JPH0365877B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a method for removing sodium from a cover gas system of a fast breeder reactor, and in particular, a method for removing sodium suitable for application to a recirculating cover gas system of a fast breeder reactor. Regarding the method.

[Background of the invention]

Figure 1 shows an example of the configuration of a recirculating cover gas system for a fast breeder reactor. In Figure 1, a reactor vessel 1 is filled with coolant sodium 3 with a free liquid level in order to remove the heat generated in the reactor core 2, and is kept at a high temperature of approximately 500°C during reactor operation. become. In the space 4 above the free liquid surface of the sodium coolant 3, argon gas, which is an inert gas, is filled as a cover gas from the viewpoint of preventing oxidation of the sodium.

During reactor operation, sodium mist and vapor migrate into the cover gas from above the free liquid surface of coolant sodium 3, as well as radioactive argon ( ⁴¹ Ar) generated when argon is activated and xenon in the event of fuel failure. This system includes sodium removal devices 7 and 14, ⁴¹ Ar attenuation tank 24 ^and A rare gas removal/recovery facility 23 is provided and operated in a closed loop by a compressor 22.

A conventional sodium removal method will be explained based on FIGS. 1 and 2. In Figure 1, reactor vessel 1
Argon gas containing sodium mist and vapor in the space 4 above the free liquid surface of the sodium coolant 3 is removed by condensation from the reactor vessel outlet 5 through a passage (piping) 6 heated at a high temperature of approximately 500°C. is guided to device 7. The argon gas flowing into the removal device 7 from the inlet nozzle 8 is cooled by using a combination of a cooling device 10 provided outside and a heating device (not shown in the figure) when passing through the filling material 9. It is cooled from a high temperature of 500℃ to about 130℃, which is higher than the freezing point of sodium. Here, the sodium vapor in the argon gas is condensed on the surface of the filler 9 and removed.
The removed liquid sodium falls under its own weight against the surface tension of the filler portion and is returned into the reactor vessel 1 from the inlet nozzle 8 via the pipe 6 having a drain slope. On the other hand, the argon gas from which most of the sodium vapor has been removed is sent to outlet nozzle 1.
2, the passage (piping) 13 is preheated to approximately the same temperature as the outlet temperature of the condensing type removal device 7.
The liquid is then guided to the coagulation type removal device 14. The argon gas that has flowed into the removal device 14 from the inlet nozzle 15 is cooled by using a combination of an external cooling device 17 and a heating device (not shown in the figure) when passing through the filling material 16. 130℃
It is then further cooled to about 50° C., which is lower than the sodium freezing point, and here the sodium vapor or sodium mist in the argon gas is solidified and removed by the filler 16 as minute particles. Since most of the removed sodium is deposited in the filler 16 in solid form, this becomes a factor that increases the pressure loss and pressure drop fluctuation of the system during operation of the system. In the condensation type removal device 7 and the coagulation type removal device 14,
As shown in FIG. 2, it is important to cool the argon gas smoothly along the flow direction from the viewpoint of the removal performance of the device.
8 controls the temperature distribution. The passage (piping) 13 connecting the condensation type removal device 7 and the solidification type removal device 14 is provided with a drain pipe 20, and the pressure loss of the solidification type removal device 14 increases due to the above-mentioned reason, making continuous operation of the system impossible. If this becomes difficult, the solidified sodium is melted and drained by heating at a high temperature, and then returned to the reactor vessel 1 by opening the drain valve 21.

