JP5340237B2 - Radioactive liquid processing equipment - Google Patents

Description

  The present invention relates to a radioactive liquid waste treatment apparatus that is generated during the operation of a nuclear reactor, and in particular, reduces the load caused by the clad on the LCW filtration apparatus on the process line and makes it difficult to settle without HCW concentration treatment of the clad. The present invention relates to a radioactive liquid waste treatment apparatus suitable for treating a radioactive insoluble component.

  In the conventional treatment around sedimentation separation tanks at nuclear power plants, the backwash water of the condensate filtration device is transferred to the CUW sedimentation separation tank, and after solids are settled by sedimentation separation, the decant water is transferred to the LCW collection tank. And processed in an LCW waste liquid treatment system. The clad and used resin that have been settled and separated in the sedimentation separation tank are sufficiently attenuated in radioactivity, and then uniformly mixed with the supernatant in the sedimentation separation tank, and then transferred to the solidification system in a slurry state of about 10 wt%. .

Here, the suspended solids in the settling tank are caused by corrosion of the steel materials constituting the equipment and piping of the condensate system of the power plant contained in the backwash water of the condensate filtration device in contact with the condensate. The generated iron rust component is the main component, and its chemical form is Fe ₃ O ₄ and Fe ₂ O ₃ iron oxide, and FeOOH iron hydroxide. Condensate at nuclear power plants has few impurities, and its water quality is close to that of pure water. Therefore, the supernatant water of the sedimentation tank is also water quality close to that of pure water, its conductivity is as low as 1 μS / cm, and the pH value is around 6. Under such conditions, FeOOH, which is an iron hydroxide, is dispersed in a colloidal state in the liquid and sedimentation due to gravity is less likely to occur. Therefore, the iron concentration of the decant water does not decrease over time, and a considerable amount of fine cladding is mixed in the decant water. The decant water is transferred to the LCW collection tank on the process line and filtered by the subsequent LCW filtration device. Therefore, the LCW filtration device is clogged by the clad and the differential pressure rises quickly. At present, the clad concentration in the decant water is about 500 ppm at the maximum, greatly exceeding 20 ppm which is a standard for the acceptance processing in the LCW system, which is a main cause of the increase in the differential pressure of the LCW filtration device. For this reason, the frequency of backwashing for recovering the processing capacity is increased, and the operation of the LCW system is not realized.

  On the other hand, there is known one that promotes sedimentation of the clad by adjusting the pH in the sedimentation separation tank and reduces the amount of clad flowing into the LCW system (see, for example, Patent Document 1).

  However, in the method described in Patent Document 1, since the clad settled by adjusting the pH has a very small sediment bulk density and a large sediment clad volume, the maximum sludge layer height that can be stored in the sedimentation tank is reached before the design storage years. There was a fear of doing. Therefore, it was necessary to increase the capacity of the sedimentation tank to ensure the sludge storage capacity.

  On the other hand, there is known one in which a sedimentation tank is provided with a filter and decanted water filtered by the filter is transferred to an LCW collection tank on the process line (see, for example, Patent Document 2).

JP-A-62-161096 Japanese Patent Laid-Open No. 11-153696

  However, in the thing of patent document 2, the used resin of the CUW filtration desalination apparatus is also transferred to a sedimentation separation tank other than the backwash water of a condensate filtration apparatus. Since the radiation dose rate of the used resin is high, the radioactivity concentration of decant water also becomes high, and it is necessary to solidify after sufficiently reducing the radioactivity.

  An object of the present invention is to provide a radioactive liquid waste treatment apparatus capable of reducing the clad load on the LCW filtration device, reducing the increase in the radioactive concentration of decant water, and reducing the concentration rate of the concentrated waste liquid and thus the dose rate of the solidified body. It is in.

