JPH10109019A - Uranium enrichment and other element isotope separation utilizing parametric resonance phenomenon and ultrahigh purity ion source or plasma source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform all the isotope separations including uranium enrichment by one-step operation and to provide a technique of constituting an ultrahigh purity ion source or plasm source. SOLUTION: Only an object isotope element to be separated is separated by utilizing a parametric resonance phenomenon. The principle of operation is as follows. First, an isotope element is made plasma by a plasma source 01, and is led to a high frequency quadrupole 05 present in the central part. High frequency waves of frequency about two times the ion cyclotron frequency of the object isotope element are applied there, and only the object isotope is selectively accelerated and overcomes the voltage of a blocking electrode 06 and is recovered by a recovery electrode 7. Since other elements are not accelerated, they cannot overcome the blocking voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to uranium (U-235) which is a nuclear fuel of a nuclear reactor (mainly a boiling water type (BWR) and a pressurized water type (PWR) which is a light water reactor) utilizing a parametric resonance phenomenon. Enrichment and future fusion reactors (D
-T reactor) and a method for economically, efficiently, and in large amounts, capable of processing isotope separation of hydrogen, helium, lithium and the like in connection with nuclear fuel and reprocessing thereof.

[0002] In addition to the nuclear power industry, in the semiconductor industry, new material manufacturing industry, etc., deposition by ion beams (Ion
beam deposition and ion implantation (I
onimplantation) and CVD (Chemi
It can be used as an ultra-high purity ion source or a plasma source required for cal vapor deposition or the like.

[0003]

BACKGROUND OF THE INVENTION The main object of the present invention is to provide an isotope separation method for elements such as hydrogen, helium and lithium necessary for uranium enrichment and nuclear fusion and a method for obtaining an ion source or a plasma source of ultra-high purity ion species. The progress of conventional technology development for these is described below.

[0004] Concentration of uranium-235 is an important issue related to the success or failure of nuclear power, and although various methods have been proposed, the important point is a problem belonging to the state secret of each country. It has not been announced including Japan.

At present, uranium enrichment methods are practically used industrially in the gas diffusion method and the centrifugal separation method. [For example, H. See Benedict et al. (Translated by Toyohei Kiyose), Nuclear Chemical Engineering (Part VII), "Chemical Engineering of Uranium Enrichment" (Nikkan Kogyo Shimbun, 1985), Chapter 14. However, in both methods, the separation coefficient α per stage is
In order to obtain uranium having extremely small values of α _g = 1.004 and α _C = 1.04-1.10 and having a target enrichment, it is necessary to connect cascades of hundreds to thousands and hundreds of stages, and to reduce power consumption. There are various problems with the maintenance of the equipment. However, anyway, since only these two methods have been put into practical use, the current situation is that they rely on these methods. Therefore, if there is a method that can significantly improve power consumption, equipment production cost, and maintenance method for these in the future,
It is inevitable that it will be replaced.

[0006] On the other hand, the laser method is expected as the next new system. There are two methods, the atomic method and the molecular method. [For example, see Yota Nakai et al .: Journal of the Atomic Energy Society of Japan, 35 (1993) 280]. High power is required for the laser itself, which is the heart of this laser method, and various problems must be solved, such as the necessity of developing a laser with a repetition frequency of more than tens of kilohertz for pulse oscillation. The reality is that they have problems and are in the R & D stage.

In addition, uranium enrichment by a chemical method is currently under development. In this method, however, the number of separation stages per stage is even larger than that of the gas diffusion method, and it is necessary to cascade many units of 10,000 units. There is. [Kunihiko Takeda et al .: Journal of the Atomic Energy Society of Japan, 28 (1986) 82. reference. For the above reasons, it is questionable whether this method will be put to practical use.

In addition to the above, there is uranium enrichment by an electromagnetic method. Uranium enrichment by this method is the oldest, with 19
In 1944, the United States Manhattan Project (A-bomb production) first produced kilograms of highly enriched uranium with an isotope separator called Caltron.
However, it was stopped because production costs were higher than gas diffusion.

