3 m × H 2.6 m) of a typical 1000 MWe pool plant. The results of the linear sloshing tests have shown that: (1) the vessel wall stiffness has no effect on the sloshing natural frequency; (2) sloshing wave heights are lowered by 30% to 50% in the presence of the deck-mounted components; and (3) damping factors of sloshing are not influenced by the wall stiffness while they are increased by the presence of the deck-mounted components. The results of the nonlinear sloshing tests are that: (1) the maximum impulsive pressure occurs when the first effective wave strikes at the roof-deck, and thereafter the impulsive pressure decreases irrespective of the impact velocity of the fluid; (2) the first effective wave refers to the case in which the height of the fluid free surface becomes nearly twice the height of the cover gas space; and (3) the structural integrity of the thermal baffles for the roof-deck against the sloshing load was confirmed. In addition to these results, two sloshing-caused problems were identified. The first one is the spillover of hot sodium into the gas-dam type thermal insulator. The second one is cover-gas entrainment into sodium which might lead to a transient overpower (TOP) incident because of the presence of gas bubbles in the reactor core. Their countermeasures have been suggested.