  (1) In order to achieve the above object, the present invention is provided separately from a sedimentation separation tank for separating an insoluble component from a CUW filtration desalting apparatus from a liquid by sedimentation separation, and the sedimentation separation tank. A backwash water receiving and concentrating tank that accepts backwash water of the condensate filtration device and separates the hard-to-settling suspended solids by sedimentation; and a filtration device that filters and separates the liquid in the backwash water receiving and concentrating tank. The supernatant of the sedimentation tank and the filtrate of the filtration device are returned to the LCW collection tank, and the concentrate of the filtration device is returned to the backwash water receiving and concentration tank, and the backwash is further performed. A heater for heating the liquid in the water receiving and concentrating tank is provided.

  With this configuration, it is possible to reduce the clad load on the LCW filtration device, reduce the increase in the radioactive concentration of decant water, and reduce the increase in the dose rate of the concentrated waste liquid and thus the solidified body.

  (2) In the above (1), preferably, a cross-flow type filtration device is used as the filtration device.

  (3) In the above (1), the heater is connected to a circulation line for returning waste liquid from the backwash water receiving and concentrating tank to the backwash water receiving and concentrating tank through the filtration device or backwashing water receiving and concentrating. It is designed to be installed inside the tank or upstream of the backwash water receiving / concentrating tank.

According to the present invention, it is possible to reduce the cladding load on the LCW filtration device, reduce the increase in the radioactivity concentration of decant water, and reduce the increase in the dose rate of the concentrated waste liquid and thus the solidified body.

It is a system flowchart which shows the structure of the radioactive liquid waste processing apparatus in the nuclear power plant by one Embodiment of this invention. It is explanatory drawing of the sedimentation speed by the radioactive waste liquid processing apparatus in the nuclear power station by one Embodiment of this invention.

Hereinafter, the configuration and operation of the radioactive liquid waste processing apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a system flow diagram showing a configuration of a radioactive liquid waste treatment apparatus in a nuclear power plant according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of the sedimentation speed by the radioactive liquid waste treatment apparatus in the nuclear power plant according to one embodiment of the present invention.

  Steam generated in the nuclear reactor 1 is condensed by the main condenser 2. The condensed water is filtered by the condensate filtering device 3, desalted by the condensate desalting device 4, and then returned to the reactor 1. Further, the reactor coolant filtering and desalting apparatus 5 performs filtering and desalting of the reactor coolant.

  On the other hand, the LCW system waste liquid 11 generated in the reactor system, the turbine system, etc. is collected in the LCW collection tank 12 and transferred to the LCW filtration device (hollow fiber membrane filter) 14 by the LCW collection pump 13. At 14 the solids are separated by filtration. The differential pressure of the LCW filtration device 14 is measured by a differential pressure gauge DP. When the differential pressure reaches a specified value, the hollow fiber membrane surface inside the filtration device 14 is backwashed, and the backwash water is sent to the reactor coolant purification system (CUW) sedimentation separation tank 8. The waste liquid from which the solid content has been separated by the LCW filtration device 14 is subjected to removal of ionic impurities by the LCW desalting device 15, sampled in the LCW sample tank 16, and then transferred to the condensate storage tank 18 by the LCW sample pump 17. Then, it is transferred by the condensate transfer pump 19 and reused as plant water.

  Further, the spent resin 7 of the CUW filtration desalting apparatus 5 is transferred to the CUW sedimentation separation tank 8, and after the solid content is settled by sedimentation separation, the sedimentation tank supernatant water (decant water) 9 is decanted pump 21. Is transferred to the LCW collection tank 12 and processed in the LCW waste liquid treatment system. The used resin settled and separated in the sedimentation separation tank 8 is sufficiently attenuated in radioactivity and then uniformly mixed with the supernatant liquid in the sedimentation separation tank 8, and then the sedimentation sludge 22 is reduced by the sludge extraction pump 23. It is transferred to a solidification system in a 10 wt% slurry state.

  In the present embodiment, the backwash water 6 of the condensate filtration device 3 is once received in the CF backwash water receiving tank 50. It is transferred to a CF backwash water concentration tank 52 by a CF backwash water pump 51.

