CN107863162B - The method that reactor is transformed into critical state from subcritical state - Google Patents

Abstract

An embodiment of the present invention discloses a method for converting a reactor from a subcritical state to a critical state, the method comprising: a beam intensity reducing step: reducing the beam intensity of an accelerator for a reactor in a subcritical state by a predetermined beam intensity; a first control rod adjustment step: adjusting the length of the first control rod in the reactor core; and a stable operation step: making the reactor work stably for a predetermined time, wherein the beam intensity reduction step, the first control rod The adjusting step and the stabilizing working step are until the beam intensity decreases to a predetermined value, and the method further includes: cutting off the accelerator beam; and gradually pulling out the second control rod, so that the reactor reactivity is gradually increased to the predetermined reactivity. By adopting the method of the embodiment of the present invention, the transition of the reactor from the subcritical state to the critical state is realized without stopping the reactor.

Description

Method for transitioning a reactor from a subcritical state to a critical state

technical field

Embodiments of the invention relate to a method of transitioning a reactor from a subcritical state to a critical state.

Background technique

The accelerator-driven advanced nuclear energy system provides exogenous neutrons from the accelerator to drive the reactor to operate at subcritical.

Contents of the invention

It is an object of embodiments of the present invention to provide a method for transitioning a reactor from a subcritical state to a critical state, whereby, for example, the transition of a reactor from a subcritical state to a critical state is achieved without shutting down the reactor.

Embodiments of the present invention provide a method of transitioning a reactor from a subcritical state to a critical state, the reactor comprising first control rods having a first cross-sectional area and a second cross-sectional area smaller than the first cross-sectional area area of the second control rod, the method comprising: a beam intensity reducing step: reducing the beam intensity of an accelerator for a reactor in a subcritical state to a predetermined beam intensity; a first control rod adjusting step: adjusting the first control rod the length of the rods in the core of the reactor; and a stabilizing operation step: stabilizing the reactor for a predetermined time, wherein the beam intensity reducing step, the first control rod adjusting step and the stabilizing operation step are cyclically performed until the beam intensity is reduced to a predetermined value, The method further includes: cutting off the beam current of the accelerator; and gradually pulling out the second control rod, so that the reactor reactivity is gradually increased to a predetermined reactivity.

According to an embodiment of the present invention, adjusting the length of the first control rod within the core of the reactor includes pulling out the first control rod by a predetermined distance.

According to an embodiment of the present invention, reducing the beam intensity to the predetermined value includes reducing the rated beam intensity of the accelerator for the reactor in the subcritical state to the predetermined value stepwise within a predetermined time.

According to an embodiment of the present invention, the length of the first control rod in the reactor is adjusted so that the temperature variation of the reactor core is less than ±5° C., the reactivity variation is less than 50 pcm/hour, and the effective multiplication factor keff<0.98.

According to an embodiment of the present invention, the first control rod and the second control rod have circular cross-sections, and the diameter of the first control rod is 1.5-2.5 times the diameter of the second control rod.

According to an embodiment of the invention, the first control rod and the second control rod have substantially the same length.

According to an embodiment of the present invention, reducing the beam intensity to a predetermined value includes reducing the rated beam intensity of the accelerator for the reactor in the subcritical state by a proportional beam intensity value in a plurality of equal time periods.

According to an embodiment of the present invention, the predetermined distance is a ratio of a change in reactivity of the reactor that needs to be adjusted to a change in reactivity of the reactor core caused by moving the first control rod per unit distance.

According to an embodiment of the invention, the accelerator beam is switched off when the power of the reactor is reduced to a predetermined percentage of the power of the reactor in a subcritical state.

According to an embodiment of the present invention, the predetermined percentage ranges from 50% to 70%.

Using the method for converting a reactor from a subcritical state to a critical state according to an embodiment of the present invention, for example, realizes the conversion of a reactor from a subcritical state to a critical state without stopping the reactor.

Description of drawings

1 is a flowchart of a method of transitioning a reactor from a subcritical state to a critical state according to an embodiment of the present invention;

Figure 2 is a flowchart of the operation of an accelerator-driven reactor according to an embodiment of the present invention;

3 is a schematic diagram of a beam intensity reduction method according to an embodiment of the present invention; and

Fig. 4 is a structural diagram of a reactor core according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Referring to Figures 1 and 4, an embodiment of the present invention provides a method for transitioning a reactor from a subcritical state to a critical state. The reactor comprises first control rods 2 having a first cross-sectional area and second control rods 3 having a second cross-sectional area smaller than the first cross-sectional area. The method includes: a beam intensity reducing step: reducing the beam intensity of an accelerator for a reactor in a subcritical state to a predetermined beam intensity; a first control rod 2 adjusting step: adjusting the first control rod 2 in the reactor stack The length inside the core 1; and the step of stabilizing operation: making the reactor stably operate for a predetermined time. The step of reducing the beam current intensity, the step of adjusting the first control rod 2 and the step of stabilizing the work are executed cyclically until the beam current intensity is reduced to a predetermined value. That is, it is judged whether the beam intensity is lower than the predetermined value, if the beam intensity is greater than the predetermined value, then return to the beam intensity reduction step, and if the beam intensity is less than or equal to the predetermined value, then perform the following steps. The method further includes: cutting off the beam current of the accelerator; and gradually pulling out the second control rod 3 to gradually increase the reactor reactivity to a predetermined reactivity.

