RU2755811C1 - Method for controlled nuclear fission and nuclear reactor - Google Patents

Abstract

FIELD: nuclear science.

SUBSTANCE: invention relates to a method for controlled nuclear fission and a reactor for its implementation. Fast neutrons are slowed down and a field of thermal neutrons is formed, and thermal neutrons are selected and returned to the fission zone. The fission zone of the reactor is performed without a moderator, the fissile material is introduced with a concentration of ²³⁵U comparable to or less than the concentration in natural uranium, the flux of thermal neutrons is deeply introduced through the channels in the fissile material before the interaction, increasing the return path of fast neutrons in it, the flux is moved relative to the fissile material of the fission zone reactor. The reactor contains a decelerating focusing structure, a fission zone, an energy pickup device, and the fission zone of the reactor does not contain moderators, the decelerating focusing structure has spacer grids, neutron interception sections, one or more neutron return sections, whose selection plates are oriented into the channels between the plates with a spacer grid with fissile matter of the fission zone.

EFFECT: simplification, growth of the specific power in the reactor and ensuring energy efficiency, safety and environmental acceptability, expanding the technical capabilities of nuclear reactors and the range of areas of their technical application.

5 cl, 4 dwg, 2 tbl

Description

Technology area

The group of inventions relates to the field of nuclear physics, in particular to the physics of energy production processes and the useful application of nuclear fission reactors.

Prior art

A method of obtaining energy in the process of controlled fission of nuclei (described in patent US 2708656, dated 17.03.1955) is known from the prior art, in which natural or enriched uranium is used as a fissile substance. The fission process is carried out with the help of thermal neutrons generated in the process of slowing down fast fission neutrons. Plain water, heavy water, or graphite are used as moderators. Nuclear fission energy is converted into thermal energy, transferred to the coolant, which is used as water or liquid metals. The disadvantages of this method are low fuel efficiency, the risk of large-scale accidents and low environmental acceptability of the method due to the unsolved problem of the useful use of spent fuel.

There is a known method of generating energy (RU 2088981 dated 02/01/1996), in which during the operation of the reactor, it is produced in the bridging mode and burned out Pu-239 on fast neutrons. The irradiated fuel is discharged and processed. During reprocessing, the fuel formed during irradiation is separated from the existing fertile substance (U-238) mixture, fissile substance (Pu-239) and uranium is purified from fission products, then the fuel mixture is re-formed in its original enriched concentrations. The burnup depth is determined by the value of the initial fuel enrichment with the working isotope, taking into account the periodic renewal in the open fuel cycle. The fuel has excessive thermal neutron composition criticality. The disadvantages of this method are low efficiency of fuel use, the risk of large-scale accidents and low environmental acceptability of the method, since in the process of chemical processing of irradiated fuel part of the radionuclides enters the environment.

There is a known method of obtaining energy (UFN volume 163, No. 8) in which a reactor based on a neutron-fission wave on fast and on thermal neutrons is proposed, which is implemented in the concept of a reactor with an evaporating core. The disadvantages are low fuel efficiency, low energy release.

A known method of controlled fission of nuclei which slows down fast neutrons and forms a field of thermal neutrons, carry out selection and return of thermal neutrons to the fission zone, remove the fission energy, (Patent RU 2075116 from 12/30/1994) adopted by us as a prototype. The method is characterized by a high burn-up rate of fissile matter.

The disadvantages include some complexity of the process.

The state of the art also knows a reactor for generating energy in the process of controlled fission of nuclei, which we adopted as a prototype containing an anisotropic moderator, made in the form of a moderating-focusing structure for the formation of a directed neutron flux from the moderator with channels between them, fissile matter and a fission zone with a region of thermal and in the area of fast neutrons, a device for moving fissile matter, a device for converting the released energy with a coolant circuit (Patent RU 2075116 from 12/30/1994). The reactor is characterized by a high fissile material burnup.

The disadvantages include some complexity of the process.

