Boiling water reactor

Abstract

To provide a boiling water reactor capable of shortening the maximum value of the insertion time of each control rod required for scram when one HCU drives two or more control rods.SOLUTION: A plurality of control rods 201a, 201c, 201d via first scram pipes 104a, 302a, 104c, 302c, 104d, 302d, and one or more control rods 201b via second scram pipes 104b, 302b are connected to the same hydraulic control rod drive. The pressure-loss of the first scram pipes 104a, 302a, 104c, 302c, 104d, 302d is made larger than that of the second scram pipes 104b, 302b.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to boiling water nuclear reactors. [Background technology]

[0002] As an example of a control rod drive hydraulic system that can optimally control the filling water pressure according to the reactor pressure, Patent Document 1 describes a control rod drive hydraulic system of a reactor that includes a control rod drive mechanism that uses high-pressure water to perform emergency insertion of a control rod, an emergency insertion valve that is normally closed and opens during emergency control rod insertion, an accumulator that stores high-pressure water to be supplied to the control rod drive mechanism, a pump, a first pipe connecting the control rod drive mechanism and the emergency insertion valve, a second pipe connecting the emergency insertion valve and the accumulator, a third pipe connected to the outlet of the pump and joining the first pipe, and a fourth pipe that branches off midway through the third pipe and joins the second pipe, and that a pressure regulating valve capable of adjusting pressure loss according to the reactor pressure is provided in a portion of the third pipe between the outlet of the pump and the branching point of the fourth pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-136788 Summary of the Invention [Problem to be solved by the invention]

[0004] Boiling water reactors are equipped with a control rod drive mechanism to drive the control rods inside the reactor. The control rod drive has two functions: one is the drive function for controlling the reactor's power output and reactivity, and the other is the scram function, which is the function to rapidly insert the control rods into the reactor core when an emergency shutdown of the reactor is required, such as in the case of an earthquake.

[0005] To achieve a scram, the hydraulic control unit (HCU) generally uses high-pressure water that has been stored in advance. High-pressure nitrogen gas is stored in an accumulator in the HCU, and the high-pressure water is generated by releasing it all at once. This high-pressure water starts from the HCU and travels through the scram piping to the control rod drive mechanism. The high-pressure water pushes up the piston in the control rod drive mechanism, and the control rod connected to the piston is inserted into the reactor.

[0006] The HCU, scram piping, control rod drive mechanism, control rods, etc. related to the scram are called the control rod drive system. In the current type of advanced boiling water reactor (ABWR), a control rod drive system that sends high-pressure water to two control rod drive mechanisms per HCU is mixed with a control rod drive system that sends high-pressure water to one control rod drive mechanism per HCU.

[0007] Scram is one of the safety functions of a nuclear reactor, and its function evaluation during an earthquake is important for seismic evaluation. The method for evaluating the function of control rods during an earthquake is described in the "Nuclear Power Plant Seismic Design Technical Provisions (JEAG4601-2015)." The basic idea of ​​this evaluation method is that "the function required of control rods during an earthquake is to be inserted into the reactor core to ensure that the reactor is shut down, so the insertability of control rods during an earthquake is evaluated."

[0008] The evaluation item for control rod insertion during an earthquake is the insertion time, and it is required that the insertion time be kept within the target time. Analysis and experiments are used for the evaluation, and it has been confirmed that current nuclear reactors are sufficiently safe, but further safety improvements are required.

[0009] There are several technologies for structures that improve the safety of scram, such as a control rod hydraulic system that can optimally control the pressure of the high-pressure water used in scram according to the reactor pressure (see, for example, Patent Document 1).

[0010] When two or more control rods are connected to one HCU, there may be a difference in the insertion time of those control rods during scram. This difference is thought to be caused by the difference in the mass of the control rods and the difference in pressure loss in the scram piping.

[0011] The difference in mass of the control rods is due to, for example, the difference in the neutron absorbing material used in some of the control rods. The neutron absorbing material is made of boron carbide or hafnium, and the difference in density between these and the structure of the control rods using these materials causes a difference in the mass of the control rods.

