A method for first loading and criticality of a high-temperature gas-cooled reactor

Abstract

The present invention discloses a method for first-time fuel loading and achieving criticality in a high-temperature gas-cooled reactor (HTGR). The method comprises: adjusting the system to an initial state for the first partial fuel addition operation, loading a plurality of graphite balls with an equivalent height of 6.05 m at the bottom of the reactor core, installing a neutron source and a physical startup system, and performing debugging; performing the first partial fuel addition operation in the reactor core until the reactor Keff reaches ≥ 0.998, allowing transition to criticality or supercriticality; during transition to criticality or supercriticality, when the source range count rate rises to greater than 3000 cps, adjusting the control rod positions to stabilize the source range count rate and achieving criticality; adjusting the system to an initial state for the second partial fuel addition operation, and performing the second partial fuel addition operation in the reactor core until the initial fully loaded core height is reached; and repeatedly raising all control rods except the safety rod horizontally to extrapolate the critical rod positions until criticality is achieved. The present invention enables the reactor to complete first-time fuel loading and achieve criticality more safely and efficiently.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear reactor commissioning and operation, and in particular to a method for first loading and criticality of a high-temperature gas-cooled reactor. Background Art

[0002] The core loading and reactivity control methods of the pebble bed high-temperature gas-cooled reactor are quite different from those of the pressurized water reactor: a reactivity control system, namely the control rod system, is set up in the graphite side reflector layer near the active area of ​​the high-temperature gas-cooled reactor. At the same time, another independent reactivity control system based on a different working principle is also set up, namely the absorption ball shutdown system.

[0003] The control rod system is the primary reactivity control system and includes safety rods, compensating rods, and regulating rods. It has the following functions: 1) It is used for reactivity regulation during operating conditions such as reactor startup, power adjustment and down-regulation, and normal power operation adjustment; 2) It is used for emergency shutdown; 3) Using only the control rod system, the reactor can reach and remain in a normal shutdown state.

[0004] The absorber ball shutdown system is an auxiliary shutdown system that is used together with the control rod system to enable the reactor to maintain shutdown margin to meet requirements during cold shutdown and maintenance shutdown.

[0005] The high-temperature gas-cooled reactor adopts a non-stop refueling mode. The fuel elements used are spherical fuel elements with UO2 coated particles, with an outer diameter of 6 cm, of which the outer diameter of the fuel area is 5 cm, and the thickness of the graphite shell is 0.5 cm. Each fuel ball contains 7 grams of heavy metals. 235 The U enrichment is 4.2%, and the core is also equipped with graphite balls with a diameter of 6 cm.

[0006] Because HTGRs have significant negative temperature feedback, unique fuel loading and unloading methods, and reactivity control methods, they differ from PWRs. Consequently, initial fuel loading and criticality approaches for HTGRs differ somewhat from those for PWRs, and currently, methods for initial fuel loading and achieving criticality in HTGRs are lacking. Summary of the Invention

[0007] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0008] To achieve the above-mentioned object, the present invention proposes a method for first-time loading and criticality of a high-temperature gas-cooled reactor, comprising the following steps:

[0009] S1. Adjust the system to the initial state of the first part of the addition operation. Load several graphite balls with an equivalent height of 6.05m at the bottom of the core. Plan and install the neutron source and physical start-up system according to the height of the graphite balls. Debug the neutron source and physical start-up system.

[0010] S2. Add the first part of the mixed fuel to the core until the reactor Keff is ≥ 0.998, allowing the transition to criticality or supercriticality;

[0011] S3, transition to criticality or supercriticality. When the source range count rate rises to more than 3000 cps, the control rod position is adjusted to stabilize the source range count rate and the reactor reaches criticality.

[0012] S4, adjusting the system to the initial state of the second part addition operation, and performing the second part addition operation of the mixed fuel into the core until the initial fully loaded core height is reached;

[0013] S5. Lift all control rods except the safety rod horizontally multiple times to extrapolate the critical rod position, and observe the count rate of the physical start-up system counter tube in real time until the critical state is reached and the position of the critical control rod is determined.

