Molten salt reactor fluid control components, molten salt reactor system and control methods

Abstract

This invention discloses a molten salt reactor fluid control component, a molten salt reactor system, and a control method thereof. The molten salt reactor fluid control component includes a cladding shell, a cladding shell support, a combustible poison, and a counterweight. The cladding shell encloses the combustible poison and the counterweight. The space within the cladding shell, excluding the combustible poison and the counterweight, forms a cavity filled with gas. The counterweight, the combustible poison, and the cavity are arranged sequentially along the direction of gravity within the cladding shell. The cladding shell support is externally disposed on the outer wall of the cladding shell. The molten salt reactor fluid control component of this invention can suppress the reactivity introduction caused by the flow of delayed neutron precursor nuclei, reducing the risk of accidents under uninterrupted operating conditions.

Description

Technical Field

[0001] This invention relates to the field of nuclear energy, specifically to a molten salt reactor fluid control component, a molten salt reactor system, and a control method thereof. Background Technology

[0002] Molten salt reactors use molten salt as both fuel and coolant. The fuel and molten salt flow and mix in the primary loop, exhibiting core physical characteristics significantly different from traditional component fuel reactors. These physical characteristics give molten salt reactors certain advantages in reactivity control. For example, liquid fuel can be fed and reprocessed online, keeping reactor backup reactivity low and reducing reactivity control requirements. Furthermore, molten salt reactors can achieve long-term shutdowns through salt evacuation. However, the flowing molten salt also presents certain challenges to reactivity control, primarily in the following aspects:

[0003] (1) Delayed neutron loss effect. At high flow rates, the loss of delayed neutron precursor nuclei in the reactor core is severe, resulting in a significant loss of the effective delayed neutron fraction. Conversely, in the event of a pump shutdown, the reactor core will exhibit greater reactivity due to the retention of delayed precursor nuclei. Without timely intervention from control rods, power reduction can only be achieved by relying on a negative temperature reactivity coefficient. This requires a large average core temperature rise and limited exhaust of core decay heat, leading to a continuous increase in core temperature. Related simulation studies suggest that in the event of a complete power outage or other uninterrupted accidents, the outlet temperature of a large molten salt reactor can easily exceed the normal operating temperature by 50-100°C, causing a significant thermal shock to the molten salt reactor body.

[0004] (2) Radioactive Isolation of Control Rod System. Control rods are typically driven by motors triggered by control signals, moving up and down within the reactor core to rapidly control reactivity. Since highly radioactive molten salt is not constrained by the cladding within the reactor, isolating it from the control rod system is a unique challenge in molten salt reactors. One method successfully used in experimental molten salt reactors involves installing control rod sleeves within the core, which act as the boundary of the molten salt fuel. The control rod system is essentially positioned outside the core boundary but still penetrates deep into the core. However, the thin walls of the control rod sleeves pose a risk of rupture under long-term high-temperature irradiation and corrosion. In breeder molten salt reactor designs, to reduce neutron absorption losses in the control rod sleeves, the control rods are typically inserted directly into the core fuel salt. However, practical motors are difficult to operate in high-temperature, high-radioactivity environments. Therefore, achieving reliable movement of the control rods while ensuring effective radioactive isolation remains a challenging problem to be solved. Summary of the Invention

[0005] This invention addresses the problem that the control rod system cannot effectively isolate radioactivity when operating at high temperatures, and proposes a molten salt reactor fluid control component, a molten salt reactor system, and a control method thereof.

[0006] This invention provides a molten salt reactor fluid control assembly, including a cladding shell, a cladding shell support, a combustible poison, and a counterweight. The cladding shell encloses the combustible poison and the counterweight. The space inside the cladding shell, excluding the combustible poison and the counterweight, forms a cavity, which is filled with gas. The counterweight, the combustible poison, and the cavity are arranged sequentially along the direction of gravity inside the cladding shell. The cladding shell support is disposed on the outer wall of the cladding shell.

[0007] Preferably, the combustible poison is a neutron absorber;

[0008] And / or, the density of the counterweight is greater than the density of the molten salt;

[0009] And / or, the cladding is made of nickel-based alloy, carbon-carbon composite material or silicon carbide fiber.

[0010] Preferably, the neutron absorber is boron carbide or a mixture of gadolinium oxide and aluminum oxide;

[0011] And / or, the counterweight is a nickel-based alloy.

[0012] Preferably, both the combustible poison and the counterweight are block structures, and the combustible poison and / or the counterweight has at least one block.

[0013] Preferably, there are gaps between the core blocks.

[0014] Preferably, the interior of the shell, from top to bottom along the direction of gravity, comprises the cavity, the flammable poison, and the counterweight.