In the method and device adopted as a prototype, deep burning of nuclear fuel is performed during the process of periodically finding it in the region of fast neutrons, in the region of thermal neutrons and in the cooling zone, with constant introduction of fertile nuclear fuel from U ²³⁸ , Th ²³² or their mixture , instead of their burnt out part.

But, for some technical problems, it is necessary to achieve high fuel burnup in its original composition without introducing a replenishing fertile substance.

Disclosure of inventions

The task to be solved by the claimed group of inventions is the development of a method and a nuclear reactor for generating energy in the process of controlled fission of nuclear fissile matter with a high burnup depth.

The technical result achieved when implementing a group of inventions is to simplify, increase the specific power in the reactor, and ensure energy efficiency, safety and environmental acceptability, which makes it possible to improve the quality and expand the technical capabilities of nuclear reactors and the range of areas of their technical application.

The specified technical result is achieved in a method of controlled fission of nuclei in which fast neutrons are slowed down and a field of thermal neutrons is formed, selection and return of thermal neutrons to the fission zone is carried out, characterized in that the fission zone of the reactor is performed without a moderator, the fissile substance is introduced with a concentration of ²³⁵ U comparable or lower, concentration in natural uranium, deeply introduce the flux of thermal neutrons through the channels in the fissile substance before the interaction, increasing the return path of fast neutrons in it, move the flux relative to the fissile substance of the fission zone of the reactor.

The specified technical result is also achieved due to the fact that a nuclear reactor is carried out containing a slowing focusing structure, a fission zone, an energy pickup device, characterized in that the fission zone of the reactor does not contain moderators, the slowing focusing structure has spacer gratings has sections for intercepting neutrons, one or more a neutron return section, whose selection plates are oriented into the channels between the plates with a spacer lattice with fissile matter of the fission zone.

A nuclear reactor is possible, characterized in that it contains a drive device that provides a relative movement of the neutron return section of the slowing focusing structure relative to the plates with fissile matter in the fission zone.

A nuclear reactor is possible, characterized in that the energy pickup device is made in the form of a coolant contour of the fission zone, which contains a thermosyphon with a heat exchange device located above the fission zone, a device for sorption cleaning of the coolant is located behind the heat exchange device of the loop.

A nuclear reactor is possible, characterized by the fact that the coolant circuit is made open with an accelerating nozzle, has a container with a coolant, a compressor, channels for removing energy from the selection plates, channels for removing energy from the plates with fissile material of the fission zone and channels for removing energy from the accelerating nozzle.

The essence of this method is that fast neutrons are slowed down by the moderator substance, transferring their excess energy to the nuclei of its substance. Then, neutrons entering the capture area at the corners and moving along the channels from the depth of the moderator are removed in the direction of the fissile material, and the fission zone of the reactor is performed without a moderator, the fissile material is introduced with a concentration of ²³⁵ U comparable or lower than the concentration in natural uranium.

At the same time, a flux of thermal neutrons is deeply introduced through the channels in the fissile substance before interacting with it, increasing the return path of fast neutrons in it, the flux is moved relative to the fissile substance of the fission zone of the reactor, and the fission energy is removed.

On enriched uranium, the PFS reactor core is energetically intensive, can be small, but only 1 out of 2.5 neutrons is used useful.

Of particular interest is the operation of the reactor using cheap depleted uranium.

(13). А выход нейтронов из топливного состава формируемого в этом случае на тепловых нейтронах, мал, но положителен:For the initial depleted uranium, the neutron yield from nuclear fission reaches the value: η _tn = 0.74, η _fn = 1.12. But the basis is that during long-term irradiation with thermal neutrons of the initial fissile material from ²³⁸ U, it produces ²³⁹ Pu with a high fission cross section, and the equilibrium concentration of ²³⁹ Pu, in long-term compositions, is low.

(13). And the yield of neutrons from the fuel composition formed in this case on thermal neutrons is small, but positive:

This is not a disadvantage, but an advantage of this reactor, since with the effective return of thermal neutrons there is no need to pointlessly burn out neutrons by the CPS system to ensure its safe operation.

