JPS6140441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the operation of a cold trap for removing impurities from sodium used as a coolant in a nuclear reactor.

Sodium has good thermal properties such as low specific gravity, high thermal conductivity, and high boiling point, so it is used as a coolant in nuclear reactors. However, on the other hand, sodium has high chemical activity and has bad properties as a coolant for nuclear reactors, such as combining with various substances and melting them. In particular, the degree of bonding with oxygen is large.

Sodium, which is used as a coolant in nuclear reactors, flows through containers and pipes made of stainless steel, and the liquid surface is filled with an inert gas such as argon gas to prevent oxidation. However, even in a well-controlled inert atmosphere, trace amounts of oxygen cannot be avoided over a long period of time, increasing the amount of sodium oxide in the sodium.

The increase in oxides causes the following problems in nuclear reactor plants.

(1) The amount of corrosion of structural materials increases.

(2) Oxides precipitate in the low-temperature region, and when their amount increases, they clog the flow path.

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

For these reasons, sodium purification equipment for nuclear reactors is always installed in sodium reactor plants to constantly control the purity of sodium.

Two types of sodium purification equipment are cold traps, which cool impurity-containing sodium and precipitate supersaturated impurities, and purify zirconium, which has higher oxidation activity than sodium at high temperatures, and impurities in sodium (especially There is a hot trap that removes oxygen by reacting with it.

Cold traps can be operated at relatively low temperatures and are easy to handle, so they are often used in sodium purification equipment.

In addition, cold traps include a filter type that removes precipitated impurities by cooling the sodium using a metal filter such as SUS wool, and a filter type that removes precipitated impurities by sedimentation and separation using the difference in specific gravity between the impurities and the liquid. It can be roughly divided into meshless types.

FIG. 1 shows a commonly used filter type cold trap, in which a container 4, a mesh 5 provided on the outer periphery of a sodium inlet pipe 3 inserted into the center of the container 4, and a mesh 5 provided on the outside thereof. fins 6 provided, a cooling duct 7 provided on the outer periphery of the fins 6, a settling chamber 8 formed at the bottom of the mesh 5, a sodium outlet pipe 9 connected to the top of the mesh 5 in the container 4,
A cooling fan 10 provided below the settling chamber 8, a damper 11 for adjusting air volume, an exhaust outlet 12, and a temperature measuring device 1 for sodium to be purified.
3. A cooled sodium temperature measuring device 14 is provided.

The sodium to be purified flows from the main line 1 of the sodium plant through the pump 2 and the sodium inlet line 3 into a vessel 4 and reaches a settling chamber 8 .

The settling chamber 8 is cooled by cold air blown from the cooling fan 10 and flowing from the bottom of the settling chamber 8 through the outer peripheral surface, and is kept at the lowest temperature in the cold trap.

The sodium that has flowed into the settling chamber 8 is cooled within the settling chamber 8, and since impurities in the sodium are cooled, they are precipitated in an amount that reaches supersaturation.

And the sodium to be purified is mesh 5
The precipitated impurities are trapped in the mesh 5, and the purified sodium is discharged from the sodium outlet pipe 9.

In this type of cold trap, as mentioned above, the temperature of the settling chamber 8 is the lowest, and this temperature is set as the sodium refining temperature, the temperature of the sodium flowing through the settling chamber 8 is measured, and the rotational speed of the fan 10 is Alternatively, the refining temperature is controlled by the opening degree of the damper 11.

In FIG. 1, arrow A indicates the flow direction of sodium, and arrow B indicates the flow direction of cold air.

In other conventional methods, a heater and a cooler are provided outside the purifier, and a combination of heating and cooling is used to control the refining temperature of the cold trap.

However, all of the conventional methods have poor refining temperature controllability. For example, when a disturbance such as a temperature change occurs in the sodium on the main piping side, the response is poor and the refining temperature changes significantly. It has the disadvantage that the purification characteristics of impurities are disturbed. Particularly in the case of high-purity purification settings, precise temperature control near the melting point of sodium is required, which is not possible with conventional cold traps.

An object of the present invention is to provide a method for controlling the operation of a cold trap that has good responsiveness to disturbances and is capable of high-purity purification.