[0014] The present invention decomposes the entire mixed fuel addition operation into a first addition operation and a second addition operation. The first addition operation allows the reactor to transition to criticality or supercriticality, and through criticality operation, the reactor reaches net criticality. After the first addition operation is completed, the mixed fuel is continued to be added, thereby completing the overall mixed fuel addition operation. The control rod is lifted so that the mixed fuel reaches a critical state after the initial full-load core height. The reactor can safely and effectively complete the first loading and achieve criticality on the basis of graphite balls with an equivalent height of about 6.05 meters already loaded at the bottom of the core.

[0015] Optionally, the initial state of the first part of the addition operation is: the reactor is in a normal pressure state, the primary circuit of the core is in an air atmosphere, the core temperature is lower than 100°C, all control rods including safety rods, regulating rods and compensating rods are in the upper limit position, and all absorption balls are in the upper core spherical storage tank.

[0016] Furthermore, in S1, the installation height of the neutron source is set within 0.5m higher than the height of the graphite ball layer, and the physical starting system includes three counting tubes located in the side reflection layer channel, and the distribution heights of the three counting tubes are respectively below the height of the graphite ball layer, equal to the height of the neutron source, and above the height of the neutron source.

[0017] Furthermore, the counting rate of the counter tube under neutron source conditions is ≥2 cps.

[0018] Furthermore, the S2 specifically includes the following steps:

[0019] S21. 1 / 3 of the critical fuel ball loading provided by physical calculation is used as the initial fuel loading. The first fuel ball addition amount is 1 / 3 of the difference between the critical fuel loading provided by physical calculation and the initial fuel loading.

[0020] S22, the second fuel ball addition amount is 1 / 3 of the difference between the minimum value of the critical fuel ball loading amount obtained by physical extrapolation of the three counter tubes and the critical fuel ball loading amount obtained by physical calculation and the current fuel loading amount;

[0021] S23. The amount of fuel added each time thereafter is 1 / 3 of the difference between the minimum value of the physical extrapolation of the three counter tubes and the current loading of the core, and this step is repeated until the reactor Keff ≥ 0.998, at which time the transition to criticality or supercriticality is allowed.

[0022] Furthermore, in S3, when transitioning to criticality or supercriticality, the following steps are specifically included:

[0023] S31. Insert a control rod below the height of the graphite sphere layer, then load additional mixed fuel capable of introducing 100 pcm of reactivity. During the loading process, observe the changes in the neutron count rate in the counter tube and source range.

[0024] S32. After all the mixed fuel in S31 is loaded into the core, gradually lift the control rods inserted into the graphite ball layer, and record the cumulative loading of the mixed fuel, the reactor doubling cycle, and the position of the control rods inserted;

[0025] S33. When the source range count rate rises to above 3000cps, adjust the control rod position to make the source range count rate stabilize and the reactor reach critical state. Record the control rod critical rod position and source range count rate, and then insert a control rod below the height of the graphite ball layer.

[0026] Furthermore, during the transition to supercriticality, when the counting rate of the physical starting system counter tube approaches the upper limit of the range, the power supply of the corresponding channel counter tube is turned off, and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of system equipment and critical operations during the test.

[0027] Furthermore, in S32, when any of the following situations occurs, the stick lifting is stopped, as follows:

[0028] Case a: The neutron counting rate tends to increase steadily;

[0029] Case b: The reactor has a stable doubling cycle.

[0030] Furthermore, in S4, the initial state of the second part of the addition operation is: the reactor is in a normal pressure state, the primary circuit of the core is in an air atmosphere, the core temperature is lower than 100°C, all the safety rods in the control rods are raised from the core and are at the top of the core, all the regulating rods and all the compensating rods in the control rods are at the lower limit position, and all the absorption balls are in the ball storage tanks at the upper part of the core.

[0031] Furthermore, in S4, the second part of the adding operation specifically includes the following steps:

[0032] S41, loading the mixed fuel into the reactor core according to 1 / 3 of the difference between the initial full loading amount and the current mixed fuel loading amount;

[0033] S42: After all the mixed fuel is loaded into the reactor core and the counting rate of the counter tube is stable, the mixed fuel loading amount and the cumulative count of the counter tube are recorded;

[0034] S43, calculating an extrapolated critical loading amount based on the counting rate of each counter tube, taking 1 / 3 of the difference between the three extrapolated critical loading amounts and the current mixed fuel loading amount and the difference between the initial full loading amount and the current mixed fuel loading amount, and comparing them, and using the minimum value as the loading amount for the next step;

[0035] S44. Repeat steps S42-S43 until the height of the mixed fuel in the core reaches the initial fully loaded core height.