The introduction of the initial fissile material with a concentration close to or slightly lower than the concentration of ²³⁵ U in natural uranium allows, during the initial stage of the reactor operation, to form a composition for subsequent long-term operation with a high fuel burnup in it - a long-term stationary composition.

So, for example, under the conditional CANDU mode (when the initial composition is natural uranium, the outer zone is absent, the PFS completely returns a fast neutron flux, thermal) with a starting composition of 0.5% at ²³⁵ U each, Table 1 shows the composition formed in the long-term operation mode with a flux neutrons: F _f = 3.7⋅10 ¹³ cm - ² s - ¹ , F _t = 10 ¹³ cm - ² s - ¹ , F _act = 1, N _full / N _act = 1.

Table 1 Stationary composition based on depleted uranium

F _t = 10 ¹³ cm- ² s- ¹ , F _f = 10 ¹³ cm- ² s- ¹ , N _full / N _act = 1

Isotope ²³⁸ U ²⁴² Pu ²⁴⁰ Pu ²³⁹ Pu ²⁴³ Am ²³⁶ U ²⁴⁴ Cm Content, % 98.010 0.879 0.315 0.282 0.231 0.092 traces

The yield of neutrons from the composition: η _t = 1.075 for thermal and η _f = 1.368 for fast neutrons, the dynamics of its formation is shown in Fig. 4.

During the operation of the reactor, during the capture of fast and thermal neutrons by the fuel composition and subsequent β-decays, there is a sequential burnout (fission) of all actinides formed during the operation. The fission zone of the reactor does not contain moderators, the decelerating focusing structure has spacer grids, it has sections for intercepting neutrons, one or more sections for neutron return, whose selection plates are oriented into channels between the plates with a spacer lattice with fissile material of the fission zone.

In the reactor, the pitch of the plates of the slowing-focusing structure for the formation of a directed neutron flux coincides with the pitch of the fuel elements.

The thermal neutron flux formed by the PFS selection plates has a divergence (up to 5'-10 ') at a high flux density. Between the plates, it expands deeply into the reactor core before interacting with fissile material and before interacting with the produced plutonium-239 and other actinides. As a result, the return path of generated fast neutrons from the depth of the reactor core increases, and the effective ratio of the dimensions of the fast reactor zone to the thermal zone increases. At the same time, plutonium-239 is being produced, the characteristic dimensions of the core, the total mass of fissile material in the reactor and the service life of the reactor are growing.

и

It is important that during long-term thermal neutron irradiation of the initial fissile material from ²³⁸ U or ²³² Th, it produces ²³⁹ Pu or ²³³ U with a high fission cross section, but because of the real ratio of their capture and fission cross sections on thermal neutrons, the equilibrium concentrations of these isotopes in long-term formulations, are small.

and

At the same time, the equilibrium concentrations of these isotopes upon irradiation of the initial fissile substances with fast neutrons are much higher:

и

and

That is, the main fission occurs when interacting with thermal neutrons of the reactor, and the production of fissile isotopes should occur when interacting with fast neutrons of this reactor, therefore, an increase in the return path of fast neutrons increases the production of plutonium-239. The reactor contains a drive device that provides a relative movement of the neutron return section of the slowing focusing structure relative to the fissile plates of the fission zone. In this case, the flux of thermal neutrons sequentially moves from the areas where the accumulated plutonium-239 is burned out, to the areas where it is being produced.

A variant is possible when the fissile matter of the fission zone is made in the form of disk plates, the selection plates of the neutron return section of the slowing down focusing structure are made by the sectors of the rings, profiled and oriented into the channels between the plates with fissile matter of the fission zone.

A variant is possible when the fissile matter of the fission zone is made in the form of flat plates, the selection plates of the neutron return section of the moderating focusing structure are made coaxially with the axis of the reactor and are oriented into the channels between the plates with fissile matter of the fission zone.

A variant is possible when the energy pickup device is made in the form of a coolant contour of the dividing zone, which contains a thermosyphon with a heat exchange device located above the dividing zone, the sorption cleaning device of the coolant is placed behind the heat exchange device of the loop. It is possible to use thermoelectric power converters.