[0012] The difference in pressure loss in the scram piping is due to differences in the length, number of bends, and angle of the bends. The longer the length, the greater the number of bends, and the sharper the angle of the bends, the greater the pressure loss. Differences in the mass of the control rods and differences in pressure loss in the scram piping can cause differences in the resistance force that occurs when the control rods are inserted, which can result in differences in the insertion time for each of the multiple control rods operated by one HCU.

[0013] In addition, during an earthquake, the control rods come into contact with the fuel assemblies that have been deformed into a bow shape by the seismic motion during the control rod insertion process, increasing the resistance acting on the control rods, causing a delay in insertion time compared to when there is no earthquake. As a result, if there are two or more control rods driven by one HCU, differences in the control rod insertion time can occur due to the effects of the earthquake, differences in the mass of the control rods, and differences in pressure loss in the scram piping, and a control rod hydraulic system that is less susceptible to differences in control rod insertion time is necessary to further improve safety.

[0014] An object of the present invention is to provide a boiling water reactor capable of shortening the maximum insertion time of each control rod required for scram when one HCU drives two or more control rods. [Means for solving the problem]

[0015] The present invention includes multiple means for solving the above-mentioned problems. One example is a boiling water reactor having a plurality of first control rods and one or more second control rods having a larger mass than the first control rods, characterized in that the first control rods are connected to the same hydraulic control rod drive mechanism via a first scram piping and one or more second control rods are connected to the same hydraulic control rod drive mechanism via a second scram piping, and the pressure loss in the first scram piping is made greater than the pressure loss in the second scram piping. Effect of the Invention

[0016] According to the present invention, when one HCU drives two or more control rods, the maximum insertion time of each control rod required for scram can be reduced. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0017] [Figure 1] 1 is an overall view of a boiling water reactor according to a first embodiment of the present invention. [Diagram 2] This is a schematic diagram of the scram piping that connects the HCU and the control rod drive mechanism in a boiling water reactor. [Diagram 3] 1 is a schematic diagram of the arrangement of control rods in a core of a boiling water reactor according to a first embodiment. [Figure 4] This is the result of a simulation of control rod insertion when no earthquake occurs. [Diagram 5] FIG. 13 is an enlarged view of the vicinity of the insertion completion time in the simulation results. [Figure 6] FIG. 11 is a schematic diagram showing the arrangement of control rods in a core of a boiling water reactor according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a schematic diagram of a scram piping that connects an HCU and a control rod drive mechanism in a boiling water reactor according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the boiling water reactor of the present invention will be described with reference to the drawings. In the drawings used in this specification, the same or corresponding components are designated by the same or similar reference numerals, and repeated description of these components may be omitted.

[0019] <Example 1> A boiling water reactor according to a first embodiment of the present invention will be described with reference to FIGS.

[0020] First, the overall configuration of a boiling water reactor will be described with reference to Fig. 1. Fig. 1 is an overall view of a boiling water reactor according to the first embodiment.

[0021] Figure 1 shows an example of a boiling water reactor with one HCU driving four control rods.

[0022] As shown in FIG. 1, the HCU 106 is installed in an HCU room 105 in a boiling water reactor 101 , and the HCU 106 and the control rod drive mechanism 103 are connected by a scram piping 104 .

[0023] In addition to HCU 106, many other HCUs are installed in HCU room 105 (not shown for convenience of illustration), and each of these HCUs is connected to a control rod drive mechanism (not shown). Note that the number of HCU rooms is not limited to one, and there may be multiple HCU rooms. Also, many control rod drive mechanisms 103 are fixed to the bottom of reactor pressure vessel 102, and FIG. 1 shows only a portion of them.

[0024] FIG. 2 is a schematic diagram of the scram piping connecting the HCU and the control rod drive mechanism in a boiling water reactor, and is a detailed view of FIG.

[0025] As shown in FIG. 2, the HCU 106 is composed of an accumulator 207, a pressurizing cylinder 206, a plurality of gate valves 203, a scram valve 204, and a scram pipe 205, etc.