[0015] Preferably, the shell support is located on the upper half of the outer wall of the shell.

[0016] Another aspect of the present invention provides a molten salt reactor system, including a molten salt reactor and at least one molten salt reactor fluid control component as described above. The molten salt reactor includes a molten salt reactor container and a reactor core disposed inside the molten salt reactor container. The reactor core includes a graphite assembly and molten salt channels. The reactor core is fixed in the molten salt reactor container in the direction of gravity by an upper support plate and a lower support plate. The molten salt reactor fluid control component is inserted into the molten salt channels. When the molten salt reactor fluid control component falls, it is limited and engaged with the upper support plate by the cladding bracket.

[0017] Preferably, when the cladding bracket is engaged with the upper support plate, the molten salt reactor fluid control component is in the lower limit position, and there is a gap between the lower end of the molten salt reactor fluid control component and the lower support plate.

[0018] Preferably, the molten salt stack container further includes an upper limit plate, which is located above the upper support plate, and an upper chamber is formed between the upper limit plate and the upper support plate;

[0019] When the nuclear fuel flow rate of the reactor core is at the first preset flow rate, the molten salt reactor fluid control component is at the upper limit position, the upper end of the molten salt reactor fluid control component has a gap with the upper limit plate, and the lower end of the molten salt reactor fluid control component is lower than the upper support plate.

[0020] Another aspect of the present invention provides a control method for a molten salt reactor system, the molten salt reactor system including a molten salt reactor, a second loop, and a power generation loop, the control method being implemented using the molten salt reactor system described above, the control method comprising:

[0021] S1. Add nuclear fuel to the reactor core and operate the reactor core at a first preset flow rate, so that the molten salt reactor fluid control assembly is at the upper limit position until the cold critical state is reached.

[0022] S2. Add nuclear fuel to the reactor core until the power of the reactor core is at thermal zero power;

[0023] S3. Increase the flow rates of the second circuit and the power generation circuit so that the core power reaches the first preset power.

[0024] S4. Replenish the nuclear fuel according to the temperature parameters to maintain the core temperature at the temperature threshold.

[0025] S5. Reduce the flow rate of the power generation circuit;

[0026] S6. Control the flow rates of the reactor core, the second loop, and the power generation loop to a second flow rate threshold, so that the molten salt reactor fluid control assembly is inserted into the molten salt flow channel, thereby shutting down the molten salt reactor.

[0027] In steps S1-S6, when the core temperature exceeds the maximum preset temperature, the pump of the molten salt reactor is de-energized, causing the height of the molten salt reactor fluid control component to drop.

[0028] Preferably, in steps S1-S4, the molten salt reactor fluid control components are all in the upper limit position.

[0029] Preferably, step S1 further includes: controlling the flow rates of the secondary loop and the power generation loop of the molten salt reactor system to a second flow rate threshold.

[0030] Preferably, step S4 further includes: controlling the flow rates of the second circuit and the power generation circuit to the first preset flow rate.

[0031] Preferably, step S5 further includes:

[0032] S51. Reduce the nuclear fuel flow rate of the reactor core according to the xenon poisoning effect, so that the height position of the molten salt reactor fluid control assembly is between the upper limit position and the lower limit position.

[0033] Preferably, the control method further includes: S7, after the shutdown time exceeds a preset time, controlling the nuclear fuel flow rate of the reactor core to increase, so that the height position of the fluid drive control component rises until the power of the reactor core is at a cold state of zero power.

[0034] Preferably, step S7 further includes:

[0035] S71. Control the nuclear fuel flow rate of the reactor core to increase until the power of the reactor core is at hot zero power; wherein, the nuclear fuel flow rate of the reactor core is lower than the first preset flow rate;

[0036] S72. Increase the flow rate of the second circuit and the power generation circuit to make the core power reach the first preset power, determine whether the core temperature is below the temperature threshold, and if so, increase the nuclear fuel flow rate of the core to the first preset flow rate so that the core temperature reaches the temperature threshold.

[0037] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0038] The positive and progressive effects of this invention are as follows: the molten salt reactor fluid control component of this invention can suppress the reactivity introduced by the flow of delayed neutron precursor nuclei, reducing the risk of accidents under no-intervention conditions; it can achieve a deeper shutdown depth when the main pump of the molten salt reactor stops operating; in addition, it can avoid accidents such as accidental removal of the control component and rupture of the control rod sleeve, which could lead to reactivity introduction, without external drive. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the molten salt reactor system in Embodiment 1 of the present invention.

[0040] Figure 2 This is a front sectional view of the molten salt reactor system of Embodiment 1 of the present invention.