Helium, sodium and a wide class of other liquid and gaseous substances can be used as the coolant of the reactor core. It is desirable that in this case the neutron scattering cross section by them is small and the substance is not a moderator, so that the spectrum of neutrons emerging from the active zone is not "gray".

When a reactor operates with relatively thin-walled plates with fissile material and with a protective coating at the operating temperature, diffusion and release of fission products from the material are possible. Their subsequent concentration in the sorbent is expedient in order to reduce their concentration in the core and in the coolant.

In this case, the device itself for the sorption cleaning of the coolant can be placed behind the heat exchange device of the circuit, both outside the reactor core, and in it for transmutation of actinide fission fragments accumulated in the sorbent.

The coolant moves along the surface of the fissile plates. Moreover, if the region of high energy release is thin, and the energy output is carried out along the entire region of energy release, then the maximum energy release in such a device can be extremely high.

So, for example, if: the width of the near-wall flux of the selected neutrons, and hence the thickness of the energy-stressed layer, is h _s ≤ 0.1 mm;

- temperature difference across the coolant ΔT _max = 100 K;

- coefficient of convective heat transfer from the surface α _max = 10000 W / m ² K;

That is, in this case, the maximum energy release and energy output in a thin layer of fissile matter, removed from its surface, can reach the value:

. Что в высоконапряженном ядерном реакторе при узких направленных потоках тепловых нейтронов до 3×10¹⁶ см^-2сек^-1, возможно.

... That in a highly stressed nuclear reactor with narrow directed fluxes of thermal neutrons up to 3 × 10 ¹⁶ cm ^-2 sec ^-1 is possible.

Therefore, an option is possible when the energy collection device is made so that the coolant circuit is made open with an accelerating nozzle, has a container with a coolant, a compressor, channels for removing energy from the selection plates, channels for removing energy from the plates with fissile material of the fission zone and channels for removing energy from the accelerating nozzle ... In this case, the nuclear reactor is the source of energy for the nuclear rocket engine. The coolant can be hydrogen or helium, which makes it possible to increase the specific impulse and specific thrust of the engine.

Use of air is possible.

For this, the retarder is made structured and anisotropic in the form of a package of extended profiled plates with channels between them. For this, the retarding-selective structure is made in the form of a group of curved plates of variable curvature, such that the curved channels formed between them at the edges of the sections with minimum curvature are oriented in the direction of the fuel elements made in the form of flat plates with a coolant flowing between them. In this case, the reactor core is made anisotropic with channels between the plates with fissile material, the decelerating focusing structure contains selection plates oriented into the channels between the plates with fissile material of the core.

The possibility of implementing the method is due to the fact that the behavior of neutrons in the moderator, outside the moderator and at the interface between the media are significantly different.

First of all, let us pay attention to the fact that for the total external reflection of neutrons from the surface, it is necessary that the transverse component of the kinetic energy of a neutron tangentially moving along the surface is less than the average potential energy of neutron repulsion in the medium, which can also be defined as the boundary energy of neutrons in the medium.

.The angle of total external reflection of neutrons is determined by the ratio of the boundary neutron velocity v _gr on the surface of the substance to the velocity v ₀ = 2200 m / s of thermal neutrons of the reactor

...

The following table can be presented for the boundary energy E _g , the boundary wavelength λ _g , and the transverse boundary velocity of neutrons v _g for different substances on the surface of the moderator:

table 2

Substance E _gr , neV λ _gr , nm v _gr , m / s Al 0.54 123 3.22 Cu 1.68 69.8 5.67 C (graphite density 2 g / cm ³ ) 1.73 68.7 5.67 Be 2.43 58 6.81 BeO (2.9 g / cm ³ ) 2.62 55.8 7.08 D ₂ O (1.105 g / cm ³ ) 1.66 70.2 5.63 St. steel 1Х18Н10Т 1.82 67.0 5.90 Glass 0.9 95.3 4.15 Lead 0.87 96.9 4.08

This angle is ϕ _s = 10 'for a graphite surface, ϕ _s = 12' for a beryllium surface, ϕ _s = 10.7 'for an iron surface, ϕ _s = 11.5' for a nickel surface, and ϕ _s = 5.0 'for a surface from aluminum. The angle of total neutron reflection can be increased by lowering the moderator temperature down to 4.2K, or increased to several degrees by applying supermirror coatings to the surface.

