To develop computer codes for calculating serious accidents with melting of fuel and accumulation of melt at the bottom of the reactor, it is important to determine the closing relations for the intensity of the external cooling of the reactor bottom both in nonboiling regimes (tsurf < tsat, where tsurf is the temperature of the heat-releasing surface and tsat is the saturation temperature) and with boiling of water (surface and volume boiling). The most pressing problem is to determine the maximum admissible heat fluxes (crisis of boiling and transcritical heat release). These questions have been examined in some publications and handbooks [1][2][3][4][5][6][7].We have made an experimental investigation of the intensity of single-phase heat release and the conditions of degradation of heat release during boiling on a flat, weakly inclined, plate cooled from below. Heat is supplied by an electric resistance heater. The plate width is b = 0. I m. The experiments were conducted with 18 combinations of the plate length l = 0.3 and 0.5 m and plate thickness ~ = 0.2, 1, and 2 ram and slope angles/3 of up to 9.4 and 13.3" with respect to the horizontal plane. Sheets of thermal insulation consisting of 10 nun thick teflon and 2 mm thick paronite were pressed down again.q the plate. The heat flux through the insulation was equal to qtop/(tsurf --ta) = 30 W/(m2.K). This construction and the current leads were secured to a trough-shaped framework --a 1 mm thick plate. The lateral edges of the upside down "trough" were located below the heat-releasing surface (~z = 10 mm) and prevented ma~ transfer through the side boundaries. The plate was placed in a horizontal pressure-bearing cylindrical vessel with dimensions of 219 x I0 mm and 1.6 m long. The vessel was 2-2ched to an external circulation loop, through which the water in the vessel was heated and the pressure was compensated. The elements of the vessel and circulation pump which came into contact with water were made of stainless steel, with the exception of the sheets of the thermal insulation and the copper current leads. The temperature of the plate was measured with 12 KTMS cable chromel-alumel thermocouples separated and pressed to the top surface of the plate through a 10 -2 mm thick layer of mica. The thermocouple outputs through holes drilled in the thermal insulation and the framework as well as the faces were waterproofed with organosilicon lacquer. The water temperature (tw) under the heat releasing surface and the outer surface of the vessel was also measured along the bottom, middle, and top geueratrices. Furthermore, the pressure in the vessel and the electrical power supplied to the plate were fixed.The experiments were conducted in the following range of parameters: pressure p = 0.102-7.5 MPa; t w = 20-195"C; tsurf = 40-268"C; At = tsurf --t w = 20-170"C; and, the specific heat flux to the heat-releasing surface q = 8-186 kW/m 2. For ~ < 3* monotonic increase of tsurf along the section was not observed, and the arithmetic mean value of the indications o...
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