WO2010151178A2

WO2010151178A2 - Nuclear reactor control method

Info

Publication number: WO2010151178A2
Application number: PCT/RU2010/000357
Authority: WO
Inventors: Ларион Александрович ЛЕБЕДЕВ; Валерий Иванович РАЧКОВ; Леонид Ирбекович УРУЦКОЕВ; Дмитрий Витальевич ФИЛИППОВ
Original assignee: Lebedev Larion Aleksandrovich; Rachkov Valeriy Ivanovich; Urutskoev Leonid Urbekovich; Filippov Dmitriy Vitalevich
Priority date: 2009-06-25
Filing date: 2010-06-24
Publication date: 2010-12-29
Also published as: WO2010151178A3; RU2009124202A; RU2419896C2

Abstract

The method can be used for creating safe thermal neutron and fast neutron reactors. The reactor is controlled by altering the amount of delayed neutrons through the application of a superstrong magnetic field to the core region of the reactor, which has a negative initial reactivity coefficient, thereby leading to an increase in the probability of β decay in the delayed neutron emitters.

Description

METHOD FOR NUCLEAR REACTOR MANAGEMENT

The invention relates to the field of nuclear physics, in particular to the physics of the processes of energy production in nuclear fission reactors. The problem that is solved by the invention is to improve the environmental friendliness, energy efficiency of the fuel cycle, safety and controllability of the process of nuclear fission using neutrons. It can find application in the field of nuclear reactor engineering to create reactors operating both on thermal and fast neutrons.

Great attention is paid to the issues of creating economical, environmentally friendly and safe nuclear reactors all over the world. A large number of new designs and variants of nuclear reactors and various reactor control methods are developed annually.

As a rule, the proposed developments are variants of known types of reactors: slow, intermediate or fast neutrons. For example, in a nuclear reactor (see RF patent N2 2075116), the selection and directional return of thermal neutrons to the region of thermal neutrons of the fission zone are carried out. The fuel composition is circulated in two circuits, one of the circuits passing through the region of thermal neutrons and the cooling zone, and the other through the region of fast neutrons and the cooling zone, and the substance of their fuel compositions is interchanged.

Another known method (see RF patent N ° 2167456) is to collect the nuclear mass of the core to subcritical state and its preparation for supercriticality, which is carried out by increasing the role of leakage neutrons in their overall balance, creating voids in the core and optimizing the increment of the effective neutron multiplication coefficient (k _e ψ) as a function of the ratio of the volume occupied by voids to the entire active volume zones.

Also known is a method of generating energy from nuclear fuel (see RF patent N ° 2178209) contained in the chamber, using the process of reproduction of a fissile element from a reproducing element and fuel through a β-predecessor of said fissile element and division of the fissile element. A stream of high-energy particles is directed into the chamber for interaction with the heavy nuclei contained in the chamber for producing high-energy neutrons, the neutrons thus obtained are propagated under subcritical conditions by the process of reproduction and division, wherein said process of reproduction and division is carried out inside the chamber.

The technical result of the invention consists in increasing the fraction of delayed neutrons, as well as simplifying the regulation of the reactor and increasing its safety.

The occurrence of delayed neutrons during fission of uranium nuclei is the determining physical effect that made it possible to create a nuclear reactor, and underlies the regulation of the operation of reactors of all types. Especially significant is the effect of delayed neutrons on the behavior of a reactor with circulating fuel [1]. At present, when describing the kinetics of the reactor, it is considered that the fraction of delayed neutrons of each individual emitter core does not depend on external conditions, and only a change in the average fraction of delayed neutrons that occurs during the reactor campaign due to a change in the chemical composition of the core [2-4].

An object of the present invention is to provide a method for controlling a nuclear reactor based on a change in the fraction of delayed neutrons.

