RU2095864C1 - Controlling pressurized-water reactor when extending its service life - Google Patents

Abstract

FIELD: nuclear reactors. SUBSTANCE: optimization problem of reactor control during extension of its lifetime is solved so that reactor power is reduced at maximum permissible rate. Reduced power level in each cycle is minimal permissible under operating conditions but sufficient for operation of power equipment. Power is increased in two stages; during first stage, power is raised at maximum permissible rate and during second stage it is increased at zero margin of reactivity with reactor self-controlled. During final period of cycle, reactor operates at high power level. EFFECT: improved economic efficiency of life extension procedure. 4 cl, 3 dwg

Description

 The invention relates to the physics of nuclear reactors, and more specifically to methods for controlling nuclear power reactors, and can find application mainly in the operation of a reactor as part of a nuclear power plant of a nuclear power plant.

 Campaign extension mode (RPK) is the stage of operation of the reactor following the moment of exhaustion of the reactivity margin. Operation of the reactor at nominal parameters, the most economically efficient, is not possible in the RPK mode. However, in general, PKK may be economically feasible.

 The possibility of extending the campaign of water-water type reactors is usually achieved through the use of power and temperature effects of reactivity.

 A known method of regulating the reactor in the RPK mode [1,2] in which, after exhaustion of the reactivity margin for burnup, the power and / or temperature of the coolant are reduced. Thus, an additional reactivity margin is released, which allows the reactor to be operated for several days.

 This method of extending the campaign forces the operation of power equipment for a long time in modes other than standard ones, which reduces the efficiency of the power unit in which the reactor operates and can adversely affect the operability of power equipment. In addition, additional operational costs are required to conduct the regime (adjustment of technological protection settings, justification and safety).

 Closest to the invention is a method of controlling a reactor in RPK mode / 3 / with the release of an additional reactivity margin by suppressing poisoning of the reactor with xenon-135 in a cycle (for example, daily) of reactor power change (prototype).

In accordance with the prototype, each cycle of power change in the RPK mode contains successive time intervals: lowering the power, maintaining the reactor at a low power level, maintaining the reactor at a high power level. Wherein
after lowering the power from the initial (for the next cycle) level, a certain margin of reactivity is released due to the power effect;
while the reactor is maintained at a reduced power level, xenon is re-poisoned by the reactor, however, by the end of this interval, there is still a reactivity margin that allows the increase in power to begin;
during the power increase interval, excess xenon accumulated in the second interval of the cycle is rapidly burned out, which allows the reactor to be brought to a high power level (in particular, to the initial level), having an additional reactivity margin that ensures the operation of the reactor in the fourth cycle interval;
during operation of the reactor at an increased power level, xenon burning continues, and then the reactivity margin obtained as a result of regulation is consumed, so that for the further operation of the reactor it is necessary to repeat the cycle.

 If the cycle duration is 24 hours, the reactor operation in the RPK can correspond to the load tracking mode.

As an increased power level for at least several cycles, a nominal (N _nom ) power level (100%) can be maintained. A reduced power level may decrease from cycle to cycle, reaching towards the end of the mode some minimum acceptable level. The difference in power levels should provide the possibility of the regime. In particular, it is proposed to set the reduced power level in each subsequent cycle to 3% N _nom below the previous one. The transition from a higher power level to a lower one and vice versa is proposed to be carried out either by a “jump” or by setting a fixed duration of the intervals for increasing and decreasing power. For example, a cycle is proposed in which the power decreases at a constant speed for 3 hours, then a reduced power level is maintained for 6 hours, the power is increased at a constant speed for 3 hours, and finally, the reactor operates at a higher power level for 12 hours).

 This method of regulating the reactor in the RPK allows you to operate power equipment in normal conditions, does not require significant additional operating costs, does not significantly reduce the efficiency of the power unit. The time required to prepare the power unit in the RPK is also reduced, which may be important if the RPK is carried out due to an urgent shortage of electricity in the power system.

 However, there remains a general drawback of RPK modes, a decrease in the installed capacity utilization factor in comparison with the nominal operation mode. Moreover, in RPK with cyclic regulation, the decrease in this coefficient can be greater than in RPK with reduced parameters.

 The aim of the invention is to increase the efficiency of the extension of the campaign by increasing the utilization of the power of a nuclear reactor in the above mode by optimizing the regulation of the reactor.

 This goal is achieved by the fact that in the known method of regulating the reactor in the campaign extension mode, including dividing the regulation into time intervals, reducing the power in the interval 1 from the initial predetermined level to a lower predetermined level, maintaining the reduced predetermined power level in the interval 2, increasing the power to an increased level at interval 3, maintaining an elevated predetermined level at interval 4, repeating intervals 1 to 4 the required number of times, the reactor power at interval 1 is reduced from m the maximum permissible speed under operating conditions, as the reduced power level in the interval 2, set the minimum acceptable power level for the operating conditions, sufficient for operation of power equipment, increase the power in the interval 3 in two stages, in the first of which the power is increased from the maximum permissible operating conditions at a speed, and on the second increase the power due to the burnout of xenon at zero reactivity margin of the reactor, the duration of the second of the intervals p Regulation is determined by solving the optimal control problem.