According to an embodiment of the present invention, adjusting the length of the first control rod 2 inside the reactor core 1 includes pulling out the first control rod 2 by a predetermined distance. The predetermined distance is a ratio of a change in reactivity of the reactor to be adjusted to a change in reactivity of the reactor core 1 caused by moving the first control rod 2 per unit distance. According to an example of the present invention, the length of the first control rod 2 in the reactor is adjusted so that the temperature variation of the reactor core 1 is less than ±5° C., the reactivity variation is less than 50 pcm/hour, and the effective multiplication factor keff<0.98.

According to an embodiment of the present invention, reducing the beam intensity to the predetermined value includes reducing the rated beam intensity of the accelerator for the reactor in the subcritical state to the predetermined value stepwise within a predetermined time. For example, reducing the beam intensity to a predetermined value includes reducing the rated beam intensity of the accelerator for the reactor in the subcritical state by a proportional beam intensity value respectively in a plurality of equal time periods. According to an embodiment of the present invention, in the beam intensity reducing step, the beam intensity of the accelerator for the reactor in the subcritical state is reduced by a predetermined beam intensity, and the beam intensity reducing step, the first control rod adjustment Steps and steady work steps until the beam intensity decreases to a predetermined value. When the beam current intensity reduction step, the first control rod adjustment step and the stable working step are cyclically executed, the predetermined beam current intensity can be different or the same in all cycles. For example, the predetermined beam intensity is gradually reduced in a decreasing manner or proportionally.

According to an embodiment of the present invention, the first control rod 2 and the second control rod 3 have a circular cross-section, and the diameter of the first control rod 2 is 1.5-2.5 times the diameter of the second control rod 3 . The first control rod 2 and the second control rod 3 may have approximately the same length.

According to an embodiment of the invention, the accelerator beam is switched off when the power of the reactor is reduced to a predetermined percentage of the power of the reactor in a subcritical state. The predetermined percentage may range from 50% to 70%.

According to an embodiment of the present invention, a method for transitioning a reactor from a subcritical state to a critical state is provided, which can be used for a burner subsystem (including a reactor) in an advanced nuclear energy system to go from a subcritical state to a critical state without shutting down the reactor. State transitions. The conversion method includes the following steps: (1) reducing the beam current, (2) adjusting the control rod. The control rods are divided into the first control rod 2 and the second control rod 3. The moving strategies of the two control rods and the beam current reduction strategies can be determined according to the following points: (1) The reactivity limit of the subcritical reactor (during the transition period, The reactivity change of the reactor is less than 50pcm/hour); (2) the stability limit of the core power (the power change of the reactor during the conversion period is less than 5% of the initial power); (3) the thermal shock limit of the structural material and fuel (temperature The rate of change is less than 60°C/hour).

According to an embodiment of the present invention, the accelerator-driven advanced nuclear energy system provides exogenous neutrons from the accelerator to drive the reactor to operate at subcriticality. After 3-5 years of operation, the external drive is cut off without stopping the reactor, and the reactor transitions to critical state operation.

The method for transitioning a reactor from a subcritical state to a critical state according to an embodiment of the present invention is mainly used to solve the problem that a burner subsystem in an accelerator-driven advanced nuclear energy system transitions from a subcritical state to a critical state without stopping the reactor.

According to an embodiment of the present invention, the accelerator-driven advanced nuclear energy system mainly includes: a burner subsystem (including a reactor) and a nuclear fuel regenerative post-processing subsystem. The burner subsystem includes a high-current superconducting linear accelerator, a high-power spallation neutron target, and a high-temperature fast reactor. When the reactor is first installed, the entire nuclear energy system needs to use the superconducting linear strong current proton accelerator to drive the reactor exogenously, and the burner to burn and proliferate to increase production capacity. At this time, the system operates in a subcritical state; it operates in this state After 3 to 5 years, the superconducting linear high-current proton accelerator is cut off under the condition of non-stop stacking, and the drive of the external neutron source of the burner is stopped. After that, the burner turns into a self-sustained combustion state, and the system operates in a critical state.