At the same time, a radial magnetic field separation method (Smith et al.) Was used.
para.) [L. P. Smit
het al. Phys. Rev .. , 72 (194)
7) See 989. However, at that time, there was no severe ion source technology at the time, and the space charge effect accompanying the large ion current caused severe problems such as a reduction in separation efficiency.

[0010] In 1975, Hashmi et al.
Proposals have been made to use radial magnetic field separation [M. Hashmi et al. Proc. In
t. Conf. on Uranium Isotope
Separation (Brit. Nucl. Energy
rgy Soc. , London), 7 (1975).
1. reference. It is unknown if there was any further development research since there is no disclosure.

There is no problem with high-current ion source technology based on recent research on nuclear fusion development. It has also been found that the problem of the space charge effect associated with the ion current can be reduced by using plasma. A separation method using this plasma has been proposed by Takayama [Kazuo Takayama: The 12th Japan Isotope Conference, 1975]
See November. This proposal uses a multiple cusp magnetic field, applies a high-frequency voltage of the uranium ion cyclotron frequency to a plate electrode near each cusp point, and generates a Pondelamotive force by cyclotron resonance or a high-frequency electric field (referred to as selective high-frequency containment). Uranium-235 and Uranium-238 are to be separated by utilizing the above-mentioned method. This principle has not been proved only by proposal. Also, no detailed study has been made.

On the other hand, various methods for isotopic separation of light elements related to nuclear fusion, such as cryogenic distillation, cryogenic thermal diffusion, and electrolysis, have been proposed as in uranium enrichment.
Under development. [For example, Kazuyoshi Yamamoto et al., Journal of Plasma and Fusion Society 71 (1995) 202. reference. The separation coefficient in these separation methods is as small as about 1.5 to 5, and in order to separate deuterium and tritium by 100%, units must be connected in series (cascade) in multiple stages because of uranium enrichment. Is the same as "Deep cooling" refers to cooling to 20 to 25K with liquid nitrogen, and there are various problems in maintenance and management of the apparatus, manufacturing costs, and the like.

It is anticipated that an ion source and a plasma source of ultra-high purity ion species will be increasingly required in the semiconductor industry and in the field of creating corrosion-resistant materials. At present, no ion source or plasma source of high purity has been developed, and this is a future problem. The present invention is a method that can sufficiently satisfy this condition.

[0014]

The main object of the present invention is to solve uranium enrichment more economically than the gas diffusion method and centrifugation method which are currently industrially used. It is to provide an efficient and efficient method. That is, the present invention is a method capable of separating an isotope of an arbitrary concentration by one-stage separation.

In the gas diffusion method, the theoretical separation coefficient α = 1.
Is 004, the centrifugal separation method, when the peripheral velocity _V a = 500m / s of the separator cylinder, when the cylinder radius a r / a =
Since the separation coefficient α at 0.9 is about 1.03,
In order to concentrate uranium of a concentration of 2-3%, it is necessary to cascade several hundred stages in advance, but since the separation coefficient of this method is theoretically α → ∞, Separation of the% concentration can be performed in only one stage.

Further, the method according to the present invention is applicable not only to isotope separation but also to IBD (Io) necessary for producing a high-purity metal thin film as an ion source or plasma source of ultra-high-purity ion species.
SOI (Silico) required for n beam de-position method, next generation semiconductor device technology
non In-sullator), SIMOX (Se
paration by Implanted Oxy
gen), CVD (Chemical vapor)
(e.g., deposition).

