KR20050029889A - Surface treatment system for radioactive waste - Google Patents

Abstract

A surface treatment system for radioactive waste is provided to enhance a cleaning effect and remove radioactive materials from the surface of the radioactive waste by using a reference electrode having a plurality of magnets to obtain effectively plasma of high density. A vacuum chamber(10) is provided to store radioactive waste therein and perform a surface treatment process for the radioactive waste. One or more reference electrode(30) is installed inside the vacuum chamber(10) and includes a plurality of magnets. One or more than one discharging electrodes(30) is opposite to the reference electrode(30) and provides a discharging path. A power source(40) is used for applying a predetermined voltage to generate and maintain the discharge between the reference electrode(30) and the discharging electrode(20).

Description

SURFACE TREATMENT SYSTEM FOR RADIOACTIVE WASTE

The present invention relates to a radioactive waste surface treatment apparatus for cleaning or surface treatment of radioactive waste using plasma (hereinafter surface treatment represents a concept including all treatments related to surface modification including surface cleaning). .

Cleaning or surface treatment of radioactive waste has been recognized as one of the important treatments in the process for the treatment of radioactive waste. Cleaning and treatment can remove contaminated material from the surface.

Nuclear waste is a waste produced as a result of nuclear weapon testing and nuclear power plant operations, and it is fatal to human health because it is made of radioactive materials. Radiation generated during nuclear decay includes α-ray, β-ray and γ-ray with high energy. In the case of projecting them on matter, electrons are scarce by breaking out the electrons in the matter. This state is called ionizing radiation, and in the case of humans and plants, molecules in the living body are modified to cause chemical reactions, resulting in various side effects. Accumulation of radioactive material in certain parts of the body causes various diseases such as burns, dermatitis, pain, cancer, leukemia, cataracts, mental disorders, and hair loss. These diseases appear slowly over time and may have genetic effects.

In general, nuclear power plants pose risks that can cause severe damage to humankind and the global environment. However, the number of nuclear power plants in the world is increasing, and the share of nuclear power among all energy sources is increasing. Toward this trend, the amount of nuclear waste from nuclear power plants will naturally increase. Reprocessing of spent fuel through reprocessing plants is also concerned with the impact on atmospheric concentrations, as this also results in highly radioactive waste.

Because radioactive materials are not lost by chemical change, they have to wait for their natural disappearance due to nuclear decay, so long-term contamination is inevitable once released.

Nuclear waste takes hundreds of thousands or millions of years to decompose naturally, so finding a safe and permanent way to deal with it is a major challenge. Currently, the way most countries are pushing is to seal and bury them deep in the ground, but there is a constant debate about this issue because there is no guarantee that they will remain safe in the ground until they break down.

Nuclear waste now generates far more from civilian reactors than military waste, and the cumulative total is growing rapidly. The oldest waste receptacles made in developed countries have been identified as leaking radiation, and incomplete installations of nuclear weapons and nuclear power plants have the potential problem of increasing radioactive waste in the future. In recent years, there has been a move to expand nuclear power plants as alternative energy to suppress the release of greenhouse gases due to the use of fossil fuels, but the first thing to be solved before it is confirmed is the disposal of waste from the reactor.

Solid wastes, such as work clothes, used by the operators of nuclear power plants or maintenance workers, are introduced into the automatic waste sorting facility, and collectable compact wastes are collected by high-pressure compression into iron drums and stored in nuclear waste storage rooms. In order to solve this problem, researches on plasma applications are being conducted

Research has been conducted to decontaminate low-level radioactive waste, TRU nuclides and soils using plasma torch and to reduce the volume of low- and mid-level radioactive waste using plasma arc torch. Techniques that are being studied in other fields or used in actual field include thermal destruction of various wastes using plasma torch and thermal treatment using high temperature atmosphere generated from plasma, and oil surface cleaning using micro-wave plasma torch. It is used for decontamination at work and workplaces, and is applied to decontamination of harmful substances containing U, Pu, Hg, etc. by using closed-loop plasma cleaning system.

The present invention is to solve such a conventional problem, the object is to obtain a high plasma density by using a plurality of magnets (magnet) through which the cleaning or surface treatment of the surface of metal materials such as structures in radioactive waste efficiently It is to provide a device to.

In addition, according to another aspect of the present invention, the present invention is capable of treating the surface of radioactive waste by applying a pulsed power source to solve the problem of arc lamps and to obtain a stable discharge in a discharge device using a magnet (magnet) It is for providing a device.