  The clad in the CF backwash water solution 8 is concentrated in the CF backwash water concentration tank 52. The backwash water receiving / concentrating tank 52 is provided with a circulation line 25 for returning the waste liquid to the backwash water receiving / concentrating tank through the filtration device 24 by the decant pump 10. An apparatus 24 and a waste liquid heater 53 are installed. Further, the CF backwash water is transferred to the filtration device 24 by the decant pump 10, and the clad in the decant water is concentrated by the crossflow filtration device 24. The filtrate 26 after separating the clad from the decant water is transferred to the LCW collection tank 12 and transferred to the LCW filtration device 14 together with other LCW system waste liquid 11 by the LCW collection pump 13 to separate and separate the suspended solids. After the ionic impurities are finally removed by the LCW desalinator 15, the water becomes clean water and is recovered as plant reuse water.

  The filtrate 26 has the suspended solids mainly composed of the clad removed by the filtration device 24 to 1 ppm or less, and the conductivity is about 1 μS / cm. It can be processed.

  On the other hand, the suspended solids mainly composed of the clad separated by the filtration device 24 are again collected in the CF backwash water concentration tank 52 and concentrated.

  Next, the waste liquid heater 53 will be described. The waste liquid heater 53 heats the waste liquid sent from the backwash water receiving / concentrating tank 52 to the filtration device 24 to a predetermined temperature by the decant pump 10. Since the heated waste liquid is returned to the backwash water receiving / concentrating tank 52 by the circulation line 25, the waste liquid inside the backwash water receiving / concentrating tank 52 is heated as a result.

  Here, a heat exchanger is used as the waste liquid heater 53. As a heat source of the heat exchanger, a part of the steam generated in the nuclear reactor 1 is used. The heat exchanger exchanges heat between the high temperature steam and the low temperature waste liquid to heat the waste liquid. Thus, by using a part of the steam generated in the nuclear reactor 1 as a heat source, it is not necessary to provide a separate heat source. In the present embodiment, a temperature sensor St and a controller 54 are further provided. The temperature sensor St measures the temperature inside the backwash water receiving / concentrating tank 52. The controller 54 controls heating by the waste liquid heater 53 so that the temperature inside the backwash water receiving and concentration tank 52 detected by the temperature sensor St becomes a predetermined temperature. As described above, when a heat exchanger is used as the waste liquid heater 53, the controller 54 controls the opening degree of an opening degree control valve provided in a pipe for supplying steam to the heat exchanger to Vary the amount of steam supplied to the exchanger. Since the flow rate of the waste liquid sent from the backwash water receiving / concentrating tank 52 to the filtration device 24 is, for example, about 2 m / s, it can be sufficiently heated by steam.

  As the waste liquid heater 53, an electric heater or the like can be used in addition to the heat exchanger.

  Next, changes in the sedimentation rate of the solid content caused by heating the waste liquid in the backwash water receiving and concentration tank 52 will be described with reference to FIG. In FIG. 2, the horizontal axis indicates the sedimentation time (hr), and the vertical axis indicates the solid content concentration (ppm).

  In FIG. 2, the solid content concentration of the stock solution at the start of measurement was about 400 ppm. On the other hand, when the heating according to the present embodiment is not performed, the solid content concentration is about 350 ppm after 96 hours as indicated by the alternate long and short dash line in the figure, and the solid content concentration gradually decreases. At this time, the temperature of the waste liquid in the backwash water receiving / concentrating tank 52 was normal temperature, and it fluctuated depending on the outside air temperature.

  On the other hand, the broken line indicates the solid content concentration when the waste liquid in the backwash water receiving and concentration tank 52 is heated to 50 ° C. The concentration of about 400 ppm before the start of heating decreased to about 170 ppm after 24 hours, and further decreased to 50 ppm or less after 96 hours.

  The solid line indicates the solid content concentration when the waste liquid in the backwash water receiving / concentrating tank 52 is heated to 80 ° C. The concentration of about 400 ppm before the start of heating decreased to about 20 ppm after 24 hours, and further decreased to 10 ppm or less after 96 hours.

  As described above, it is possible to improve the sedimentation rate from 10 times to 100 times that of the prior art by heating the waste liquid temperature of the hardly sedimentable clad-containing water to a temperature higher than room temperature. That is, in the present embodiment, the waste liquid of the hard-to-settling clad-containing water is concentrated by cross-flow filtration, and further, the waste liquid is heated to increase the particle size of the hard-to-settling clad and to cause aggregation. Can be improved.

