The present invention relates to nuclear engineering and is designed to produce a nuclear fission chain reaction.

The invention may be used to obtain great fluences of neutrons, gamma-ray quanta, and to produce thermal and electric power.

The commonly accepted conventional method for producing a nuclear fission chain reaction is a nuclear explosion or a fissile material fission by fast or thermal neutrons at nuclear reactors (see Weinberg A., Wigner W., Physical Theory of Nuclear Reactors, IL. M., 1961, [1] - the most pertinent prior art).

As the explosion-induced nuclear chain reaction is uncontrollable, we shall not further concern with it. To date, the fast and thermal-neutron nuclear reactions are widely employed both at research and power reactors.

They, however, suffer the following general problems:

• a great amount of nuclear fuel should be fed into the reactor (e.g. VVER-440, VVER-1000 and RBMK-1000 require 41, 66 and 192 tons of uranium, respectively) which amount is sufficient for the entire reactor operation period (generally three years) and is replaced thereafter;
• during the operation period, less than 5 percent of the entire nuclear fuel, by mass, will react, taking into account the appearance of other fissile nuclides, i.e. the fuel usage efficiency is rather low;
• while the reactor is in service, the reaction products stay in the core and interfere with the reactor operation;
• during the process, uranium-238 whose share exceeds 95 percent of the nuclear fuel, by mass, produces a large amount of various radioactive transuranic elements with a very large half-life period, that are extremely hazardous for the environment as their permissible concentration in the ambient air and water should be several thousand times lower than that of the fission products;
• an accident at a nuclear reactor, especially after a long time in service, may cause hazardous environmental impact.

It is an object of the present invention to reduce mass and improve the usage efficiency of fissile material in the reactor core, and also to spatially separate production and utilization of the nuclear power released.

The above object is attained by providing a method for producing a nuclear chain reaction, including the steps of introducing, for the reaction initiation period, a fast-neutron source into the reactor core comprising a moderator, a vacuum magnetic trap for retaining the fissile material plasma, and neutron-absorbing screens, slowing down the neutrons of said fast-neutron source to thermal energies and directing them to the magnetic trap. The fissile material is then converted into gas or plasma, accelerated and fed into the magnetic trap at the velocity that is determined, for example, in the case of the thermal neutrons and the tissue material moving at right angles to each other, according to the following formula:$${\text{V}}_{\text{fm}}\text{= C}\sqrt{\text{((}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}\text{/ (}{\mathit{\text{E}}}_{\mathit{\text{tn}}}\text{+}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}{\text{))}}^{\text{2}}\text{- (}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}\text{/(}{\mathit{\text{E}}}_{\mathit{\text{r}}}\text{+}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}{\text{))}}^{\text{2}}}$$    wherein C is the velocity of light, m/c; E_n0 is a rest energy of a neutron, eV; E_tn is an energy of thermal neutrons, eV; E_r is an energy of a selected fission resonance, eV.

Formula (1) is inferred from the universally known relationship for the kinetic energy of a traveling particle [2]:    whence it follows that$${\text{V}}_{\text{k}}\text{= C}\sqrt{\text{1-(}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}\text{/(}{\mathit{\text{E}}}_{\mathit{\text{k}}}\text{+}{\mathit{\text{E}}}_{\mathit{\text{n}}}{\text{}}_{\text{0}}{\text{))}}^{\text{2}}}$$    wherein ${\text{m}}_{\text{r}}{\text{C}}^{\text{2}}{\text{= E}}_{\text{n0}}$ is a rest energy, eV; m₀ is a rest mass of a particle, kg.

In the case of the thermal neutrons and the fissile material moving at right angles to each other, the approach velocity at a selected interaction resonance is;$${\text{V}}^{\text{2}}{}_{\text{fm}}{\text{= V}}^{\text{2}}{}_{\text{r}}{\text{- V}}^{\text{2}}{}_{\text{tn}}$$    wherein V_r is a velocity of neutrons at the resonance interaction with the fissile material, m/c.

The substitution of expression (3) in (4) gives formula (1). In this case the velocity, i.e. the energy of mutual approach of thermal neutrons and the fissile material moving nuclei, will agree with the selected energy of the resonance fission of the fissile material whose fission cross-section may be several times greater than at the thermal neutrons.

Furthermore; a path of thermal neutrons in the moving fissile material is determined according to the following formula:$$\text{L = δ}\sqrt{\text{1 + (}{\mathit{\text{V}}}_{\mathit{\text{fm}}}\text{/}{\mathit{\text{V}}}_{\mathit{\text{tn}}}{\text{)}}^{\text{2}}}$$ wherein

• δ is a thickness of the tissue material layer, m;
• V_fm is a velocity of the fissile material movement, m/c;
• V_tn is a velocity of the thermal neutrons movement, m/c.

