RU2673564C1 - Method for starting nuclear reactor for space application - Google Patents

Abstract

FIELD: nuclear physics and equipment.SUBSTANCE: invention relates to nuclear energy and can be used in the operation of nuclear reactors of space installations. Method of launching a nuclear space reactor includes the steps of determining the dependence of the effective multiplication factor on temperature with the derived absorbing elements Keff(T), dependence of the reactivity of absorbing elements on their position ρ=α(x-x), the value of the maximum play of the drive of the absorbing elements, and starting the reactor by withdrawing the absorbing elements, setting the period τprior to start-up of reactor acceleration and reactivity ρ, measuring the temperature of the reactor before starting Twith sensors and determining ρ– reactivity of the reactor at temperature T, calculating the output value of the absorbing elements xaccording to relation ρ-ρ=ƒ(x), and carrying out the output of the absorbing elements with a maximum speed to position x, then absorbing elements are introduced at the same speed by the amount of maximum play.EFFECT: ensuring the reduction of the starting time, guaranteed compliance with the limitations on the acceleration rate, elimination of parasitic power surge and the associated overheating and heat pumps.1 cl, 3 dwg

Description

Technical field

The present invention relates to space technology and nuclear energy and can be used in the development and operation of nuclear reactors in space power and propulsion systems.

State of the art

The launch of nuclear reactors as part of a spacecraft (SC) occurs, as a rule, in a fully automatic mode. Before the nuclear power plant reaches the nominal level of electric power, all power supply to the spacecraft is provided by a battery charged on Earth, whose capacity is limited. Therefore, the task of reducing the launch time is relevant for a nuclear power plant for space use with any type of conversion of fission energy into electricity - thermoelectric, thermionic or machine.

This task is all the more relevant for facilities that are brought to power in high orbit, the achievement of which requires a longer time, and due to the low temperature of the environment (outer space), the coolant can freeze.

In accordance with paragraph d) of the UN General Assembly Resolution A / RES / 47/69 of February 23, 1993 https://documents-dds-ny.un.org/doc/UNDOC/GEN/N93/104/20/IMG /N9310420.pdf?OpenElement [1] nuclear reactors of space power plants are not brought to a critical level until they reach operational orbit; up to this point, in accordance with paragraph e) of the same Resolution, the design of the reactor ensures subcriticality until it is put into operational orbit during all possible events, including a rocket explosion, return to the atmosphere, fall into water, etc. Thus, at the start of the start-up, the reactor should be in a deeply subcritical state.

A nuclear power plant (NPP) with thermoelectric or thermionic energy conversion, described in the Fundamentals of Automatic Control of Nuclear Space Power Plants, is suitable for placement onboard a spacecraft. M .: Engineering, 1974. [2]. A nuclear power plant consists of a reactor, a cooling circuit, an energy conversion system, and technological equipment. The reactor itself includes a system of fuel assemblies cooled by a coolant circulating along the cooling circuit, and a system of elements that regulate the propagating properties of the reactor. For those described in the Fundamentals of automatic control of nuclear space power plants. M .: Mashinostroenie, 1974. [2] The reactor system of regulatory elements is a set of rotary drums with neutron-absorbing overlays located in a radial reflector. The rotary drums are driven by one or more drives, each of which consists of an engine and a kinematic motion transmission system having a certain play.

To prevent freezing of the coolant in the process of putting the spacecraft into orbit, the nuclear power plant is heated to launch the carrier from the spacecraft to a specific installation design and spacecraft of temperature T _0max . In the process of putting into orbit, the installation and the reactor cool down, the extremely small value is the temperature close to the freezing temperature of the coolant T _0min . Since the effective Kef multiplication factor of any reactor depends on temperature, and this dependence for each specific reactor is studied during the design and safety study (Requirements for the content of the safety study report for nuclear power plants with a WWER reactor. Guidance document NP-006-98 [3]) , then the possible range of Kef values is also known.

The launch of the reactor includes the following stages:

the physical start-up phase is the conclusion of the reactor from a subcritical state to a supercritical one, during which an increase in neutron power occurs until a predetermined minimum controlled level (MCU) is reached,

software increase of neutron power under the control of the neutron power regulator according to the temporal law determined by the design of the installation as a whole and the method of converting fission energy into electricity up to 100-130% of the nominal neutron power;

the stage of stabilization of neutron power until stable generation of electricity;

transition to a mode of generation of constant electric power.

