JPS6016503B2 - How to operate liquid metal refining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for purifying sodium used as a coolant in a fast breeder reactor (hereinafter abbreviated as FBR) plant, and particularly to a method for operating a cold trap for removing impurities from sodium.

As a coolant for FBR, metallic sodium is widely used due to its advantages such as: ■low specific gravity, ■high thermal conductivity, ■high boiling point, and ■low absorption of nuclear neutrons. There is.

However, on the other hand, sodium is biologically active and easily combines with various substances, and has a particularly strong bond with oxygen. If a large amount of the above-mentioned sodium oxide is mixed into the sodium used as the FBR coolant, the following problems will occur.

■ Increased corrosion of structural materials. ■ Oxide precipitates in the low-temperature area, and when the amount increases, the flow path becomes clogged.

■ Parts that move in sodium, such as valves and pumps, are prone to galling.

For this reason, in FBR plants, contact between sodium and oxygen is avoided as much as possible, and an inert gas such as argon is used as a cover gas for sodium.

Despite this, oxides build up in the sodium over a long period of time due to oxygen, etc. mixed in with the inert gas. In order to avoid the harmful effects of oxides and to operate the FBR smoothly, it is necessary to remove these oxides from the sodium. A typical example of such a device is a cold trap. This is a device that cools sodium containing dissolved impurities, creates a supersaturated state, and precipitates and captures oxides. Figure 1 shows the structure of a very common cold trap.

There is a sodium inlet pipe 3 in the center of the container 4, and a mesh 7 is tied around it. At the bottom of the mesh 7 and container 4 there is a settling chamber 8. There is a sodium outlet pipe 9 in the upper part of the container 4, and cooling fins 5 are provided on the outer periphery of the container 4. The fins 5 are surrounded by a cooling duct 6, and a cooling fan 10 is provided at the bottom of the duct 6. The sodium to be purified is accelerated by pump 2 and follows sodium stream 12 to settling chamber 8 . Since the container 4 is cooled by a single cooling blower from the bottom to the outer periphery, the settling chamber 8 has the lowest temperature. Therefore, impurities in the sodium precipitate in this part. Sodium rises through the mesh. As a result, the precipitated impurities are trapped within the mesh. The filtered sodium is obtained from the outlet pipe 9. As mentioned above, in this type of cold trap, the settling chamber 8 has the lowest temperature, so the temperature 15 there (hereinafter referred to as purification temperature) has a great effect on the impurity removal characteristics.

Therefore, in order to operate a cold trap, there are two issues: (1) how to accurately control the purification temperature, and (2) how to determine the purification temperature in order to remove the amount of impurities in the entire system. This is an important point. (2) The secondary technology is a cooling amount control method that controls the refining temperature by adjusting the flow rate and temperature of a cooling medium such as air.

As explained in Fig. 1, this method has poor temperature controllability because the cooling effect appears through the container. The disadvantage is that it is difficult to maintain a constant value. In this situation, the cold trap control system
Regardless of whether it is a manual control system by an operator or a computerized automatic control system, it is almost the same. In response to this, recently, a cooling amount/flow rate control method has been proposed that uses a sodium flow rate control method with a relatively quick response in addition to the cooling amount control method.

In this method, the purification temperature is roughly refined by the amount of cooling, and then,
This is a method that finely adjusts it by adjusting the flow rate. In other words, by using this method, the purification temperature can be controlled with high precision. On the other hand, (2) concerns how far the sodium in the entire system containing impurities can reach a predetermined target purity, and the conventional method is as follows.

'a} Set the purification temperature to a value that is the same as the blockage temperature separately measured with an impurity concentration measuring device, or to a value based on the operator's feeling or experience. {b} A certain period of time (this period also often depends on the operator's experience.

) will remain in the above state until it has passed. {c} After holding, the purification temperature is reset based on the re-measured occlusion temperature.

In this way, in conventional technology, the set value and timing of changes to the refining temperature are often based on intuition or experience, and optimization is not necessarily carried out from the perspective of quickly removing impurities from the system. .

Furthermore, the purification temperature control method at this time is often the cooling amount control method described above, and it is often impossible to control and manage sodium purity with high precision. An object of the present invention is to provide a method of operating a cold trap that not only improves the controllability of purification temperature but also minimizes the sodium purification time of the entire system. In the present invention, the cold trap (
i) Air cooling amount target value (ii) The sodium flow rate target value is calculated by various process quantities, and the cold trap operation related equipment (sodium flow rate control pump, air cooling amount control blower, etc.) is used as the target value. , the cooling amount and flow rate are controlled by a computer.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which sodium 16 stored in a dump tank is purified in a cold trap 9. The sodium pumped and accelerated by the pump 4 passes through a flow meter 6 and an automatic impurity meter 7, and is purified in a cold trap 9. The purified sodium enters the heater tank 2, is heated by the heater 1, and then returns to the dump tank again. In such a configuration, the sodium flow rate, automatic impurity concentration measurement value, cold traps, mouth temperature 8, purification temperature measurement value 20, and cooling amount measurement value are input to the computer 141 by the process inlet signal system 12. The computer 14 calculates the cold trap system control signal 13 using the final purity target value input from the setting system 15 and controls the pump 4, automatic impurity concentration meter 7, and cooling system 19. That is, the control signal for the cold trap system is determined as follows. (i) The air cooling amount target value Q small is determined by the residual impurity amount R, for each sampling period T for calculating Qair.

(Refer to Figure 3) Q Maiko: Cooling amount when the cooling equipment is fully operated Minimum value Ri: amount of residual impurities in the system M at time Ti; amount of sodium in the system C(t); impurity concentration measurement value Cf at time t; final purification target value k: proportionality constant i) Sodium at time t=tn Flow rate target value G shoes (
tn) is calculated using the measured value of the process amount at time t=tn-.