In the conventional sodium removal method described above, first, the condensation type removal device 7 removes the sodium component as a vapor condensation process.
It is preferable to supply the sodium component completely in the form of vapor at the inlet section 8, and therefore it is necessary to maintain the temperature at the inlet section and the temperature at the upstream passage 6 at a fairly high temperature, for example, about 500.degree. Figure 3 shows the relationship between the sodium saturated vapor concentration in argon gas and the temperature, but the above inlet temperature actually needs to be set higher than the saturated vapor temperature corresponding to the sodium concentration at the inlet. has been done. In addition, the solidification type removal device 14 is designed to cool the sodium vapor or mist to a temperature lower than the freezing point of sodium and remove it as minute particles, so that most of the area of the filler 16 is below the freezing point temperature. Therefore, an increase in pressure loss is unavoidable, but if the sodium concentration at the inlet 15 increases for some reason, the pressure loss may increase early and cause blockage. When there is a need for long-term continuous operation with fluctuations, there are problems with long-term continuous operation.

[Purpose of the invention]

The purpose of the present invention is to change the method for removing sodium from argon gas from a method that utilizes the condensation and solidification process of sodium vapor to a method that uses the collection and solidification process of sodium mist, and to reduce the area where the temperature is below the sodium freezing point to a small portion. The object of the present invention is to provide a sodium removal method suitable for application to a recirculating cover gas system of a fast breeder reactor that is continuously operated with low pressure drop and low pressure drop fluctuation.

[Summary of the invention]

The method of the present invention is a sodium removal method in a recirculating cover gas system of a fast breeder reactor, in which the cover gas discharged from the reactor vessel of the fast breeder reactor is heated to a temperature higher than the freezing point of sodium and the sodium in the reactor vessel is After the sodium vapor component in the cover gas is made into a mist by passing through a passage whose temperature is lower than that of the cover gas, the mist is maintained at a temperature equal to or higher than the freezing point of the sodium throughout the entire area in the flow direction of the cover gas. It is passed through a collection type removal device and removed by contact collection, and the cover gas coming out of the mist collection and reflux type removal device is set to the temperature of the filler in the direction of flow so that a part of the gas outlet side is higher than the sodium freezing point. The sodium remaining in the cover gas in most of the region is passed through a mist collecting local solidification type removal device set at a temperature higher than the freezing point of sodium in most of the region upstream of the part on the outlet side. This is a method for removing sodium from a fast breeder reactor cover gas system, in which the mist to be removed is collected by contact, and is removed by solidifying it in the above-mentioned part. cover gas,
By passing through a passage whose temperature is higher than the freezing point of sodium and lower than the sodium temperature in the reactor vessel, the sodium vapor component in the cover gas is turned into a mist, and the mist is used as the temperature of the filler to rise to a temperature higher than the sodium freezing point. The mist is passed through a mist collection type removal device whose temperature is maintained, and is removed by contact collection without solidification, and the mist that cannot be completely removed is subsequently passed through a mist collection and localized solidification type removal device, where it is removed. In this case, the temperature of the filling material is set to a temperature lower than the sodium freezing point in a part of the gas outlet side, and a temperature higher than the sodium freezing point in most of the region upstream of the part on the gas outlet side. The mist that is contact-collected in a relatively high-temperature region and that cannot be completely collected here is further solidified at a temperature lower than the sodium freezing point in a partial region on the exit side, thereby ensuring that the mist is collected reliably.

[Embodiments of the invention]

The embodiments of the present invention are based on the findings described below.

Conventionally, the method of removing sodium from cover gas, both domestically and internationally, has been to remove it through the condensation process of sodium vapor. The main points of the embodiments of the present invention are to fundamentally change the conventional concept described above to the sodium mist collection method, improve the temperature distribution in the conventional coagulation type removal device, and change the sodium removal method to a sodium mist collection method. The main reason for this is that the liquid is mainly collected and solidified only in a small portion on the exit side.

First, regarding the change from the removal method based on the condensation process of sodium vapor to the removal method based on contact collection of sodium mist, if we exclude performance problems of the removal device, we need to lower the inlet temperature of the above-mentioned removal device. This can be achieved with On the other hand, from the viewpoint of the performance of the removal device, it was conventionally thought that the removal efficiency of sodium mist removal would be lower than that of sodium vapor, but in reality, both methods have a lower removal efficiency. It has been experimentally determined that there is no significant difference. The reason for this is that in the case of condensation of sodium vapor, if it were purely a condensation phenomenon on the surface of the filler material, the removal efficiency would be better than that of the removal of sodium mist, but in reality, the removal efficiency is higher than that of the removal of sodium mist. Since a considerable amount of sodium mist is generated during the condensation process, it is thought that the situation is essentially close to contact collection of sodium mist.