Supermirrors are structures of layers with different optical potentials deposited on a substrate. For example, it can be a multilayer system of a wide barrier and thin periodic layers of FeCo-Si.

It is also possible to write down the conditions for neutron reflection through the refractive index of neutrons on the surface of a substance:

; - дебройлевская длина волны нейтрона со скоростью v_n;Where:

; - de Broglie wavelength of a neutron with a velocity v _n ;

N is the concentration of nuclei; b is the length of coherent scattering of matter nuclei; μ is the magnetic moment of the neutron; B is the magnetic induction of the field acting on the neutron inside the ferromagnet; E is the neutron energy.

Possible neutron polarizing supermirrors, for example, from CoFe (V) TiZr, the efficiency of neutron reflection, which depends on the magnitude and direction of the magnetic field superimposed on the mirror.

It is essential that the neutron leaving the surface of the substance receives additional energy equal to E _gr and at the same time receives an additional transverse velocity equal to v _gr deflecting the trajectory from the surface, and the neutron entering the substance loses this energy and speed. Therefore, a flat extended uniform channel does not possess neutron-selective properties. For the same reason, an extended channel, which has a constant curvature of its surface, does not possess such properties, if the value of the boundary energy on the surface is constant.

In order for the slot channel to gain the ability to selectively capture the neutrons moving in it, it must have a variable curvature of this surface that decreases towards its exit. Or, on the other hand, the radius of curvature of this surface or the boundary energy on it must continuously increase in the direction of the exit from the channel.

In this case, in the structure, at each point of the profiled surface of the channel, there is a region of neutron capture at the angles K _sel Δϕ _s (see Fig. 2).

Therefore, such a surface has the ability to capture and remove neutrons in a preferred direction both on the entire plane of the neutron-selective plate and throughout the entire volume of the anisotropic selective moderator structure. In addition, it is important that this entire flux has a small angular spread, and at the output it has a high neutron flux density in the thin wall layer h _{s of} each selection plate.

And in a sharply anisotropic structure of the PFS in the form of a packet of selection plates, each neutron after scattering has a probability of getting into the angular region of neutron capture, any of the selection plates inside the packet of the structure. The result of the movement of neutrons near the surface of the plates, the radius of curvature R of which increases smoothly, is a series of successive reflections: a near-wall neutron, having reflected for the first time from the surface of the plate, experiences a series of subsequent reflections.

It is important that when neutrons are scattered by moderator nuclei, on average, the angle of deflection of neutrons from the initial trajectory is close to the right angle.

Considering the selection of neutrons by a moderating - selection structure with curvilinear selection channels, first of all, let us pay attention to the regularities that determine the reflection of neutrons from the surface of these channels. And if the angle of external surface reflection of neutrons is ϕ _s , and the radius of curvature of the surface is equal to ≈ R, then the length of the chord along which the reflected neutron moves will be L _s ≈ R · sin (ϕ _s ), and the distance between the chord and the channel surface will be h _s ≈ R · (1 - cos (ϕ _s )).

Therefore, the value of ϕ _s mainly affects the number of reflections of neutrons already selected by the structure from the surface of the channels before leaving them.

. Здесь поверхность селектирующей пластины ЗФС задается в координатах (x,y). Где R'_x - производная изменения радиуса кривизны R селектирующей пластины вдоль ее длины, и y'_x - производная профиля селектирующей пластины вдоль ее длины.It can also be shown that the coefficient of the neutron capture efficiency in the course of selection K _sel can be represented as

... Here, the surface of the PFS selection plate is set in coordinates (x, y). Where R ' _x is the derivative of the change in the radius of curvature R of the selection plate along its length, and y' _x is the derivative of the profile of the selection plate along its length.

