Reactor passive starting device and reactor passive starting method

Abstract

The invention relates to the technical field of nuclear power, and provides a reactor passive starting device and a reactor passive starting method in order to reduce or eliminate a blind area range during passive starting of a nuclear power reactor. The device comprises a detector arranged in an out-of-reactor detection duct and a neutron channel box arranged in a descending section coolant layer between a pressure vessel and a hanging basket of a reactor, wherein the neutron channel box is close to the out-of-reactor detector; when the neutron channel box is a hollow channel, the passive starting method of the reactor comprises the following steps: in the starting process of the reactor, keeping that the neutron channel box is filled with high-pressure gas, keeping that a coolant does not circulate in the neutron channel box, and keeping that the coolant still circulates in other areas between the hanging basket and the pressure vessel; after the critical start of the reactor is completed, injecting a coolant into the neutron channel box; according to the method, the critical monitoring blind area in the critical starting process of the first-cycle reactor is eliminated, and blind-area-free passive starting of the first-cycle reactor is realized.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and in particular to a reactor passive starting device and a reactor passive starting method. Background Art

[0002] The physical startup of a nuclear reactor is a process of gradually introducing reactivity into the core. Criticality safety requires strict control of the core k eff The growth rate of the core neutron flux is controlled to prevent the reactor from reaching an uncontrollable instantaneous critical state. Therefore, the core criticality safety must be strictly monitored to prevent dangerous situations such as accidental criticality. Conventional nuclear pressure water reactors usually use the method of introducing an external neutron source into the core, that is, starting the neutron source, to increase the neutron flux rate level of the reactor in the subcritical state, so that the neutron detector of the nuclear instrument system outside the core always has an effective counting rate signal, and can "explicitly" monitor the changes in the core neutron flux rate, ensuring that criticality safety supervision is carried out during the process of reactor loading to criticality, thereby ensuring the criticality safety of the reactor. In addition, during the process of reactive introduction such as reactor loading, control rod lifting or boron dilution, it is also necessary to provide guidance through the signal changes of the neutron detector in order to efficiently complete the reactor loading and startup.

[0003] Commonly used reactor startup neutron sources are divided into primary neutron sources and secondary neutron sources. Usually, in the first cycle, the primary neutron source is relied on for criticality safety supervision. The primary neutron source can spontaneously produce neutrons. Usually, a californium source is used, and its source neutrons come from the spontaneous fission of Cf-252. From the second cycle, the secondary neutron source is relied on for criticality safety supervision. The secondary neutron source needs to be activated by irradiation in the reactor before it can produce neutrons. It is usually placed in the reactor for activation in the first cycle and used for reactor startup from the second cycle. It is usually an antimony-beryllium source (Sb-Be source), and the source neutrons come from the photon fission of beryllium. At present, there is no mature supply source of primary neutron source in my country. In addition, the use of external neutron source to start the nuclear reactor has the disadvantages of increasing the cost of nuclear power plants to deal with the high-level waste generated by the startup neutron source, limiting the reactor construction period due to the long production and procurement cycle of the primary neutron source and the continuous attenuation of the source strength, and the damage of the secondary neutron source components or the long shutdown time for refueling and overhaul, which will have a great impact on the loading and startup of the reactor.

[0004] Therefore, it is necessary to develop a passive start technology, which refers to the technology of using the neutrons spontaneously released by nuclear fuel as the starting neutron source of the nuclear reactor to complete the reactor startup without an external neutron source (i.e., primary neutron source assembly or secondary neutron source assembly). This technology can effectively eliminate the dependence of my country's nuclear power reactor startup on imported primary neutron source materials, while avoiding the economic and environmental burden brought by the use of neutron sources, and has great application prospects in nuclear power reactors.