The power released in the reactor is proportional to the neutron density n. It is well known [1–4] that for a qualitative description of the effect of delayed neutrons on the dynamics of the reactor, kinetic equations can be used within the framework of a homogeneous homogeneous isotropic model. For a qualitative analysis of the behavior of the reactor when the β decay constants λ change, we will use the widespread approximation of one effective group of delayed neutrons. We define the following variables: n is the density of all neutrons in the reactor core;

Y is the density of all nuclei of emitting delayed neutrons in the core, including those emitters whose decay did not lead to the formation of a neutron (this value is significantly different from that of the density of emitting nuclei that is used in classical kinetics equations, where only nuclei tested decay with the birth of a neutron); χ is the multiplication factor for instant neutrons - the ratio of the rate of creation of instant neutrons to the absorption rate of all neutrons (the ratio of the number of instant neutrons produced per unit time in a unit volume to the number of all absorbed neutrons in the same volume at the same time); R is the ratio of the number of generated nuclei-emitters of delayed neutrons to the number of generated instantaneous neutrons;

G is the effective lifetime of the generation of instant neutrons such that nT ^x is, by definition, the rate of production of instant neutrons (the number of instant neutrons produced per unit time in a unit volume);

X _n is the decay constant of delayed neutron emitting nuclei along the β-decay channel with neutron production, that is, X _n Y is, by definition, the rate of creation of delayed neutrons

(the number of delayed neutrons produced per unit time in a unit volume); λ is the total decay constant of delayed-neutron emitting nuclei over all channels in which the emitting nucleus decays into a nucleus that is not a delayed-neutron emitter (β-decays that led to the birth of a new delayed-neutron emitting nucleus are not taken into account - it is believed that the nucleus remains in the composition of nuclei described by density Y).

In the indicated notation, the equations of balance of neutrons and nuclei emitting delayed neutrons will be as follows:

dt T χ T '

^ = R ^ -XY dt T

On the right side of the first equation, the first term describes the production of instant neutrons, the second describes the absorption of neutrons, and the third describes the creation of delayed neutrons. On the right side of the second equation, the first term describes the birth, and the second, the disappearance of delayed neutron emitting nuclei. In known reactors, regulation is carried out by means of control rods, and the reactor itself is carried out with a reactivity margin [5]. In the claimed technical solution, the regulation of the reactor is carried out without the use of control rods, therefore, it is necessary that the initial reactivity of the reactor is guaranteed to be negative.

The essence of the proposed method lies in the fact that an external action is applied to the reactor core with a given negative reactivity that weakly affects the process of forced fission and absorption of neutrons, but increases the probability of β decays (for example, ionization [6, 7] or an ultrahigh magnetic field [ 8]). In this case, in equations (1) only the coefficients λ _p and λ will change, and the rest will remain unchanged. It is well known that β-decays of delayed-neutron emitting nuclei leading to neutron production (occurring at excited levels of intermediate nuclei) have significantly lower decay energies than β-decays without neutron production [6, 9]. Therefore, the relative change in X _n (during ionization or when an external superstrong magnetic field is applied to an atom) is much larger than the relative change in λ [6–8, 10, 11]. Under the considered effect on the active zone, the β-decay probabilities change: λ = λ _o + Δλ, λ _i = λ _i0 + Δλ _l .

Then

Δλ _w Δλ T ^ ^> 1Г - ⁽²⁾ We define η - the fraction of delayed neutrons as follows:

then the considered change in the probabilities of β decay leads to an increase in the fraction of delayed neutrons η = η _o + Δη (η ₀ is the unperturbed fraction of delayed neutrons):

Reactor Reactivity χ - i

P = - + Lo. (5)

1 From system (1) we obtain in the new notation

dt T - ^d L - R- ^p χγ ⁽⁶⁾ dt T

Consider the behavior of a reactor which, in an unperturbed state, operates in a stationary mode, that is, p = 0. Let the changes Δλ and Δλ _n occur instantly (in time "T).

Consider the behavior of a reactor with new time-independent λ = λ ₀ + Δλ and X _n - X _n Q + Δλ _n . From (6) we obtain the equation:

which describes the behavior of the reactor when deviating from the equilibrium state. If equilibrium was achieved with some effect on the core (with perturbed values of λ and η), then a deviation from this equilibrium will occur when the effect is turned off (removal of the perturbation). Thus, in the general case in (7) we can consider both positive Δλ and Δη (when the exposure is turned on) and negative (when turned off).