  In the above description, the waste liquid heater 53 is provided in the circulation line 25 between the decant pump 10 and the filtration device 24, but in the circulation line 25 between the filtration device 24 and the backwash water receiving and concentration tank 52. It may be provided.

The waste liquid heater 53 can also be provided inside the backwash water receiving / concentrating tank 52. In this case, an electric heater is used as the waste liquid heater. At this time, the capacity of the backwash water receiving / concentrating tank 52 is about several m ³ , and in order to make the inside of the backwash water receiving / concentrating tank 52 as uniform as possible, the waste liquid inside the backwash water receiving / concentrating tank 52 is reduced. It is preferable to provide a stirring mechanism for stirring.

  Further, since the waste liquid heater 53 only needs to heat the waste liquid inside the backwash water receiving and concentrating tank 52, the waste liquid heater 53 is disposed in the flow path between the CF backwash water tank 50 and the backwash water receiving and concentrating tank 52. It can also be provided. In this case, a heat exchanger or an electric heater can be used as the waste liquid heater. Further, a waste liquid heater can be provided inside the CF backwash water tank 50.

  The filtration device 24 can be concentrated to about 1 to 10 wt% if it is a suspended solid content with relatively good filterability, such as iron oxide and iron hydroxide, so that the clad concentration is about 500 ppm at maximum. It can be continuously concentrated up to about 20 to 200 times. Since the solid content concentration in the supernatant of the sedimentation separation tank 8 can be concentrated to 1 to 10 wt%, the solid content in the sedimentation separation tank 8 need not be taken into consideration, and the solid matter is stored in the sedimentation separation tank 8. -It can also be stored.

  As a result, it is possible to prevent the hard-to-seduce clad from being brought into the sedimentation separation tank 8 and to reduce the storage capacity of the sedimentation separation tank 8.

  Moreover, the use of the CUW filtration desalination apparatus 5 having a high dose is provided by providing a cross flow type filtration device 24 from the CF backwash water receiving tank 50 upstream of the sedimentation separation tank 8 to the CF backwash water concentration tank 52. The clad can be handled as a low dose without being affected by the spent resin, and the clad can be handled as a low dose. By directly solidifying the concentrated clad, it is possible to bring the hardly settled clad into the sedimentation tank 8. Since it can suppress, the decant water of the sedimentation tank 8 is clean, and can perform the LCW type | system | group process efficiently.

  As described above, since the floating clad in the decant water is separated and recovered before the decant water is transferred to the LCW collection tank 12, the clad in the decant water is not transferred to the LCW collection tank 12. The cladding load can be reduced.

  Further, since the water quality of the decant water is low in conductivity and the suspended solid content is clad mainly composed of iron rust, a filtration method can be adopted as a method for recovering the clad in the decant water.

  Moreover, there are the following effects by adopting the cross flow filtration method as the decant water filtration method. That is, as a method for filtering suspended solids in the waste liquid, there is a once-through filtration type hollow fiber membrane filter adopted as the LCW filtration device 14, for example, but the processing capacity is recovered depending on the amount of solids captured on the filtration surface. Therefore, since it is necessary to perform backwashing, waste liquid treatment with a solid content concentration of about 50 ppm or less is a standard. Therefore, when waste liquid with a solid concentration of about 500 ppm at maximum is treated like decant water, it is necessary to frequently perform backwashing. Compared to this, the cross-flow filtration method can perform stable treatment even when the solid concentration is high. The cross-flow filtration method is a method of performing filtration while flowing the stock solution parallel to the surface of the filtration membrane. The clear filtrate from which suspended fine particles have been removed is transferred to the next step, and the concentrated solution is recovered to the stock solution side. In the cross-flow filtration method, the filter cake that accumulates on the filtration surface is removed by the force generated by the flow of the stock solution parallel to the filter membrane surface, and the formation of the filter cake is kept to a minimum. For this reason, even when a waste liquid having a high solid content concentration is treated, the filtration surface is relatively less clogged, and high-efficiency filtration is possible over a long period of time. As a result, even if the floating clad is mixed in the decant water, only the clear filtration treatment liquid is transferred to the LCW collection tank 12, the clad load on the LCW filtration device 14 is eliminated, and the backwash frequency of the filtration surface is reduced. Reduction, that is, generation of useless waste water can be prevented.