It is important that the efficiency of neutron capture in the course of selection K _sel does not depend on ϕ _s , but in this case it is essentially determined by the curvature of the selection plates.

, при p = 0.005 м, то радиус кривизны этой параболы может быть представлен, как

, и если пластина имеет длину около L_p = 150 мм, то радиус ее кривизны на краю достигает R = 3 м. И при этом соответственно увеличивается длина траектории нейтронов между отражениями до L_s ≤ 2 см, причем ширина пристеночного потока отселектированных нейтронов h_s ≤ 0.01 мм, остается узкой, что определяет высокую плотность потока нейтронов в нем.For example, if the surface of a plate forming a channel can be described as a parabola

, for p = 0.005 m, then the radius of curvature of this parabola can be represented as

, and if the plate has a length of about L _p = 150 mm, then the radius of its curvature at the edge reaches R = 3 _{m.And at the same time, the length of the neutron trajectory between reflections increases accordingly to L s} ≤ 2 cm, and the width of the near-wall flux of selected neutrons h _s ≤ 0.01 mm, remains narrow, which determines a high neutron flux density in it.

Changes along the channel length and the efficiency of neutron capture in the selection process K _sel , with a selection area of 150 mm, it is greater than K _sel ≥ 10 over a significant part of its length (see Fig. 2), or Δϕ _s ≥ 10 · ϕ _s , which significantly affects the increase in the efficiency of neutron selection by a single plate of the structure.

.In this case, the density of the near-wall neutron flux emerging from a single PFS plate can be estimated as

...

Assuming, for example, that the density of the diffuse flux of thermal neutrons in the structure, for example, is equal to n ₀ = 5 × 10 ¹³ cm ^-2 s ^-1 , and K _sel ≈ 20, we obtain at a flux thickness h _s ≈ 0.01 mm that K _s ≈ 60, and that the density of the near-wall neutron flux emerging from a single channel of the selective structure increased to n _out ≈ 1.2 × 10 ¹⁶ cm ^-2 s ^-1 .

The deceleration of fast neutrons occurs in the depth of the PPS and the flow of neutrons that have returned to the fission zone is thermal. There are no intermediate neutrons in the neutron spectrum of the thermal core.

Formed narrow high-density fluxes of thermal neutrons are directed to the fissile substance, as a result of which the processes of capture of fission, thermal neutrons and neutron scattering take place in it. As a result of fission, nuclear energy is released, and fast neutrons are born. Fast neutrons, having passed through the fissile substance, partially interact with it and go into the moderating-selection structure where they are thermalized on its substance, selected and again directed in the form of a narrow dense flux of thermal neutrons to the fissile substance. The cycle of their life is closed.

The implementation of the method is possible in a nuclear reactor containing a slowing focusing structure, a fission zone, an energy pickup device, characterized by the fact that the fission zone of the reactor does not contain moderators, the slowing focusing structure has spacing gratings, has neutron interception sections, one or more neutron return sections, whose selection plates oriented in the channels between the plates with a spacer grid with fissile material of the fission zone.

The reactor control process can be multichannel:

1) it is, first of all, the management of selection processes in the PFS;

2) control of the ratio of the volumes of the fast zone of the reactor to the volume of the thermal zone of the reactor by reducing the return zone in the PFS package and increasing the depth of introduction of thermal neutrons before the interaction, into the fission zone;

3) the usual absorption of excess, from the point of view of the fission process, neutrons at the absorber in the emergency operation of the reactor; absorption of excess neutrons is also possible in additional focal areas of the device for forming a directed neutron flux;

6) control of the efficiency of heat removal with the temperature dependence of the process;

7) control of the movement of the zone of localization of regions of thermal neutrons in fissile matter.

Brief Description of the Figures of the Drawings

The essence of the invention is illustrated by drawings, where:

in fig. 1. is a schematic view of a deep fuel burnup reactor.

in fig. 2. is a schematic view of a rocket engine reactor.

in fig. 3. - selection of neutrons in a curvilinear selection channel.

in fig. 4. - Dynamics of changes in the criticality of the composition on depleted uranium.

