BOILED-UP POOL HEAT TRANSFER FOR A HORIZONTAL TUBE BUNDLE

摘要

Isolation condensers are effective means of emergency decay heat removal for commercial nuclear power plants when they encounter rapid transients such as a loss of load. Many of these designs use horizontal tube bundles to transport steam to, and through the primary side of the condenser. Steam generated on secondary side causes the water pool to boil-up (level swell) such that the water level is considerably higher than the collapsed level. Consequently, when the collapsed level is below the top of the tube bundles, the boiled-up level is the parameter that determines the extent of heat removal from the condenser. To determine the functional dependence between the heat removal rate within the bundle and the water level swell, water pool heat transfer experiments have been performed with a horizontal bundle of instrumented electrical heaters. The primary objective was to ascertain the collapsed water level that corresponded to the top row of heater elements no longer being covered by the water level swell (incipient dry-out). To accomplish this, the power was increased in small increments and remained at the new power for several minutes to assure that any possibility for dry-out of the upper elements would be detected. These experimental results show that standard representation of pool boil-up (liquid level swell) conditions also provides a good characterization of the behavior for a horizontal tube/heater bundle. This paper describes the experiments performed and compares the test results with a well characterized drift flux model. With the expanded use of isolation condensers in the recent, more passively orientated safety system designs for commercial nuclear power plants, this experimental data provides a much needed technical basis to illustrate the influence of the steam generation rate on the "wetted surface" of the horizontal condenser tubes. It is this parameter that determines the maximum heat extraction rate.