[0041] Figure 3 This is a schematic cross-sectional view of the molten salt reactor system in Embodiment 1 of the present invention along the axial direction.

[0042] Figure 4 The curves show the absolute values ​​of the reactivity and delayed neutron loss reactivity of the molten salt reactor fluid control component in Embodiment 1 of the present invention.

[0043] Figure 5 This is the curve showing the change of core outlet temperature over time under the condition of full power outage and no rod intervention in Embodiment 1 of the present invention.

[0044] Figure 6 The curve of core power variation over time under the condition of full-field power outage and no rod intervention in Embodiment 1 of the present invention.

[0045] Figure 7 This is the core reactive power change during the power reduction process based on power generation loop flow reduction control in Embodiment 1 of the present invention.

[0046] Figure 8 The changes in core inlet and outlet and average temperature during the power reduction process based on power generation loop flow reduction control in Embodiment 1 of the present invention are shown.

[0047] Figure 9 This is a flowchart of the control method for the molten salt reactor system in Embodiment 2 of the present invention. Detailed Implementation

[0048] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0049] Example 1

[0050] like Figure 1-3 As shown, this embodiment provides a molten salt reactor fluid control assembly 1, including a shell 11, a shell support 12, a combustible poison 15, and a counterweight 16. The shell 11 encloses the combustible poison 15 and the counterweight 16. The space inside the shell 11, excluding the combustible poison 15 and the counterweight 16, forms a cavity 13. The cavity 13 is filled with gas. The counterweight 16, the combustible poison 15, and the cavity 13 are arranged sequentially along the direction of gravity inside the shell 11. The shell support 12 is disposed on the outer wall of the shell 11.

[0051] The cavity 13 is used to contain the gas released after the nuclear reaction of the combustible poison 15, and at the same time, it also plays a role in regulating the density of the molten salt reactor fluid control component 1.

[0052] In this embodiment, the cladding support 12 is used to limit the lower limit of the molten salt reactor fluid control assembly 1 in the molten salt flow channel 6. Without the operation of an external driving device, it can suppress the reactivity introduced by the flow of delayed neutron precursor nuclei and reduce the risk of accidents under uninterrupted operation.

[0053] In this embodiment, the cladding 11 is made of a material that is resistant to neutron radiation, resistant to high-temperature corrosion of molten salt, and has good mechanical properties. Preferably, the cladding 11 is made of nickel-based alloy, carbon-carbon composite material, or silicon carbide fiber. The cladding 11 can completely isolate the combustible poison 15, the counterweight 16, and the fuel salt.

[0054] In this embodiment, the combustible poison 15 is a neutron absorber, preferably boron carbide or a mixture of gadolinium oxide and aluminum oxide.

[0055] In this embodiment, the density of the counterweight 16 is greater than that of the molten salt. Preferably, the counterweight 16 is a nickel-based alloy. By setting the counterweight 16 and the cavity 13, the overall density of the molten salt stack fluid control assembly 1 can be adjusted, allowing it to move up and down within the molten salt channel 6 as the flow rate increases or decreases.

[0056] In this embodiment, both the combustible poison 15 and the counterweight 16 are block structures, and there is at least one block for both the combustible poison 15 and the counterweight 16; there is a gap 14 between the blocks. Those skilled in the art can select the number of combustible poison 15 blocks and the number of counterweight blocks as needed. This embodiment is merely an example of selecting five combustible poison 15 blocks and one counterweight 16 block.

[0057] In this embodiment, the interior of the cladding 11, from top to bottom along the direction of gravity, consists of a cavity 13, a combustible poison 15, and a counterweight 16. This arrangement of the cavity 13, combustible poison 15, and counterweight 16 meets the requirements for floating within the reactor core.

[0058] Preferably, the cladding support 12 is located on the upper half of the outer wall of the cladding 11. This arrangement of the cladding support 12 ensures that the molten salt reactor fluid control assembly does not fall too deep, allowing it to rest on the upper limit of the upper support plate 2 of the molten salt reactor core.

[0059] The diameter and length of the molten salt reactor fluid control assembly 1 provided in this embodiment are determined by the reactivity value being controlled. The diameter of the molten salt reactor fluid control assembly 1 is slightly smaller than the molten salt flow channel 6 in the reactor core, preferably 2-10 cm. The length design from the cladding support 12 to the bottom of the assembly can be divided into two categories according to its function. The first category is a design length that allows the differential reactivity value caused by the fluid impact and movement to offset the reactivity change caused by the flow-induced slow-emission neutron fraction. The reactivity caused by the flow-induced slow-emission neutron fraction is the reactivity value introduced by slow-emission neutrons from the flow rate of the reactor core nuclear fuel from full flow to zero flow. This can be used to suppress the reactivity change caused by the flow. The second category is a design length that allows the maximum total reactivity value absorbed to be the sum of the reactivity change caused by the flow-induced slow-emission neutron fraction and the shutdown depth. The shutdown depth is the reactivity change from hot full power to cold zero power, including reactivity changes caused by xenon poisoning, samarium poisoning, protactinium effect, and temperature. This can achieve automatic reactor shutdown after pump shutdown. The total reactivity value of the molten salt reactor fluid control component 1 can be composed of one or more fluid-driven control components superimposed.

