Characteristics of heat transfer of models of core and steam generator surfaces with regulation of impurity content in a loop with lead coolant

Abstract

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.

Components of small and medium sized HLMC reactor plant circuits

“…This result of investigating (simulating) one of the most potentially dangerous HLMC reactor accidents ("large SG break") makes it possible to mitigate in a qua- Figure 1. Schematic of the BRS-GPG reactor HLMC circuit: a) sectional drawing; b) top view; 1 -free coolant level; 2 -coolant entering the pump from SG; 3 -core; 4 -horizontal SG's superheating section; 5 -horizontal SG's evaporating section; 6 -RCP$ litative manner the accident effects by using a horizontal steam generator design, the tubes in which are as near as possible to the HLMC level (up to ~ 1.0 m), this preventing water from entering the reactor core and the reactor circuit from being overpressurized, and so on (Beznosov et al 2013). Such approach, in the event of the SG emergency breakdown ("large break") and with practically the greatest possible fluid emergency outflow rate, provides for the safe localization of an accident with a steam channel formed spontaneously between the fluid outflow point and the gas (steam-gas) space above the free coolant level in the SG's failed section and with the subsequent steam, water and gas escape through the rupture disk and into the condenser, and further to the atmosphere via the condenser and the gas cleaning system (Beznosov et al 2012a).…”

“…The amount of the removed heat is efficiently controlled by varying the water content in the two-component flow based on sensor signals and the heat exchanger outlet temperature . The characteristics of such system are studied and optimized at NNSTU's test facilities, including the FT-4 NGTU test facility for the removal of the heat produced by the BREST-OD-300 reactor RCP model's electrical pump (Beznosov et al 2008a). It is considered for the BRS-GPG that self-contained air-to-water heat exchangers should be installed inside of the SG or the SG evaporator surfaces should be used in air-to-water modes (Beznosov et al 2016b).…”