Progress on lower plenum voiding. Quarterly progress report, January 1--March 31, 1978. [PWR]

Recent results of a continuing program to develop an analytical and empirical model of plenum filling in a /sup 1///sub 15/-scale model of a Pressurized Water Reactor (PWR) are described. The topical section of the report presents new lower plenum voiding (LPV) experimental data from three vessels ranging in size from approximately /sup 1///sub 30/ to /sup 1///sub 10/ PWR scale. As in previous investigations of lower plenum voiding, extensive parametric studies have been performed to determine the effects of steam and water flow rates and geometry, particularly on the equilibrium water level depression. The current work has focused on tests in a transparent vessel (1/30 scale) with an extended range of the flow parameters and various special studies all intended to directly examine the fluid dynamic behaviors. The major flow regimes in these tests have been identified and documented with photographs. In particular, an abrupt flow regime transition has been found which is a likely cause of apparent inconsistencies between previous experiments. The report also briefly describes the past quarter's efforts which included condensation-induced transient tests at a vessel pressure of 115 psia, and scoping tests of the effect of lower plenum flashing on plenum liquid inventory in themore » /sup 1///sub 15/-scale vessel model.« less