Using the path passed by thermal neutrons when intersecting the moving fissile material, the so-called "efficient" fission cross-section of the fissile material moving with thermal neutrons can be determined as:    wherein σ_r is a fission cross-section at resonance, barn.

Fast neutrons emitted in the fission process are directed to a moderator whereupon they are returned to a magnetic trap as thermal neutrons to provide the self-sustaining nuclear fission chain reaction at the selected resonance. The critical mass is maintained constant by continuously feeding the fissile material into and withdrawing the reaction products from the core. The amount of the thermal neutrons returned to the magnetic trap is controlled by the neutron-absorbing screens connected with the reactor control system.

Using the efficient macroscopic fission cross-section [6], values of fissile material plasma density "n_n" and thickness "δ" can be selected so that the tissue material is not be excessively transparent to thermal neutrons, and, furthermore, a wasteful movement of its great mass does not occur. These characteristics should be selected such that the multiple of density reduction of the flux of the thermal neutrons intersecting the moving fissile material plasma satisfies the condition:$$\text{1.01 ≤ K ≤ 100}$$    wherein$${\text{K = 1/exp(-n}}_{\text{n}}{\text{δσ}}_{\text{r}}\sqrt{\text{1+(}{\mathit{\text{V}}}_{\mathit{\text{fm}}}\text{/}{\mathit{\text{V}}}_{\mathit{\text{tn}}}{\text{)}}^{\text{2}}}$$

The present invention is essentially based on the fact that all of the fast neutrons can be slowed down, generally without loss, to thermal energies at which they can be considered stationary when arrive at the vacuum magnetic trap, as their velocity is low as compared to the velocity of the fissile material nuclei, and, therefore, all of them may react even at a relatively low density of the fissile material. Therefore, the above method of producing a nuclear fission resonance chain reaction provides the following three favorable circumstances:

• 1. Efficient slowing down of the fast neutrons to thermal energies and movement of the tissue material nuclei in their field produce a high density of substantially monoenergetic neutrons whose energy falls on some selected fission resonance of the tissue material.
• 2. The use of the most favorable resonance fission cross-section of the tissue material allows the selection of the resonance fission considerably exceeding the thermal neutron fission of this material.
• 3. Owing to the fact that the velocity of the moving fissile material can be much higher than that of thermal neutrons, the fissile material density may be considerably reduced to obtain the macroscopic cross-section similar to that of the stationary fissile material for the same resonant neutrons.

Consequently, if in a method for producing a nuclear fission resonance chain reaction in accordance with the present invention, a fissile material is e.g. plutonium-239 (σ_tn=742 barn), then Table 1 shows values of fissile material movement velocity "V_fm"; multiple "K₁" of the increase in the length of the thermal neutron path in the moving fissile material; "efficient" fission cross-section and "efficient" and resonance fission cross-section/Pu-239 thermal neutron fission cross-section ratio, for different Pu-239 resonance energy values.

As follows from the data in Table 1, when plutonium-239 is bombarded by a method in accordance with the present invention, using resonance energy E_r=75.21 eV for this purpose, the "efficient" fission cross-section will increase, as compared to the thermal neutron fission, approximately by 180 times or 55 times in the ease the stationary plutonium is bombarded by monoenergetic neutrons having the energy of 75.21 eV. Consequently, the data above shows that plutonium-239 critical mass required to initiate a nuclear chain reaction can be reduced approximately by the same degree when using the present method of plutonium-239 resonance fission (i.e. using the present method for producing a nuclear fission resonance chain reaction, plutonium-239 minimum critical mass may be 2-4 g instead of 460 g of plutonium in aqueous solution used in a conventional thermal neutron fission method [3]).

For the other fissile materials, the resonance energies, at which minimum critical masses are provided, are: plutonium-241 (E = 14.78 eV), uranium-235 (E = 19,3 eV), uranium-233 (E = 22 eV), etc. In this case, the resonance values at which the most complete burnup of fissile materials will take place, i.e. those providing the minimum value of parameter "α" defined by formula:$${\text{α = σ}}_{\text{c}}{\text{/σ}}_{\text{f}}$$    wherein σ_c is a capture cross-section; σ_f is a fission cross-section, will be: plutonium-239 (E = 15.5 eV, α = 0.05); plutonium-241 (E = 5.91 eV, α = 0.03), uranium-235 (E = 13.98 eV, α = 0.23), uranium-233 (E = 33.95 eV, α = 0.025) [4,5].

Therefore, in accordance with the present method for producing a nuclear chain reaction, a tissue material will be in the plasma form in the reactor core, and its general amount may be as little as several tens of grams, consequently, the environmental impact will be minimal even in the case of complete destruction of the reactor,.