[0026] The pressurizing cylinder 206 is filled with high-pressure nitrogen gas, and is connected to an accumulator 207 via a pipe 209 .

[0027] The accumulator 207 is connected to a scram pipe 205 in which a scram valve 204 is provided, and the scram pipe 104 branches in four directions downstream of the scram valve 204, and each scram pipe 104 has a gate valve 203 inserted therein, and is connected to a control rod drive mechanism 103.

[0028] The control rod drive mechanism 103 is fixed to the lower part of the reactor pressure vessel 102 inside the reactor containment vessel 202 , and the control rod drive mechanism 103 is connected to a total of four control rods 201 .

[0029] When a scram becomes necessary due to an earthquake or other factors, the scram valve 204 opens, and at the same time, high-pressure nitrogen gas passes through piping 209 to push up a piston 208 in an accumulator 207, producing high-pressure water. The high-pressure water passes through scram piping 205 and scram piping 104 to push up a piston (not shown) in a control rod drive mechanism 103, and the control rod 201 is rapidly inserted into the reactor core.

[0030] Fig. 3 shows a schematic diagram of the arrangement of the control rods shown in Fig. 2 in the reactor core. The reactor pressure vessel 102 is seen from above in Fig. 1, and the scram piping 104 is connected to the HCU 106. One control rod drive mechanism 103 and control rods 201a, 201b, 201c, and 201d are arranged in an upper lattice plate 301 in the reactor pressure vessel 102.

[0031] Here, control rod 201b has a larger mass than control rods 201a, 201c, and 201d. The difference in mass may be caused by different neutron absorbing materials used in control rod 201 or by different structures of control rod 201. For example, when control rod 201 uses different neutron absorbing materials, the difference in mass occurs due to the difference in density of the neutron absorbing materials.

[0032] In addition, control rod 201a is connected to the same hydraulic control rod drive mechanism via first scram piping 302a, 104a, control rod 201b is connected to the second scram piping 302b, 104b, control rod 201c is connected to the first scram piping 302c, 104c, and control rod 201d is connected to the first scram piping 302d, 104d.

[0033] As shown in Figure 1, when one HCU drives two or more control rods, differences in the mass of the control rods and differences in pressure loss in the scram piping can cause differences in the insertion time of the control rods. In addition, when an earthquake occurs, the bow-shaped deformed fuel assembly comes into contact with the control rod, increasing the resistance generated during insertion, which can delay the insertion time.

[0034] Among the multiple control rods driven by one HCU, the control rods with a large mass experience a larger resistance during insertion than the control rods with a small mass due to their own weight during a scram. This is the reason why the insertion time of the control rods with a large mass is relatively slower than that of the control rods with a small mass.

[0035] Furthermore, among the multiple scram pipes connected to one HCU, those with large pressure losses have a stronger resistance to the inflow of high-pressure water than those with small pressure losses, resulting in an increase in the flow rate to the scram pipes with small pressure losses. In other words, as the flow rate to the scram pipes with large pressure losses decreases, the driving force generated by the control rod drive mechanism connected to them decreases, and the insertion time is delayed.

[0036] Possible measures to shorten the insertion time of the heavy control rods include reducing the mass of the control rods and increasing the output of the accumulators, but these design changes are not realistic because they would have a significant impact on related equipment.

[0037] Therefore, we focus on the pressure loss in the scram piping. Specifically, we make the pressure loss in the scram piping connected to the control rods with a large mass relatively small, and the pressure loss in the scram piping connected to the control rods with a small mass relatively large. This makes the flow rate of high-pressure water flowing through the control rods with a large mass greater than the flow rate of high-pressure water flowing through the control rods with a small mass, and the increase in the flow rate counteracts the resistance force caused by the large mass, thereby increasing the driving force and shortening the insertion time of the control rods with a large mass, which is thought to further improve the safety of the reactor.

[0038] Figure 4 shows the results of a simulation of control rod insertion when no earthquake occurs. This simulation result is the comparison of two cases with different pressure loss distributions in the scram piping in a control rod drive system in which one HCU drives four control rods.