[0036] Furthermore, the mixed fuel added each time in the first and second adding operations is a mixed fuel with a ratio of 4.2% enrichment fuel balls to graphite balls of 7:8.

[0037] Furthermore, in S2 and S4, the mixed fuel loading amount and the counting rate are recorded every time 1000 mixed fuels are loaded, so as to ensure that the reactivity introduction during the loading process is always safe and controllable.

[0038] Furthermore, in S2 and S4, if the buffer tube section of the core buffer charging device needs to be removed, the charging needs to be suspended, the pneumatic lifting gas source needs to be turned off, and the counting rate of the neutron counter tube before and after the removal needs to be recorded.

[0039] Furthermore, in S2 and S4, when the counter tube reading of the physical start system approaches the upper limit of the range, the counter tube needs to be moved. Each extrapolation is only allowed to move one of the three counter tubes, and the counting rate and position information of the three counter tubes before and after the movement are recorded.

[0040] Furthermore, in said S5, all control rods except the safety rods include regulating rods and compensating rods, and specifically include the following steps:

[0041] S51. Lift all control rods except the safety rod to the height of the graphite ball layer;

[0042] S52. Lift all control rods except the safety rod horizontally by 200 mm;

[0043] S53: Calculate the extrapolated critical rod positions based on the count rate of each counter tube, take the minimum value between 1 / 3 of the difference between the three extrapolated critical rod positions and the current average rod position and 200 mm to determine the next rod raising height, further determine the next target rod raising position, and raise all control rods except the safety rod horizontally to the target rod raising position;

[0044] S54, repeating step S53 until the difference between two or more extrapolated critical rod positions and the current average rod position is less than 50 mm, allowing transition to critical or supercritical;

[0045] S55. Perform critical operation, slowly lift all control rods except the safety rod by 100 mm one by one, record the critical rod position of the control rod and the source range count rate, and then insert a control rod below the height of the graphite ball layer.

[0046] Furthermore, during the transition to supercriticality, when the counting rate of the physical starting system counter tube approaches the upper limit of the range, the power supply of the corresponding channel counter tube is turned off, and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of system equipment and critical operations during the test.

[0047] Furthermore, in the operation step of lifting multiple control rods horizontally, the control rods should be lifted symmetrically to the specified positions as much as possible to avoid a large flux tilt in the reactor.

[0048] Furthermore, when the source range count rate rises above 3000 cps, the control rod positions are adjusted to stabilize the source range count rate and the reactor reaches a critical state.

[0049] Furthermore, in S55, all control rods except the safety rod are slowly raised 100 mm one by one, and the changes in the neutron count rate in the counter tube and source range are observed during the process. If any of the following situations occurs, the rod raising is stopped. The situations are as follows:

[0050] Case a: The neutron counting rate tends to increase steadily;

[0051] Case b: The reactor experiences a stable doubling cycle.

[0052] Furthermore, after S55 , it is necessary to record the temperature of each measuring point of the side reflective layer, and then sequentially insert all the adjustment rods and compensation rods to the lower limit position, and close the physical start system after completing the movement of the adjustment rods and compensation rods.

[0053] Furthermore, before moving the counter tube and removing the buffer tube section of the core buffer charging device during the extrapolation process, a control rod was inserted below the height of the graphite ball layer. After confirming that the operation of the counter tube and the buffer tube section of the core buffer charging device was completed and the staff had evacuated, the control rod inserted into the graphite ball layer was lifted again.

[0054] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0056] Figure 1 This is an overall method flow chart of a high-temperature gas-cooled reactor first-time loading and criticality method according to the present invention;

[0057] Figure 2 This is a flowchart of the specific steps of step S2 in the method for initial loading and criticality of a high-temperature gas-cooled reactor according to the present invention;

[0058] Figure 3 This is a flowchart of the specific steps of step S3 in the method for first loading and criticality of a high-temperature gas-cooled reactor according to the present invention;

[0059] Figure 4 This is a flowchart of the specific steps of step S4 in the method for first loading and criticality of a high-temperature gas-cooled reactor according to the present invention;

[0060] Figure 5 This is a flowchart of the specific steps of step S5 in the method for first loading and criticality of a high-temperature gas-cooled reactor according to the present invention. DETAILED DESCRIPTION

[0061] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but are not to be construed as limiting the present invention.