It is easy to find the eigenvalues of the resulting equation by analyzing the eigenvalues of the increment k from the corresponding characteristic equation:

In the approximation λT «β ₀ we get:

moreover, this solution (9) is applicable for small Δη «η and large Δη> η perturbations.

When the effect in question is turned on (Δη> 0), the neutron density n will increase with an increment of k ₊ (9), and when the exposure is subsequently turned off, the growth of n will stop. Since the power released in the reactor is proportional to the neutron density p [1 → 4], thus, acting on the reactor core using external superstrong magnetic fields or ionization, its power can be changed. In the proposed method, the reactor is controlled without a complex control system for the control rods. Thus, a technical result is achieved - simplification of reactor control.

Compare this method of regulation with the classic. To go over to the classical kinetics equations, we define the value C used in the textbooks [1–4] - the density of nuclei — f of the delayed-neutron emitters that have experienced decay through the channel with the production of the neutron ^{R λ} '(10) β = ηo-

In the classical statement of the problem, X _n , X, and β are constants, only in this case, substitution (10) in (6) leads to the well-known equations [1 ^ 4]

^ L- ^P zI _{n +} Xc dt T

Thus, the system of equations (6) is more general than (11), since the latter is valid only for constants X _n , X, and β. For constant reactivity p from (11) we obtain:

Known [1-4] are the own solutions of the obtained equation: for example, “β and λГ β β λ β

apir ~ β »λГ λр р-β к, = - - к = ^L - - (\ £ \

⁺ β-p '^" T ^{• {}}

Equation (12) is similar to equation (7) and coincides in the first order for small perturbations Δη «η ₀ if we put p = Δη.

However, with large perturbations Δη ~ η _0, these equations qualitatively differ. We pay attention to the fact that equations (7) and (12) are applicable for Δη> η ₀ and p> β, respectively, and in a superstrong magnetic field, the fraction of magnetic fields can increase by several times [8]. It is well known that if in the classical case (12) the reactivity becomes larger than the fraction of delayed neutrons p> β, then the signs of the roots of k ₊ (14) are reversed and the large increment of

that is, the reactor begins to "accelerate" on instant neutrons and, thus, becomes uncontrollable. In the case under consideration (7), always λ> 0 and the sign of the root k_ ∞ T ^~] (8) can never change (9). Therefore, with the proposed new control method, the reactor will never be accelerated by instant neutrons (with a large increment of os 7 " ¹ ), but always its power will increase with an increment proportional to λ, that is, inversely proportional to the lifetime of the emitting nuclei of delayed neutrons. the technical result is achieved - increasing the safety of the reactor due to the fundamental impossibility of accelerating the reactor using instant neutrons.

As an example, we propose a method for regulating a circulating fuel reactor. Nuclear fuel circulates in a closed loop of a sufficiently large length of constant cross section. The Pe actor is performed with a small constant constant negative reactivity over the entire length (negative reactivity margin) p = - P ₀ <0 (ρ ₀ “β ₀ ). At the entrance to the reactor core, an external effect is imposed (for example, ionization or superstrong magnetic field), which leads to an increase in the probability of β-decay of delayed neutron emitting nuclei and the fraction of delayed neutrons in accordance with formula (4).

In the proposed variant of the reactor control method, the regulation can be carried out, for example, by changing the speed of the fuel, with a constant intensity of exposure. The reactor works if the speed of the fuel lies in the interval between two critical velocities, the values of which are determined by the intensity and type of impact on the core. When the fuel speed is less than the first critical and more than the second critical, the reactor power decreases. The presence of a second critical speed gives an additional guarantee of the safety of this method of regulation.

Thus, changing through external influences

(for example, using an ultrahigh magnetic field or ionization) the fraction of delayed neutrons, you can adjust the power of the reactor. The reactor is created initially subcritical, and turns on and works when externally acting on the core.

Such a method will be much safer than the traditional one, since even with large disturbances the reactor will not accelerate at instant neutrons and will not lose its “correctability”.

The invention is illustrated by a specific embodiment with reference to the drawings, in which:

FIG. 1 - depicts a generalized diagram of a nuclear reactor.