[0005] When the reactor implements passive startup, the neutrons spontaneously released by nuclear fuel are used as the startup neutron source, and its source strength may be weaker than that of the external startup neutron source. In particular, the first cycle of nuclear power reactors is usually loaded with new fuel assemblies, and the neutron source strength of its spontaneous release is 2 to 3 orders of magnitude weaker than that of the external startup neutron source. Under such weak source conditions, the neutron flux density in the core is already very low, and the neutron flux density at the neutron detector outside the core will drop by several orders of magnitude after experiencing layer-by-layer attenuation from the core to the outside of the core. At this time, if only traditional neutron detectors are used in the detection channels outside the core or high-sensitivity neutron detectors are added, there will inevitably be a certain range of monitoring "blind spots" in the detectors outside the core when the pre-criticality is deep, and it is impossible to carry out "explicit" criticality safety supervision, and it is also impossible to effectively guide the reactive introduction process such as control rod lifting or boron dilution, which is not conducive to the safety and efficiency of passive startup. Taking the passive start of the first cycle of the VVER nuclear power reactor that has been built in my country as an example, due to the presence of a certain range of monitoring "blind spots" during the startup, it is necessary to use additional means to control the boron dilution channel to prevent accidental criticality, and it is also necessary to perform the boron dilution operation more cautiously during the criticality process, which increases the startup time to a certain extent. Therefore, reducing or eliminating the blind area range during the passive start of nuclear power reactors is a key technical issue that needs to be urgently solved in the passive start of reactors. Summary of the invention

[0006] The purpose of the present invention is to provide a reactor passive starting device and a reactor passive starting method, which is intended to eliminate the critical monitoring blind area during the critical starting process of the first cycle reactor and realize the blind area-free passive starting of the first cycle reactor.

[0007] The embodiments of the present invention are achieved through the following technical solutions:

[0008] A reactor passive starting device comprises a detector arranged in an external detection channel of the reactor and a neutron channel box arranged in a coolant layer of a descending section between a pressure vessel and a hanging basket of the reactor, wherein the neutron channel box is close to the detector outside the reactor.

[0009] Furthermore, the neutron channel box is a channel connecting the reactor pressure vessel and the hanging basket.

[0010] Furthermore, the neutron channel box is a channel box body, and is fixedly arranged in the coolant layer of the descending section between the pressure vessel and the hanging basket.

[0011] Furthermore, in the axial direction, the height range of the neutron channel box is the same as the height range of the reactor core active area; in the radial direction, the symmetry line of the neutron channel box and the line connecting the midpoint of the reactor core to the detector outside the reactor are the same straight line.

[0012] Furthermore, the neutron channel box is a solid channel or a hollow channel; the hollow channel is filled with high-pressure gas, such as high-pressure helium, nitrogen or air; the solid channel material includes but is not limited to stainless steel, zirconium, etc., and the cross-sectional shape of the solid channel includes but is not limited to arc, trapezoid, rectangle; the volume of the neutron channel box is 1% to 100% of the volume of the coolant layer of the descent section between the pressure vessel and the hanging basket.

[0013] Furthermore, during the reactor startup process, coolant does not flow in the neutron channel box, while coolant still flows in other areas between the hanging basket and the pressure vessel.

[0014] Furthermore, in the radial direction, the structure of the neutron channel box consists of a first arc segment at the hanging basket close to the core, a second arc segment close to the pressure vessel, and a tangent segment connecting the first arc segment and the second arc segment, wherein the length of the first arc segment is not less than the length of the second arc segment.

[0015] A reactor passive startup method, if the neutron channel box is a hollow channel, comprises the following steps:

[0016] S1. Using the above device, during the reactor startup process, the neutron channel box is kept filled with high-pressure gas, and the coolant is kept not flowing in the neutron channel box, while the coolant is still flowing in other areas between the hanging basket and the pressure vessel;

[0017] This increases the probability of neutrons being transported from the core to the external detectors, thereby reducing the blind area of ​​the first cycle reactor startup process and even achieving blind-area-free passive startup.