[0062] The present invention provides a method for first loading and criticality of a high temperature gas-cooled reactor. Figures 1 to 5 Elaborate in detail.

[0063] A method for first loading and criticality of a high-temperature gas-cooled reactor comprises the following steps:

[0064] S1. Adjust the system to the initial state of the first part of the addition operation. Load several graphite balls with an equivalent height of 6.05m at the bottom of the core. Plan and install the neutron source and physical start-up system according to the height of the graphite balls. Debug the neutron source and physical start-up system.

[0065] S2. Add the first part of the mixed fuel to the core until the reactor Keff is ≥ 0.998, allowing the transition to criticality or supercriticality;

[0066] S3, transition to criticality or supercriticality. When the source range count rate rises to more than 3000 cps, the control rod position is adjusted to stabilize the source range count rate and the reactor reaches criticality.

[0067] S4, adjusting the system to the initial state of the second part addition operation, and performing the second part addition operation of the mixed fuel into the core until the initial fully loaded core height is reached;

[0068] S5. Lift all 18 control rods except the safety rod multiple times to extrapolate the critical rod position, and observe the count rate of the physical start-up system counter tube in real time until the critical state is reached and the position of the critical control rod is determined; the control rods include safety rods, adjustment rods, and compensation rods.

[0069] The present invention decomposes the entire mixed fuel addition operation into a first addition operation and a second addition operation. The mixed fuel added in each of the first and second addition operations is a mixture of fuel balls with a 4.2% enrichment and graphite balls in a ratio of 7:8. The first addition operation allows the reactor to transition to criticality or supercriticality, and achieves net criticality of the reactor through criticality-reaching operation. The mixed fuel is then added to perform the second addition operation after the first addition operation is completed, thereby completing the entire mixed fuel addition operation. The control rod is lifted so that the mixed fuel reaches a critical state after reaching the initial full-load core height. The reactor can safely and effectively complete the initial loading and achieve criticality on the basis of graphite balls having an equivalent height of approximately 6.05 meters already loaded at the bottom of the core.

[0070] S1 to S3 are the first part of the mixed fuel addition operation, which makes the core reach net criticality. S4 and S5 are the second part of the mixed fuel addition operation after the first part of the addition operation, which makes the mixed fuel in the core reach the initial full core height and reach criticality. In the entire loading process, including the first part of the addition operation and the second part of the addition operation, that is, S2 and S4, it is always necessary to keep the record of the mixed fuel loading amount and counting rate every time 1000 mixed fuels are loaded, so as to ensure that the reactivity introduction during the loading process is always safe and controllable. And in the addition process of S2 and S4, as the core loading height increases, the mixed fuel loading amount and counting rate are kept constant. To increase the fuel supply, it is necessary to remove some buffer tube sections of the core buffer loading device to ensure the smooth addition of the mixed fuel. When removing some buffer tubes of the buffer loading device, the loading must be suspended and the pneumatic lifting gas source must be turned off. At the same time, considering the impact of the removal of the buffer tube sections of the loading buffer device on the neutron counting rate, the counting rate of the neutron counting tube must be recorded before and after the removal; and during the addition operation of S2 and S4, when the counting tube reading of the physical starting system is close to the upper limit of the range, the counting tube needs to be moved. After each extrapolation, only one of the three counting tubes is allowed to be moved, and the counting rate and position information of the moved counting tube before and after the movement are recorded to ensure the effectiveness of the extrapolation.

[0071] In order to ensure the safety of the operators, before moving the neutron counting tube and removing the buffer tube section of the core buffer charging device, a control rod should be inserted below the height of the graphite ball layer. After confirming that the operation of the neutron counting tube and the buffer tube section of the core buffer charging device is completed and the personnel have evacuated, the inserted control rod can be lifted.

[0072] The following describes in detail the operation of adding the first portion of the mixed fuel and the critical steps S1 to S3.

[0073] Among them, S1 is the initial preparation step for the first part of the addition operation. In S1, before starting to load the fuel elements, a graphite ball bed with an equivalent height of 6.05m is first loaded at the bottom of the reactor. This can prevent excessive residual reactivity when the core is loaded to the designed height, and can also prevent the fuel elements from exceeding the designed drop height limit when being loaded into the core.