(See Figure 4) That is, the temporal change in the impurity concentration of the purification system shown in Figure 2 is shown in Section d.

=・=Shu4(C(t)−C地)……{31 is given. Here, G: Sodium flow rate; Capture efficiency of cold trap C shoes: Saturated impurity concentration corresponding to the purification temperature of cold trap On the other hand, C glue has a saturated impurity concentration corresponding to the purification temperature T, so C starvation NiA・eXp(-B/TSet)
…,．． , [41 (A, B are constants).

Furthermore, since Twill is the lowest temperature of sodium in the cold trap, the following functional relationship is established depending on the heat balance with the cooling amount Qa;r.

T Snake t=f (GNa Tjo Galr T糾) …'5
'GNa; sodium flow rate T; sodium cold trap inlet temperature G; air cooling flow rate T; air inlet temperature; keep the air inlet temperature T, r; Considering the time interval T that is maintained, the G trajectory is constant during that time, so ``T curve t = g (GN3
, T ship) (during time T). ...It is expressed as '61.

This functional formula is stored in advance in the computer for each air cooling amount. In this way, the temporal change in the impurity concentration of the entire system is calculated as follows.・・・．・・・． ...Given by t7'.

Here, Gset target value G ship t(tn) at t=tn
is the measured value TinNa(tn-,
), C(tn-,), and use a computer to calculate the maximum value of '71 formula 1 within the physically possible range of Gs milk.

(See FIG. 4) The refining temperature T of crucian carp at this time can be associated with the G side (tn) already calculated using the measured value T index (tn-,) according to the Tsukuda formula. That is, TSet and G*t have a one-to-one correspondence according to the '61 equation, but in this embodiment, the G history t is used as the control target value. A further physical explanation of what has been stated above is as follows. That is, in the present invention, the amount of air cooling in the cold trap is determined in proportion to the amount of impurities in the entire system. In other words, since the amount of impurities is large when the system is started up, the amount of air cooling is increased (if necessary, the maximum value of the cooling system is set to Q) to rapidly precipitate the impurities. On the other hand, when the system reaches almost the final target purity, the amount of impurities to be removed is small, so the amount of air cooling is also small, and unnecessary cooling is not performed. That is, according to the present invention, the cooling amount determination method adjusts the air cooling amount in accordance with the amount of impurities to be removed from the system. On the other hand, regarding the refining temperature, since the refining temperature Ts milk is controlled by the sodium flow rate G plow based on a quasi-constant cooling amount control method, temperature controllability is good.

Also, in response to changes in the cold trap inlet temperature,
The control method is able to absorb this influence. (Refer to the '7} formula) Furthermore, G skin, T snake t are '7 wipe's 1
It goes without saying that the impurity concentration in the system will reach the target purified concentration in the shortest time if the cold trap is operated in accordance with the calculation, since it is determined to maximize the amount of hot water. FIG. 5 shows another embodiment of the present invention, in which the present invention is applied to a purification system for a liquid metal coolant nuclear reactor. In this case, as in Fig. 2, the change over time in the sodium impurity concentration of the entire system (in this case, as shown below, IM. The cold trap's air cooling amount target value, refining temperature target value, and sodium flow rate target are calculated by a computer from various process quantities, and using these target values, the cooling amount and flow rate control method for the cold trap's operation-related equipment is established. With computer control, the cold trap can be operated optimally with good temperature control. In this case, the inside of the reactor in the capacity ground is 10
The relationship between the rate of change between the impurity concentration C2 at 0 and the impurity concentration C in the dump tank 1 with a capacity M is more like a saucer type. ．．・．． M size M stylish GI.

{CI(t)-C fence(t)} ...00 In an actual plant, since M<<other, the impurity concentration in the furnace is
It can be seen that by optimally operating the cold trap system in the same machine as in the case shown in the figure, purification can be achieved in the shortest possible time. As described above, according to the present invention, the impurity concentration in a liquid metal plant can reach a predetermined target purity in the shortest possible time while the purification temperature is well controlled.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of the most standard cold trap, FIG. 2 is a configuration diagram of a liquid metal purification plant showing an embodiment of the present invention, and FIGS. 3 a and b are cold trap cooling in the present invention. Figures 4a to 4d are diagrams showing the temporal relationship between various target values determined by the present invention and impurity concentration measurement values. , a is the cooling amount of the cold trap, b is the measured value of the impurity concentration, c is the target value of the liquid metal flow rate, and d is the target value of the cold trap purification temperature. FIG. 5 is a schematic diagram showing another embodiment of the present invention. 6.
...Liquid metal flow meter, 7...Impurity meter, 9...Co-
Ludo Trap, 14...Calculator. Chi 4 Prisoner Z' Diagram 〆 2 Diagram 3 Diagram

Claims (1)

[Claims] 1. In a liquid metal refining device that precipitates impurities by cooling the liquid metal with a cooling device and captures the impurities, the amount of impurities to be captured in the liquid metal is measured, and the amount of impurities is determined according to the amount of impurities. The refiner cooling amount target value is obtained, and during a predetermined cooling amount retention period, the refiner cooling equipment is controlled according to this cooling amount target value, and the liquid metal refiner flow rate during the period is controlled. The liquid metal target value that maximizes the impurity concentration change rate in the system is determined from the inlet temperature, impurity concentration measurement value, and cooling amount target value, and the flow rate is controlled according to this flow rate target value, and both of these controls are performed every cooling amount retention period. A method of operating a liquid metal refining equipment characterized by repeating.