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-
The salient features of the use of lead and lead-bismuth in the power-generating loops removing heat from the blanket of a tokamak reactor are set forth. The results of experimental and theoretical investigations and analysis in substantiation of the use of heavy liquid-metal coolants in systems converting the energy of a blanket in a tokamak reactor into electricity are presented.One of the main requirements of nuclear power -inherent safety of reactors -is initiating studies of heavy liquidmetal coolants as alternatives to sodium coolant, which has been mastered and has better thermophysical characteristics and other advantages. This requirement also makes it useful to study them as alternatives to lithium in the energy conversion systems of thermonuclear reactors, specifically, in the blanket of a tokamak reactor.Characteristics of Lithium, Lead, Lead-Bismuth as the Coolant for a Tokamak Reactor. The thermophysical properties of lithium as a coolant (heat capacity, thermal conductivity, density) are undoubtedly better than those of lead and lead-bismuth: lithium is less corrosive, and experience in using lithium in research and semicommercial stands and setups has been accumulated in this country and abroad. A serious drawback of lithium as a coolant is that it presents a fire hazard. Fire safety in loops and systems with lithium, just as with sodium, can be achieved by augmenting with complicated engineering safety systems and with protection and containment systems and by decreasing the cost-effectiveness of the setup. When lead and lead-bismuth come into contact with air the free surface gradually oxidizes, and when a continuous layer of slag remains on the surface of the liquid metal oxidation slows down.The interaction of lithium with water, a steam-water mixture, and steam with formation of a corrosive alkali and explosion-dangerous hydrogen, just as with the use of sodium, requires an additional intermediate loop using water as the working body of the Rankine cycle for converting heat into electricity. When the blanket is cooled by lithium, using carbon dioxide gas as the working body and the Brayton cycle also requires an intermediate high-temperature loop because of the formation of lithium carbides during a possible accident with an interloop leak in the heat exchangers. The use of lead or lead-bismuth makes it possible to use in such cases simpler and more cost-effective two-loop schemes, which makes the setup as a whole safer.In designs of thermonuclear reactors, as a rule, breeding of tritium occurs as a result of reactions of neutrons with lithium nuclei. This is possible if liquid lithium is used as the coolant. However, the operation, repair, and decommissioning of a branched, complicated, power-generating, lithium cooling loop, containing, aside from conventional radionuclides, the biologically dangerous volatile substance tritium are complex and dangerous. The well-known technological process for pro-
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