где λ₁, λ₂, γ₁, γ₂ постоянные распада и выходы при делении ядер горючего для йода-135 и ксенона-135 соответственно;
λ $\genfrac{}{}{0ex}{}{\text{*}}{\text{ном}}$ = λ₂+σΦ_ном эффективная постоянная распада ксенона-135 для номинального уровня мощности N_ном;
X₁, X₄ концентрации йода-135 и ксенона-135 соответственно нормированные на стационарные значения этих концентраций при N_ном;
X₃, X₄, U запас реактивности, мощность реактора и скорость изменения мощности (управление) соответственно нормированные на N_ном;
δ мощностной коэффициент реактивности;
e коэффициент выгорания;
r нормированная на N_ном максимальная величина стационарного отравления реактора ксеноном-135 при ограничениях:

g₁(X)=X₄-X_4max≅0;
g₂(X)=X_4min-X₄≅0;
g₃(X)= X_g≅0
где X_4min, X_4max, U_max предельно допустимые уровни мощности и скорости изменения мощности,
требуется найти такое оптимальное управление U(t), чтобы при переводе реактора из заданного начального состояния

(для начала РПК

(1,1,0,1)) в заданное конечное

за заданное время T (продолжительность цикла регулирования) минимизировался функционал

В этом случае энерговыработка ΔQ за цикл регулирования будет максимальной. Начальное и конечное значение X₂ в цикле регулирования должны удовлетворять соотношению
X_2нач - X_2кон = εΔQ/ρ.
Решение задачи дает следующий оптимальный режим регулирования:
из исходного состояния мощность снижается со скоростью U_max до величины X_4min, продолжительность перехода определяется величинами X₄₀, U_max, X_4min;
значение X₄ поддерживается равным X_4min (движение по границе g₂(X)), продолжительность участка определяется векторами

;
мощность увеличивается со скоростью U_max до исчерпания запаса реактивности;
реактор поддерживается в состоянии X₃ 0 (движение по границе g₃(X)) при увеличении мощности до конечного заданного уровня X_4K;
реактор работает на мощности X_4K до конца цикла регулирования.Within the framework of the point model, the optimization problem for the PKK is posed as follows. In a space whose phase variables X ₁ - X ₄ satisfy the equations

where λ ₁ , λ ₂ , γ ₁ , γ ₂ are the decay and exit constants in the fission of fuel nuclei for iodine-135 and xenon-135, respectively;
λ $\genfrac{}{}{0ex}{}{\text{*}}{\text{nom}}$ = λ ₂ + σΦ _nom effective decay constant of xenon-135 for the nominal power level N _nom ;
X ₁ , X ₄ concentrations of iodine-135 and xenon-135, respectively, normalized to the stationary values of these concentrations at N _nom ;
X ₃ , X ₄ , U reactivity margin, reactor power and rate of change of power (control), respectively, normalized to N _nom ;
δ power reactivity coefficient;
e burnout coefficient;
r normalized to N _{nom the} maximum value of the stationary poisoning of the reactor by xenon-135 with the restrictions:

g ₁ (X) = X ₄ -X _4max ≅ 0;
g ₂ (X) = X _4min -X ₄ ≅ 0;
g ₃ (X) = X _g ≅0
where X _4min , X _4max , U _{max the} maximum allowable power levels and rates of change of power,
it is required to find an optimal control U (t) such that when transferring the reactor from a given initial state

(to start the PKK

(1,1,0,1)) to the given final

for a given time T (the duration of the control cycle) the functional was minimized

In this case, the energy production ΔQ per regulation cycle will be maximum. The initial and final value of X ₂ in the control cycle must satisfy the ratio
X _2nach - X _2con = εΔQ / ρ.
The solution to the problem gives the following optimal regulation mode:
from the initial state, the power decreases at a speed of U _max to a value of X _4min , the duration of the transition is determined by the values of X ₄₀ , U _max , X _4min ;
the value of X _{4 is} maintained equal to X _4min (movement along the boundary of g ₂ (X)), the duration of the section is determined by the vectors

;
power increases with speed U _max until the reactivity reserve is exhausted;
the reactor is maintained in a state of X ₃ 0 (movement along the boundary of g ₃ (X)) with increasing power to a final predetermined level of X _4K ;
the reactor runs at X _4K power until the end of the control cycle.

 Thus, in the invention new in relation to the prototype are the requirements in each of the control cycles to reduce the power to the minimum acceptable level, and with increasing power for some part of the time to maintain the reactor at zero margin of reactivity. Each of these requirements is essential, since only their implementation provides the maximum energy output of the reactor.