FIG. 2 - depicts a generalized diagram of a nuclear reactor with a circulation of fuel.

The following describes specific embodiments of the claimed invention.

A nuclear reactor contains a fuel core 1 having an initial negative reactivity margin; system 2 for the selection of heat from the core 1 by means of a coolant; a system 3 for converting thermal energy of a heat carrier, for example, into electrical energy; control system 4 and exposure system 5, capable of creating ionization or superstrong magnetic fields in the whole or part of the volume of the reactor core (for example, with using femtosecond lasers [12]). The initial stock of negative reactivity can be obtained, for example, due to the structural design of the reactor or the composition of nuclear fuel. The process of regulation of the reactor consists, as noted earlier, in switching on and off the action in the reactor core 1, leading to a change in the fraction of delayed neutrons.

A nuclear reactor may also include a fuel circulation system 6 through the core 1 and a circulation speed change system 7 associated with the control system 4.

In this case, the process of regulating the reactor consists in simultaneously acting at the fuel inlet to the reactor core 1 and changing the speed of fuel circulation through the core 1.

Figure 1 shows by shading that the effect is on the entire active zone, and in figure 2 - at the inlet of the circulating fuel into the active zone.

Bibliography

1. Megreblian R., Holmes D. Theory of Reactors. - M .: GosAtom Izdat, 1962.

2. Schultz. M. Regulation of nuclear power reactors. - M .: IL, 1957.

3. Dollezhal H. A., Emelyanov I. Ya. Channel nuclear power reactor. - M .: Atomizdat, 1980.

4. Galanin A. D. Theory of nuclear reactors with thermal neutrons. - M .: Atomizdat, 1957. 5. Shirokov Yu. M., Yudin H. P. Nuclear Physics, - M .: Nauka,

1972, p. 513.

6. Rukhadze A. A., Urutskoev L. I., Filippov D. V. Taking into account the influence of β-decay into bound states in ionized atoms on the fraction of delayed neutrons. - Nuclear Physics, 2006, vol. 69, N ° 5, p. 820-823.

7. Gangrsky Yu. P., Karpeshin F. F., Trzhaskovskaya M. B., Penionzhkevich Yu. E. Effect of β-electron capture in a bound state on the emission of delayed neutrons. - Nuclear Physics, 2008, v. 71, jY2b, p. 979-9837 8. Rukhadze A. A., Urutskoev L. I., Filippov D. V. Increase in the fraction of delayed neutrons from emitting nuclei in a superstrong magnetic field. - Applied Physics, 2006, N ° 5, p. 8 - 10.

9. Gangra Yu. P., Dalhsuren B., Markov B. H. Fragments of nuclear fission. - M .: Energoatomizdat, 1986. 10. Filippov D.V. Increase in the probability of allowed electronic β-decays in a superstrong magnetic field. - Nuclear Physics, 2007, v. 70, W, p. 280-287. 11. Filippov D. V. Increasing the probability of forbidden electron β-decays in a superstrong magnetic field. - Nuclear Physics, 2007, v. 70, JVe 12, p. 2068-2076.

12. Wagper U., Tatarakis M., Goral A., et al. LABORATORU MEASUREMEPTS OF 0.7 GG MAGPETIS FIELDS HEPERATED DURIPG HIGH-IPTESITU LASER IPERTASTIOPS WITH DEPSE RESULTS // Рhus. Rev. E 70, 026401 (2004).

Claims

CLAIM

1. A method of controlling a nuclear reactor, characterized in that the initial negative reactivity p of the reactor is set, and the reactor is controlled by changing the fraction of delayed neutrons by applying external influence to the reactor core, which increases the probability of β decays in the delay emitting neutron nuclei .

2. The method according to p. 1, characterized in that as an external effect on the reactor core, an ultra-strong magnetic field is used.

3. The method according to p. 1, characterized in that ionization is used as an external influence on the reactor core.

4. The method according to p. 1-3, characterized in that the circulation of nuclear fuel through the active zone of the reactor, and the regulation of the reactor is carried out by changing the speed of movement of nuclear fuel.