[en] Short communication

[en] Gaseous UF₆ is withdrawn from a first system and directed into a second system for converting the gas to liquid UF₆ at an elevated temperature. An improved method for withdrawing the liquid UF₆ from the second system and storing it as a solid in a plurality of storage vessel is claimed. The method comprises the steps of: (a) directing an increment of liquid UF₆ from the second system into a first closed storage vessel; (b) flash-evaporating UF₆ from the first vessel into one of the first system and second system to cool and solidify UF₆ in the first vessel while directing an increment of liquid UF₆ from the second system into a second closed storage vessel; (c) flash-evaporating UF₆ from the second vessel into one of the first system and second system to cool and solidify UF₆ in the second vessel while directing another increment of liquid UF₆ from the second system into the first vessel; and (d) flash-evaporating UF₆ from the first vessel into one of the first system and second system to cool and solidify additional UF₆ in the first vessel

[en] The purpose of this research was to investigate the de-entrainment of boron for evaporators used in nuclear power plants. The forced circulation and semi-continuous type evaporator was used in the experiment. Cyclone and glass-wool packed column which is supposed to provide good decontamination factor as well as easy maintenance, were selected as de-entrainment device to be used in the evaporation of radioactive liquid wastes. The de-entrainment device combined with cyclone and glass-wool column has shown overall DF more than 1000 for boron. (Author)

[en] The unit described includes an evaporation chamber holding water vapour, a pumping chamber containing a rotor, automatically centred in a cowl, driven by a motor placed above the level of the liquid, and a chamber containing a heat exchanger. According to the invention the pump, the top part of the chamber and the heat exchanger may all be removed from above for cleaning and scaling. This system is applicable to the evaporation of radioactive liquid wastes which must be concentrated before discharge

[en] A thermal evaporation unit has been ,especially, designed and constructed to fit in the laboratory chamber, which is already constructed for laser isotope separation project. The evaporation unit consists of three parts: an evaporator, a thermal isolation unit and a cooling jacket. The evaporator designed so that it produces the Yb metal vapour through a thin slit. The sheet of the vapour that comes out of the slit diverts and crosses the three laser beams that are needed for the isotope separation process. The diversion of the metal vapour sheet helps in optimizing the interaction volume between the metal vapour and the laser beams. The temperature of the evaporator can reach up to 800 Centigrade homogeneously along the slit. Less than 800 Centigrade temperature is needed to sublimate the Yb metal (powder form) in the vacuum chamber at about 10-6 mbar as has been tested. The temperature of the evaporator is controlled by the current , which passes through the heating wires. (author)

[en] This article shows how evaporation can be an effective and economical means of reducing radwaste and recovering relatively pure water, performing 2 functions in the nuclear plant: reduction of the waste volume through evaporation of the volatile solvent (water), resulting in a smaller volume and smaller mass of contaminated material for ultimate storage or disposal; and reduction of relatively pure water (condensed vapor), which can be recycled and reused within the plant or discharged to the environment with little or no additional treatment. Some of the improvements and problems that have become evident as a result of actual operation of a well-designed forced-circulation evaporator are discussed. The focus is on volume reduction and removal of ammonia

[en] Evaporation is one of the radioactive effluent treatments used, enabling a purified distillate to be obtained and giving excellent decontamination factors for all the radionuclides present, if the pH conditions are correctly chosen and in the absence of volatile solvents. SGN has acquired a wide experience in the concentration of radioactive effluents and possesses a specific know-how in the field of droplet abatement and demisting for this application. The report describes the evaporation system optimized for the treatment of low and medium activity effluents, developed by SGN, which includes a special highly performant scrubbing column and, if necessary an additional lamella separator for droplet abatement. It also presents the ACEREN evaporator offered by SGN under CEA licence and based on the principle of a thin film natural evaporation at low temperature, without condensation of vapors

[en] Experience of the pilot plant operation for evaporation of the liquid radioactive wastes from atomic power station is described. Evaporation is done at the temperature below boiling point. The installation used for experiments provides opportunity to verify two differentversions of technology, namely: application of the tank-concentrator hawing double walls permitting to use it for transportation wastes to bureal place outside of the site and use of a single walled tank. Following parameters were measured and registered: medium temperature in different points; qooling water and air expenditure; condensate accumulation; air heater power. On determining the heat engineering parameters of the insatllation the main task of experiments performed was determination of heat and mass transfer laws ower the surface of water in condition of vortical movement of air and development of the mathematical model for computation of installation's operation conditions and development of design calculation methodology. Influence of substances with densities less than the density of solution, especially of lubricants, with productivity of the device. Metods of romowal of these substances from the solution surface were inve stigated. Also the results of investigation on salts crystallization in course of long time operation of the device are given. (I.T.)

[en] Recent theoretical and experimental studies of evaporation have suggested that on average, molecules in the higher-energy tail of the Boltzmann distribution are more readily transferred into the vapor during evaporation. To test these conclusions, the evaporative cooling rates of a droplet train of liquid water injected into vacuum have been studied via Raman thermometry. The resulting cooling rates are fit to an evaporative cooling model based on Knudsen's maximum rate of evaporation, in which we explicitly account for surface cooling. We have determined that the value of the evaporation coefficient (γ_e) of liquid water is 0.62 ± 0.09, confirming that a rate-limiting barrier impedes the evaporation rate. Such insight will facilitate the formulation of a microscopic mechanism for the evaporation of liquid water

[en] The 242-A Evaporator Campaign 95-1 was started on June 6, 1995 and finished July 27, 1995. An overall Waste Volume Reduction (WVR) of 8.18 million liters (2.16 mGAL OR 87.6% WVRF) was achieved from 9.35 million liters (2.47 Mgal) of processable waste contained in 108-AP, 107-AP, 106-AW and 102-AW. Slurry generated from Campaign 95-1 consisted of 1.05 million liters (278,000 gal) of dilute double-shell slurry feed (DDSSF) with a SpG of approximately 1.34. Total process condensate discharged to LERF was 10.3 million liters (2.72 Mgal), achieving a condensate/WVR efficiency ratio of 1.26. Total throughout for Campaign 95-1 was 18.1 million liters (4.79 Mgal). B Pond discharges from steam condensate and cooling water were 15.8 and 583 million liters (4.17 and 154 Mgal) respectively. Based on 145 hours of unplanned downtime, the 242-A Evaporator maintained an operating efficiency of 86% during the 49 day campaign