During the first (physical) start-up phase, the reactor power increases by 12-16 orders of magnitude. Placing a powerful neutron launching source on board a spacecraft to control neutron power in a deep subcritic is technically difficult to implement (unlike ground-based reactors), in addition, the presence of an onboard source significantly complicates spacecraft pre-launch operations at the technical and starting positions of the test site. Thus, the acceleration of the reactor to a supercritical state during the physical start-up phase occurs in the absence of power control. The flow rate of the coolant at the physical start-up phase is zero, because, due to the smallness of the cooling capacity of the reactor is not required; coolant circulation is switched on after reaching a certain power.

раз - ограничен снизу) величиной, регламентируемой требованиями ядерной безопасности.The relatively small value of the minimally controlled power level (not more than 0.5% - 3% of the nominal) allows under normal conditions to increase power at a speed limited only by the requirement to prevent acceleration by instantaneous neutrons. In the conditions of ground-based bench tests, the rate of power increase is limited from above (or, which is the same, the acceleration period is the time of power increase in

times - is limited from below) by the quantity regulated by the requirements of nuclear safety.

Closest to the claimed technical solution is a method of carrying out the physical launch phase described in the Fundamentals of automatic control of nuclear space power plants. M .: Mashinostroenie, 1974. [2], which consists in continuous unidirectional piecewise linear extraction of the absorbing elements of the reactor (rods or absorbing pads of rotary drums) at different speeds without pauses and stops.

Preliminarily, in the process of designing and substantiating the safety of the construction and operation of a nuclear power plant, a determination is made of the dependence of the multiplication factors on temperature, the efficiency of the group of absorbing elements on their position, as well as the backlash of the kinematic system - the drive of the regulatory bodies.

Initially, the extraction is performed at the speed most technically possible for the given control system to a position that guarantees subcriticality over the entire range of possible temperature values of the elements of the reactor core at the time of start-up (this takes about 1 minute). After that, the speed decreases by about 10-12 times to prevent instant criticality in the absence of power control. Extraction at a low speed continuously continues, respectively, the effective multiplication coefficient K _{eff is} constantly increasing. The neutron power continues to grow with a constantly decreasing period to the Minimally Controlled Level (MCU) N _MCU (1-5% of the nominal, according to calculations and experimental data, the duration of this procedure is about 15 minutes), after which the neutron power regulator automatically turns on, the power setting of which increases programmatically with a predetermined fixed speed from scratch at the initial moment. The initial power level N ₀ is determined by spontaneous fission, cosmic radiation (Space technology and technology No. 1 (4). Pp. 15-21, 2014 [4]) or an integrated starting neutron source.

The disadvantages of this method are:

1. The need to choose the smallest possible position of the absorbing elements at which their output speed should change - based on the maximum possible effective multiplication factor at the time of launch, which leads to a waste of time to reach the critical state at the actual (at the time of launch) temperature of the reactor .

2. The inevitable occurrence of a parasitic power run-out up to 30% -100% of the nominal power due to drive backlash: when the minimum controlled power level is reached, possible drive backlashes are selected for output, compensation of power and task imbalance occurs with a delay, which generates a power run-off ↑ The proposed methods of dealing with this undesirable phenomenon, such as reducing the minimum extraction speed of absorbing elements, reducing the drive backlash, reducing the minimum controlled power level by several times, increase the start-up time, complicate the measurement path and possibly reduce the drive resource of the reactor control system.

3. Since the initial reactor power at the time of start-up is known to within several orders of magnitude, and the acceleration rate with this method is higher, the lower the initial power, acceleration of the reactor can occur much faster than the regulated values, which is undesirable from the point of view of nuclear safety requirements.

4. Zero initial value of the power task when the neutron power controller is turned on in this method is necessary for guaranteed suppression of acceleration. However, in the process of programmatically increasing the task and the controller’s operation, the neutron power cannot follow the task precisely enough because of the inevitable oscillations 5. The initial speed of increasing the power task is in no way connected with the true acceleration rate of the reactor. To optimize the time course of the power, it is necessary to relate the acceleration rate of the reactor and the reference speed at the moment the power regulator is turned on, that is, the achievement of the minimum controlled power level.

