Patent Number: 044302924
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a main condenser 10 is disposed downstream of a steam turbine, not shown, and an air extractor 11 is connected to the upper portion of the main condenser 10 to extract radioactive gaseous wastes staying in the upper portion thereof. The air extractor 11 is communicated with an inlet of a recombining unit 13 including a preheater 12 and a recombiner 14, which are aligned vertically with a slight space therebetween. The recombining unit 13 is usually a cylindrical container and is dividable into upper and lower halves at substantially the intermediate portion of the container 13 as shown by flanges 40 so that the recombiner 14 is disposed in the upper half and the preheater 12 in the lower half when the container 13 is disassembled. The preheater 12 serves to heat the gaseous wastes to a temperature suitable for effectively disposing of the wastes, and the preheated gaseous wastes passing through the preheater 12 is fed into the recombiner 14 in which the oxygen and the hydrogen in the gaseous wastes are recombined into vapour. A condenser 15 is connected to an outlet of the recombining unit 13 downstream thereof, and in the condenser 15, the recombined water vapour and steam from the turbine system for driving the air extractor 11 are cooled into condensed water. A device 16 for holding up the radioactive gaseous wastes with activated carbon is connected downstream of the condenser 15 for attenuating the radioactivity of the radioactive gaseous wastes to a level below a permissible radioactivity. The outlet of the hold-up device 16 is connected to gas discharging stack 17 for discharging the waste gas having substantially no radioactivity or a radioactivity below the permissible level into atmosphere. A pipe line 19 is also arranged to feed cooling water from the main condenser 10 to the condenser 15 by means of a pump 18. Thus, the cooling water flows in a closed loop. Referring now to FIG. 2 in which the condenser 15 and the recombining unit 13 are installed on a common skid 50 as one assembly 20. The recombining unit 13 essentially comprises an inlet pipe 21 through which the gaseous wastes from the main condenser 10 are introduced, the preheater 12, the recombiner 14, and an outlet pipe 22. The preheater 12 is of a shell and tube type heat exchanger and comprises a plurality of heat transfer tubes 23 which utilize steam flowing from an inlet pipe 21 towards an outlet pipe 25 as a heating medium. Usually a trap 26 is connected to the outlet pipe 25. The outlet pipe 22 of the recombining unit 13 is connected to an inlet pipe 27 of the condenser 15 through an expansion joint 37. The condenser 15 comprises a cooling water injector 28, a baffle 29 located below the injector 28, an outlet pipe 30 disposed at the bottom of the condenser 15 for discharging condensed water and used cooling water, and a gaseous waste outlet pipe 31 on the side wall of the condenser 15. To the outlet pipe 31 is connected a steam separator 32 provided with a gaseous waste outlet pipe 33 at the upper end thereof and a drain duct 34 at the lower end thereof. Water level controlling means 35 which adjusts the water level of the condensed water and cooling water in the condenser 15 is installed in a by-pass line disposed at the lower portion of the condenser 15. A valve 36 for adjusting the flow of the condensed water from the condenser 15 is provided downstream of the outlet pipe 30. In a case where a recombining unit of the type utilizing a catalyst is used, a wire net 38, shown in FIG. 2, may be provided within the recombining unit 13 for preventing the catalyst from dispersing towards the downstream side. The radioactive gaseous waste disposing system according to this invention operates as follows. The gaseous wastes passing through the air extractor 11 enters into the recombining unit 13 through the inlet pipe 21. The wastes are heated in the preheater 12 by steam fed through the steam inlet pipe 24 so as to efficiently combine the oxygen with the hydrogen in the gaseous wastes at a time when it is fed into the recombiner 14 without heat loss. The preheater 12 and the recombiner 14 are vertically aligned in the recombining unit 13 so that preheated gas flows directly upwardly to effectively contact the catalyst 38. The recombined water vapour and the gaseous wastes are then fed into the condenser 15 through the outlet pipe 22. The steam for heating the gaseous wastes enters into the outside of the heat transfer tubes 23 through the inlet pipe 24 and the steam transfers its heat to the gaseous wastes in the tubes 23. In this heat exchanging step, a portion of the steam changes into condensed