Next, regarding improving the temperature distribution of conventional coagulation type removal equipment, when removing sodium components by solidifying them, if solid sodium is captured in the filler during operation, it will accumulate under pressure. Although the increase in loss itself is an unavoidable phenomenon, if the area below the freezing point temperature is widened as in the past, if the sodium concentration at the inlet increases for some unexpected reason, the area relatively close to the inlet will increase. If there is a need for long-term continuous operation with low pressure loss and low pressure drop fluctuations, improve the temperature distribution so that the temperature region below the freezing point is only a small part of the outlet side. death,
Even if solid sodium accumulates in the low-temperature section on the outlet side, long-term continuous operation is possible with low pressure drop and low pressure drop fluctuation if the accumulated sodium is blown through with a pressure difference equivalent to the allowable pressure drop. It has been confirmed that this can be done, and it has also been confirmed that there is no problem in terms of removal performance if the outlet temperature is set slightly lower than the freezing point temperature.

A concrete implementation method of the present invention will be described below.

FIG. 4 shows a temperature diagram of each part of an embodiment of the sodium removal method according to the present invention. In this figure, since the principle is different from the conventional removal method shown in Fig. 2, the conventional condensation type removal device is replaced by a mist collection type removal device, and the coagulation type removal device is replaced by a mist collection local coagulation type removal device. The name has been changed to distinguish it.

Embodiments of the present invention will be described below with reference to FIGS. 1 and 4. Sodium coolant 3 in reactor vessel 1
After leaving the reactor vessel outlet 5, the high-temperature argon gas containing sodium mist or vapor in the space 4 above the free liquid surface of For example, when passing through a passageway (piping) 6 that is preheated at about 200°C, it is naturally cooled by heat radiation and drops to almost the above preheating temperature, so that the sodium vapor contained in the space 4 is turned into mist. At the same time, the sodium concentration is attenuated because it is removed from the inner surface of the passage (piping) by gravity deposition or collision phenomenon within the passage (piping) 6. However, in the space 4, it is said that due to the ripples on the free liquid surface of the coolant sodium 3 and the rapid temperature gradient near the liquid surface, the concentration of vapor becomes several tens of times higher than the saturated vapor concentration corresponding to the sodium temperature. Even after the sodium mist is attenuated in the passageway (piping) 6, approximately several thousand ppm of sodium is contained in the argon gas.
As shown in Figure 2, at about 200°C, the saturated vapor concentration is on the order of about 0.1 ppm, so it can be seen that almost all the sodium components in the gas are in a mist state. After the sodium vapor is made into a mist in advance in the above-mentioned passageway (space) 6, it is guided to the mist collection type removal device 7, where most of the sodium mist in the argon gas is collected by contact with the filler 9. removed. In this device, unlike conventional condensation-type removal devices, the sodium removal performance does not change significantly depending on the temperature distribution in the gas flow direction, and the removal performance is mainly determined by the specifications of the filler 9 and the flow conditions. Therefore, the temperature of the filler 9 only needs to be maintained at a temperature higher than the freezing point of sodium over the entire region. For example, if the inlet temperature is about 200 degrees Celsius and the outlet temperature is about 150 degrees Celsius, the temperature difference at the entrance and exit portions is small, so the heating device The above temperature conditions can be achieved only by