According to the embodiment of the present invention, the general operation process of the burner subsystem in the accelerator-driven advanced nuclear energy system is shown in Figure 2: (1) Particle injection, flow preheating. When the reactor is initially installed, solid particles used as neutron targets and coolant need to be injected into the reactor from the outside. During the injection process, the particles flow while being preheated. The preheating work is completed in the particle storage device. The preheated particles will Heat is transferred to the reactor, and the preheating is stopped when the temperature inside the reactor equilibrates. (2) The control rods are in place, so that the initial reactivity of the reactor is controlled between 0.96 and 0.98. The first control rod 2 is completely pulled out, the second control rod 3 is partially inserted, and the value of the inserted part of the second control rod 3 is β _eff ~ 2β _eff (β _eff is the proportion of delayed neutrons). The first control rod 2 is used for: 1. Reactivity control during the subcritical operation stage of the reactor; 2. Combined with the second control rod 3 to switch from the subcritical to critical process of the reactor; 3. Used as a safety rod during the critical operation of the reactor. The second control rod 3 is used for: 1. controlling the transition of the reactor from subcritical to critical; 2. controlling the reactivity of the reactor in the critical state. (3) Add beam current. After everything is ready, the superconducting linear high-current proton accelerator starts to generate proton beams, and the generated beams bombard the particle targets to drive the burners for combustion. (4) Normal subcritical reactor operating conditions. After the reactor is started, due to the staged changes in the reactivity of the reactor, it is necessary to alternately adjust the first control rod 2 and the beam intensity at this time, so that the reactivity and power of the reactor can be maintained within the safety threshold, and the system can operate stably under normal subcritical reactor conditions Down. At this moment, the first control rod 2 has been inserted into the reactor for a certain distance. (5) Subcritical-critical transition. When the reactor has been in operation for 3 to 5 years, and the reactivity of the reactor reaches a certain threshold and the operation is stable, the superconducting linear high-current proton accelerator cuts off its external neutron source drive to the burner, and the first control rod 2 and the second control rod 3 Synergy makes the reactivity of the reactor critical. (6) Operation of normal critical reactor conditions. After the burner is completely transformed into a self-sustained combustion state, the system operates in a critical state, and the critical state is completely controlled by the second control rod 3 in the reactor, and the function of the first control rod 2 becomes a safety rod . (7) shutdown. After the reactor has been in operation for 30-50 years, when the nuclear fuel burns to a certain extent, the reactor needs to be shut down for processing, that is, the fuel assembly in the core is disassembled and transported to the nuclear fuel regeneration post-processing subsystem for nuclear fuel processing. (8) The coolant is stopped and discharged. Although the reactor stops working, the internal temperature is still very high, and the coolant particles still need to circulate to take away the heat. When the internal temperature of the reactor reaches the specified value, the particle coolant can stop flowing and be discharged to the designated container.

Reactor subcritical to critical conversion needs a process, an example of the present invention proposes a method for conversion, the specific steps are:

(1) Reduce the beam current: reduce the rated beam intensity I ₀ of the accelerator in the subcritical reactor to I ₀ in a stepwise manner within h (h ≤ 30 days) times, 50≤Z≤100, that is, as shown in Figure 3, there is the following relationship between the beam current drop intensity before and after the time period: Where W is the number of divided time periods, that is, it is set to reduce the beam intensity from I ₀ to It needs W times to complete, W≥15, each period is equal, and the duration is t, I _kt is the beam intensity at time kt, I _(k-1)t is the beam intensity at time (k-1)t, (k=1, 2, 3...W), and the unit is mA.

(2) Adjust the first control rod 2: as shown in Figure 4, the length of the first control rod 2 in the reactor core 1 is the same as that of the second control rod 3, which is consistent with the height of the reactor core 1, and the first control rod 2 The diameter of the second control rod 3 is about 1.5-2.5 times, and both can use the same material, such as boron carbide, cadmium, silver indium cadmium and the like. When the beam current decreases, the neutrons produced by the spallation target will decrease, and the reactor's reactivity, temperature and other parameters will decrease. Fluctuates within a small range, the temperature fluctuation is less than ±5°C, the reactivity change is less than 50pcm/hour, and the effective proliferation factor keff is less than 0.98. This requires slowly adjusting the first control rod 2 while reducing the beam current, the withdrawal of the first control rod 2 will increase the reactivity, and the insertion will inhibit the reactivity.

