Liquid metals circulation type

In evaporation, heat is added to a solution to vaporize the solvent, which is usually water. The heat is generally provided by the condensation of a vapor such as steam on one side of a metal surface with the evaporating liquid on the other side. The type of equipment used depends primarily on the configuration of the heat-transfer surface and on the means employed to provide agitation or circulation of the liquid. These general types are discussed below. 

Deposition of corrosion products in a circulating AT liquid metal system is important for three reasons. First, the degradation of heat transfer perfonmance of heat exchangers must be predicted. Second, radiation exposure limits for maintenance in certain areas of nuclear reactor systems that transport and deposit radioactive species must be controlled. Third, the tendency for all deposits to become detached by thermal shock or flow perturbations must be known since there is concern that these types of debris could block critical coolant channels. It is therefore valuable, when possible, to monitor reactions involving deposition as well as dissolution. 

Decay heat removal. Several types of passive decay heat removal systems have been used in liquid-metal reactors. The AHTR, like S-PRISM, uses RVACs. There are other options such as DRACs, a secondary natural circulation loop to remove heat from the reactor vessel to the environment. This provides multiple longer-term cooling options including the options that may ultimately allow larger power outputs. 

The time-dependence of void formation in Inconel, as observed both in thermal-convection and forced-circulation systems, indicates that the attack is initially quite rapid but that, it then decreases until a straight-line relationship exists between depth of void formation and time. This effect can 1)0 explained in terms of the corrosion reactions discussed above. The initial rapid attack found for both types of loops stems from the reaction of cliromium with impurities in the molt [reactions (13-1) and (13-2)] and with the FF4 constituent of the salt [reaction (13-3)] to establish a quasi-etiuilibrium amount of CrF2 in the salt. At this point attack proceeds linearly with time and occurs by a mass-transfer mechanism which, although it arises from a different cause, is similar to the phenomenon of temperature-gradient mass transfer observed in liquid metal corrosion. 

Externally cooled LMFR. In an externally cooled LMFR the fuel is circulated through the core to an external heat exchanger, where the heat is removed l>y the secondary fluid. This type provides the simplest core design, re< uiring. simply an assembly of graphite pierced with holes for circulation of liquid-metal fuel. The major problems of heat transfer are essentially removed from the core design. 

In another experiment [27] NF.PA circulated bismuth with a 50-gpm centrifugal pump for 100 hr at a mean temperature of 1500°F with a temperature differential of 500°F. An accumulation in the sump of a residue high in oxide content and dissolved elements reduced the flow and forced suspension of operation. This residue probably resulted from an impure inert atmosphere above the liquid metal. The container material selected was AISI type-347 stainless steel which had shown some promi.se in bismuth solubility tests at temperatures up to 1800°F. 

This report provides the presented papers and summarizes the discussions at an IAEA Technical Committee Meeting (TCM) on Natural Circulation Data and Methods for Innovative Nuclear Power Plant Design. While the planned scope of the TCM involved all types of reactor designs (light water reactors, heavy water reactors, gas-cooled reactors and liquid metal-cooled reactors), the meeting participants and papers addressed only light water reactors (LWRs) and heavy water reactors (HWRs). Furthermore, the papers and discussion addressed both evolutionary and innovative water cooled reactors, as defined by the IAEA. ... 

For the preparation of samples suitable for electrical measurements, special types of purification methods are employed. Reduction of the self-conductivity of the sample requires removal of traces of water and of particles from the liquid samples and from the walls of the test cell and filling tubes. Powerful drying agents used are activated silica gel or molecular sieves, phosphorus pentoxide, or alkali metals, especially sodium-potassium alloys. The liquid samples are either percolated through columns of silica gel or molecular sieves in an atmosphere of dry argon or nitrogen gas, or they are refluxed in a container with sodium potassium alloys for many hours. In order to remove adsorbed water from the walls of the test equipment, circulation of purified liquid and continuous drying are necessary. 

The liciuid-metal system that has received the greatest emphasis to date is of the heterogeneous, circulating fuel type. This reactor, known as the Liquid iMetal Fuel Reactor (LMFR), has as its fuel a dilute solution of enriched uranium in liquid bismuth, and graphite is u.scd as both moderator and reflector. With as the fuel and Th as the fertile material, the reactor can be designed as a thermal breeder. Consideration is restricted here to this reactor type but, wherever possible, information of a general nature is included. 

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