[0017]

The isotope separation method utilizing the parametric resonance phenomenon and the ultra-high purity ion source or plasma source of the present invention are characterized by operating by the following mechanisms. (1) Plasma is used to avoid a decrease in separation efficiency due to the space charge effect. (2) The ions and electrons in the plasma are g
By utilizing the property of performing rad B-drift and E × B drift, a unidirectional plasma flow required for separation is created. (3) By selecting the frequency of the high frequency applied to the quadrupole to be about twice the cyclotron frequency of the ion to be separated, energy can be selectively applied only to that ion. (4) Only ions accelerated by the quadrupole high-frequency electric field are subjected to the potential barrier (pot) by the blocking electrode set at the next stage.
It is possible to get over the initial barrier and to be selectively separated. (5) In particular, when utilizing as a plasma source, an electron beam is separately injected into ions after separation,
It is electrically neutralized to a plasma state.

The above contents will be described more specifically.
In the present invention, the parametric resonance phenomenon of charged particles in an inhomogeneous magnetic field is used for isotope separation. The parametric resonance occurs, for example, when the equation of motion of the system is given by a second-order differential equation having a periodic coefficient having the same period, as shown in Equation 1.

[0019]

(Equation 1)

In particular, even if the term of the forced external force is not explicitly present, under certain conditions, the amplitude may increase endlessly with time. Such a phenomenon is called “parametric resonance”. The non-uniform electromagnetic field used in this method is, specifically, a toroidal static magnetic field, a static electric field, and a high-frequency electric field. In this method, the motion of the charged particles in these electromagnetic fields, particularly the drift motion in the direction perpendicular to the static magnetic field, is used.

FIG. 1 is a conceptual diagram showing the configuration of the isotope separation device of the present invention and the arrangement of magnetic field coils, electrodes and the like.

The principle of operation of the present system as an entire separation system will be described. First, natural uranium (metal) is formed into a monovalent completely ionized plasma state by any method [plasma source 01]. If necessary, the ion component is raised to a certain temperature by means such as electron cyclotron resonance heating (ECRH).

Such uranium plasma is extracted from the plasma source by the E × B drift motion due to the interaction between the electrostatic field E formed by the twelve electrodes and the toroidal static magnetic field B, and grad B = above a certain plane. It flows out in the direction.

The quadrupole electrode 05 at the center has ²³⁵
A high frequency voltage about twice as high as the ion cyclotron frequency _ωc5 of U is applied. ²³⁵ U by this high frequency electric field
Only one is accelerated selectively, increasing the kinetic energy.

This kinetic energy of ²³⁵
U overcomes the voltage at the blocking electrode 06 slightly above the quadrupole electrode and reaches the recovery electrode 07 further above,
It is collected there.

On the other hand, since ²³⁸ U is not accelerated by the quadrupole electric field, it cannot overcome the blocking voltage, and its track is bent halfway, and is collected by the waste collecting electrode 08. .

[0027]

DETAILED DESCRIPTION OF THE INVENTION The isotope separation method of the present invention can selectively separate specific ions in plasma efficiently by utilizing the parametric resonance phenomenon of a high-frequency electric field of a quadrupole electrode. It is possible to provide methods that are indispensable for advanced technologies such as enrichment, reprocessing of nuclear reactor nuclear fuel, ultra-high purity ion source and plasma source.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The main part of the present invention is as shown in FIG. Hereinafter, the role of each component will be described with reference to FIG. (Hiroshige Watanabe et al .: Journal of Plasma and Nuclear Fusion Society 72
(1996) 347. See also. )

The portion denoted by 01 in FIG. 1 is a plasma generating portion, and if the object is a gas, it can be turned into plasma by means such as electron cyclotron resonance (ECR). If the target object is a metal, it can be heated and evaporated to form an atomic state by irradiating a strong high-energy electron beam, and ionized to generate plasma. Such extraction of the plasma to the separation region utilizes the E × B drift motion.

The toroidal coil 09 is for generating a toroidal magnetic field. The toroidal magnetic field is necessary to cause electrons to perform cyclotron motion when plasma is generated by ECR, and also plays a role in determining the flow of ion components in the plasma in a fixed direction by grad B drift.

The electrostatic field generated by the introduction electrodes 03 and 04 serves to introduce the plasma extracted from the plasma source to the center and to control the speed of the flow of the plasma. Since the grad B drift due to the toroidal magnetic field is in the opposite direction for ions and electrons, the plasma is charged and separated. To prevent this, the E × B drift speed is g
The electrostatic field E is applied so as to be higher than the rad B drift speed.