The fission reactor contains an anisotropically structured moderating-selective structure (PFS) for the formation of a directed neutron flux 1, including a moderating substance 2, profiled plates for neutron selection 3, channels of the coolant of the energy collection system 4, a section for intercepting neutrons PFS 5, a section for neutron return MFS 6, reactor core 7, reactor core plates 8, coolant 9, core coolant loop in the form of a thermosyphon 10, heat exchange device 11, device for sorption cleaning of coolant 12, shielding PFS jacket 13, CPS system elements 14, tank with coolant 15, compressor 16 , engine nozzle 17.

Implementation of a group of inventions

The operation of the device is considered on the example of the variant shown in Fig. 1.

Fast neutrons of the reactor are thermalized in an anisotropically structured moderating-focusing structure (PFS) to form a directed neutron flux on moderating substance 2, made in the form of profiled plates for neutron selection 3, forming a diffuse field of thermal neutrons. The braking energy of fast neutrons is removed by the coolant flowing through the channels of the coolant of the PPS energy collection system 4. After deceleration, thermal neutrons are separated at the angles of their propagation on profiled plates for neutron selection 3 and at the same time their fluxes are released, moving in the direction of the minimum curvature of the plate surface. The decelerating focusing structure contains sections for intercepting neutrons PPS 5 located in the end areas of the PPS to reduce neutron losses and sections for neutron return PPS 6 directed to the reactor core 7. Plates with fissile material of the reactor core 8 and profiled plates for neutron selection 3 are made with equal or a multiple step, so that the fluxes of thermal neutrons selected by the PPS were directed into the gaps between the plates with fissile material 8. The coolant 9 of the coolant circuit of the core 10 made in the form of a thermosyphon removes the energy released during fission and then transfers it through the heat exchange device 11 to external energy conversion devices. The coolant circuit of the core 10 contains a device for sorption cleaning of the coolant 12, a compressor (not shown). Shielding PPS shirt 13, also made in the form of PPS, serves to reduce neutron losses by intercepting that part of them that is not captured by the main PPS. The CPS system 14 is used to control the operation of the reactor, the device for moving the zone of localization of the regions of thermal neutrons is not shown in the fissile material.

When the reactor is implemented as a power supply device for a nuclear reactor, the coolant circuit contains a tank with a coolant 15, behind it is a compressor 16, at the outlet there is an engine nozzle 17 that converts the energy of the coolant heated in the reactor's division zone into a flow rate.

, где σ_s и σ_a - сечения рассеяния и поглощения нейтронов; N_s - число последовательных перерассеяний теплового нейтрона на ядрах вещества до поглощения; ω - угол расходимости селектированного потока вдоль плоскости селекции. Для графита:

В пределе тепловой нейтрон может быть отселектирован в выделенном направлении и пройти через фокусную ее область за время жизни до 1.3⋅10³/300 ≈ 4 раз (технологическое альбедо 4).To slow down and select thermal neutrons with the entire volume of the structure, it is necessary that:

, where σ _s and σ _a are neutron scattering and absorption cross sections; N _s is the number of successive rescattering of a thermal neutron on the nuclei of matter before absorption; ω is the angle of divergence of the selected flow along the selection plane. For graphite:

In the limit of thermal neutron can be been accumulated in the preferred direction and pass through the focal region of its lifetime before 1.3⋅10 ^3/300 ≈ 4 times (4 technological albedo).

Length of selection of neutrons in the structure:

.The distance between the plates at which the entire fast flow entering the end is thermalized and returned as thermal:

...

In the basic version, the FSL can be performed in the form:

- structures in the form of a package of retarding-selective elements made of graphite with a helium-4 coolant in the channels between them and containing a coolant from heavy water in the outer annular cavity,

- a variant including the implementation of deuterated PTFE-40 - (CF ₂ -CF ₂ -CD ₂ -CD ₂ ) n (radiation resistance of the material up to 10 ⁸ rad) with a helium-4 coolant in the channels between them.