[0074] The initial conditions for the first addition operation in S1 are: the reactor is at atmospheric pressure, the primary core circuit is in air, the core temperature is below 100°C, all control rods, including safety rods, regulating rods, and compensating rods, are in their upper limits, and all absorption balls are blown out of the core and contained in the upper core storage tank. The physical startup system parameters must be adjusted to within reasonable ranges, and the cumulative count rate of the counter tube and the reactor core temperature must be recorded.

[0075] In S1, the installation height of the neutron source is set within 0.5m higher than the height of the graphite ball layer, and the physical starting system includes three counting tubes located in the side reflection layer channel. The distribution heights of the three counting tubes are respectively below the height of the graphite ball layer, equal to the height of the neutron source, and above the height of the neutron source. The counting rate of the counting tubes under the neutron source conditions is ≥2cps.

[0076] The specific steps of adding the first part of the mixed fuel in S2 include:

[0077] S21. 1 / 3 of the critical fuel ball loading provided by physical calculation is used as the initial fuel loading. The first fuel ball addition amount is 1 / 3 of the difference between the critical fuel loading provided by physical calculation and the initial fuel loading.

[0078] S22, the second fuel ball addition amount is 1 / 3 of the difference between the minimum value of the critical fuel ball loading amount obtained by physical extrapolation of the three counter tubes and the critical fuel ball loading amount obtained by physical calculation and the current fuel loading amount;

[0079] S23. The amount of fuel added each time thereafter is 1 / 3 of the difference between the minimum value of the physical extrapolation of the three counter tubes and the current loading of the core, and this step is repeated until the reactor Keff ≥ 0.998, at which time the transition to criticality or supercriticality is allowed, and criticality operation is performed.

[0080] Furthermore, in S3, when transitioning to criticality or supercriticality, performing criticality operation specifically includes the following steps:

[0081] S31. Lower a control rod to below the graphite sphere layer height, specifically to the 6050mm rod position. The control rod position must not be lowered below the graphite sphere height, i.e., the 6050mm rod position. Then, load additional mixed fuel capable of introducing 100 pcm of reactivity. Observe the changes in the neutron count rate in the counter tube and source range during the loading process.

[0082] S32. After all the mixed fuel in S31 is loaded into the core, gradually lift the control rods inserted into the graphite ball layer, and record the cumulative loading of the mixed fuel, the reactor doubling cycle, and the position of the control rods inserted;

[0083] S33. When the source range count rate rises to above 3000cps, adjust the control rod position to make the source range count rate stabilize and the reactor reach critical state. Record the control rod critical rod position and source range count rate, and then insert a control rod below the height of the graphite ball layer.

[0084] During the transition to supercriticality, when the counting rate of the physical start-up system counter tube approaches the upper limit of the range, the corresponding channel counter tube power is turned off and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of the system equipment and critical operation during the test. In addition, in S32, if any of the following situations occurs, the rod lifting is stopped, as follows:

[0085] Case a: The neutron counting rate tends to increase steadily;

[0086] Case b: The reactor has a stable doubling cycle.

[0087] In S3, criticality is achieved by adjusting the control rods. This ensures that the accuracy of reactivity introduction during the criticality process is high enough and the response speed is fast enough, thereby improving the reactivity control effect of critical operation. In addition, on the basis of the extrapolated critical loading, an additional reactivity of about 100 pcm is introduced through loading to ensure that even if the extrapolated calculation error is taken into account, criticality will not occur. Moreover, even if all the control rods are accidentally pulled out of the core, short-term criticality will not occur, thereby ensuring both test efficiency and safety.

[0088] After completing the operations in S3, record the temperature of each measuring point of the side reflector, calculate the average temperature of the side reflector, and insert all adjustment rods and compensation rods in sequence to confirm that all safety rods are at the top of the core, providing an initial environment for the second part of the addition operation.

[0089] The following describes in detail the operation of adding the second portion of the mixed fuel and steps S4 to S5 when the fuel reaches criticality.

[0090] During S4 of the second partial addition operation, the initial conditions are: the reactor is at atmospheric pressure, the primary core circuit is in air, the core temperature is below 100°C, all safety rods in the control rod system are raised out of the core and positioned at the top of the core, all regulating rods and compensating rods are at their lower limits, and all absorber spheres are in the upper core sphere tanks. Prior to the second partial addition operation, the mixed fuel loading amount and the counter tube cumulative count are recorded.