The selective separation of ions is performed by the quadrupole electrode 05 and the blocking electrode 06. As shown in FIG. 2, the quadrupole electrode is composed of four annular electrodes parallel to the torus axis.
The electrodes adjacent to each other are connected so that high frequency voltages of opposite signs are applied. This To increase its kinetic energy. The electric field near the origin in FIG. 2 is approximated as follows.

[0033]

(Equation 2)

[0034]

(Equation 3)

Here, d is the distance from the origin to the quadrupole electrode. Now, assuming that the static magnetic field _Bo is applied in the negative direction of the z-axis, the equation of motion of the mass m and the charge Ze with respect to the charged particles is expressed as follows.

[0036]

(Equation 4)

[0037]

(Equation 5)

[0038] Now, (x + y) / d = X, (xy) d = Y and ωt
= 2τ. In this case, the above equation can be written as

[0039]

(Equation 6)

[0040]

(Equation 7)

[0041] Equations 6 and 7 are both standard Mathieu equations. As is well known, the Mathieu equation is divided into a stable solution and an unstable solution depending on the values of the parameters (a, q). In FIG. 3, q is a horizontal axis and a is a vertical axis.
Shows the region of stable and unstable solutions. The hatched area is the area of the unstable solution.

Here, as one example, monovalent ²³⁵ U-
If the static magnetic field and the frequency and voltage of the high frequency applied to the quadrupole electrode are appropriately selected for the ions, (a, q) = (0.
8, 0.24). This parameter point is located at U in FIG.
The solution of Equation 7 becomes unstable. The parameters of ²³⁸ U corresponding to the same conditions as ²³⁵ U are (0.78, 0.23
7), which is represented by v in FIG. 3, and in this case, it is a stable solution.

Numerical calculations of Equation 6 with these parameters for ²³⁵ U and ²³⁸ U are as shown in FIG. Obviously, the solution of ²³⁵ U increases with time, and the solution becomes unstable. Physically, ²³⁵ U-
Since it corresponds to the increase in the Larmor radius of ions, ²³⁵ U
-Means an increase in the kinetic energy of the ions. Meanwhile, 2
It can be seen that the 38 U-ion is a more stable solution and is not accelerated by the high frequency quadrupole. In this way,
Only the isotopes to be separated can be energized by the high frequency quadrupole electric field.

The blocking electrode 06 plays a role in separating ions that have gained energy from the quadrupole electric field from ions that have not. An electrostatic voltage having a polarity opposite to that of the introduction electrodes 03 and 04 is applied to this electrode. Therefore, only ions that have obtained kinetic energy in the high-frequency quadrupole electric field can pass over this potential and be collected by the collection electrode 07. Other ions cannot cross this potential barrier, the trajectory is bent to the outside of the torus, and is collected by the waste collection electrode 08.

The reason why the waste collection is performed outside the torus is to facilitate the recovery operation, and can be achieved by slightly shifting the center axis of the electrostatic field electrode toward the inside of the torus. .

The collecting electrode 07 or the waste collecting electrode 08 is for recovering the isotope to be separated and for processing the waste. In the case of gas,
As a neutral gas at the electrode, it will be recovered by a vacuum pump. In the case of metals such as uranium, extensive research has been conducted on atomic laser isotope separation, and it will be recovered by exactly the same method. (For example, OGURA,
K. et al. : Jpn. J. Appl. Phys. 3
1 (1992) 1485, NISHIO, R.A. et a
l. : J. Nucl, Sci. and Tech. , 3
2 (1995) 180. See etc. )

The above is a description of the principle of operation of the main components of the present invention, but it should be noted that the separator is in the form of a torus. The first reason is that in a torus magnetic field, charged particles use the property that grad B = a constant surface drifts. When the method of the present invention uses a uniform magnetic field by a linear solenoid coil,
Even with charged particles accelerated by the quadrupole, even if the drift trajectory is bent and the blocking voltage can be overcome,
In some cases, it does not reach the collection electrode well. The grad B-drift caused by the toroidal magnetic field can be said to play a role of guiding the recovery electrode. In addition, the toroidal shape has the advantage that the apparatus can be made compact in response to the requirement that the working area be as large as possible in order to increase the separation capacity per stage.

