JPS5837139A - Regeneration of cold trap - Google Patents

Abstract

PURPOSE:To regenerate a cold trap having decreased refining capacity easily by heating the trap to prescribed temp. and removing the hydride captured in the trap with circulating sodium. CONSTITUTION:A cold trap having decreased impurity capturing capacity is temporarily heated to 200-250 deg.C to release hydride into sodium without disconnecting the same from the system. The hydride dissolved in the sodium is released as gaseous hydrogen into the equipment covering gaseous phase in the system. Further the hydrogen released into the covering gaseous phase is exchanged with the covering gas or refined and is discharged to the outside of the system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating a cold trap used for refining sodium in a liquid sodium-cooled fast breeder reactor or various sodium testing facilities, and particularly relates to a method for regenerating a cold trap used for refining sodium in a liquid sodium-cooled fast breeder reactor or various sodium testing facilities, and in particular, it relates to a method for regenerating a cold trap used for refining sodium in a liquid sodium-cooled fast breeder reactor or various sodium test facilities. The present invention relates to a simple method for removing hydrogen impurities, which account for a considerable proportion of hydrogen, from a cold trap and discharging them out of the system.

For example, in a fast breeder reactor, cold traps are provided in the secondary and secondary sodium cooling systems, and the sodium circulating in each system is purified using these cold traps. −
In the next system, it covers the time of reactor operation and its maintenance inspection. As gas flows in and out and fuel is exchanged, moisture and W1 elements enter the system from the outside, and these moisture and oxygen change into hydrogen compounds and oxides in the sodium. In the secondary system, however, hydrogen diffuses into the sodium from the steam side of the steam generator and forms hydrogen compounds. Therefore, impurities in the secondary system are mainly hydrogen compounds, and these impurities are captured in the cold trap to purify sodium. The lifespan of a nuclear reactor is usually 20~
It took 25 years, but during this time, the cold trap became full of collected impurities, and a state occurred where it lost its ability to purify.

In particular, the sodium test 1i, which simulates the cooling system of a nuclear reactor!
! At the i facility, equipment is replaced relatively frequently for testing purposes, so the time it takes for the cold trap to run out of refining capacity is short, typically 3 to 6 years. In an actual nuclear reactor, this time range is expected to be longer, but in any case, this kind of reduction in refining capacity will occur after several years or even years, so cold traps should not be closed during the life of the reactor. It becomes necessary to replace or regenerate.

One method of regenerating a cold trap is to melt the impurities inside by heating them to a fairly high temperature and discharge them to the outside of the cold trap. This regeneration method has been developed in recent years, and because it restores the refining ability of the cold trap in a short period of time and is easy to operate, this heating regeneration method is often used for sodium test ml.

The use of this method in cold traps in the nuclear reactor system is also being considered. However, with this method, the impurities cannot be discharged because the cold trap cannot be heated to fluid NaOH unless it is heated to 430-450°C and the impurities contain both oxides and hydrides in a certain proportion. The disadvantage is that it is not possible to In particular, 43
In order to heat the cold trap to above 0℃, the cold trap must be isolated from the reactor's sodium system for at least two days, and there is a risk that the captured impurities will flow back into the sodium system and contaminate the system with impurities. be. In addition, in the cold trap of the secondary reactor system, most of the impurities are hydrides, so even such heating does not melt the impurities. Draining methods are ineffective.

For this reason, in the secondary system, although the same heating method is used, the cold trap is heated, the hydride inside is decomposed, and the hydrogen gas produced by the decomposition is passed through a nickel diffusion chamber via a cover gas. A method of exhausting the air to the outside is currently being considered. However, even with this method, the complexity and inconvenience of heating the temperature to between 400 and 100 degrees Celsius are not much different from those of the above-mentioned cold trap regeneration process, and moreover, it uses nickel, etc., which has a slow diffusion rate, so it is less complicated and inconvenient. Both require a long time of several weeks, which is unrealistic.

The object of the present invention is to provide a method that avoids such difficulties, removes hydrides from among the impurities collected in the cold trap, regenerates the cold trap, and discharges hydrogen to the outside of the cooling system. The goal is to provide the following.

To achieve this objective, the present invention employs the following method. Among the impurities collected in the cold trap,
At least several tens of percent or more is hydride, and especially in the cold trap of the secondary system of a nuclear reactor, the majority is hydride, as described above.