[0060] The average density of the molten salt reactor fluid control component 1 can be lower or higher than the density of the molten salt. When it functions as the first type of component, its density is lower than the density of the molten salt, and it is called a floating component. When it functions as the second type of component, its density is higher than the density of the molten salt, and it is called a suspending component. Its density should be designed so that the self-weight of the molten salt reactor fluid control component 1 is equal to the sum of the buoyancy of the molten salt and the frictional resistance of the full-flow molten salt on the control component. In this way, under full-flow impact, the fluid-driven control component rises to its upper limit, but the lower end of the fluid-driven control component still does not reach the upper support plate, preventing the fluid-driven control component from detaching from the molten salt channel.

[0061] The magnitude of the fluid driving force on the molten salt reactor fluid control component 1 can be adjusted through the structural design of the molten salt flow channel 6. When it is necessary to increase the fluid driving force, the upper diameter of the molten salt flow channel 6 where the molten salt reactor fluid control component 1 is located can be reduced, and the lower diameter of the channel can be increased; conversely, the upper diameter of the molten salt flow channel 6 can be increased, and the lower diameter of the channel can be decreased.

[0062] This embodiment also provides a molten salt reactor system, such as Figure 2-3 As shown, the molten salt reactor system includes a molten salt reactor and six molten salt reactor fluid control components 1 as described above. The molten salt reactor includes a molten salt reactor container and a reactor core located inside the molten salt reactor container. The reactor core includes a graphite assembly 7 and a molten salt flow channel 6. The reactor core is fixed in the molten salt reactor container in the direction of gravity by an upper support plate 2 and a lower support plate 8. The molten salt reactor fluid control components 1 are inserted into the molten salt flow channel 6. When the molten salt reactor fluid control components 1 fall, they are limited and engaged with the upper support plate 2 by the cladding bracket 12.

[0063] Preferably, the six molten salt reactor fluid control components 1 are as follows: Figure 3 The numbers 1#-6# are evenly distributed in a hexagonal pattern within the molten salt channel 6.

[0064] Preferably, when the shell support 12 is in a limiting engagement with the upper support plate 2, the molten salt reactor fluid control component 1 is in the lower limit position, and there is a gap between the lower end of the molten salt reactor fluid control component 1 and the lower support plate 8.

[0065] The molten salt stack container also includes an upper limit plate 5, which is located above the upper support plate 2, and an upper chamber 4 is formed between the upper limit plate 5 and the upper support plate 2;

[0066] When the nuclear fuel flow rate of the reactor core is at the first preset flow rate, the molten salt reactor fluid control assembly 1 is at the upper limit position, the upper end of the molten salt reactor fluid control assembly 1 has a gap with the upper limit plate 5, and the lower end of the molten salt reactor fluid control assembly 1 is lower than the upper support plate 2.

[0067] The molten salt reactor system provided in this embodiment includes a molten salt reactor fluid control component 1, such as... Figure 1In the diagonal section, when the fuel salt 3 within the molten salt reactor is not flowing, the molten salt reactor fluid control assembly 1 rests on the upper support plate 2. As the fuel salt 3 in the reactor core flows upward from the lower molten salt chamber 9 along the molten salt channel 6, it exerts a thrust on the molten salt reactor fluid control assembly 1, causing it to move upward. The magnitude of this upward movement is related to the flow rate. When the nuclear fuel flow rate in the reactor core is at full capacity, the upper end of the molten salt reactor fluid control assembly 1 is close to the upper limit plate 5, while its lower end has not yet detached from the upper support plate 2. As the flow rate decreases, the molten salt reactor fluid control assembly 1 will naturally fall back into the molten salt channel 6.

[0068] The molten salt reactor system provided in this embodiment includes a molten salt reactor fluid control component 1 that can suppress the reactivity introduced by the flow of delayed neutron precursor nuclei, reducing the risk of accidents under no-intervention conditions; it can achieve a deeper shutdown depth when the main pump of the molten salt reactor stops operating; in addition, it can avoid accidents such as accidental removal of the control component and rupture of the control rod sleeve, which could lead to reactivity introduction, without external drive.