The role of each component of the separation device has been described above. In order to know the operation as one system integrating these components, ²³⁵ U in a given electromagnetic field is required.
^It is necessary to perform a trajectory calculation for ²³⁸ U ions to confirm the separation function. Here, FIG. 5 shows a specific arrangement of the electrodes described with reference to FIG. 1 in order to perform a numerical analysis of the orbit. Here, for the sake of simplicity, the static magnetic field has a toroidal shape, but since the curvature effect of the toroid is essentially insignificant for the other electrodes, an infinitely long linear conductor placed in the z-axis direction By approximation.

The linear charge density generated when a voltage is applied to the high-frequency quadrupole electrode 05 is ± σ, the linear charge density on the introduction electrode is ± λ _1,2 and that on the blocking electrode is ± λ ₃ . The equation of motion for a charged particle is given by the following equation.

[0050]

(Equation 8) Here, it is assumed that the static magnetic field is applied in a negative direction with respect to the Z axis. The size is given by the following equation.

[0051]

(Equation 9) Here, B ₀ = μ ₀ I / 2πR, R is the large radius of the torus near the center of the diameter of the plasma source.

The electric fields generated by the quadrupole, the introducing electrode and the blocking electrode are all composed of x and y components. Can be written in

[0053]

(Equation 10)

[0054]

[Equation 11] Here, τ = (ωt) / 2, a and q are parameters of the Mathieu equation (Equation 6), ε is a constant representing the strength of the electrostatic field, and is given by ε = λo / 2πε ₀ d.

Also,

(Equation 12)

[0056]

(Equation 13)

[0057]

[Equation 14]

[0058]

(Equation 15) It is. Here, η _i = λ ₁ / λ _0, l = 1 / √2. In the above formula, the quantity representing the distance is normalized by dividing by d,
It is a dimensionless quantity. X / d →) to save symbols
_x, it is again used written as _{h i} / d → _h i.

Here, the equations of motion for the charged particles of Equations 10 and 11 will be specifically calculated numerically. Hereinafter, ²³⁵ U-ions in uranium plasma are considered as targets for selective separation. The angular frequency ω of the high frequency for the ²³⁵ U-ion is, as shown in FIG. Set. ω _C5 is the cyclotron angular frequency for ²³⁵ U monovalent ions. The high frequency applied voltage at this time is set so that q = 0.2. These ²³⁵ U
The Mathieu parameters (a, q) of ²³⁸ U-ions relative to -ions = (0.78, 0.222).

[0060] This corresponds to a kinetic energy of about 0.3 eV. In the figure, for convenience, the introduction electrodes 03 and 04 used in this calculation,
The positions of the blocking electrode 06, the recovery electrode 07, the waste auxiliary electrode 08, the quadrupole electrode 05, the plasma source extraction electrode 12, and the like are shown.

The x and y-components of the electrostatic field on the y-axis are also shown. The electric field is between the introduction and blocking electrodes,
Its direction has been reversed. Therefore, the charged particles passing through the quadrupole electrode are applied in the direction of pushing back. The parameters for this electrostatic field are ε = 0.015, η ₁ =
0.8, η ₂ = 1.0, η ₃ = −0.8.

As is clear from this figure, ²³⁵ U-
It can be seen that the ions are accelerated by the high frequency quadrupole electric field and the kinetic energy is increased. Then, the voltage exceeds the blocking voltage and reaches the recovery electrode. On the other hand, the ²³⁸ U-ion is not accelerated by the quadrupole electric field and cannot overcome the blocking voltage, so that the orbit is bent toward the outside of the torus on the way, and is trapped by the waste collection electrode. Is done.