[0039] In Figure 4, the mass of the control rods is the same in both cases, with one control rod having a mass of 100 kg and the other three control rods having masses of 80 kg. In Case 1, the pressure loss of all four scram pipes connecting the four control rods is A, while in Case 2, the pressure loss of the scram pipes connecting the three control rods with small masses is A, and the pressure loss of the scram pipe connecting the one control rod with large mass is B (a value smaller than A).

[0040] Looking at Figure 4, all of the control rods receive the scram signal and begin to be inserted at time t0. After time t0, the insertion positions of all of the control rods increase monotonically, reaching the insertion completion position D at times t1 to t4, and the control rods that reach the insertion completion position maintain that position.

[0041] 5 is an enlarged view of the vicinity of the insertion completion time, which corresponds to the range indicated by the dashed line 401 in FIG 4. In the graph of FIG 5, the solid line indicates the simulation result of Case 1, and the dashed line indicates the simulation result of Case 2.

[0042] 5, solid line 501 shows the insertion history of control rods with small masses in case 1, and solid line 504 shows the insertion history of control rods with large masses in case 1. Also, dashed line 502 shows the insertion history of control rods with small masses in case 2, and dashed line 503 shows the insertion history of control rods with large masses in case 2.

[0043] As shown in Figure 5, in Case 1, the control rod with the larger mass is inserted at time t4, and the control rod with the smaller mass is inserted at time t1. In contrast, in Case 2, the control rod with the larger mass is inserted at time t3, and the control rod with the smaller mass is inserted at time t2. Comparing Case 1 and Case 2, the insertion time of the control rods driven by one HCU is shortened from time t4 to time t3.

[0044] These results show that the total insertion time tends to be shortened by adjusting the pressure loss in the scram piping, making the pressure loss in the scram piping connected to the control rods with a large mass relatively small, and making the pressure loss in the scram piping connected to the control rods with a small mass relatively large.

[0045] Here, pressure loss in scram piping occurs due to friction loss at the walls inside the pipe, loss due to fluid separation at bends, etc. If the pipe friction coefficient is λ, the pipe length is l, the pipe diameter is d, the fluid density is ρ, and the average flow velocity is u, then the friction loss ΔP at the walls inside the pipe can be expressed as in the following formula (1).

[0046]

number

[0047] Furthermore, if the loss coefficient is ζ, the loss ΔPse due to fluid separation at the bend can be expressed as the following equation (2).

[0048]

number

[0049] The loss factor ζ has been approximately determined from the results of numerous experiments, and increases as the angle of the bend becomes acute.

[0050] Therefore, pressure loss in scram piping is determined by the length of the piping, the number of bends, the angle of the bends, etc., and the longer the length, the greater the number of bends with the same angle, or the sharper the angle of the bends when the number is the same, the greater the pressure loss.

[0051] Therefore, in order to shorten the control rod insertion time, it is expected that the pressure loss in the first scram piping 302a, 302c, 302d can be made greater than the pressure loss in the second scram piping 302b by adjusting the length of the piping and the number and angle of bends.

[0052] For example, as shown in FIG. 3, it is desirable to take one or more of the following measures: making the number of bends in the first scram piping 302a, 302c, 302d greater than the number of bends in the second scram piping 302b; making the angles of the bends in the first scram piping 302a, 302c, 302d greater than the angles of the bends in the second scram piping 302b; or making the sum of the angles of the bends in the first scram piping 302a, 302c, 302d greater than the sum of the angles of the bends in the second scram piping 302b.

[0053] In addition, when considering applying the above options to boiling water reactors, the degree of freedom in adjusting the length of the piping is small due to the installation space inside the reactor, so it may be difficult to adjust the pressure loss enough to shorten the control rod insertion time by only changing the length of the scram piping. On the other hand, adding more bends or intentionally increasing the bending angle may be a relatively feasible option even if the installation space for the piping is small.

[0054] In the first embodiment shown in FIG. 3, attention is focused on the bend in the scram piping.