Disclosure of invention

The technical problem to which the claimed invention is directed is the reduction of the total start-up time due to a significant reduction in the time of the physical start-up phase and the exclusion of stray power overruns.

The technical result of the claimed invention is to reduce the start-up time, guaranteed compliance with the acceleration speed limits, the exclusion of spurious power surges and the associated overheating and thermal shock.

In our invention, we consider the physical stage of start-up — the reactor is brought out of a subcritical state into a supercritical one, during which an increase in neutron power occurs until a predetermined minimum controlled level (MCU) is reached.

To achieve a technical result, a method for launching a space nuclear reactor is proposed, which consists in preliminarily determining the dependence of the effective multiplication coefficient on temperature with extracted absorbing elements Kef (T), the dependence of the reactivity of the absorbing elements on their position

значение максимального люфта привода поглощающих элементов, и осуществляют пуск реактора путем его вывода на минимально контролируемый уровень мощности N_МКУ за счет вывода поглощающих элементов с последующим автоматическим включением регулятора нейтронной мощности с программным увеличением задания мощности, при этом дополнительно до начала пуска задают период τ₀ разгона реактора и реактивность ρ₀, измеряют температуру реактора в момент, предшествующий пуску Т₀₀, определяют истинную реактивность реактора ρ₀₀ при фактической температуре Т₀₀, вычисляют величину вывода поглощающих элементов х₃ по зависимости

the value of the maximum backlash of the drive of the absorbing elements, and the reactor is started by bringing it to a minimally controlled power level N _MCU due to the output of the absorbing elements, followed by the automatic switching on of the neutron power controller with a programmed increase in the power set, in addition to the start of the start, set the acceleration period τ ₀ reactor and reactivity ρ ₀ , measure the temperature of the reactor at the time preceding the start of T ₀₀ , determine the true reactivity of the reactor ρ ₀₀ at the actual temperature atura T ₀₀ , calculate the output value of the absorbing elements x ₃ according to

and the output of the absorbing elements is carried out with a maximum speed v1 to the calculated position x ₃ , after which the absorbing elements are introduced at the same speed by the maximum backlash and fixed in this position.

Besides:

- measure the temperature of the reactor at the time preceding the start of T ₀₀ , with sensors of in-reactor control or by measuring the temperature of the coolant.

The above set of essential features leads to the fact that the unproductive time spent on reaching the power level is significantly reduced, while causing a noticeable heating of the structure, with the simultaneous elimination of the possibility of undesirable power surges, this reduces the value of thermal jets, thereby increasing the resource and lowering the limits of energy reserves by board a nuclear installation.

Brief Description of the Drawings

The invention is illustrated by drawings.

In FIG. 1 shows a diagram of calculating the start parameters for the known and proposed start methods, which shows the dependence of reactivity ρ _{p the} reactor 1 with extracted absorbing elements on the temperature T of the reactor core elements, the dependence of the reactivity ρ _x reactor 2 on the position of the absorbing elements x, steady-state period τ curve 3 from the (constant) reactivity ρ, where

ρ _p reactivity of the reactor with removed absorbing elements

ρ _x reactivity of absorbing elements

T _0min ; T ₀₀ ; T _0max ; minimum possible, true and maximum possible temperature of the elements of the reactor core

τ - steady period

τ ₀ - set steady period

ρ _0max ; ρ ₀₀ - maximum and true reactivity of the reactor with the removed absorbing elements

ρ ₀ - reactor reactivity corresponding to a given period τ ₀

x is the position of the absorbing elements

x _{cr min} ; x _{cr 00} - the minimum possible and true at the time of launch critical (Keff = 1) position of the absorbing elements

x ₃ ; x _max - calculated in the proposed method and the maximum derived position of the absorbing elements

