The objective of the present work was to investigate experimentally the flow velocity of lead coolant in a ring-shaped gap on horizontal and vertical experimental sections during monitoring and regulation of the thermodynamic activity of oxygen. The experiments were motivated by an interest in validating the concept of the BREST-OD-300 fast reactor, in which a lead melt is to be used.The experiments were performed on an experimental stand. The stand contained experimental sections -horizontal and vertical with sensors for measuring the local velocity in the ring-shaped channel (Fig. 1). The low rate of the liquid metal was monitored with a magnetic flowmeter and by the volume method -calibration flow container; the thermodynamic activity of oxygen in the lead was monitored by sensors placed in flow and buffer containers. The equipment and pipelines were made of 08Kh18N10T steel and are electrically heated and possess thermal insulation.The sensors for measuring the flow velocity of the lead coolant were placed in two experimental sections: vertical and horizontal.The vertical section consisted of two coaxially arranged pipes (d 2 /d 1 = 4.2). The outer pipe, 45 mm in diameter, 2.5 mm thick, and 1570 mm long, was made of 12Kh18N10T austenitic steel. The inner pipe consists of a 2100 mm long tubular electric heater with a regular BREST-OD-300 fuel-element cladding made of 16Kh12MVSFBAR-Sh ferrite-martensite steel and a 1600 mm long active part. The flow direction in the ring-shaped gap is bottom to top.The horizontal section tilts at an angle of 3°along the direction of motion of the lead in the form of two coaxially positions pipes (d 2 /d 1 = 2.35). The outer tube is 1348 mm long, 45 mm in diameter, and 2.5 mm thick and consists of 12Kh18N10T austenitic steel. The inner pipe is 2095 mm long, 17 mm in diameter, and 3 mm thick; this pipe is a regular tube of a steam generator in the BREST-OD-300 reactor and is made of 10Kh9NSMFB ferrite-martensite steel.The sensor makes it possible to measure the potential and full head of the liquid-metal flow. The local velocity is calculated from the difference of these heads. The full head was measured with a capillary (tube with inner diameter 1 mm and wall thickness 0.25 mm), whose free end was directed opposite to the coolant flow. The coolant flows through the capillary and the system of pipes into the tank used to measure the full head. The potential head was measured through an opening in the wall of the experimental section. The free end of the capillary and the opening, for measuring the head, in the wall are located in the same transverse section of the tube. The lead flows through the measuring opening and through the system of pipes into the tank for determining the potential head.Using nuts, the entrance end of the capillary is moved in the radial direction over the cross section of the channel by means of a spacing plate. The plate is connected with a tie rod, whose other end is secured to a probe with the open end of the capillary.

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The results of experimental investigations of the heat transfer by lead coolant in the ring-shaped gaps of a circulation loop during monitored and controlled mass transfer and mass exchange of oxygen and impurity are presented. The investigations were performed in a loop with circulation of lead coolant at temperature of 450-550°C, average velocity 0.1-1.5 m/sec, Peclet number 500-6000, and heat flux 50-160 kW/m 2 . The oxygen content in the loop was varied from the value for thermodynamic activity 10 −5 -10 0 to saturation and above with formation of lead oxide deposits on the heat transfer surface. The processes in a non-isothermal liquid metal loop with heating (core) and cooling (steam generator) experimental sections simulate the dependence of the heat transfer characteristics in the loop on the impurity mass transfer.Liquid metals are attractive high temperature coolants for nuclear power because of their physical characteristics: low pressure, high heat transfer coefficient, and therefore low temperature difference between the surface of fuel elements and coolant with high heat flux density. The experimental and computational techniques, the new approaches to solving heat transfer problems, and operating experience make it possible to study the simultaneous effect of the impurity content, the technological processes of cleaning in the loop, and accident processes where impurities enter the loop on the characteristics of heat transfer in hot and cold zones of the loop. The results of the investigations make it possible to formulate more accurate recommendations about the norm for the impurity content and more accurate computational formulas for determining heat transfer surfaces.In Nizhnii Novgorod Technical University, an experimental stand has been developed and investigations in which the local characteristics of heat transfer from a tube wall to the lead coolant and from the lead coolant to the tube wall were determined simultaneously while monitoring and regulating the oxygen content in the coolant have been performed. Previously, the characteristics of heat transfer in lead and lead-bismuth coolants were performed separately under conditions of heating and cooling of the coolant [1, 2]. The present experiments [3] differ from previous experiments in that while monitoring and controlling the variation of the state and composition of impurities in the coolant and envelope the characteristics of heat transfer on heating and cooling sections are measured simultaneously.The experimental stand possesses two loops: one with lead and the other with lead-bismuth alloy with centrifugal pumps. The flow rate of the liquid metals is monitored with magnetic flowmeters and by a volume method -a calibration flow-measuring volume -and the oxygen content and lead was measured with thermodynamic activity sensors based on a solid galvanic concentration element. The equipment and pipelines in contact with lead were made of 08Kh18N10T steel and are electrically heated and thermally insulated.

The purpose of the present work was to investigate experimentally the flow velocity of lead-bismuth eutectic in a channel whose cross section is circular and where the oxygen content is monitored and regulated [1].The high-temperature liquid-metal stand FT1 was developed to perform these investigations. The stand contains an experimental section with a sensor for measuring the local velocity in the cross section of the channel (Fig. 1). The experimental section consists of a tube (tube material -08Kh18N10T austenitic steel) with inner diameter 26 mm and wall thickness 3 mm. The velocity was measured in the lead-bismuth coolant flow.The sensor permits measuring the potential H pot and total H tot heads of the liquid metal flow. The local velocity at a given point of the flow is calculated according to the difference of the total and potential heads. The total head was measured with a capillary (tube with inner diameter 1 mm and wall thickness 0.25 mm); the free end of the tube is directed toward the flow of the lead-bismuth eutectic and the other end is embedded in the flow deflector on the probe (Fig. 2). The alloy flows through the capillary and system of pipes into a tank for measuring the total head of the flow. The potential head was measured through an opening in the wall of the experimental section. The free end of the capillary and the opening for measuring the potential head are located in the same pipe segment in the experimental section. The eutectic flows through the opening for measuring the potential head and then through a system of pipes into a tank for measuring the potential head.The capillary can be moved in a radial direction along the section of the channel by moving a spacer plate by means of a nut. The spacer plate is connected to the tube; a probe with the capillary is secured at the opposite end of the tube.The tanks for measuring the total and potential heads are vertical and made from identical tube sections with inner diameter 25 mm, wall thickness 3.5 mm, and length 500 mm. A corresponding line for measuring the head (total or potential) is connected to the bottom of each tank; the seal of a movable electric-contact rod is placed in the cover.Experimental Procedure. The experiments were performed with lead-bismuth eutectic temperature 400-420°C, thermodynamic activity of oxygen a = 10 -4 -10 0 , coolant flow through the experimental section 1.8-3 m 3 /h, average velocity 1-1.7 m/sec, and Reynolds number (1.6-3)·10 5 . A magnetic flow meter was used to determine the flow rate in real-time; the meter was calibrated at least once per day by the volume method. The oxygen content in the liquid-metal coolant was measured by feeding oxygen into the stand's gas system in a mixture with atmospheric air or hydrogen.The experimental program consisted of several stages. At each one, a definite thermodynamic activity of oxygen was attained and maintained in the lead-bismuth eutectic and loop, after which the velocity was measured. Measurements in the steady-state regime were performed for three val...

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