[0018] S2. After the critical start-up of the reactor is completed, coolant (boron-containing coolant water) is injected into the neutron channel box to act as a shielding layer during the operation of the reactor to prevent the pressure vessel from being subjected to excessive neutron irradiation and affecting its service life.

[0019] A method for passively starting a reactor using a neutron channel box. If the neutron channel box is a solid channel, the difference from a hollow channel is that there is no S2 step, that is, during the reactor startup process, in addition to the neutron channel box, coolant continues to flow in other areas between the hanging basket and the pressure vessel. In this case, the coolant cannot flow in some areas between the hanging basket and the pressure vessel, and the cooling capacity may be weakened to a certain extent, but the cooling capacity can be improved by increasing the coolant flow rate.

[0020] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0021] 1. The present invention partially replaces the coolant with strong neutron absorption effect by setting a neutron channel between the hanging basket and the pressure vessel. Under the premise of not affecting the overall cooling capacity of the core, it effectively reduces the attenuation effect of neutrons spontaneously generated by the core fuel and transported to the outside of the core, increases the neutron flux density in the detector channel outside the core during the reactor startup process, and cooperates with the high-sensitivity detector set outside the core to ensure that there is no detection blind spot in the passive startup of the first cycle reactor, so that the whole process of neutron injection rate growth during the physical startup of the reactor is placed under effective supervision, thereby ensuring the safe startup of the reactor.

[0022] 2. Compared with the situation that the first cycle of the traditional nuclear pressurized water reactor adopts an external neutron source, the present invention eliminates the use of primary neutron source components and secondary neutron source components, saves the procurement cost of primary neutron sources and secondary neutron sources (the primary sources are all purchased from abroad, and the procurement cost of the two primary neutron sources required for the first cycle core is generally around RMB 20 million, and the procurement cost is greatly affected by the international political and economic situation), avoids the technical risks brought by international monopoly, avoids the risk of excessive attenuation of the californium source intensity due to uncertainty in the construction period, reduces the output of primary source radioactive waste and its disposal cost, and is beneficial to environmental protection; at the same time, it reduces the output of secondary neutron source radioactive waste and its disposal cost, eliminates tritium emissions caused by secondary sources, improves the environmental protection indicators of the reactor, and improves the flexibility of the loading and commissioning of nuclear power plants.

[0023] 3. Compared with the currently implemented passive startup scheme for the first cycle of VVER nuclear power reactors, the present invention can eliminate the detection blind spots, ensure that the core is always under the "explicit" critical safety supervision of the neutron detectors in the nuclear measurement system, and can also effectively guide the reactive introduction processes such as control rod lifting or boron dilution through the signal changes of the detectors, thereby relaxing the requirements on the boron dilution rate, etc., and improving the safety and efficiency of reactor startup.

[0024] 4. The present invention can effectively improve the safety of passive reactor startup, while eliminating the dependence of reactor startup on imported primary neutron source materials, thereby improving the economy and environmental protection indicators of my country's nuclear power reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 A schematic diagram of the structure of a neutron channel box provided in Example 1 of the present invention;

[0027] Figure 2 For the present invention Figure 1 The enlarged view of point A in the middle;

[0028] Figure 3 A schematic structural diagram of a neutron channel box provided in Example 2 of the present invention;

[0029] Icons: 1-detector, 2-neutron channel box, 21-first arc segment, 22-tangent segment, 23-second arc segment, 3-pressure vessel, 4-basket, 5-coolant layer, 6-core. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0031] A reactor passive starting device and a reactor passive starting method provided by an embodiment of the present invention are described in detail below.

[0032] Traditional pressurized water reactors are mainly composed of fuel assemblies and related components, internal components, control rod drive mechanisms, reactor pressure vessels and their supports, insulation layers, and top structures. In the absence of an external neutron source, the neutrons spontaneously released by the fuel proliferate from the core and need to pass through the reflector layer, basket, descending coolant layer, pressure vessel, insulation layer and other structures. They will be absorbed and scattered by various materials, especially the thick descending coolant water layer between the basket and the pressure vessel, which usually contains a certain concentration of boric acid, which has a strong absorption effect on neutrons, so the number of neutrons reaching the external detectors will be reduced by several orders of magnitude. By adjusting the reactor structure design and material replacement, the absorption of neutrons by various structural materials and key coolants can be reduced, which is expected to increase the probability of neutrons being transported from the core to the external detectors, so as to reduce the blind area range of the first cycle reactor startup process and even achieve the purpose of blind area-free passive startup.