[0069] The following specific experimental data demonstrates the excellent performance of the molten salt reactor fluid control component 1 provided in this embodiment.

[0070] When the molten salt reactor fluid control assembly 1 is used solely to counteract reaction changes caused by the slowed precursor nuclear flow, its design reactivity value is as follows: Figure 4 The graph shows the reactivity change, where the horizontal axis represents the core flow velocity and the vertical axis represents the reactivity change. Numerically, as the flow velocity increases, the reactivity released by the molten salt reactor fluid control assembly 1 is essentially equivalent to the reactivity lost due to the delayed precursor nucleus flow, with a maximum difference of approximately 25 pcm. This means the reactivity change can be automatically reduced from 250 pcm to 25 pcm. Furthermore, in a full-field power outage without intervention, the difference in core outlet temperature between these two factors is as follows: Figure 5 As shown, the horizontal axis represents time, and the vertical axis represents the core outlet temperature. Figure 51 shows the temperature curve under the molten salt reactor fluid control assembly 1, and Figure 52 shows the temperature curve with the molten salt reactor fluid control assembly 1. Under the molten salt reactor fluid control assembly 1, the maximum core outlet temperature rises by 80°C, reaching 780°C, and remains at 766°C for an extended period, exceeding the current material's allowable operating limit of 750°C. However, when using the molten salt reactor fluid control assembly 1, the maximum core outlet temperature is 736°C, remaining stable at 688°C for an extended period, without any molten salt reactor overheating. In fact, the temperature rise in the first 200 seconds is not due to an increase in core power, but mainly because the slow rise in the average core temperature results in a slower power decrease, and the accumulated heat in the early stages exceeds the heat dissipated by the residual heat. Figure 6The horizontal axis represents time, and the vertical axis represents power fraction. 61 represents the process in which the core power first increases and then gradually decreases without molten salt reactor fluid control component 1, while 62 represents the process in which the core power increases almost no when molten salt reactor fluid control component 1 is present.

[0071] The power ramp-up process under the operation of the molten salt-free reactor fluid control assembly 1 is shown below. Figure 7 and Figure 8 .in, Figure 7 The three curves, from top to bottom, represent the changes in reactivity, power, and flow rate of the power generation circuit under the operation of the non-molten salt reactor fluid control component 1. Figure 8 The horizontal axis represents time, and the vertical axis represents temperature. Curve 81 shows the core outlet temperature, curve 82 shows the core inlet temperature, and curve 83 shows the core average temperature. Taking power reduction as an example, the flow rate of the power generation loop is decreased in a stepwise manner at 25% of full flow every 1500 seconds. In the initial stage of flow reduction, the core average temperature rises slightly due to the decrease in heat exchange capacity. At this time, reactivity decreases rapidly, and power also continues to decrease, further promoting a slow temperature decrease. Through continuous temperature feedback, the core reaches a new stable power value. The temperature difference between the core inlet and outlet also further narrows. The stabilization time is approximately 500 seconds, or about 8 minutes, during which there are no fluctuations, indicating good inertness of the molten salt and demonstrating the feasibility of core power increase / decrease based on power generation loop load tracking control.

[0072] Example 2

[0073] This embodiment provides a control method for a molten salt reactor system, wherein the molten salt reactor system includes a molten salt reactor, a second loop, and a power generation loop. The control method of this embodiment is implemented using the molten salt reactor system as described in Embodiment 1. Figure 9 As shown, the control methods for the molten salt reactor system include:

[0074] S1. Nuclear fuel is added to the reactor core to operate at a first preset flow rate, causing the molten salt reactor fluid control component 1 to be at its upper limit until cold criticality is reached. Step S1 further includes controlling the flow rates of the secondary loop and power generation loop of the molten salt reactor system to a second flow rate threshold. In this embodiment, the first preset flow rate is the full core flow rate, i.e., the maximum rated flow rate; the second flow rate threshold is zero flow rate. Preferably, multiple fuel additions are performed using a 1 / n (e.g., 1 / 2) fuel addition rule, with the fuel being mixed outside the reactor core each time before being transferred to the core and filling the core loop. The reactor core is then operated at full flow rate via the main pump.

[0075] S2. Add nuclear fuel to the reactor core until the core power is at thermal zero power;

[0076] Preferably, nuclear power heating is achieved by supplementing the reactor core with a small amount of nuclear fuel, allowing the reactor core to operate at hot zero power. At this time, the inlet and outlet temperatures of the reactor core are relatively uniform, the reactor core operates at full flow, the molten salt reactor fluid control assembly 1 is at the upper limit, and the flow rates of the secondary loop and the power generation loop are zero.