In FIG. 2 shows the dependence of the position of the drive of the absorbing elements on time — curve 3, the dependence of the position of the absorbing elements on time — curve 4, the backlash of the drive of the absorbing elements — 5, and also the dependence on time:

reactivity - curve 1, reactor power - curve 6, power settings for the power controller - curve 7

with the launch method adopted, also used for testing the known space reactors of the Buk and Topaz installations (The role of nuclear power and nuclear propulsion in the peaceful exploration of space. International Atomic Energy Agency, Vienna, 2005 ISBN 92-0-107404- 2 [5]), where

t ₀ - start start time

t ₁ - the time at which there is a decrease in the rate of extraction of absorbing elements

t _cr - time to reach the critical state of the reactor (Keff = 1)

t _mku - time to reach the minimum controlled power level

x ₁ - the set value of the position of the absorbing elements, at which there is a change in the speed of extraction; x ₁ <x _{cr min}

x _{cr min} ; x _{cr 00} - the minimum possible and true at the time of launch critical position of the absorbing elements

x ₂ - the position of the absorbing elements, in which there is a transition to a programmed increase in power under the control of a power regulator

ρ ₁ - reactivity corresponding to the position of the absorbing elements x ₁ at the actual temperature of the reactor at the time of start-up

N ₀ - initial power level

N _MKU - minimum controlled power level

N ↑ - power surge at the moment of reaching the minimum controlled level

In FIG. 3 shows the dependence of the position of the drive of the absorbing elements on time - curve 3, the dependence of the position of the absorbing elements on time - curve 4, the backlash of the drive of the absorbing elements - 5, as well as the dependence on time:

reactivity - curve 1, reactor power - curve 6, power settings for the power controller - curve 7 for the proposed method, where

t ₀ - start start time

t _kp is the time to reach the critical state of the reactor (Keff = 1)

t _mku - time to reach the minimum controlled power level

x _{cr 00} - critical position of the absorbing elements at the actual temperature of the reactor at the time of start-up

x ₃ - the calculated position of the absorbing elements corresponding to the necessary reactivity, taking into account the actual value of the effective multiplication coefficient, calculated from the temperature measured at the time of launch and the regulatory value of the period

ρ ₀ - reactivity corresponding to the regulatory value of the period

N ₀ - initial power level

N _MKU - minimum controlled power level

The implementation and examples of implementation of the invention

. В известном способе пуска время t_кр-1₁ определяется минимально возможным на момент пуска критическим положением х_{кр min} поглощающих элементов (см. Фиг. 1, 2), поскольку х₁<х_{кр min} (разница x_{кр min}-х₁ идет в запас расчетов), то, следовательно, t₁ минимально, а время достижения критического состояния, с чего, собственно, начинается разгон реактора, является максимальным. Малая скорость вывода поглощающих элементов ν₂, использованная в традиционном методе пуска, диктуется соображениями безопасности и результатами предварительных расчетов.For the Buk and Topaz space systems, reducing the launch time was not particularly relevant (The role of nuclear power and nuclear propulsion in the peaceful exploration of space. International Atomic Energy Agency, Vienna, 2005 ISBN 92-0-107404-2 [ 5]) this can be seen in FIG. 1 which shows the time course of the position of the absorbing elements, reactivity and power of the reactor in the starting method used in these plants. The time to reach power is directly proportional to the difference t _cr -t ₁ and inversely proportional

. In the known start-up method, the time t _kr -1 ₁ is determined by the critical position x _{kr min of the} absorbing elements that is the minimum possible at the time of start-up (see Fig. 1, 2), since x ₁ <x _{kr min} (the difference x _{kr min} -x ₁ goes to stock of calculations), then, therefore, t _{1 is} minimal, and the time to reach a critical state, with which, in fact, the acceleration of the reactor begins, is maximum. The low output rate of absorbing elements ν ₂ used in the traditional start-up method is dictated by safety considerations and the results of preliminary calculations.

In the absence of strict restrictions on the start time, a conservative choice of the values of x ₁ and ν _{2, the} described method was considered acceptable. However, it is necessary to pay attention to its main disadvantages:

• Long start-up time (15-20 minutes only until the MCU is reached);

• Risk of violation of safety requirements - the period for ground testing is limited from below. In the adopted starting method, it depends on values known with fundamentally low accuracy - on the initial power and initial temperature.