In this case, the length of deceleration of fast reactor 1 MeV neutrons by the structure is (depending on the substance from which it is made) from 8 cm to 16 cm.

We accept, as in the experiment, the profile of the plates of the selective elements in the form of a part of ellipses, the axes of which are: a = 300 mm, b = 30 mm, and the maximum selection efficiency K _sel = 15, lies in the section of length from 10 to 200 mm.

.The diffusion length of thermal neutrons in the PPS substance is ≈ 68 cm, but it is essential that, is the number of successive rescattering of thermal neutrons on the nuclei of the substance before being captured by the selective structure and extracted, is small:

...

. Принимаем длину (ширину) селектирующих пластин - L_plast = 200 мм, тогда, толщина селектированного пристеночного потока, h_s ≈13 мк, а его фазовая плотность -

,And as a result, the selection length (the size of the PPS region) in which neutrons are captured by the structure -

... We accept the length (width) of the selection plates - L _plast = 200 mm, then, the thickness of the selected wall flow, h _s ≈ 13 microns, and its phase density -

,

.with flow in the reactor

...

.With efficient operation, the fast heat fluxes of neutrons entering and exiting the PPS are preserved, but for this, the step between the selection plates in the axial region must be:

...

When operating on enriched uranium, the PFS reactor core can be small in size and power, but only 1 in 2.5 neutrons is useful.

Of particular interest is the operation of the reactor using cheap depleted uranium.

The basis is that the equilibrium concentration of ²³⁹ Pu under long-term irradiation of ²³⁸ U by thermal neutrons, to which the process with _Pu239 = 0.27% tends, and the criticality tends to η _t = 1.058.

- для сборки из UO₂.At the same time, an assembly of flat fuel rods placed in the axial region of the PFS should have a diameter comparable, at least with the doubled diffusion length of thermal neutrons in the material of the assembly, for example,

- for assembly from UO ₂ .

In this case, making the reactor core anisotropic with channels between the plates with fissile material, when the decelerating focusing structure contains selection plates oriented into the channels between the plates with fissile material of the core, it makes it possible to increase the characteristic dimensions of the core.

Thus, in this case, the return run of fast neutrons from the depth of the reactor core increases, and the effective ratio of the dimensions of the fast reactor zone to the thermal zone increases. At the same time, plutonium is being produced, the characteristic dimensions of the core, the total mass of fissile material in the reactor and the service life of the reactor grow.

Claims (5)

1. A method of controlled fission of nuclei, in which fast neutrons are slowed down and a field of thermal neutrons is formed, selection and return of thermal neutrons to the fission zone is carried out, characterized in that the fission zone of the reactor is performed without a moderator, the fissile substance is introduced with a concentration of ²³⁵ U comparable or less concentration in natural uranium, deeply introduce the flux of thermal neutrons through the channels in the fissile substance before interaction, increasing the return path of fast neutrons in it, move the flux relative to the fissile substance of the fission zone of the reactor. 2. A nuclear reactor containing a slowing focusing structure, a fission zone, an energy pickup device, characterized in that the fission zone of the reactor does not contain moderators, the slowing focusing structure has spacer grids, has sections for neutron interception, one or more sections for neutron return, whose selection plates are oriented into the channels between the plates with the spacer grid with the fissile material of the fission zone. 3. Nuclear reactor according to claim 2, characterized in that it comprises a drive device that provides relative movement of the neutron return section of the slowing focusing structure relative to the fissile plates of the fission zone. 4. Nuclear reactor according to claim 2, characterized in that the energy pickup device is made in the form of a coolant contour of the fission zone, which contains a thermosyphon with a heat exchange device located above the fission zone, the device for sorption cleaning of the coolant is located behind the heat exchange device of the loop. 5. The nuclear reactor according to claim 2, characterized in that the coolant circuit is made open with an accelerating nozzle, has a container with a coolant, a compressor, channels for removing energy from the selection plates, channels for removing energy from the plates with fissile material of the fission zone and channels for removing energy from accelerating nozzle.

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