[0077] S3. Increase the flow rates of the second loop and the power generation loop to bring the core power to the first preset power.

[0078] Specifically, at this point, the temperature difference between the inlet and outlet of the reactor core increases, causing the average core temperature to initially decrease. This temperature negative feedback introduces positive reactivity, increasing the core power. Once the original average temperature is reached, the reactivity becomes zero, and the core's nuclear power stabilizes at a certain value. By repeatedly increasing the flow rates of the secondary loop and the power generation loop, the core power can be increased to full power, i.e., the maximum rated power. Due to the increased temperature difference and flow rate, the secondary loop drives the power generation system to generate electricity, removing the full-power load from the core. During this stage, the core remains at full flow rate, and the molten salt reactor fluid control assembly 1 remains at its upper limit. The flow rates of the secondary loop and the power generation loop are increased in stages.

[0079] S4. Replenish nuclear fuel according to temperature parameters to maintain the core temperature at the temperature threshold; step S4 further includes: controlling the flow rates of the second loop and the power generation loop to a first preset flow rate. In this embodiment, the first preset flow rate is the rated flow rate of the second loop and the power generation loop.

[0080] During two days of full-power operation, as xenon toxicity gradually accumulates, the nuclear reactivity of the reactor core decreases. At this point, the core power output begins to decline, and the overall inlet and outlet temperatures of the core begin to decrease. Temperature reactivity increases to compensate for the xenon toxicity. In this embodiment, temperature parameters include temperature change values ​​and a temperature negative reactivity coefficient. These parameters are used to estimate the amount of nuclear fuel that should be replenished, and the core temperature is maintained within the original hot-state design range, i.e., within the temperature threshold, through nuclear fuel replenishment. During this stage, the core remains at full flow, and the molten salt reactor fluid control component 1 remains at its upper limit. The secondary loop and power generation loop operate at their rated flow rates.

[0081] In steps S1-S4, the molten salt reactor fluid control component 1 is always at its upper limit.

[0082] S5. Reduce the flow rate in the power generation circuit; step S5 also includes:

[0083] S51. Reduce the nuclear fuel flow rate in the reactor core based on the effects of xenon poisoning, so that the height of the molten salt reactor fluid control assembly is between the upper and lower limits.

[0084] In this embodiment, by reducing the flow rate of the power generation loop, the temperature difference between the second loop and the core gradually decreases, and the core power begins to decline. At this time, the core is still at full flow, and the molten salt reactor fluid control assembly 1 is at its upper limit. If the power reduction time is long, reaching the xenon rebalancing time, the positive reactivity of xenon poisoning needs to be considered. In this case, the nuclear fuel flow rate of the core can be appropriately reduced, allowing the molten salt reactor fluid control assembly 1 to be inserted into the molten salt flow channel 6, thereby suppressing the xenon poisoning effect at this stage. At this time, the core flow control should cause the height of the molten salt reactor fluid control assembly 1 to decrease, and its reactivity change should be able to offset the xenon poisoning and delayed neutron fraction loss effects.

[0085] S6. Control the flow rate of the core, second loop and power generation loop to the second flow rate threshold, so that the molten salt reactor fluid control assembly is inserted into the molten salt flow channel, thereby shutting down the molten salt reactor;

[0086] In this embodiment, the flow rates of the core, secondary loop, and power generation loop are reduced to zero. Since the core is at zero flow, the molten salt reactor fluid control assembly 1 introduces negative reactivity, and the reactor is shut down. At this point, the shutdown depth is the sum of the reactivity caused by the hot and cold state temperature and the reactivity caused by equilibrium xenon. After shutdown, due to the decay of iodine, xenon toxicity continues to increase, commonly known as an iodine pit. After 11 hours, the core enters a deep shutdown state. Subsequently, xenon continues to decay, approaching a lower level after 30 hours. At this point, it will leave the iodine pit and release positive reactivity equivalent to equilibrium xenon toxicity, and its shutdown depth becomes the hot and cold state temperature reactivity. This is shutdown stage 1. As time progresses, the core temperature will drop to a cold state due to heat leakage from the reactor compartment and passive exhaust, at which point the shutdown depth will be 0. Since the samarium toxicity effect appears after 100 hours and the protactinium effect appears after about 90 days, their impact can be considered zero at this point. As the temperature further decreases, the reactor returns to criticality and heats the core using nuclear power to maintain a stable core temperature in a cold state; this is shutdown phase 2. During prolonged shutdown, samarium poisoning begins to increase. In a molten salt reactor, the neutron toxicity of Sm-149 is approximately 400 pcm, and at equilibrium, Pm-149 is about 20% of Sm-149. The negative reactivity increases by about 80 pcm in the first 100 hours after shutdown, increasing the shutdown depth. As the core continues to be cooled by the residual heat removal system, the temperature gradually decreases, reaching a lower equilibrium temperature (still significantly lower than the melting point). At this point, negative temperature feedback causes the reactor to become critical again; this is shutdown phase 3. Over even longer shutdown periods (on a 90-day timescale), the continuous decay of Pa-233 into U-233 within the reactor core causes a slow increase in core reactivity. The reactor maintains low nuclear power, and the temperature rises slowly to offset the increased reactivity caused by Pa-233 decay. The reactivity of Pa-233 release is closely related to the initial power share of U-233 in the reactor. When the reactivity of Pa-233 release is not significant, reactivity can be controlled by increasing the temperature. When the temperature is insufficient to compensate for the reactivity of Pa-233 release, reactor shutdown can be considered by releasing fuel salt.