[0091] Then, the second part of the adding operation is performed. In S4, the second part of the adding operation specifically includes the following steps:

[0092] S41, loading the mixed fuel into the reactor core according to 1 / 3 of the difference between the initial full loading amount and the current mixed fuel loading amount;

[0093] S42: After all the mixed fuel is loaded into the reactor core and the counting rate of the counter tube is stable, the mixed fuel loading amount and the cumulative count of the counter tube are recorded;

[0094] S43, calculating an extrapolated critical loading amount based on the counting rate of each counter tube, taking 1 / 3 of the difference between the three extrapolated critical loading amounts and the current mixed fuel loading amount and the difference between the initial full loading amount and the current mixed fuel loading amount, and comparing them, and using the minimum value as the loading amount for the next step;

[0095] S44. Repeat steps S42-S43 until the height of the mixed fuel in the core reaches the initial fully loaded core height.

[0096] After completing step S4, the rod lifting operation is started to allow transition to criticality or supercriticality, and then the criticality operation is carried out until the reactor reaches the critical state, which is step S5.

[0097] In S5, all control rods except the safety rods, including the regulating rod and the compensating rod, specifically include the following steps:

[0098] S51. Lift all control rods except the safety rod to the height of the graphite ball layer;

[0099] S52. Lift all control rods except the safety rod horizontally by 200 mm;

[0100] S53: Calculate the extrapolated critical rod positions based on the count rate of each counter tube, take the minimum value between 1 / 3 of the difference between the three extrapolated critical rod positions and the current average rod position and 200 mm to determine the next rod raising height, further determine the next target rod raising position, and raise all control rods except the safety rod horizontally to the target rod raising position;

[0101] S54, repeating step S53 until the difference between two or more extrapolated critical rod positions and the current average rod position is less than 50 mm, allowing transition to critical or supercritical;

[0102] S55. Perform criticality operation and slowly lift up all control rods except the safety rod by 100 mm one by one. After lifting all control rods except the safety rod by 100 mm, the reactor is in critical state. Record the critical rod position of the control rod and the source range count rate. Then, insert a control rod below the height of the graphite ball layer.

[0103] During the initial full load and rod lifting process to reach the critical level, the control rods have almost no value below the graphite ball layer height. First, lift them to the 6050mm rod position at one time, and then repeat the S53 step. This can ensure the test efficiency while avoiding excessive introduction of reactivity caused by uneven control rod value.

[0104] Among them, during the transition to supercriticality, when the counting rate of the physical starting system counter tube approaches the upper limit of the range, the power supply of the corresponding channel counter tube is turned off, and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of system equipment and critical operations during the test.

[0105] In the operation step of lifting multiple control rods horizontally in S5, the control rods should be lifted symmetrically to the specified position as much as possible to avoid large flux tilt of the reactor.

[0106] In S55, after all control rods except the safety rod are lifted by 100 mm, when the source range count rate rises above 3000 cps, the control rod positions are adjusted to stabilize the source range count rate and the reactor reaches a critical state.

[0107] Furthermore, in S55, all control rods except the safety rod are slowly raised 100 mm one by one. During this process, the changes in the neutron count rate in the counter tube and source range need to be closely observed. If any of the following situations occurs, the rod raising is stopped. The situations are as follows:

[0108] Case a: The neutron counting rate tends to increase steadily;

[0109] Case b: The reactor experiences a stable doubling cycle.

[0110] After completing step S55 in S5, it is necessary to record the temperature of each measuring point of the side reflective layer, and then insert all the adjustment rods and compensation rods to the lower limit position in sequence. After completing the movement of the adjustment rods and compensation rods, turn off the physical start system.