Furthermore, according to another aspect of the present invention, the present invention is not significantly affected by the type of radioactive waste, the distance between the discharge electrode and the radioactive waste, there is no damage or contamination of the radioactive waste by the arc, It is to provide a surface treatment apparatus for radioactive waste using plasma that can overcome the problems such as the risk of radioactive exposure of workers, the increase in the cost of radioactive waste treatment. In particular, according to the method proposed in the present invention, it is possible to stably maintain a plasma which has a stable and excellent effect on the removal of radioactive material from radioactive waste, thereby obtaining an excellent surface treatment effect.

According to an aspect of the present invention, there is provided a surface treatment apparatus comprising: an apparatus for surface cleaning or surface treatment of radioactive waste using plasma, and including: a friendly chamber for introducing the radioactive waste into the inside to perform the surface treatment; At least one device mounted in the chamber and having a plurality of magnets for increasing plasma density; A reference electrode providing a discharge path from the discharge electrode; And a power source for applying a voltage to generate and maintain a discharge between the discharge electrode and the reference electrode.

Preferably the voltage in the surface treatment apparatus of the radioactive waste of the present invention is a voltage in the form of a pulse. Preferably the voltage in the surface treatment apparatus of the radioactive waste of the present invention is a voltage in the form of pulses of alternating polarity. Preferably, the voltage in the surface treatment apparatus of the radioactive waste of the present invention is characterized in that the voltage in the form of pulses with alternating polarity and the voltage magnitude during the negative period is equal to or greater than the voltage magnitude during the positive period. Preferably, the magnitude of the voltage during the positive period of the surface treatment apparatus of the radioactive waste of the present invention is 0 to 500V. Preferably the surface treatment apparatus of the radioactive waste of the present invention further comprises a gas injection unit for injecting the reaction gas into the vacuum chamber, wherein the reaction gas includes an inert gas and / or oxygen. Preferably, the reference electrode of the surface treatment apparatus of the radioactive waste of the present invention is a plate-type electrode incorporating a plurality of magnets. Preferably, the reference electrode of the radioactive waste surface treatment apparatus of the present invention is a round electrode having a plurality of magnets embedded therein. Preferably, the reference electrode of the surface treatment apparatus of the radioactive waste of the present invention is an electrode of two or more angles having a plurality of magnets embedded therein.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the spirit of the present invention to those skilled in the art will fully convey. Portions denoted by like reference numerals denote like elements throughout the specification.

1 shows a schematic view of one preferred embodiment of the plasma surface treatment apparatus of the present invention.

As shown in FIG. 1, one embodiment of the surface treatment apparatus of the radioactive waste of the present invention includes a vacuum chamber 10, a discharge electrode 20, a reference electrode 30, a power supply 40, and a gas supply unit 50. do.

The vacuum chamber 10 surrounds the discharge electrode 20 and the reference electrode 30 from the outside and draws the radioactive waste 60 to be processed into the inside to block the outside and maintain a low pressure during the process. It is for. Here, the inner wall of the vacuum chamber 10 may replace the function as the reference electrode 30, as usual, or a separate reference electrode plate 32 may be provided. The vacuum chamber 10 is preferably grounded but may not be as desired.

As shown in FIG. 1, plasma is formed due to the discharge between the discharge electrode 20 and the reference electrode 30. After introducing the radioactive waste 60 at the beginning of the process, a predetermined vacuum system (vacuum pumps, valves and manometers, etc., not shown) is used to drain out the unnecessary gas inside the system and the base pressure inside the vacuum chamber 10. After exhausting to (base pressure), a reaction gas and a carrier gas (generally inert gas) necessary for the process are injected into the chamber and adjusted to a pressure required for discharge (typically several mTorr to several tens Torr).

The discharge electrode 20 is installed in the vacuum chamber 10 as shown in FIG. 1, and is connected to the power source 40 to supply power for generating plasma. The power source 40 may be a direct current, alternating current, or a pulse (power) type power source. In the case of using direct current, a negative electrode is connected to the discharge electrode 20.

The reference electrode 30 is an electrode for providing a path of the discharge current between the discharge electrode 20 and the discharge electrode 20. It is also possible to have the inner wall of the vacuum chamber 10 play a role without having the reference electrode set aside, and it is common that the reference electrode 30 becomes a ground electrode. In the present invention, a separate reference electrode plate 32 is further provided.