[0087] In steps S1-S6, when the core temperature exceeds the maximum preset temperature, the pumps of the molten salt reactor are de-energized, causing the height of the molten salt reactor fluid control component 1 to drop. This establishes a temperature protection interlock; when the temperature exceeds the preset limit, the pumps of the molten salt reactor automatically lose power, causing the molten salt reactor fluid control component 1 to drop and stop the reactor core, ensuring its safety.

[0088] S7. After the shutdown time exceeds the preset time, the nuclear fuel flow rate of the reactor core is increased, causing the height of the fluid-driven control assembly to rise until the reactor core power is at zero power in a cold state.

[0089] In this embodiment, this step involves restarting the reactor from a shutdown state, specifically during the xenon toxicity period (within 40 hours of shutdown). At this time, the reactor is in the iodine pit phase, resulting in a significant shutdown depth, making normal startup impossible. However, in the later stages of xenon toxicity, i.e., after 40 hours of shutdown, the disappearance of xenon toxicity leads to positive reactivity. Therefore, it is not advisable to directly increase the core fuel flow rate to full flow as in step S1. Instead, the increase in core flow rate should be determined based on reactivity value, and the molten salt reactor fluid control assembly 1 should be gradually increased to allow the reactor to gradually reach a cold, zero-power state.

[0090] S71. Control the increase of nuclear fuel flow rate in the reactor core until the core power is at hot zero power; wherein, the nuclear fuel flow rate in the reactor core is lower than the first preset flow rate, that is, the nuclear fuel flow rate in the reactor core has not yet reached the full flow rate.

[0091] S72. Increase the flow rate of the second loop and the power generation loop to make the core power reach the first preset power. Determine whether the core temperature is below the temperature threshold. If so, increase the core nuclear fuel flow rate to the first preset flow rate so that the core temperature reaches the temperature threshold.

[0092] In this embodiment, the core power is gradually increased to full power by increasing the flow rates of the second loop and the power generation loop, and the core inlet and outlet temperatures are gradually increased. After a period of operation, burnup and xenon toxicity lead to a decrease in reactivity, and the core average temperature decreases to compensate for the burnup reactivity. When a certain temperature range is reached, the core nuclear fuel flow rate is increased to full flow rate, causing the core average temperature to return to the rated hot state temperature. This completes the entire restart process. To ensure core safety, the increase in core nuclear fuel flow rate can be phased, not reaching the rated flow rate all at once. Additionally, there is the Pa-233 effect leading to salt removal restart. When Pa-233 introduces significant reactivity, criticality control cannot be achieved within the reactor. A certain amount of thorium or natural uranium fuel needs to be added to the salt removal vessel to counteract the Pa-233 effect. Afterward, the core is injected again, the count is observed, and the core flow rate is gradually increased to achieve criticality.

[0093] The control method for the molten salt reactor system provided in this embodiment controls the molten salt reactor fluid control component 1 by changing the flow rate of nuclear fuel in the reactor core, secondary loop, and power generation loop. It does not require additional mechanical structures, can avoid the risk of radioactive leakage caused by the control system and the reactor control reliability problem caused by control system failure, and can avoid reactive accidents such as accidental removal of control rods and rupture of control rod sleeves.

[0094] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A molten salt reactor fluid control assembly, characterized in that, The molten salt reactor fluid control assembly includes a cladding shell, a cladding shell support, a combustible poison, and a counterweight. The cladding shell encloses the combustible poison and the counterweight. The space inside the cladding shell, excluding the combustible poison and the counterweight, forms a cavity. The interior of the cladding shell, along the direction of gravity from top to bottom, consists of the cavity, the combustible poison, and the counterweight. The cladding shell support is located on the upper half of the outer wall of the cladding shell.