The reason why the flow of the waste ( ^238U ) is bent outward of the torus is due to the function of the diverging lens (or E × B-drift) of the blocking electric field. It is something that is considered. This is achieved by slightly displacing the central axis of the electrostatic field electrode inside the torus.

Next, the effect of the initial conditions on the charged particle trajectory will be considered.

1. Regarding the initial position (x _o , y _o ): Since the particle trajectory drifts along the y axis, the position of X _o plays an important role in whether or not it is accelerated by the quadrupole field. If _Xo is far away from the y-axis, it will not be accelerated. Depending on various conditions such as the position of the plasma source, in the case of uranium enrichment, o ≦ x _o ≦
If it is in the range of 0.3, it is possible to accelerate by a quadrupole electric field.

2. Phase angle of initial speed The phase angle of initial speed here is the initial position (x _o ,
In y _o ), it is assumed that the angle represents the initial velocity of the particle with respect to the y-axis. The effect of θ on the trajectory is difficult to predict in advance because Equations 8 and 9 are nonlinear differential equations, and the behavior is complicated.

FIG. 7 shows an example of this. This figure shows that ²³⁵ U and ²³⁸ U are collected by the collection electrode 07 or the waste collection electrode 08 depending on the phase angle when the initial position y _o = −3.0 is fixed and x _o is changed. It is shown. Open circles represent ²³⁵ U and black dots represent ²³⁸ U. As is clear from this figure, depending on the phase angle θ and the initial position _xo , ²³⁸ U may be accelerated or ²³⁵ U may not be accelerated by the high-frequency quadrupole electric field. In the case of uranium, the relative mass difference ΔM / M = 0.013
And due to being small. Such a phenomenon does not occur when the relative mass difference is large, such as in a hydrogen isotope or a helium isotope.

Therefore, it is possible to separate ²³⁵ U by 100% only in a limited area of the initial position _xo , but it is not necessary to separate 100% from nuclear fuel for a light water reactor. Since it is only necessary to obtain a uranium enrichment of about%, the present method can be sufficiently used for uranium enrichment.

Here, it will be evaluated how much uranium can be concentrated per one-stage separation according to the present invention. In the evaluation, various conditions are intricately entangled, and therefore, optimization is not performed. It is simply an evaluation of the zero order approximation. ²³⁵ U is 0.711% for real natural uranium
Although it is included, it is set to 0.7% here.

Tables 1 and 2 show examples of specific dimensions and plasma parameters of the separation apparatus used below.

[0071]

[Table 1]

[0072]

[Table 2]

The trajectory analysis for the charged particle so far is as follows.
For a single particle. It is important to clarify up to what density plasma this model can be applied in a real device.

Generally, in order to increase the separation ability, the density of the working substance may be increased. However, when the density is increased, the orbit is disturbed by Coulomb collision between charged particles, and a single particle model cannot be used. As a guide for determining how high the density can be applied, the mean free path due to Coulomb collision may be examined. In the case of the present invention, the mean free path λ _ie by ion-electron collision and the mean free path λ _ii by ion-ion collision are important.

As is well known, in ion-ion collision, the center of mass before and after the collision is invariable,
In addition, since there is no change in the overall momentum, the orbital diffusion phenomenon caused by this is negligible, so that the ion-electron collision plays an important role solely on the particle orbit [Ref. F. Chen: "Introduction
n to PLASMA PHYSICS, "Plen
um Press, New York, Chap. 5,
155 (1976). ].

Mean free path λ due to ion-electron collision
_ie

(Equation 16) Given by [Reference: R. A. Gross: "F
usion Energy ", John Wiley
& Sons Inc. , New York, 51 (19
84). ].

[0077] If nｎ5 × 10 ¹⁸ m ⁻³ , then λ _ie = 2 m.
Here, the ion temperature is set to 0.3 eV, but it is not so difficult with current technology to raise the ion temperature to one digit or more if necessary. It is possible to make λ _ie a required value. Therefore, n to 5 × 1
A plasma with a density of 0 ¹⁸ m ^-3 may be sufficient for a single particle model.