[0111] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0112] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0113] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for first loading and criticality of a high temperature gas-cooled reactor, characterized in that: The steps include: S1. Adjust the system to the initial state of the first part of the addition operation. Load several graphite balls with an equivalent height of 6.05m at the bottom of the core. Plan and install the neutron source and physical start-up system according to the height of the graphite balls. Debug the neutron source and physical start-up system. S2. Add the first part of the mixed fuel to the core until the reactor Keff is ≥ 0.998, allowing the transition to criticality or supercriticality; S3, transition to criticality or supercriticality. When the source range count rate rises to more than 3000 cps, the control rod position is adjusted to stabilize the source range count rate and the reactor reaches criticality. S4, adjusting the system to the initial state of the second part addition operation, and performing the second part addition operation of the mixed fuel into the core until the initial fully loaded core height is reached; S5. Lift all control rods except the safety rod horizontally multiple times to extrapolate the critical rod position, and observe the count rate of the physical start-up system counter tube in real time until the critical state is reached and the position of the critical control rod is determined; The initial state of the first addition operation is: the reactor is at normal pressure, the primary circuit of the core is in air atmosphere, the core temperature is below 100°C, all control rods including safety rods, regulating rods and compensating rods are in the upper position, and all absorption balls are in the upper core storage tank; In S1, the neutron source is installed at a height within 0.5 m higher than the graphite ball layer, and the physical starting system includes three counting tubes located in the side reflector channel, and the three counting tubes are distributed at heights below the graphite ball layer, equal to the neutron source height, and above the neutron source height, respectively; In S5, all control rods except the safety rod include regulating rod and compensating rod. The following steps are involved: S51. Lift all control rods except the safety rod to the height of the graphite ball layer; S52. Lift all control rods except the safety rod horizontally by 200 mm; S53: Calculate the extrapolated critical rod positions based on the count rate of each counter tube, take the minimum value between 1 / 3 of the difference between the three extrapolated critical rod positions and the current average rod position and 200 mm to determine the next rod raising height, further determine the next target rod raising position, and raise all control rods except the safety rod horizontally to the target rod raising position; S54, repeating step S53 until the difference between two or more extrapolated critical rod positions and the current average rod position is less than 50 mm, allowing transition to critical or supercritical; S55. Perform critical operation, slowly lift all control rods except the safety rod by 100 mm one by one, record the critical rod position of the control rod and the source range count rate, and then insert a control rod below the height of the graphite ball layer.

2. The method for initial charging and criticality of a high-temperature gas-cooled reactor according to claim 1, wherein: The counting rate of the counter tube under neutron source conditions is ≥2cps.

3. The method for initial charging and criticality of a high temperature gas-cooled reactor according to claim 2, wherein: The S2 specifically includes the following steps: S21. 1 / 3 of the critical fuel ball loading provided by physical calculation is used as the initial fuel loading. The first fuel ball addition amount is 1 / 3 of the difference between the critical fuel loading provided by physical calculation and the initial fuel loading. S22, the second fuel ball addition amount is 1 / 3 of the difference between the minimum value of the critical fuel ball loading amount obtained by physical extrapolation of the three counter tubes and the critical fuel ball loading amount obtained by physical calculation and the current fuel loading amount; S23. The amount of fuel added each time thereafter is 1 / 3 of the difference between the minimum value of the physical extrapolation of the three counter tubes and the current loading of the core, and this step is repeated until the reactor Keff ≥ 0.998, at which time the transition to criticality or supercriticality is allowed.

4. The method for initial charging and criticality of a high-temperature gas-cooled reactor according to claim 3, wherein: In S3, the transition to criticality or supercriticality specifically includes the following steps: S31. Insert a control rod below the height of the graphite sphere layer, then load additional mixed fuel capable of introducing 100 pcm of reactivity. During the loading process, observe the changes in the neutron count rate in the counter tube and source range. S32. After all the mixed fuel in S31 is loaded into the core, gradually lift the control rods inserted into the graphite ball layer, and record the cumulative loading of the mixed fuel, the reactor doubling cycle, and the position of the control rods inserted; S33. When the source range count rate rises to above 3000cps, adjust the control rod position to make the source range count rate stabilize and the reactor reach critical state. Record the control rod critical rod position and source range count rate, and then insert a control rod below the height of the graphite ball layer.

5. The method for initial charging and criticality of a high-temperature gas-cooled reactor according to claim 4, characterized in that: During the transition to supercriticality, when the counting rate of the physical starting system counter tube approaches the upper limit of the range, the power supply of the corresponding channel counter tube is turned off, and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of system equipment and critical operations during the test.

6. The method for initial charging and criticality of a high-temperature gas-cooled reactor according to claim 5, characterized in that: In S32, when any of the following situations occurs, the stick lifting is stopped, as follows: Case a: The neutron counting rate tends to increase steadily; Case b: The reactor has a stable doubling cycle.