[0055] The scram piping 302 shows a portion of the scram piping 104 starting from the HCU 106. The second scram piping 302b connected to the control rod 201b with a large mass has no bends, while the first scram piping 302a, 302c, and 302d connected to the control rods 201a, 201c, and 201d with a small mass have multiple bends intentionally created.

[0056] The second scram piping 302b and the first scram piping 302a, 302c, 302d have the same length, and the first scram piping 302a, 302c, 302d have a bent portion, so that the pressure loss is larger than that of the second scram piping 302b. This makes it possible to shorten the insertion time of the control rod 201b, which has a large mass.

[0057] The position of the control rod and the magnitude of the pressure loss in the piping can be set, for example, as follows. Hafnium, which is used as the neutron absorbing material for the mass-rich control rod, has a long life and is often used for controlling the power output of the nuclear reactor, and when the purpose is to control the power output of the nuclear reactor, the position of the control rod is determined from the viewpoint of improving the economic efficiency of the nuclear reactor. In other words, the position of the mass-rich control rod 201b is determined from the viewpoint of control rod insertability.

[0058] In addition, the entrance (not shown) of the scram piping 104 into the reactor containment vessel 202 is determined by the positions of the HCU room 105, the HCU 106, and the reactor pressure vessel 102. As a result, the path of the control rod 201b, which has a large mass, and the second scram piping 104b, 302b connected to it is determined from a viewpoint different from the control rod insertability, and the pressure loss of the second scram piping 104b, 302b is also determined from a viewpoint different from the control rod insertability.

[0059] Therefore, the pressure loss of the second scram piping 104b, 302b is used as a standard, and the number and angle of bends of the first scram piping 302a, 302c, 302d connected to the control rods 201a, 201c, 201d having a small mass may be set to be larger than this standard. Note that the relationship of pressure loss between the first scram piping 302a, 302c, 302d is not particularly limited, and is not particularly limited, but it is possible to set them all at the same level, for example.

[0060] Next, the effects of this embodiment will be described.

[0061] In the boiling water reactor having the multiple control rods 201a, 201c, 201d of the above-mentioned embodiment 1 of the present invention and one or more control rods 201b having a larger mass than the control rods 201a, 201c, 201d, the multiple control rods 201a, 201c, 201d are connected to the same hydraulic control rod drive mechanism via first scram piping 104a, 302a, 104c, 302c, 104d, 302d, and the one or more control rods 201b are connected to the same hydraulic control rod drive mechanism via second scram piping 104b, 302b, and the pressure loss in the first scram piping 302a, 302c, 302d is made greater than the pressure loss in the second scram piping 302b.

[0062] This allows the difference in insertion time to be reduced by combining a control rod 203b with a large mass with a second scram piping 302b with a small pressure loss, thereby shortening the maximum insertion time of multiple control rods 201a, 201b, 201c, and 201d driven by a single HCU 106.

[0063] In addition, since the number of bends in the first scram piping 302a, 302c, 302d is greater than the number of bends in the second scram piping 302b, the angle of the bends in the first scram piping 302a, 302c, 302d is greater than the angle of the bends in the second scram piping 302b, or the sum of the angles of the bends in the first scram piping 302a, 302c, 302d is greater than the sum of the angles of the bends in the second scram piping 302b, it is easy to make the pressure loss in the second scram piping 302b connected to the control rod 203b with a large mass smaller than the pressure loss in the first scram piping 302a, 302c, 302d connected to the control rods 201a, 201c, 201d.

[0064] <Example 2> A boiling water reactor according to a second embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a schematic diagram showing the arrangement of control rods in the core of the boiling water reactor according to the second embodiment.

[0065] The boiling water reactor of this embodiment differs from the boiling water reactor of embodiment 1 in two points, the length of the scram piping and the arrangement position of the control rods, as shown in Fig. 6. In Fig. 6, the scram piping 601 also shows a part of the scram piping 104 starting from the HCU 106.

