Experimental Studies of the Characteristics of Contact Heat Exchange Between Lead Coolant and the Working Body

Abstract

The results of computational and experimental studies of the thermohydraulic characteristics of lead coolant-working body contact heat exchange are presented. Water, a steam-water mixture, and 100-350°C, 1-25 MPa steam were bubbled through 0.6-2 mm in diameter openings, under a layer of lead ranging in thickness from 100 to 3000 mm, at temperatures 350-600°C into a free space in a steam generator and into space of a steam generator crowded with piping-system simulaters in the case of bubble and plume efflux and with fragmentation of the working body stream against a tubular barrier. The following were determined in the experiments: the bubble size distribution, the rise velocity of the bubbles, the structure of the two-component flow (bubble distribution inside the lead), the change of the temperature of the bubbles as they rise, the characteristics of the vaporization of a water drop in a bubble, and the temperature pulsations in the two-component lead-working body flow.Studies of the contact heat exchange during bubbling of water, a steam-water mixture, and 100-350°C, 1-25 MPa steam through 0.6-10 mm in diameter openings in a layer of lead ranging in thickness from 100 to 3000 mm at temperatures 350-600°C into a free space in a steam generator and into a space in a steam generator crowded with piping-system simulators were performed at the Nizhegorod University for bubble and plume efflux of a stream of the working body and for a working-body stream fragmented against a tubular barrier. The following were determined in the experiments: the bubble size distribution, the rise velocity of the bubbles, the change in temperature as the bubbles rise, the structure of the two-component flow (distribution of the bubbles inside the lead), and the characteristics of the vaporization of a water drop inside a bubble and the temperature pulsations.The experimental data and computational analysis are used as a basis to propose a model of contact heat exchange in the presence of an interloop leak in the steam generators of BREST type reactors. According to the "leak before rupture" concept, the initial efflux of water will occur through a small opening (crack, ruptured thin section of an abraded wall, and so on). The working body (355°C, 30 MPa) passing through such an opening will partially vaporize and partially condense as a result of a decrease of the pressure to the static level inside the lead-coolant loop (0.8 MPa); this is illustrated in Fig. 1 [1, 2]. It was confirmed experimentally and theoretically that the working-body stream formed breaks up as a result of volume boil-

Validation of the two-fluid model of interaction of a water jet with a melt

“…As was experimentally revealed in [2], when a steam generator tube ruptures, due to the instability of the interphase surfaces, fragmentation of the water jet can occur and the formation of a mixture of water droplets and molten lead can take place. In this case, water droplets are separated from direct contact with molten lead by a steam film.…”

Numerical Modeling of Water Jet Plunging in Molten Heavy Metal Pool

“…In these conditions, heat transfer from melt to water proceeds in the film-boiling regime, with the convective flow of vapor in the film determining the heat exchange intensity. In the experimental work [5], a value of 145 W/m 2 K was obtained for the heat exchange coefficient for the film boiling of water droplets with a diameter under 1 cm, surrounded by vapor film and rising in molten lead with the temperature of 500-600 • C. This value is about two orders of magnitude lower than in the case of direct water-melt contact. The relatively low heat transfer rate, limited by the film boiling, allows the quite long existence (about dozens of seconds) of the "melt-vapor-water" multiphase system.…”

Economic Advantages of Starting-up of Inherently Safe Fast Reactors with a Closed Fuel Cycle on Fortificated Uranium

“…In addition, as mentioned earlier, the chemical interaction of lead with water and air is very slow / relatively inert, not supporting significant energy release in the event of accidents. In fact, although the reaction is exothermic, reaction kinetics and oxide formation are slow and the energy releases small [28]. It has been demonstrated experimentally that in situations mimicking steam generator tube ruptures, involving injection of a pressurized steam/water into high-temperature molten lead, steam explosions do not occur.…”