[0033] Based on this, in order to shorten the path of neutron transport to the off-core detector and to achieve the purpose of increasing the count rate response of the off-core detection system, the present invention provides a reactor passive starting device, including a detector 1 arranged in an off-core detection channel, and a neutron channel box 2 arranged in the descending coolant layer 5 between the reactor pressure vessel 3 and the hanging basket 4, wherein the neutron channel box 2 is close to the off-core detector 1; a neutron channel box 2 is arranged in the descending coolant layer 5 between the reactor pressure vessel 3 and the hanging basket 4, and the neutron channel box 2 can be directly connected to the pressure vessel 3 and the hanging basket 4, or can be arranged as an independent channel box in the descending coolant layer 5 between the pressure vessel 3 and the hanging basket 4 during the first cycle passive starting, and it is determined whether to remove the reactor after the first cycle is completed or continue to be arranged in the reactor according to the actual needs of the reactor.

[0034] Furthermore, the neutron channel box 2 is a channel box body, and is fixedly arranged in the coolant layer 5 of the descending section between the pressure vessel 3 and the hanging basket 4 .

[0035] Furthermore, in the axial direction, the height range of the neutron channel box 2 is the same as the height range of the active area of ​​the core 6; in the radial direction, the symmetry line of the neutron channel box 2 and the line connecting the midpoint of the core 6 to the detector 1 outside the core are the same straight line.

[0036] Furthermore, the neutron channel box 2 is a solid channel or a hollow channel; if it is a hollow channel, the hollow channel is filled with high-pressure gas, such as high-pressure helium, nitrogen or air; in addition, inlets and outlets and valves need to be set on the hollow channel so that boron-containing coolant can be injected into the hollow channel when the reactor needs it; in addition, the material of the neutron channel box 2 includes but is not limited to stainless steel and zirconium, and the cross-sectional shape of the solid channel includes but is not limited to arc, trapezoid, and rectangle.

[0037] Regardless of whether the neutron channel box 2 is a solid channel or a hollow channel, the material, shape and volume of the neutron channel box 2 can be changed according to the actual situation of the specific reactor. The volume of the neutron channel box 2 is 1% to 100% of the volume of the coolant layer 5 in the descending section between the pressure vessel 3 and the hanging basket 4.

[0038] Furthermore, during the reactor startup process, the coolant does not flow in the neutron channel box 2 , while the coolant still flows in other areas between the hanging basket 4 and the pressure vessel 3 .

[0039] Furthermore, in the radial direction, the structure of the neutron channel box 2 consists of a first arc segment 21 close to the core 6 basket 4, a second arc segment 23 close to the pressure vessel 3, and a tangent segment 22 connecting the first arc segment 21 and the second arc segment 23, wherein the length of the first arc segment 21 is not less than the length of the second arc segment 23.

[0040] In order to achieve the purpose of using the neutron channel box 2 to realize the reactor start-up without blind spots and minimize the impact on the reactor structure, it is also necessary to use the following reactor passive start-up method. If the neutron channel box 2 is a hollow channel, it includes the following steps:

[0041] S1. During the reactor startup process, the neutron channel box 2 is kept filled with high-pressure gas, and the coolant is kept not flowing in the neutron channel box 2, while the coolant is still flowing in other areas between the hanging basket 4 and the pressure vessel 3;

[0042] Thereby, the probability of neutrons being transported from the core 6 to the external detector 1 is increased, so as to reduce the blind area range of the first cycle reactor startup process and even achieve a blind area-free passive startup;

[0043] S2. After the critical start-up of the reactor is completed, coolant (such as boron-containing coolant water) is injected into the neutron channel box 2 to play the role of a shielding layer during the operation of the reactor to prevent the pressure vessel 3 from being subjected to excessive neutron irradiation and affecting its service life.