A feature of the present invention is that the target purity value of sodium and the performance characteristics of the cold trap are stored in advance in a computer, and then the temperature, flow rate, and purity of the sodium to be purified are measured and input into the computer. Compare the purity target value with the purity of the sodium to be purified, and if the deviation value is large, increase the flow rate of the sodium to be purified to the cold trap and the amount of cooling medium sent to cool the sodium. control is carried out, and when the deviation value is reduced to an allowable range, switching to qualitative control in which the flow rate of sodium to be purified and the amount of cooling medium sent to the cold trap are relatively reduced, This configuration provides good response to disturbances,
A method for controlling the operation of a cold trap that enables high-purity purification has been obtained.

The present invention will be explained below based on the drawings.

FIGS. 2, 3, and 4 show an embodiment of the present invention, and the embodiment shown in FIG. 2 of a cold trap for carrying out the present invention is as follows:
A container 4 having a sodium inlet pipe 3 at the center of the interior; a sodium inlet pipe 3 inside the container 4;
A mesh 5 packed around the outer periphery of the mesh 5, fins 6 provided on the outside of the mesh 5, a cooling duct 7 provided on the outer periphery of the fin 6, a settling chamber 8 formed at the lower part of the mesh 5 within the container 4,
a sodium outlet pipe 9 connected to the upper part of the mesh 5; a cooling fan 10 provided below the settling chamber 8;
Damper 1 for adjusting the volume of cold air that is the cooling medium from
1 and an exhaust port 12 provided at the top of the cooling duct 7.

The sodium to be purified is then sent from the main line 1 of the sodium plant to the sodium inlet line 3 by a pump 2, and the sodium flows into a settling chamber 8 as indicated by arrow A in FIG.

On the other hand, cold air is sent from the cooling fan 10 to the outside of the settling chamber 8, as shown by arrow B in FIG.
Sodium is discharged from the exhaust port 12 through the bottom, the outer peripheral surface and the fin 5, and the sodium that flows into the settling chamber 8 is cooled by the cold air, and the impurities in the sodium are cooled and become supersaturated. amount is precipitated.

Next, the sodium in the settling chamber 8 rises through the mesh 5, where the precipitated oxygen is filtered and the sodium is purified. returned to its normal position.

The sodium inlet pipe 3 of the cold trap having the above configuration is provided with a first temperature measuring device 13 for measuring the temperature of the sodium to be purified. A second temperature measuring device 14 is provided in the settling chamber 8 to measure the purification temperature of sodium, that is, the minimum temperature of the cold trap, and a Although a purity measuring device is provided, this purity measuring device is omitted in the drawing.

By the way, in the present invention, the target purity value of sodium and the performance characteristics of the cold trap are stored in advance in a computer, and the temperature, flow rate, and purity (oxygen amount, hereinafter referred to as O ₂ concentration) of the sodium to be purified are each measured. The computer compares the purity target value with the O ₂ concentration of the sodium to be purified, and if the deviation value is large, the flow rate of the sodium to be purified to the cold trap and the sodium are cooled. Quantitative control is performed to increase the amount of cooling medium sent to the cold trap (hereinafter referred to as the cooling amount), and when the deviation value is reduced to an allowable range, the flow rate of sodium to be purified to the cold trap and the cooling amount are increased. This is a change to qualitative control that relatively reduces the amount of water.

That is, in FIG. 2, a purity target value 17 and cold trap performance characteristics 18 are inserted into the computer 16 and stored.

Next, the computer 16 includes a first temperature measuring device 1.
3, the flow rate signal 20 of the sodium to be purified measured by the flowmeter 15, and the O ₂ concentration signal of the sodium to be purified measured by the purity measuring device. 21 are respectively taken in.

By the way, Fig. 3 qualitatively illustrates the performance of the cold trap 20, but when performing purification operation using a cold trap with a certain specific performance, sodium with a certain value of O ₂ concentration is The larger the difference between the O 2 concentration and the set O ₂ concentration in the cold trap, the greater the operating load of the cold trap (temperature difference ΔC corresponding to the concentration difference).
and the sodium flow rate F) increases.

However, since the O ₂ concentration of sodium has a logarithmic relationship with the saturation temperature, a curve like the one shown in Figure 3 is obtained. In other words, if we take the set value of O ₂ concentration on the horizontal axis and the cold trap load on the vertical axis, we get
A ₁ to a ₄ show the case where the cooling amount of the cold trap is decreased, that is, when ΔC is gradually decreased. The maximum point of cold trap load can be obtained without any problem. Therefore, it can be said that it is most effective to operate under conditions near this maximum point (arrow b in Figure 3). In other words, as shown in Figure 4, when a sodium plant starts up, the O ₂ concentration is high, so quantitative control is mainly performed to increase the amount of cooling and also the flow rate of sodium. During steady operation, the sodium plant reduces the cooling amount and the sodium flow rate, and also quickly controls the lowest temperature of the cold trap.
Shift to qualitative control to adjust sodium flow.