  If the sedimentation tank 8 has a relatively low dose rate of the resin 8 of the CUW filtration desalination apparatus 5 and the condensate filtration apparatus 3 and a low sedimentation rate and a refractory clad is present, Although it has a high radioactivity concentration and it is necessary to attenuate the radioactivity for a long period of time, in this embodiment, the CF backwash water is not put into the sedimentation separation tank 8 without the clad having a comparatively low dose rate of the condensate filtration device 3. By removing and concentrating with the cross-flow filter 24 installed in the tank 50 and the CF backwash water concentration tank 52, it is possible to ensure the quality of the decant water without bringing the sedimentation tank 8 into the sedimentation separation tank 8. In addition, the concentrated high-concentration clad does not require long-term radiation attenuation because the radiation dose rate is low, and can be directly solidified. Even when the decant water is subjected to the HCW concentration treatment, the fine clad is not mixed, so there is no problem of carry-over due to the fine clad, and sludge can be stored and stored without increasing the sedimentation separation tank 8.

Moreover, since the sedimentation rate can be improved by heating the waste liquid temperature of the hard-to-settling clad-containing water to a temperature higher than room temperature, the waste liquid of the hard-to-seduce clad-containing water is concentrated by cross-flow filtration, and the waste liquid is heated. As a result, the particle size of the hard-to-settling clad can be increased and aggregated to improve the sedimentation rate.

DESCRIPTION OF SYMBOLS 1 ... Reactor 2 ... Main condenser 3 ... Condensate filtration apparatus 4 ... Condensate demineralization apparatus 5 ... Reactor coolant filtration demineralization apparatus 6 ... Condensation filtration apparatus backwash water 7 ... Used resin 8 ... CUW Sedimentation separation tank 9 ... Sedimentation separation tank supernatant water (decant water)
DESCRIPTION OF SYMBOLS 10 ... Decant pump 11 ... LCW system waste liquid 12 ... LCW collection tank 13 ... LCW collection pump 14 ... LCW filtration apparatus 15 ... LCW desalination apparatus 16 ... LCW sample tank 17 ... LCW sample pump 18 ... Condensate storage tank 19 ... Condensate Transfer pump 20 ... LCW filter backwash water 21 ... Pump 22 ... Sediment sludge 23 ... Sludge extraction pump 24 ... Cross flow filter 25 ... Concentrate 26 ... Filtrate 50 ... CF backwash water tank 51 ... CF backwash water pump 52 ... CF backwash water concentration tank 53 ... Waste liquid heater 54 ... Controller St ... Temperature sensor

Claims (3)

A sedimentation separation tank for separating insoluble components from the CUW filtration desalination apparatus from the liquid by sedimentation;
A backwash water receiving and concentrating tank that is provided separately from the settling separation tank, receives backwash water of a condensate filtration device, and settles and separates hard-to-settle suspended solids;
A filtration device for filtering and separating the liquid in the backwash water receiving and concentration tank,
The supernatant liquid of the sedimentation tank and the filtrate of the filtration device are returned to the LCW collection tank, and the concentrate of the filtration device is returned to the backwash water receiving and concentration tank,
Furthermore, the radioactive waste liquid processing apparatus provided with the heater which heats the liquid in the said backwash water receiving concentration tank. In the radioactive liquid waste processing apparatus of Claim 1,
A radioactive waste liquid treatment apparatus using a cross flow filtration apparatus as the filtration apparatus. In the radioactive liquid waste processing apparatus of Claim 1,
The heater is provided in a circulation line for returning waste liquid from the backwash water receiving / concentrating tank to the backwash water receiving / concentrating tank via the filtration device, in the backwash water receiving / concentrating tank, or in the backwashing. A radioactive liquid waste treatment apparatus installed on the upstream side of a water receiving and concentration tank.

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