water. The steam containing the condensed water flows out through the outlet pipe 25 and the condensed water is separated from the steam by the trap 26 and discharged to the outside of the system. The cooling water fed from the main condenser 10 by means of the pump 18 for circulating the cooling water is injected through the injector 28 into the condenser 15 and cools the gaseous wastes in direct contact thereto, thereby condensing the water vapour contained in the gaseous wastes into the condensed water, which will be recovered into the main condenser 10. The heat transfer efficiency between the cooling water and the gaseous wastes in the condenser 15 will be increased by using a spraying device as the injector 28 which sprays the cooling water or by using a wire net or a flat plate for enlarging the area of contacting the cooling water to the gaseous wastes. The heat transfer efficiency attained by the direct contact, described above, can be considerably improved in comparison with the use of a conventional shell and tube heat exchanger. In addition, the preheater 12 can be made to be compact by directly contacting the gaseous wastes to the cooling water over a relatively wide area, and the latent heat of evaporation of the cooling water makes it possible to use a smaller quantity of cooling water than that in the conventional system. The condensed water obtained in the condenser 15 is returned to the main condenser 10 under a head similar to that in the conventional system. Thus, since the water in the main condenser 10 can be utilized as a cooling water, it is not necessary to supply the cooling water into the condenser 15 from an external source. The fact that the cooling water does not flow out of the waste disposing system efficiently prevents leakage of the cooling water having radioactivity to the outside of the system. Namely, in a case where the conventional shell and tube type heat exchanger is used as the condenser 15, if a portion of a pipe for supplying the cooling water were broken, the radioactive gaseous wastes would leak into the cooling water and the contaminated cooling water flows out of the system. However, according to the system of this invention, the possibility of the breaking of the pipe for supplying the cooling water is considerably low and even if the pipe were accidentally broken, the smaller amount of the contaminated cooling water flows into the main condenser 10 and does not flow out of the system. Although the gaseous wastes also contain mist, it is caught by the steam separator 32 connected to the outlet pipe 31 of the condenser 15, and the gaseous wastes containing substantially no mist is fed into the hold-up device 16 for adsorbing the radioactive gaseous wastes with the activated carbon. The water level of the water containing the condensed water and the used cooling water in the condenser 15 is maintained at a predetermined level by level controlling means 35 and the level adjusting valve 36. It will of course be understood that although the steam separator 32, the water level control means 35, and the adjusting valve 36 were incorporated into the assembly 20 comprising the recombining unit 13 and the condenser 15 as shown in the embodiment of FIG. 2, it is possible to install them on the outside of the assembly 20. According to the radioactive gaseous waste disposing system of this invention, a recombining unit and a condenser are installed on a common skid and combined as one assembly, so that the pipes connecting these equipment can be eliminated thereby making compact the system and minimizing the space for installation thereof. The constructional advantages allow workers to use a wide space for maintenance and operation of the system. The direct contact of the cooling water to the radioactive gaseous wastes in the condenser allows to use a small amount of the cooling water and prevents the wastes from leaking out of the system, thus providing the safe and reliable system. In addition, the elimination of the pipes necessary to connect respective equipments of the system makes simple the installation works in the field without connecting the pipes by welding, etc. Moreover, since the cylindrical containers are constructed to be dividable into two upper and lower parts so that the recombiner is disposed in the upper half and the preheater is disposed in the lower half when the recombining unit is disassembled, the periodical maintenance or inspection of the preheater and the recombiner can be performed independently, and these members are arranged vertically, so that the water vapour formed in the recombiner drops and does not stay there. Thus, if a catalyst is used, it will not be damaged by the water vapour.