[0044] A method for passively starting a reactor using a neutron channel box 2, if the neutron channel box 2 is a solid channel, the difference from a hollow channel is that there is no S2 step, that is, during the reactor startup process, in addition to the neutron channel box, the coolant continues to flow in other areas between the hanging basket and the pressure vessel. In this case, the coolant cannot flow in some areas between the hanging basket 4 and the pressure vessel 3, and the cooling capacity may be weakened to a certain extent, but the cooling capacity can be improved by increasing the coolant flow rate and other methods.

[0045] Example 1

[0046] like Figure 1 As shown, this embodiment provides a reactor passive starting device, including a detector 1 arranged in an off-core detection channel and a neutron channel box 2 arranged in a descending coolant layer 5 between a reactor pressure vessel 3 and a hanging basket 4, wherein the neutron channel box 2 is close to the off-core detector 1; a hollow neutron channel box 2 is arranged in the descending coolant layer 5 between the reactor pressure vessel 3 and the hanging basket 4, and the hollow neutron channel box 2 is filled with high-pressure helium. In this scheme, the cross-section of the neutron channel box 2 is 1435cm 2 ;

[0047] The neutron channel box 2 is fixedly arranged in the coolant layer 5 of the descending section between the pressure vessel 3 and the hanging basket 4, and in the axial direction, the height range of the neutron channel box 2 is the same as the height range of the active area of ​​the core 6; in the radial direction, the symmetry line of the neutron channel box 2 and the line connecting the midpoint of the core 6 to the detector 1 outside the core are the same straight line, and in the radial direction, the structure of the neutron channel box 2 consists of a first arc segment 21 close to the hanging basket 4 of the core 6, a second arc segment 23 close to the pressure vessel 3, and a tangent segment 22 connecting the first arc segment 21 and the second arc segment 23, wherein the length of the first arc segment 21 is not less than the length of the second arc segment 23.

[0048] This embodiment also provides a reactor passive startup method, comprising the following steps:

[0049] S1. During the start-up of the first cycle reactor, the neutron channel box 2 is kept filled with high-pressure helium, and the coolant is kept not flowing in the neutron channel box 2, while the coolant is still flowing in other areas between the hanging basket 4 and the pressure vessel 3;

[0050] S2. After the critical start of the reactor, a boron-containing coolant is injected into the neutron channel box 2 to play the role of a shielding layer during the operation of the reactor, thereby preventing the pressure vessel 3 from being subjected to excessive neutron irradiation and affecting its service life.

[0051] In this embodiment, when the sensitivity of the high-sensitivity detector is 1020 cps / (n·cm -2 ·s -1 ), the count rate of the external detector in the reactor core under cold shutdown and ARI state is 0.75cps, which meets the requirements of EJ / T1114-2000, NB / T 20434-2017RK, RG 1.68 (2007) and other standards for monitoring the neutron count rate during reactor startup. It can be seen that by setting a neutron channel box in the coolant layer of the descending section, the count of the high-sensitivity detector can be significantly improved, the range of the detection blind area during the reactor startup can be reduced, and the reactor can be started passively without blind areas. Analysis shows that when the volume of the neutron channel box is the same, when the cross-section of the neutron channel box is arc-shaped, that is, when it fits the outer side of the hanging basket and the inner side of the pressure vessel, the neutron channel box has fewer water gaps close to the core and the detector, and the probability of neutrons in the core passing through the neutron channel box to reach the high-sensitivity detector is higher, which is more conducive to improving the detector count rate.