After each beam descent is completed, the system will measure and calculate the difference ρ _x between the actual reactivity in the reactor and the set safety threshold in real time, and then adjust the first control rod 2 to make a value equivalent to ρ Control of the amount of change in _x reactivity. The moving distance of the first control rod 2 can be calculated according to the following formula: Among them, HX is the distance that the first control rod 2 needs to move; ρ _x is the amount of change in reactivity in the reactor that actually needs to be adjusted; ρ ₀ is the parameter measured by the experiment, representing the unit distance (per centimeter) of movement of this type of control rod The amount of change in reactivity in the reactor caused by H0 is the initial reference distance (according to actual needs, a position is artificially set on the first control rod ₂ as the initial position, and each parameter is based on this initial position during calculation. calculate). After the moving distance of the first control rod 2 is calculated, the first control rod 2 is adjusted to adjust the parameters such as reactivity and temperature inside the reactor within the normal range.

(3) Decrease the core power steadily. After reducing the beam current and adjusting the first control rod 2, the system needs to work stably for a certain period of time. When all parameters are in normal working conditions, the beam current can be reduced again, and repeat the above-mentioned adjustment of the first control rod 2 The adjustment process, that is, the steps (1), (2), and (3) are executed cyclically until the beam intensity is reduced to At this time, the reactor enters a subcritical state, and the core power is reduced to about 60% of the subcritical power.

(4) Adjust the second control rod 3 . The subcritical state is a short transition state between subcritical and critical. At this time, the core reactivity is about 1-β _eff . After the core state is stable, the accelerator beam is cut off, and the beam intensity is determined by It immediately dropped to 0; then, the second control rod 3 began to be pulled out, and the reactor reactivity was slowly increased from 1-β _eff to 1~1+β _eff within 2 hours. Since then, the core has entered critical mode operation, and when the power of the core rises from about 60% of the rated power to 100% of the rated power, the core completely transitions to the normal critical operating state. In the critical state, the adjustment of reactor reactivity is accomplished by the second control rod 3, and the function of the first control rod 2 becomes a safety rod.

The conversion method proposed by the embodiment of the present invention can safely and effectively realize the conversion of the burner subsystem in the advanced nuclear energy system from the subcritical state to the critical state, so that the inside of the reactor is in a normal working condition.

While various embodiments have been described above, the methods of embodiments of the present invention may be used for any suitable accelerator-driven transition of a subcritical to critical state reactor. Furthermore, although various numerical ranges and specified values are described, these numerical ranges and specified values may be adjusted according to actual conditions.

Claims (10)

1. A method of transitioning a reactor from a subcritical state to a critical state, the reactor comprising first control rods having a first cross-sectional area and second control rods having a second cross-sectional area less than the first cross-sectional area Great, The methods include: A beam intensity reducing step: reducing the beam intensity of the accelerator for the reactor in the subcritical state by a predetermined beam intensity; The first control rod adjusting step: adjusting the length of the first control rod in the core of the reactor; and Stable work steps: make the reactor work stably for a predetermined time, wherein the beam intensity reduction step, the first control rod adjustment step and the stabilization work step are executed cyclically until the beam intensity is reduced to a predetermined value, The method also includes: cut off the accelerator beam; and Gradually pull out the second control rod to gradually increase the reactor reactivity to the predetermined reactivity. 2. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1, wherein Adjusting the length of the first control rod within the core of the reactor includes pulling out the first control rod by a predetermined distance. 3. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1, wherein Decreasing the beam intensity to a predetermined value includes decreasing the rated beam intensity of the accelerator for the reactor in the subcritical state stepwise to the predetermined value within a predetermined time. 4. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1 , wherein Adjusting the length of the first control rod in the reactor makes the change of the core temperature of the reactor less than ±5°C, the change of reactivity less than 50 pcm/hour, and the effective multiplication factor keff<0.98. 5. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1, wherein The first control rod and the second control rod have circular cross-sections, and the diameter of the first control rod is 1.5-2.5 times the diameter of the second control rod. 6. A method of transitioning a reactor from a subcritical state to a critical state according to claim 1 or 5, wherein The first control rod and the second control rod have approximately the same length. 7. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1, wherein Reducing the beam intensity to a predetermined value includes reducing the rated beam intensity of the accelerator for the reactor in the subcritical state by a proportional beam intensity value respectively in a plurality of equal time periods. 8. The method of transitioning a reactor from a subcritical state to a critical state according to claim 2, wherein The predetermined distance is a ratio of a change in reactivity of the reactor that needs to be adjusted to a change in reactivity of the reactor core caused by moving the first control rod per unit distance. 9. The method of transitioning a reactor from a subcritical state to a critical state according to claim 1, wherein The accelerator beam is switched off when the power of the reactor is reduced to a predetermined percentage of the power of the reactor in subcritical conditions. 10. The method of transitioning a reactor from a subcritical state to a critical state according to claim 9, wherein The predetermined percentage ranges from 50% to 70%.