7. The method for initial charging and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: In S4, the initial state of the second addition operation is: the reactor is at normal pressure, the primary circuit of the core is in air atmosphere, the core temperature is lower than 100°C, all safety rods in the control rods are raised from the core and are at the top of the core, all regulating rods and all compensating rods in the control rods are at the lower limit positions, and all absorption balls are in the ball storage tanks above the core.

8. The method for initial charging and criticality of a high-temperature gas-cooled reactor according to claim 7, characterized in that: In S4, the second part of the adding operation specifically includes the following steps: S41, loading the mixed fuel into the reactor core according to 1 / 3 of the difference between the initial full loading amount and the current mixed fuel loading amount; S42: After all the mixed fuel is loaded into the reactor core and the counting rate of the counter tube is stable, the mixed fuel loading amount and the cumulative count of the counter tube are recorded; S43, calculating an extrapolated critical loading amount based on the counting rate of each counter tube, taking 1 / 3 of the difference between the three extrapolated critical loading amounts and the current mixed fuel loading amount and the difference between the initial full loading amount and the current mixed fuel loading amount, and comparing them, and using the minimum value as the loading amount for the next step; S44. Repeat steps S42-S43 until the height of the mixed fuel in the core reaches the initial fully loaded core height.

9. A method for initial charging and criticality of a high temperature gas-cooled reactor according to any one of claims 1 to 8, characterized in that: The mixed fuel added each time in the first and second addition operations is a mixed fuel of 4.2% enrichment fuel balls and graphite balls in a ratio of 7:

8.

10. The method for initial charging and criticality of a high temperature gas-cooled reactor according to any one of claims 1 to 8, characterized in that: In S2 and S4, the mixed fuel loading amount and the count rate are recorded every time 1000 mixed fuels are loaded, so as to ensure that the reactivity introduction during the loading process is always safe and controllable.

11. A method for initial charging and criticality of a high temperature gas-cooled reactor according to any one of claims 1 to 8, characterized in that: In S2 and S4, if the buffer tube section of the core buffer charging device needs to be removed, the charging needs to be suspended, the pneumatic lifting gas source needs to be turned off, and the counting rate of the neutron counter tube before and after the removal needs to be recorded.

12. A method for initial charging and criticality of a high temperature gas-cooled reactor according to any one of claims 1 to 8, characterized in that: In S2 and S4, when the counter tube reading of the physical start system approaches the upper limit of the range, the counter tube needs to be moved. Each extrapolation is allowed to move only one of the three counter tubes, and the counting rate and position information of the three counter tubes before and after the movement are recorded.

13. The method for initial charging and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: During the transition to supercriticality, when the counting rate of the physical starting system counter tube approaches the upper limit of the range, the power supply of the corresponding channel counter tube is turned off, and the counting rate is monitored through the nuclear measurement system source range to ensure the safety of system equipment and critical operations during the test.

14. The method for initial loading and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: During the operation of lifting multiple control rods horizontally, the control rods should be lifted symmetrically to the designated positions as much as possible to avoid large flux tilt in the reactor.

15. The method for initial loading and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: When the source range count rate rises above 3000cps, the control rod position is adjusted to make the source range count rate tend to be stable and the reactor reaches a critical state.

16. The method for initial loading and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: In S55, all control rods except the safety rod are slowly raised 100 mm one by one. During this process, the changes in the neutron count rate in the counter tube and source range are observed. If any of the following situations occurs, stop raising the rods. The situations are as follows: Case a: The neutron counting rate tends to increase steadily; Case b: The reactor experiences a stable doubling cycle.

17. The method for initial loading and criticality of a high temperature gas-cooled reactor according to claim 1, wherein: After S55, it is necessary to record the temperature of each measuring point of the side reflective layer, and then insert all the adjustment rods and compensation rods to the lower limit in sequence. After completing the movement of the adjustment rods and compensation rods, turn off the physical start system.

18. A method for initial loading and criticality of a high temperature gas-cooled reactor according to any one of claims 1-8 and 13-17, characterized in that: During the extrapolation process, before moving the counter tube and removing the buffer tube section of the core buffer charging device, a control rod is inserted below the height of the graphite ball layer. After confirming that the operation of the counter tube and the buffer tube section of the core buffer charging device is completed and the staff have evacuated, the control rod inserted into the graphite ball layer is lifted again.

Images