Therefore, in order to remove these hydrides, the temperature of the cold trap whose impurity collecting ability has decreased is temporarily raised to about 200 to 250° C. without being separated from the system to release the hydrides into sodium. The hydride released into the sodium is released in the form of hydrogen gas into the cover gas phase of the equipment in the cooling loop within a very short time. According to experiments,
The concentration of hydrogen gas thus released into the cover gas is at least ten times higher than the hydrogen concentration contained in the hydride in sodium. That is, hydrogen gas tends to be concentrated in the cover dregs. When the hydrogen gas concentrated in this cover gas phase is discharged to the outside of the system, the hydrides in the cold trap can be removed from the cooling system, albeit indirectly, and the cold trap can be regenerated.

A specific method for discharging hydrogen gas from the cover gas phase may be a simple method such as replacing the cover dregs with cutting gas or installing a hydrogen removal device in the cover gas circulation system. One possible way to remove hydrogen from the cover gas phase is to reduce the pressure of the cover gas and exhaust it, but this method has the risk of sucking in outside air due to vacuum evacuation, and is not suitable for actual nuclear reactors or sodium loop systems. Difficult to hire.

Next, we will discuss the heating temperature when both cold traps are generated in the method of the present invention.Usually, cold traps are operated at a temperature of 120 to 150°C at the mesh part.
Heating of at least about 200° C. is required to decompose the hydride collected during regeneration. On the other hand, some cooling system piping and sodium valves are operated at temperatures of 300 to 400°C. When a cold trap is heated above this temperature, impurities eluted from the cold trap are returned to the inside of these pipes and valves. There is a risk of being trapped.
Heating the cold trap above this temperature must be avoided.

Therefore, in the method of the present invention, the upper limit of the heating temperature of the cold trap is set to about 250° C. in consideration of safety.

The method of the present invention may be carried out, for example, as follows. As for the device, as shown in the drawings, the conventional device can be used almost as is. The reactor vessel 1, primary cooling system pump 2, and intermediate heat exchanger 3 constitute a primary cooling system, and the intermediate heat exchanger 3, secondary system bomb/4, and steam generator 5 constitute a secondary cooling system. A secondary cold trap 6 and a secondary cold trap 7 are provided in the secondary cooling system and the secondary cooling system.

This drawing shows the case of regeneration of the secondary cold trap 6, in which a new gas injection pipe 9 and a cover gas discharge pipe 10 are provided in the cover gas phase 8 of the furnace vessel 1. To heat the cold trap 6 to about 200-250°C, it is only necessary to reduce the cooling capacity of the cold trap compared to normal. In other words, reduce or stop the air flow rate of the cold trap cooling blower (1').

When this is done, hydrogen gas is released into the cover gas as described above. Therefore, by performing gas exchange using the new gas injection pipe 9 and the cover gas pipe 10, hydrogen can be discharged to the outside of the system. Furthermore, hydrogen gas released into the cover gas can be removed by connecting the new gas injection pipe and the cover gas discharge pipe via a hydrogen removal device.

Similarly to the secondary system of the nuclear reactor, hydrogen gas can be removed by attaching a new gas injection pipe and a cover gas discharge pipe to the cover gas phase of the intermediate heat exchanger or steam generator.

Since the present invention is configured as described above, there is no need to cut off the cold trap from the cooling system loop during cold trap regeneration, so normal sodium circulation is ensured even during regeneration, and a spare cold trap and its This has the advantage of not requiring a piping system. In addition, according to the present invention, sufficient effects can be achieved within a few hours required for the regeneration operation, and therefore, the time for re-release of impurities into the sodium cooling system is shortened, and the heating temperature is lower than in the past. Since the concentration of oxygen impurities is low, the concentration of oxygen impurities re-released is also low, which does not accelerate sodium corrosion in the cooling system, and many other excellent effects can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] The drawing is an explanatory diagram showing an embodiment of Mizumoto. 1...Reactor vessel, 2...-secondary system pump, 3...
Intermediate heat exchanger, 4...Secondary system pump, 5...Steam generator, 6...Secondary system cold trap, 7...Secondary system cold trap, 8...Cover gas Oath, 9...New gas injection pipe, 10...Cover gas discharge pipe.

Claims (1)

[Claims] 1.1 Cold trap with reduced production capacity of about 200 ~
By raising the temperature to 250°C, the hydrogen impurities collected in the cold trap are re-eluted into the circulating sodium, and the hydrogen impurities dissolved in the sodium are released as hydrogen gas into the bar gas phase in the system; A cold trap regeneration method characterized by discharging hydrogen loosely released into the cover gas phase to the outside of the system by replacing or purifying the cover gas.