In the method of the present invention, uranium fuel having an arbitrary enrichment can be obtained by appropriately selecting the width of the radius of the plasma source. In the following, let's consider the case of 3% concentration. For this purpose, the inner and outer diameters of the bore radius of the plasma source _{x o} is chosen such that 0.09 ≦ _{x o} ≦ 0.25. This corresponds to an aperture width h = 0.032 m.

Here, the initial velocity (x _o , at the initial position (x _o , y _o ) of the charged particle corresponding to the aperture surface
Assume that the phase angle of y _o ) is isotropic. ²³⁵ U in natural uranium plasma entering the separation zone from the plasma source
The probability that the ion component is collected by the collection electrode 07 is as shown in FIG.
From 0.86. Also, that of ²³⁸ U-ion is 0.18.

In 1 kg of natural uranium, ²³⁵ U contains 7 g,
^{Since 238} U contains 993 g, under the above conditions, 3.2% of enriched uranium of 18% from 1 kg of natural uranium can be obtained.
5 g can be obtained.

The radius of the plasma source is set to 0.05 ≦ x
_{When o} ≦ 0.25, the concentration is 2%, and 0.1 ≦ x _o ≦
If it is selected to be 0.25, uranium with an enrichment of 4% can be obtained.

Next, how much uranium can be concentrated in one stage of separation in the method of the present invention will be evaluated. The amount depends, of course, on the enrichment of uranium and the dimensions of the apparatus, but in order to give a specific measure of the separation capacity of the present invention, the enrichment is about 3%, and the apparatus parameters are as follows. Evaluation is made using the examples shown in Table 1 as examples.

The area of the diameter of the plasma source is given by S = 2πRh. Here, R is the large radius of the torus, and h is the width of the caliber. Assuming that the density of the plasma is n and the flow velocity is v, the supply rate F from the plasma source to the separation region is:

[Equation 17] Given by Here, A is the atomic weight, and N is the Avogadro number.

In the case of this method, the flow velocity v is equal to the E × B of the plasma.
-Given by the drift speed. If the extraction voltage of the plasma source is 150 V, E _e ≡350 V / m. Since the ^{_{B T = 0.35T v = 10 3}} m / s
It is. R = 0.8 m, h = 0.032 m, A = 238
Substituting m, n = 5 × 10 ¹⁸ m ⁻³ into Equation 17 gives
F = 0.32 gU / s is obtained. This is 27.6gU
/ Day. That is, in the method of the present invention, about 5 kg of 3.2% enriched uranium can be obtained per day by one-stage separation. It is 1.8 tons in one year.

[0085]

As described above, the present invention proposes to enrich ²³⁵ U by utilizing the parametric resonance phenomenon of charged particles caused by a high-frequency quadrupole electric field in a toroidal static magnetic field. Since the present invention is an electromagnetic system,
The flow of the separation work material (plasma state) can be controlled freely, and the separation coefficient α can be very large, 10 ≦ α <∞, so that the number of separation stages is one, and uranium nuclear fuel of any enrichment can be obtained. Obtainable.

In the conventional gas diffusion method and centrifugal separation method, the separation coefficient is as small as α = 1.0041 and 1, and in order to obtain a nuclear fuel with a desired enrichment, thousands of units are connected in series (cascade). Therefore, there are various difficulties in equipment cost, operation and maintenance, power consumption, and the like. However, since the method of the present invention requires only one separation, significant improvement in equipment cost and operation management can be expected.

Further, only by changing the frequency and voltage of the high frequency applied to the quadrupole electrode, it is possible to separate and purify deuterium (D) and tritium (T), which are nuclear fuels in a future fusion reactor, and to produce ash. removal of impurities helium ⁽⁴ the He), etc. isotope separation of Lithium _{^{(6 L i, 7 L i}} ) requiring the production of tritium, it is a very wide variety of isotopes applicable method to separate elements .