[0052] Example 2

[0053] The difference between this embodiment and embodiment 1 is that the neutron channel box is a solid channel. During the passive start of the first cycle, an independent solid neutron channel box 2 with an arc-shaped box cross section is arranged in the descending section boron-containing coolant layer 5 near the off-core high-sensitivity detector 1. The box material of the solid neutron channel box 2 is a stainless steel plate. In this solution, the box cross section is 1435 cm 2 . Figure 3 A schematic diagram of a solid neutron channel box 2 with an arc-shaped box cross section arranged in a coolant layer 5 between a reactor pressure vessel 3 and a hanging basket 4 is given.

[0054] In this embodiment, under the same cross-sectional area of ​​the neutron channel box, the solid arc-shaped neutron channel box has increased neutron absorption compared with the hollow arc-shaped neutron channel box filled with high-pressure helium, and the count rate of the out-of-core detector is reduced. When the sensitivity of the high-sensitivity detector is 1020cps / (n·cm -2 ·s -1 ), the count rate of the external detector in the reactor core under cold shutdown and ARI state is 0.58cps, which meets the requirements of EJ / T1114-2000, NB / T 20434-2017RK, RG 1.68 (2007) and other standards for monitoring the neutron count rate during reactor startup. Compared with the neutron-free channel box, the external detector using the solid arc neutron channel box is still significantly larger, which shows that the use of a solid neutron channel box is also a feasible solution to improve the count rate of the external detector.

[0055] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A reactor passive starting device, characterized in that: It comprises a detector arranged in an out-of-core detection channel and a neutron channel box arranged in a coolant layer of a descending section between a pressure vessel and a hanging basket of the reactor, wherein the neutron channel box is close to the out-of-core detector.

2. The reactor passive starting device according to claim 1, characterized in that: The neutron channel box is a channel connecting the reactor pressure vessel and the hanging basket.

3. The reactor passive starting device according to claim 2, characterized in that: The neutron channel box is a channel box body and is fixedly arranged in the coolant layer of the descending section between the pressure vessel and the hanging basket.

4. The reactor passive starting device according to claim 3, characterized in that: In the axial direction, the height range of the neutron channel box is the same as the height range of the reactor core active area; in the radial direction, the symmetry line of the neutron channel box and the line connecting the midpoint of the reactor core to the detector outside the reactor are the same straight line.

5. The reactor passive starting device according to claim 1, characterized in that: The neutron channel box is a solid channel or a hollow channel; the hollow channel is filled with high-pressure gas; the solid channel is made of stainless steel or zirconium, and the cross-sectional shape of the solid channel is arc, trapezoidal or rectangular.

6. The reactor passive starting device according to claim 1, characterized in that: The volume of the neutron channel box is 1% to 100% of the volume of the coolant layer in the descending section between the pressure vessel and the hanging basket.

7. The reactor passive starting device according to claim 1, characterized in that: During the reactor startup process, coolant does not flow in the neutron channel box, while coolant still flows in other areas between the hanging basket and the pressure vessel.

8. The reactor passive starting device according to claim 1, characterized in that: In the radial direction, the structure of the neutron channel box consists of a first arc segment at the hanging basket close to the core, a second arc segment close to the pressure vessel, and a tangent segment connecting the first arc segment and the second arc segment, wherein the length of the first arc segment is not less than the length of the second arc segment.

9. A method for passively starting a reactor, if the neutron channel box is a hollow channel, comprising the following steps: S1. Using the reactor passive starting device according to any one of claims 1 to 8, during the reactor startup process, the neutron channel box is kept filled with high-pressure gas, and the coolant is kept not flowing in the neutron channel box, while the coolant is still flowing in other areas between the hanging basket and the pressure vessel; S2. After the critical start-up of the reactor is completed, coolant is injected into the neutron channel box.

10. A method for passively starting a reactor using a neutron channel box, if the neutron channel box is a solid channel, comprising the following steps: By using the reactor passive starting device according to any one of claims 1 to 8, during the reactor startup process, except for the neutron channel box, coolant continuously flows through other areas between the hanging basket and the pressure vessel.

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