PKK begins with the initial values of the parameters X ₁ 1; X ₂ 1; X ₃ 0; X ₄ 1. The duration of one regulation cycle can be 24 hours. In this case, the work in the PKK corresponds to the load tracking mode. The moment of regulation start is chosen so that the regulation interval during which the reactor power X _4min falls on the night minimum load of the power system. Accordingly, the control interval with the maximum reactor power X _4K will fall on the daily maximum load of the power system.

In the first control cycles during the fourth interval, the reactor can operate at a power of N _nom (X _4K X _4max 1) while reducing the duration of this interval from cycle to cycle. Further reactor operation in the RPK will be carried out with a decrease in X _4K .

A control option can be implemented with a duration interval of increased power not less than the specified one. In this case, the condition for a decrease in X _4K in the next cycle will be the inability to maintain the previous increased power level during an interval of a given duration.

 In FIG. 1 shows the change in iodine and xenon concentrations during the first and part of the second regulation cycles; in FIG. Figures 2 and 3 show the corresponding changes in the reactivity margin and reactor power.

 The numbers 1–4 mark the moments of the end of time intervals within the cycle into which the regulation is divided. Sign 3a marks the moment of the end of the increase in power at maximum speed in the third interval and the transition to the second stage of this interval.

 Regulation of the reactor according to the proposed method can be implemented as follows.

 In the initial state for each control cycle, the reactivity margin is zero. In this case, the control rods are removed from the reactor as much as possible according to operating conditions. The liquid absorber (if used to control this reactor) has the lowest possible concentration, which remains unchanged throughout the entire RPK.

 At the first time interval, the power decreases. The control rods are introduced into the core to compensate for the released reactivity margin by reducing the power.

 In the second time interval, at a constant reactor power, the rods are partially removed from the zone, compensating for the decrease in the reactivity margin due to xenon-135 reactor poisoning and burnout.

 At the first stage of the third time interval, the power increases. The control rods are brought to the initial position for the control cycle and are held in this position during the second stage of the third time interval of the control cycle. The operation of the reactor at this stage is carried out with self-regulation. The reactivity margin released during xenon burn-out is compensated by a decrease in the margin due to the power effect of reactivity when the power is increased to an increased predetermined level.

 At the fourth time interval, an increased power level is maintained. The control rods are first introduced into the core, and by the end of the interval return to their original state, compensating for the change in reactivity margin due to changes in xenon concentration and fuel burnout.

 The effectiveness of the proposed method of regulation is verified by numerical calculation.

The calculation is carried out with the following parameters: λ $\genfrac{}{}{0ex}{}{\text{*}}{\text{nom}}$ 0.186 1 / h; δ -1.62 • 10 ^-4 1 /% N _nom ; e -6.6 • 10 ^-6 1 / h; r-1.75 • 10 ^-2 ; U _max = 5% N _{nom / min} ; X _4min = 0.1. The cycle duration was set equal to 24 hours

The calculation results show that during 20 control cycles (20 days) at X _4K 1 (N _nom ), the duration of the fourth time interval (reactor operation at N _nom ) is reduced from 18.6 hours in the first cycle to 7.96 hours in the last. Energy production over 20 days amounted to 369N _nominal hours with a change in the power utilization coefficient from 0.988 in the first cycle to 0.54 in the last.

With the above parameters, the control mode considered in the prototype was also calculated with a decrease in each cycle of X _4min by a constant value of DX ₄ and with a fixed duration of time intervals of 1 4 (3-6-3-12 hours respectively). The calculation results show that the mode may be realized by ΔX 0.13 ₄ for seven days with burnup 135N _SG h (corresponding to the magnitude of the proposed method 153N _SG h). The ratio of the installed power factor in the proposed method to the same value in the prototype changes to 1.27 in the seventh.

 Using the proposed method for regulating a nuclear reactor in the RPK provides, in comparison with the prototype, an increase in the mode efficiency by increasing the power utilization coefficient.

Claims (4)

 1. The method of regulating a nuclear water-water reactor in the campaign extension mode, including dividing the regulation into time intervals, reducing the power in the interval 1 from the initial predetermined level to a reduced predetermined level, maintaining a reduced predetermined power level in an interval 2, increasing the power to an increased predetermined power level in the interval 3, maintaining an increased predetermined power level in the interval 4 and repeating the intervals 1.4 the required number of times, characterized in that the power react ora in the interval 1 is reduced with the maximum permissible operating conditions for the operating conditions, as a reduced power level in the interval 2, the minimum permissible operating conditions for the power level sufficient for operation of the power equipment are set, the power increase in the interval 3 is carried out in two stages, the first of which the power is increased at the indicated maximum speed, and in the second stage, the power is increased at a zero reactivity margin of the reactor, while the duration of interval 2 determines the solution optimal control problem.  2. The method according to claim 1, characterized in that the total duration of the intervals 1.4 is set equal to 24 hours  3. The method according to claim 1 or 2, characterized in that the increased power level in the interval 4 is set equal to 100% of the rated power of the reactor.  4. The method according to claim 1 or 2, characterized in that the increased power level in the interval 4 is set so as to ensure the duration of the interval 4 is not less than the specified.

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