In order to carry out such control, it is necessary to previously store in the calculator 16 the relationship shown in FIG. 3, which is the performance of the cold trap.

Next, the computer 16 uses the O ₂ concentration signal 21 of the sodium to be purified measured by a purity measuring device such as a pugging indicator and the temperature signal 19 of the sodium to be purified from the first temperature measuring device 13 to calculate the temperature of the sodium plant. Check the saturation state on the side and compare it with the purity target value 17.

When the deviation value is large, the cooling amount setting value 22 is sent from the computer 16 to the cooling amount controller 24 in a direction to increase the amount of sodium cooling corresponding to the deviation value, as shown in FIG. , a control signal 27 is transmitted from the cooling amount regulator 24 to the cooling fan 10, and the rotation speed of the cooling fan 10 is increased;
The minimum temperature of the cold trap is reduced and the flow of sodium to be purified from pump 2 is increased in this control phase.

For example, even when a disturbance such as an increase in O ₂ concentration occurs on the sodium plant side, quantitative control is performed to increase the cooling amount of the cold trap.

On the other hand, if the O ₂ concentration on the sodium plant side is sufficiently close to the purity target value of 17 and the deviation value is within the allowable range, there is no need to introduce that large amount of sodium into the cold trap, and the cold trap The amount of cooling is also small. Therefore, as shown in FIG. 2, the computer 16 outputs the purity set value 23 corresponding to the purity target value 17 to the pump pressure regulator 25, and the purity set value 23 and the second purity value are output from the pump pressure regulator 25. A pump control signal 28 is sent to the pump 2 in response to a change in the cold trap minimum temperature signal 26 measured by the temperature measuring device 14, and the flow rate of sodium to be purified into the cold trap is adjusted.

In addition, in the method of the present invention, the adjustment of the cooling amount of the cold trap is not limited to controlling the cooling fan 10 shown in FIG. 2, but may also adjust the opening degree of the damper 11 provided in the cold air flow path. . Further, the flow rate of sodium may be adjusted by controlling the output of an electromagnetic pump or by controlling a flow control valve. Furthermore, it is effective to use a microcomputer, minicomputer, etc. as the computer 16.

The method of the present invention has the configuration described above, and when impurities increase in the early stages of startup or steady operation of a sodium plant, quantitative control to control the amount of cooling is carried out, and cold trap load control is carried out during steady operation. If less is needed, qualitative control is performed, so the recovery response is good against disturbances in temperature and purity.Also, since the response of temperature control is good, the purity setting temperature is lowered to a temperature near the melting point of sodium. This has the effect of making high-purity purification possible.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the structure of a conventionally commonly used cold trap, Fig. 2 is an explanatory diagram of an embodiment of the present invention, Fig. 3 is a performance diagram of the cold trap, and Fig. 4 is an explanatory diagram of an embodiment of the present invention. It is a control characteristic diagram. 1... Main piping of the sodium plant, 2... Pump, 3... Sodium inlet piping, 4... Cold trap container, 8... Settling chamber,
9... Sodium output pipe, 10... Cooling fan, 11... Damper, 13, 14... First, second
temperature measuring device, 15...flow meter, 16...calculator, 17...purity target value, 18...performance characteristics of cold trap, 19...sodium temperature signal, 20...sodium flow signal, 21 ……
O ₂ concentration signal, 22...Cooling amount setting value, 23...
Purity set value, 24...Cooling amount regulator, 25...Pump pressure regulator, 26...Cold trap minimum temperature signal, 27...Cooling amount control signal, 28...
Control signal for sodium flow.

Claims (1)

[Claims] 1. Store the target purity value of sodium and the performance characteristics of the cold trap in advance in a computer, then measure the temperature, flow rate, and purity of the sodium to be purified and input them into the computer, and calculate the purity target value and the performance characteristics of the cold trap by the computer. Compare the purity of sodium to be purified,
When the deviation value is large, quantitative control is performed to increase the flow rate of sodium to be purified to the cold trap and the amount of cooling medium sent to cool the sodium, and when the deviation value is reduced to an allowable range, A cold trap operation control method is characterized in that the flow rate of sodium to be purified and the amount of cooling medium sent to the cold trap are changed to qualitative control in which the flow rate is relatively reduced.