2. The molten salt reactor fluid control assembly as described in claim 1, characterized in that, The flammable poison is a neutron absorber; And / or, the density of the counterweight is greater than the density of the molten salt; And / or, the cladding is made of nickel-based alloy, carbon-carbon composite material or silicon carbide fiber.

3. The molten salt reactor fluid control assembly as described in claim 2, characterized in that, The neutron absorber is boron carbide or a mixture of gadolinium oxide and aluminum oxide; And / or, the counterweight is a nickel-based alloy.

4. The molten salt reactor fluid control assembly as described in claim 1, characterized in that, Both the flammable poison and the counterweight are core block structures, and there is at least one core block for the flammable poison and / or the counterweight.

5. A molten salt reactor system, characterized in that, The device includes a molten salt reactor and at least one molten salt reactor fluid control assembly as described in any one of claims 1-4. The molten salt reactor includes a molten salt reactor container and a reactor core disposed inside the molten salt reactor container. The reactor core includes a graphite assembly and molten salt channels. The reactor core is fixed inside the molten salt reactor container in the direction of gravity by an upper support plate and a lower support plate. The molten salt reactor fluid control assembly is inserted into the molten salt channels. When the molten salt reactor fluid control assembly falls, it is limited and engaged with the upper support plate by the cladding bracket.

6. The molten salt reactor system as described in claim 5, characterized in that, When the cladding bracket is engaged with the upper support plate, the molten salt reactor fluid control component is in the lower limit position, and there is a gap between the lower end of the molten salt reactor fluid control component and the lower support plate.

7. The molten salt reactor system as described in claim 5, characterized in that, The molten salt stack container also includes an upper limit plate, which is located above the upper support plate, and an upper chamber is formed between the upper limit plate and the upper support plate; When the nuclear fuel flow rate of the reactor core is at the first preset flow rate, the molten salt reactor fluid control component is at the upper limit position, the upper end of the molten salt reactor fluid control component has a gap with the upper limit plate, and the lower end of the molten salt reactor fluid control component is lower than the upper support plate.

8. A control method for a molten salt reactor system, characterized in that, The molten salt reactor system includes a molten salt reactor, a second loop, and a power generation loop. The control method is implemented using the molten salt reactor system according to any one of claims 5-7, and the control method includes: S1. Add nuclear fuel to the reactor core and operate the reactor core at a first preset flow rate, so that the molten salt reactor fluid control assembly is at the upper limit position until the cold critical state is reached. S2. Add nuclear fuel to the reactor core until the power of the reactor core is at thermal zero power; S3. Increase the flow rates of the second circuit and the power generation circuit so that the core power reaches the first preset power. S4. Replenish the nuclear fuel according to the temperature parameters to maintain the core temperature at the temperature threshold. S5. Reduce the flow rate of the power generation circuit; S6. Control the flow rates of the reactor core, the second loop, and the power generation loop to a second flow rate threshold, so that the molten salt reactor fluid control assembly is inserted into the molten salt flow channel, thereby shutting down the molten salt reactor. In steps S1-S6, when the core temperature exceeds the maximum preset temperature, the pump of the molten salt reactor is de-energized, causing the height of the molten salt reactor fluid control component to drop.

9. The control method as described in claim 8, characterized in that, In steps S1-S4, the molten salt reactor fluid control components are all at their upper limit positions.

10. The control method as described in claim 8, characterized in that, Step S1 further includes controlling the flow rates of the secondary loop and the power generation loop of the molten salt reactor system to a second flow rate threshold.

11. The control method as described in claim 8, characterized in that, Step S4 further includes: controlling the flow rates of the second circuit and the power generation circuit to the first preset flow rate.

12. The control method as described in claim 8, characterized in that, Step S5 also includes: S51. Reduce the nuclear fuel flow rate of the reactor core according to the xenon poisoning effect, so that the height position of the molten salt reactor fluid control assembly is between the upper limit and the lower limit.

13. The control method as described in claim 8, characterized in that, The control method further includes: S7, after the shutdown time exceeds a preset time, controlling the nuclear fuel flow rate of the reactor core to increase, so that the height position of the molten salt reactor fluid drive control component rises until the power of the reactor core is at a cold state of zero power.

14. The control method as described in claim 13, characterized in that, Step S7 also includes: S71. Control the nuclear fuel flow rate of the reactor core to increase until the power of the reactor core is at hot zero power; wherein, the nuclear fuel flow rate of the reactor core is lower than the first preset flow rate; S72. Increase the flow rate of the second circuit and the power generation circuit to make the core power reach the first preset power, determine whether the core temperature is below the temperature threshold, and if so, increase the nuclear fuel flow rate of the core to the first preset flow rate so that the core temperature reaches the temperature threshold.

Images