In addition to the above isotope separation, the method of the present invention can also be used as an ion source or a plasma source containing only a single kind of ultrapure ion.

In the above description, uranium has been described assuming that a single metal uranium is converted into plasma.
When uranium fluoride (UF ₆ ) is used, since UF ₆ is a gas, it is easy to ionize. FIG. 8 shows UF
_6- Gives the time evolution of the solution of the Matthew equation for ions.
Thus, separation in the state of ²³⁵ UF ₆ is also possible.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an isotope separation apparatus according to one embodiment of the present invention.

FIG. 2 is a connection diagram of a high-frequency quadrupole electrode and a high-frequency power supply.

FIG. 3. Parameter space (a.q) of Matthew equation
Stability and instability diagram. The hatched portion indicates an unstable region.

FIG. 4 is a solution of the Matthew equation corresponding to the Larmor radius of ²³⁵ U and ²³⁸ U-ions. ^The solution for ²³⁵ U-ion is unstable (increased), indicating that the solution for ²³⁸ U-ion is stable.

FIG. 5 shows the positions of the quadrupole electrode, the introduction electrode, the blocking electrode, and the charge density given to each electrode.

FIG. 6 shows an example of particle trajectories of ²³⁵ U and ²³⁸ U-ions by numerical analysis, and a component distribution of an electric field by an introduction electrode and a blocking electrode.

FIG. 7 shows the dependence of the initial velocity ( _xo , _yo ) on the incident phase angle at the initial position ( _xo , _yo ).

FIG. 8: Time dependence of the solution of the Matthew equation for UF ₆ -ions. As in FIG. 4, the solution for ²³⁵ UF ₆ -ions diverges and the solution for ²³⁸ UF ₆ is stable.

[Explanation of symbols]

 Reference Signs List 01 Plasma generation unit 02 Plasma outlet 03 Introducing electrode-1 04 Introducing electrode-2 05 High frequency quadrupole electrode 06 Blocking electrode 07 Recovery electrode 08 Waste collecting electrode 09 Toroidal coil 10 Atomic beam introducing tube 11 Microwave waveguide for electron resonance heating Tube 12 Plasma extraction electrode 13 Vacuum container

Claims (4)

[Claims] An energy is given by selectively accelerating only isotope (for example, U-235) ions to be separated by utilizing a parametric resonance phenomenon of charged particles caused by a high-frequency quadrupole electric field. The ions having increased energy cross the potential (potential barrier) created by the blocking electrode and are collected by the collecting electrode. On the other hand, other isotopes (e.g., U-238) are not accelerated by the quadrupole field and therefore cannot cross the potential barrier. The particle trajectory is bent on the way and is collected by the waste collection electrode. By changing the frequency and voltage of the high frequency applied to the quadrupole electrode, all the isotopes can be separated. An isotope separation method characterized by separation based on the above principle. (2) When a high current ion beam is used alone in the selective separation of isotopes, the space resolution effect of ions causes a reduction in separation resolution. In order to utilize a certain plasma effectively, grad B-drift and ExB-drift motion of charged particles are used. The non-uniform magnetic field (grad B ≠ 0) used in the present separation device can be realized by making the shape of the device into a truss shape (also called a donut shape) and using a toroidal coil. The isotope is characterized in that it is possible to give a flow in a certain direction to the plasma-like isotope element by combining this magnetic field with E × B-drift, and to carry out steady-state and large-scale isotope separation. Separation method. 3. If nuclear fuel waste from a nuclear reactor can be turned into plasma by any method, technetium-99 (Tc-99, half-life 210,000 years) and iodine-129 (I- 129, half-life of 12 million years), and the storage period of waste can be significantly reduced to several hundred years, which is extremely effective in terms of safety measures. Isotope separation method. 4. A method characterized in that an ultrahigh-purity ion source or a plasma source containing only one kind of ion is constituted by applying the same principle in addition to the above-mentioned isotope separation method.