To reliably solve the problem of accelerating start-up and limiting the acceleration period, the following steps are required: a) calculating the effective multiplication factor of the reactor at the time of start-up Kef, for which immediately before starting the average temperature of the reactor is measured, which determines the effective multiplication factor at the time of start-up; b) The very movement of the absorbing elements of the reactor is always carried out in different directions always at the maximum possible speed - the output is reached to a pre-calculated position determined by the magnitude of the input reactivity, then immediately input back to the maximum backlash of the motion transmission system and locked in this position until the minimum controlled power level is reached, at which the power regulator is automatically turned on; c) The parameters of the law of motion of the absorbing elements are determined on the basis of the desired (permissible) value of the steady-state acceleration period of the reactor τ ₀ , d) the initial level of the power setting at the time of reaching the MCU Z _{MCU is} taken to be N _MCU , and the initial speed of the program power increase ν _ZNM (controller task power) after reaching the minimum controlled level N _{MCU is} calculated by the formula ν _ZNM = N _MCU / τ ₀ . The implementation of the invention.

In the process of developing a nuclear power plant on the basis of theoretical and experimental and experimental work, the dependence of the effective multiplication coefficient on temperature is determined;

the reactivity of the regulating elements depends on their position, and the maximum backlash of the kinematic system of drives of absorbing elements is also established. These studies are an integral part of the design of any type of nuclear power plant (see Requirements for the content of the safety justification report for nuclear power plants with a WWER reactor. Guidance document NP-006-98 [3]). Calculations and full-scale experiments have established that, prior to the start-up of the reactor, the isothermal condition for core elements is satisfied with good accuracy.

1. At the time the start command is issued, the reactor temperature T ₀₀ is measured. To measure the temperature, either appropriate sensors inside the reactor are used, or for a short (5-10 seconds) the coolant flow is switched on and the coolant temperature is measured.

2. Based on the measured temperature, the effective multiplication factor Kef and reactivity ρ _p = Kef-1 at the time of start-up is calculated (see Fig. 1). In the range of possible values of the reactor temperature T _0min <T <T _{0 max,} we can approximately assume that the reactivity of the reactor is linearly dependent on temperature:

α _p is the temperature coefficient of reactivity, which can be either positive (for example, for TOPAZ and Yenisei nuclear reactors) or negative (for example, Romashka and Buk nuclear power plants (see Fig. 1).

3. Based on the measured temperature T ₀₀ and formula (1), the true value of reactivity at the time of start-up is calculated as

In the case of a more complex nonlinear dependence

ρ _p (T) = ƒ _ρ (T)

ρ ₀₀ value is determined by this calculated dependence ρ _p (T ₀₀ ) = ƒ _ρ (T ₀₀ ) or according to schedule 1 of FIG. 1, reflecting such a calculated dependence.

4. In the interval of interest for the position of the drive, we can approximately assume that the reactivity introduced by the absorbing elements linearly depends on the position:

0 <x <x _max :

4. Given the value of the desired period of acceleration of the reactor (ground tests or regular operation) t about, according to the tables from Kipin, J. Physical fundamentals of the kinetics of nuclear reactors. Moscow: Atomizdat, 1967 [6] or according to the schedule of FIG. 1, the target reactivity value ρ ₀ corresponding to the steady-state period τ _{0 is} calculated.

5. By reactivity p o and equation (2) or the graph of FIG. 1 calculated position x ₃ absorbing elements

Or, in the case of a more complex dependence ρ _x (x) = ƒ _x (x), the position x ₃ is determined according to the graph of FIG. 1 or by solving the equation

ρ ₀₀ -ρ ₀ = ƒ _x (x ₃ )

relative to x ₃ .

6. Absorbing elements, as described above, are displayed at maximum speed to the calculated position x ₃ , after which they are immediately entered by the amount of play and fixed in this position. In contrast to the method described in the prototype, where the movement of the regulating elements is unidirectional i.e. they are only removed, in the claimed technical solution, the movement of the regulatory elements is multidirectional, since the absorbing elements are removed from the reactor at a maximum speed to the final position x ₃ , after which they are immediately introduced by the measured backlash of the kinematic system and fixed in this position. Upon completion of this operation, the acceleration of the reactor occurs according to an exponential law with a period equal to the selected regulatory value.