To maintain the constant density of plutonium nuclei in the course of the nuclear chain reaction, it is essential that the fissile material plasma should be continuously fed into and the fission products containing more than 90 percent of the nuclear energy released should be continuously removed from the reactor core and directed to the facilities for direct conversion of their energy, e.g., into electricity. Such separation of the processes allows very great energies, considerably exceeding 1000 megawatt, to be released in the reactor core, since the energy remaining in the moderator and the reactor structure is provided by neutron and gamma-ray quantum energies that constitute not more than 5 percent of the entire nuclear energy released.

The efficiency of the fissile material usage will be rather high since at any given time the reactor core constantly contains not more than several tens of grams, i.e. the amount required for the nuclear chain reaction to proceed.

Additionally, owing to absence of uranium-238 in the reactor core, substantially no transuranic radioactive elements will form in the course of the nuclear chain reaction.

A practical implementation of the present method of neutrons/fissile material interaction will depend on a feasibility of moving the fissile material at the velocity of 10³-10⁵ m/c. To this end, the fissile material should be converted into a gas plasma mixture. To date, the velocity of partially ionized gas movement for various types of material in plasma centrifuges, plasmatron guns and plasma accelerators has the upper limit equal to "V_crit":$${\text{V}}_{\text{crit}}{\text{= 5x10}}^{\text{3}}{\text{... 5x10}}^{\text{4}}\text{m/c}$$

This velocity is related to the magnitude of ionization energy of the partially ionized plasma being moved, and the higher velocity can be achieved only upon complete ionization of the plasma. The velocities can be further increased using the plasma accelerators described in references [5] to [9].

Table 2 lists characteristics of some plasmatron facilities and fields of their application, in which gas/plasma mixtures have been accelerated up to the velocities that may be of interest to attain the object of the invention.

Characteristics of plasmatron installations

Installation or investigation field

Plasma material

Plasma velocity, m/c

Plasma density, nuclei/cm³

Comment

Reference

"Homopolar" and "Ixion" plasma chambers

helium/uranium mixture

2.2 x 10^3--5 x 10⁴

10¹⁵-10¹⁶

[6]

"F1"

argon/helium mixture

10⁴-10⁵

5x10¹³--5x10¹⁵

highly ionized plasma

[6]

"Supper"

argon/helium mixture

10⁴

5x10¹⁵--5x10¹⁷

partially ionized plasma

[6]

Aerodynamic tests

hydrogen and helium

5 x 10⁴

tests of thermally heated structures when entering Jupiter atmosphere

[7]

Plasmatroms

nitrogen, argon, helium, hydrogen

10⁵

10¹⁶-10¹⁸

continuous conditions,

[7]

10⁴

10¹⁸-10¹⁹

pulse conditions

MK-200 pulse accelerator

hydrogen,

5x10⁵

10¹⁵-10¹⁶

[5-9]

nitrogen,

4x10⁵

10¹⁴-10¹⁶

neon

4.5x10⁵

7x10¹⁴

References Cited:

• 1. Weinberg A., Wigner U., Physical Theory of Nuclear Reactors, II., M., 1961.
• 2. Kukhlin Kh. Handbook of Physics, translated from German, M., Mir, 1985.
• 3. Dubovskii B.G., Kamaev A.B., Kuznetzov F.M. et al., Critical Characteristics of Systems With Fissile Materials and Nuclear Safety, Reference Book, Atomizdat, M., 1966.
• 4. Bulletin of the Nuclear information Center, Issue 3, Suppl.4, Atomizdat, 1967.
• 5. Donald G. Hudge and Robert E. Shwartz, Atlas of Neutron Cross Sections, Second Edition, amended and supplemented. Brookhaven National laboratory, Upton New York, 1958.
• 6. Korobtsev S.V., Rusanov V.D., Plasma Centrifuge - New Plasma Chemical Reactor, M., TsNII of Information under the USSR State Committee for Nuclear Power Utilization, 1988.
• 7. Glebov I.A., Rutberg F.G. High Power Plasma Generators, M., Energoizdat, 1985.
• 8. Blinov I.P. et al., Vacuum High-Current Plasma Installations and Their Use in Microelectronics Process Equipment, Review, Series: Microelectronics, M., TsNII of Electronics, Issues 7 and 8, 1974.
• 9. Abramov I.S., Plasma Accelerators and Ion-Plasma Jet Engines, Lectures of Leningrad Electrotechnical Institute, Leningrad, 1978.
• 10. Leskov LV., Basic Physics of Plasma Accelerators, Part 1., MBCCO, MVTU, 1968.
• 12. Mikhailovskii F.B. Hydrodynamic Theory of Plasma Rotation in Tokamac, M., IAE named after Kurchatov, 1982.
• 13. "Physics of Plasma " Journal, vol.8, p.p.1000,1089.