The gas supply unit 50 is a portion for injecting reaction gas (oxygen, etc.) and / or carrier gas (inert gas, argon, etc.) into the vacuum chamber 10 from the outside, and a mass flow controller (mass) for controlling the flow rate It can consist of a flow controller (MFC) or a valve.

In FIG. 1, a discharge is generated between the discharge electrode 20 and the reference electrode 30 to generate a plasma, and apply a voltage to the radioactive waste 60 connected to the discharge electrode 20, thereby spreading entirely from the surface of the radioactive waste. While forming a uniform current density as a whole and the surface treatment is performed with a high current density by the reference electrode plate 32 is attached to a magnet (magnet), the present invention is not necessarily limited in this case no.

In addition, it is also possible to adopt a reference electrode with a plurality of magnets (magnet) attached to the configuration and to process a plurality of coatings, the scope of the present invention is not determined by the number of discharge electrodes and the number of radioactive waste. .

2 is a schematic view showing the configuration of a reference electrode plate according to a preferred embodiment of the present invention. The present invention makes use of a plate (34) with a magnet (36) attached as a reference electrode plate (32) as one of its main features, and the amount of ions reaching the surface of the radioactive waste by using the same. To increase the removal of radioactive material (cobalt, cesium) from the surface of the efficient radioactive waste. The radioactive materials separated by the plasma from the radioactive waste can be filtered by a separate dust collector installed in the exhaust line.

As shown in FIG. 2, the plate-type reference electrode plate 32 may be implemented as, for example, an electrode to which a magnet is attached. Magnet attached reference electrode plate 32 is easy to manufacture, through which has the advantage of significantly reducing the manufacturing and maintenance costs of the equipment. 3 illustrates a case in which the plate-shaped electrode of the present invention is implemented as a round plate 34a type reference electrode plate 32a having a plurality of magnets 36.

4 is a view showing a plasma generated in the magnet attached electrode of the present invention. In the case of using a magnet-attached electrode as described above, the discharge electrode 20 is limited to the direction in which the movement of the electrons is possible due to the sheath 70 generated near the conductor portion. By colliding and ionizing more neutral particles, a higher plasma density can be obtained.

As described above, the radioactive waste surface treatment apparatus of the present invention obtains a high plasma density by using a magnet, thereby increasing the number of ions incident on the surface of the radioactive waste, thereby treating the radioactive material on the surface of the radioactive waste. To increase.

As the reference electrode plates 32 and 32a, it is obvious that many other deformation electrodes, such as the plate-shaped and round-shaped electrodes shown in FIGS. 2 and 3, as well as a plate made of two or more angles, can be used. As long as it is intended to enhance the effect of the plasma treatment using the present invention, it is a matter of course for those skilled in the art to see that it is within the scope of the present invention.

Also, the shape of the magnet can be round or square or any other shape, and the magnet size does not have to match.

As described above, in the case of using a magnet-attached electrode, the plasma density is considerably increased due to the magnetic field formation due to the magnet, and the discharge electrode 20 or the reference by the radioactive waste material or the reactive gas used is used. If surface contamination of the electrode plate 32 is present, a transition phenomenon occurs to a local arc.

In this case, when the arc occurs, current is concentrated to the arc generating position, and melting of electrode surface material occurs due to joule heat caused by high current density. There is a fear that the quality of the process itself may be degraded by changing.

In the present invention, in order to overcome this problem, the application of the bidirectional pulse voltage to the discharge electrode 20 is another aspect. An example of such a bidirectional pulse voltage is illustrated in FIG. 5. As illustrated in FIG. 5, the illustrated bidirectional pulse power source has a wavelength in the form of alternating between a positive period and a negative period, and the lowermost part of the pulse voltage during the negative period is the highest of the pulse voltage during the positive period. The absolute value of the voltage is larger than that of the negative. During the negative period mainly plasma is generated, and the charge by the generated plasma begins to accumulate on the contaminants on the electrode surface. If the contaminant is an organic material or a dielectric, the accumulated charge does not flow and accumulates, and when such accumulated charge accumulates, arc generation starts as shown in FIG. 5. As the arc discharge starts, the current increases as shown in FIG. 5. However, since the discharge electrode is not supplied after a certain time because the voltage of the discharge electrode is pulsed, such an arc cannot be sustained, thereby preventing damage such as melting of the electrode material. Then, as the polarity of the voltage applied to the discharge electrode is changed, the charge accumulated on the contaminant is recombined and extinguished by the introduction of the opposite charge. The application of the bidirectional pulse voltage by this process can prevent damage by the arc or the generation of fine particles and serves to stabilize the discharge. The magnitude of the pulse voltage during the positive period is generally preferably about 0 to 500V.