7. When the minimum controlled power level is reached, the power regulator is turned on, the initial value of the task of which is equal to the minimum controlled level, and the initial speed of the task is equal to the ratio of the minimum controlled level to the regulated value of the period.

A further increase in power and reference occurs in accordance with a pre-calculated temporary law. Since the backlash of the actuators are selected for input of absorbing elements, the increase in the power task is linear, and acceleration to this moment is exponential, then at the moment the power regulator is turned on, the absorbing elements will be introduced without delay and smoothly implement the desired law of power growth in accordance with the task. Examples of the invention

The proposed start-up method was implemented when testing a prototype Yenisei nuclear power plant, the time of physical start-up was 202 seconds instead of 720 seconds when testing a prototype, where physical start-up was carried out according to the logic of the Buk and Topaz installations.

The measurement of the temperature of the reactor at the time of start-up T ₀₀ proposed in the inventive method makes it possible to programmatically and hardware calculate the current critical position of the absorbing elements x _{cr 00} , add to it a value determined by the known dependences of the steady-state period τ on reactivity, output the absorbing elements to a value of x ₃ calculated by formula (3) or according to the graph of FIG. 1, after which immediately enter the amount of play in the system of actuators.

In FIG. 3 shows the main parameters of the starting mode when using the proposed method of starting. Obviously, the critical state is achieved by the fastest possible means, the acceleration rate of the reactor is determined by the calculated reactivity, and, from this point of view, the process is the fastest of the technically feasible. The controlled acceleration of the reactor under the control of the neutron power control unit occurs from the task level equal to the minimum controlled power level, with the instantaneous value of the task increase rate equal to the current power increase rate.

List of sources used

1. Resolution of the UN General Assembly A / RES / 47/69 of February 23, 1993 https://documents-dds-ny.un.org/doc/UNDOC/GEN/N93/104/20/IMG/N9310420.pdf? Openelement

2. Bugrovsky V.V., Vintsevich N.A., Vishnepolsky I.M., Dushin A.N., Karmishin V.A., Martyanova T.S., Ulanov G.M., Chuprun B.E., Shevyakov A.A. Ed. Acad. Petrova BN. Fundamentals of automatic control of nuclear space power plants. M .: Mechanical Engineering, 1974.

3. Requirements for the content of the report on the safety justification of nuclear power plants with a VVER-type reactor. Guidance document NP-006-98

4. Alekseev P.A., Ehlakov I.A., Ovcharenko M.K., Pyshko A.P. On the possibility of launching a reactor in orbit due to a neutron source formed by cosmic radiation. Space Engineering and Technology No. 1 (4). pp. 15-21,2014

5. The role of nuclear power and nuclear propulsion in the peaceful exploration of space. International Atomic Energy Agency, Vienna, 2005 ISBN 92-0-107404-2

6. Kipin, J. Physical fundamentals of the kinetics of nuclear reactors. Moscow: Atom-Publishing House, 1967.

Claims (6)

1. The method of launching a nuclear reactor for space purposes, which consists in preliminarily determining the dependence of the effective multiplication factor on temperature with extracted absorbing elements Kef (T), the dependence of the reactivity of the absorbing elements on their position ρ _x = α _x (xx _max ), value of the maximum backlash of the drive of the absorbing elements and start the reactor by bringing it to a minimally controlled power level N _MKU due to the output of the absorbing elements with the subsequent automatic activation of the neutron power regulator with a programmed increase in the power set, characterized in that a period τ _{0 is} set in addition to the start of the start reactor acceleration and reactivity ρ ₀ , measure the temperature of the reactor at the time preceding the start of T ₀₀ , determine the true reactivity of the reactor ρ ₀₀ at actual temperature T ₀₀ , calculate the output value of the absorbing elements x ₃ according to ρ ₀₀ -ρ ₀ = ƒ _x (x ₃ ), and the output of the absorbing elements is carried out with a maximum speed v1 to the calculated position x ₃ , after which the absorbing elements are introduced at the same speed by the maximum backlash and fixed in this position. 2. The method according to p. 1, characterized in that the temperature of the reactor is measured at the time preceding the start of T ₀₀ , by sensors of internal reactor control or by measuring the temperature of the coolant.

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