After most of the sodium mist has been removed by the mist collection type removal device 7, argon gas is The temperature is raised and the mist is guided to the mist collection and local coagulation removal device 14, where the remaining sodium mist is further removed by contact collection with the filler 16 and collection of solidified fine particles of sodium. . In this device, most of the collection area including the gas inlet has a temperature above the freezing point of sodium, and a small portion on the gas outlet side has a temperature area below the freezing point. The temperature is higher than the sodium freezing point, for example 300°C, and the cooling device 17 and the heating device are used so that the outlet temperature of the filler 16 is slightly lower than the sodium freezing point, for example in the range of about 80°C to 95°C. Temperature conditions are achieved. The reason why the argon gas temperature is raised in advance in the passageway (piping) 13 leading to the mist collecting and locally coagulating removal device 14 is to raise the temperature of the argon gas in advance in order to bring most of the collection area to the sodium freezing point or higher in the main removal device 14. This is merely a case where the temperature in the passage (piping) is not increased. In this removal device, there is a region on the outlet side where the temperature is slightly lower than the freezing point temperature of sodium, so solid sodium accumulates in the filler 16 during operation and the pressure drop increases.
At the beginning of operation, the outlet temperature of the filler material is set to a low value.
If a method of gradually increasing the pressure as the operation progresses is adopted, sodium can be removed in a relatively low pressure drop state and without sudden pressure drop fluctuations.

According to the embodiment described above, since the sodium mist contact collection method is used, the temperature of the inlet and upstream piping of the mist collection type removal device can be greatly reduced. Not only can this be achieved, but the amount of attenuation of the sodium mist in the piping increases, so the effect of reducing the sodium load on the sodium removal device can also be expected. Furthermore, in the mist collection local coagulation device, most of the area is kept at a temperature above the freezing point, and a small portion on the outlet side is kept at a temperature below the freezing point, so even if the inlet sodium concentration is high, there will be no early blockage. This has the effect of allowing long-term continuous operation with low pressure loss and low pressure loss fluctuations.

〔Effect of the invention〕

According to the present invention, since a contact trapping method for sodium mist is used, the temperature of the inlet and upstream piping of the mist trapping type removal device can be reduced, and the mist trapping method that continuously receives sodium mist from the outlet of the device In the localized coagulation type removal device, the area where the temperature is below the freezing point is only a small part of the outlet side, so even if the inlet sodium concentration is high, early blockage is avoided and long-term continuous operation is possible with low pressure loss and low pressure drop conditions. There is an effect that can be done.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the recirculating cover gas system of a fast breeder reactor, Figure 2 is a temperature diagram of each part in the conventional sodium removal method, and Figure 3 is the concentration of sodium saturated vapor in argon gas. FIG. 4 is a state diagram showing the temperature state of each part in the sodium removal method according to an embodiment of the present invention. 1... Reactor vessel, 2... Core, 3... Coolant sodium, 4... Space above the free liquid level, 5... Reactor vessel outlet, 6, 13... Passage, 22... Compressor, 25... Reactor vessel inlet, 21... Drain valve, 8, 15... Inlet nozzle, 9, 16... Filler, 10, 17... Cooling device, 11, 18... Thermometer, 12, 19... Outlet nozzle.

Claims (1)

[Claims] 1. In a method for removing sodium in a recirculating cover gas system of a fast breeder reactor, the cover gas discharged from the reactor vessel of the fast breeder reactor is heated to a temperature equal to or higher than the freezing point of sodium and lower than the sodium temperature in the reactor vessel. After the sodium vapor component in the cover gas is turned into a mist by passing the sodium vapor component in the cover gas through the passage, the temperature of the cover gas is maintained at the temperature of the filler over the sodium freezing point over the entire area in the flow direction. The cover gas coming out of the mist collection and reflux type removal device is heated to a temperature of the filling material in the direction of flow, and a part of the gas outlet side is at a temperature lower than the freezing point of sodium. The target for removal remaining in the cover gas in most of the region upstream of the outlet side is passed through a mist collection local solidification type removal device set at a temperature higher than the sodium freezing point in most of the region upstream of the part on the outlet side. A method for removing sodium from a fast breeder reactor cover gas system, characterized in that the mist is collected by contact and removed by solidification in the portion.