The bidirectional pulse voltage shown in FIG. 5 is just one example, and the pulse voltage may be a combination of several pulses rather than a simple pulse, each of which may vary in magnitude. In addition, the positive period and the negative period do not necessarily have to be the same time, and the size of the interval without the voltage supply between the positive period and the negative period may also vary, and the period without the voltage supply may be configured at all. It may be. In addition, positive and negative pulses may not necessarily appear alternately in a ratio of 1: 1, for example, one positive pulse for every two negative pulses or a positive pulse for every three negative pulses. Various modifications are possible, such as one or two appearing. In addition, the positive pulse may be larger than the negative pulse, and such various modifications may vary depending on the object to be processed and the processing conditions or the shape of the electrode.

As described above, in the detailed description of the present invention, specific embodiments have been described, but it should be taken as exemplary, and various modifications may be made without departing from the technical spirit of the present invention. For example, the waveform of the voltage applied to the discharge electrode can be transformed into a plate of various different shapes within the scope of the technical idea of the present invention (for example, a complex pulse waveform, not a simple pulse waveform). In addition, the surface shape of the reference electrode may also be configured to have a three-dimensional shape rather than a simple plate shape, which may be particularly related to the type of radioactive waste to be treated. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

As described above, the present invention has the following effects. According to the present invention, in the cleaning (removal of radioactive material) and treatment of the surface of radioactive waste by using plasma, an efficient high density plasma can be obtained by using an electrode having a magnet attached to a reference electrode, and thus radioactive waste. It is possible to increase the arrival of ions in the furnace, thereby increasing the cleaning effect and effectively increasing the surface energy of radioactive waste, thereby removing contaminants (radioactive substances) attached to the surface.

In addition, by using an electrode with a magnet (magnet), by increasing the plasma density it is possible to overcome the risk of radioactive exposure, the generation of radioactive waste by the manual worker of the prior art.

In addition, by using the bi-directional pulse power supply, it is possible to effectively and inexpensively solve the problem of arc defects, which are a problem when using a DC power supply at the discharge electrode, and a problem of price and difficult process conditions when using an AC power supply such as RF. Enable surface treatment of radioactive waste.

In addition, the structure of the device is simple, the processing range is wide, economical, excellent in uniformity and effect of cleaning or surface treatment of radioactive waste.

Fig. 1 shows a schematic view of a preferred embodiment of the surface treatment apparatus for radioactive waste using the plasma of the present invention.

2 is a schematic view showing the configuration of a reference electrode according to a preferred embodiment of the present invention.

3 is a diagram illustrating a case where a round plate-shaped electrode supporting a plurality of magnets generated from a reference electrode of the present invention is implemented.

4 is a view showing a plasma generated due to the reference electrode of the present invention.

5 shows an example of the bidirectional pulse voltage applied to the gap electrode of the present invention.

<Explanation of symbols for the main parts of the drawings>

10: vacuum chamber 20: discharge electrode

30: reference electrode 40: power supply

50: gas introduction part 60: radioactive waste (material exposed to radiation)

Claims (9)

Apparatus for surface treatment of radioactive waste using plasma: A vacuum chamber for introducing the radioactive waste into the interior to perform the surface treatment; At least one reference electrode mounted in the chamber and having a plurality of magnets; A discharge electrode providing a discharge path against the reference electrode; And And a power source for applying a voltage to generate and maintain a discharge between the reference electrode and the discharge electrode. The method of claim 1, And a voltage applied to generate and maintain the discharge is a pulsed voltage. The method of claim 1, The voltage is a surface treatment apparatus for radioactive waste, wherein the polarity is a voltage in the form of alternating pulses. The method of claim 1, The voltage is a voltage in the form of pulses with alternating polarities, wherein the voltage maximum magnitude during the negative period is equal to or greater than the voltage maximum magnitude during the positive period. The method of claim 4, wherein The surface treatment apparatus of radioactive waste whose magnitude of voltage during the said positive period is 0-500V. The method of claim 1, And a gas injection portion for injecting the reaction gas into the vacuum chamber, wherein the reaction gas comprises inert gas and / or oxygen. The method of claim 1, And the reference electrode is a plate-shaped electrode. The method of claim 1, And the reference electrode is a plate type electrode having a plurality of magnets. The method of claim 1, The reference electrode is a surface treatment apparatus for radioactive waste, which is a round electrode having a plurality of magnets attached thereto.