[0066] As shown in FIG. 6, the length of first scram piping 601a, 601c, 601d connected to control rods 201a, 201c, 201d having small masses is made longer than the length of second scram piping 601b connected to control rod 201b having large mass.

[0067] Adjustment of the length of the scram piping is accompanied by changing the arrangement of the control rods. However, since the position of the control rod 203b, which has a large mass, is determined from a viewpoint other than control rod insertability, it is difficult to arrange it freely.

[0068] Therefore, among the multiple control rods 201 connected to the same HCU 106, the control rods 201a, 201c, and 201d having a smaller mass are positioned at a position farther from the entrance (not shown) of the scram piping 104 into the reactor containment vessel 202 than the distance to the control rod 201b having a larger mass, thereby making it possible to adjust the length of the scram piping.

[0069] The other configurations and operations are substantially the same as those of the boiling water reactor of the first embodiment described above, and the details are omitted here.

[0070] In the boiling water reactor according to the second embodiment of the present invention, substantially the same effects as those of the boiling water reactor according to the first embodiment described above can be obtained.

[0071] Furthermore, since the length of the first scram piping 601a, 601c, 601d is longer than that of the second scram piping 601b, the pressure loss in the second scram piping 601b connected to the control rod 203b having a large mass can be easily made smaller than the pressure loss in the first scram piping 601a, 601c, 601d connected to the control rods 201a, 201c, 201d.

[0072] <Example 3> A boiling water reactor according to a third embodiment of the present invention will be described with reference to Fig. 7. Fig. 7 is a schematic diagram of scram piping connecting the HCU and the control rod drive mechanism in the boiling water reactor according to the third embodiment.

[0073] In the first and second embodiments, the bends and length of the scram piping are adjusted, which is nothing more than adjusting the flow rate of the scram piping. Therefore, it can be said that it is also possible to adjust the flow rate of the scram water flowing through the scram piping itself and shorten the control rod insertion time by installing a flow rate control valve such as an orifice valve in the scram piping.

[0074] As shown in FIG. 7, the boiling water reactor of this embodiment differs from the boiling water reactor of the first embodiment in the presence or absence of an orifice valve 701.

[0075] As shown in Fig. 7, in order to make the flow rate of the scram water flowing through the first scram pipes 702a, 702c, and 702d smaller than the flow rate of the scram water flowing through the second scram pipe 702b, orifice valves 701a, 701b, 701c, and 701d for adjusting the flow rate of the scram water are provided in the first scram pipes 702a, 702c, and 702d and the second scram pipe 702b. In Fig. 7, the opening area of ​​the orifice valve 701b is made larger than that of the orifice valves 701a, 701c, and 701d.

[0076] The orifice valves 701a, 701b, 701c, and 701d may be valves that can adjust the flow rate.

[0077] In addition, Figure 7 shows the case where orifice valves 701a, 701b, 701c, 701d are provided as flow rate control units in both the first scram piping 702a, 702c, 702d and the second scram piping 702b, but it is sufficient that the orifice valves are provided in at least one of the first scram piping 702a, 702c, 702d and the second scram piping 702b.

[0078] The other configurations and operations are substantially the same as those of the boiling water reactor of the first embodiment described above, and the details are omitted here.

[0079] In the boiling water reactor according to the third embodiment of the present invention, substantially the same effects as those of the boiling water reactor according to the first embodiment described above can be obtained.

[0080] In addition, since the flow rate of the scram water flowing through the first scram pipes 702a, 702c, and 702d is smaller than the flow rate of the scram water flowing through the second scram pipe 702b, it is possible to adjust the flow rate and make the flow rate toward the control rods, which have a large mass, relatively larger than that toward the other pipes. As a result, the insertion time of the control rods can be shortened. In addition, since it can be handled inside the pipes, it is possible to eliminate restrictions on the placement position of the control rods.

[0081] Furthermore, by providing orifice valves 701a, 701b, 701c, 701d for adjusting the flow rate of scram water in at least one of the first scram piping 702a, 702c, 702d and the second scram piping 702b, it becomes possible to easily adjust the flow rate.

[0082] The flow rate adjusting unit as in this embodiment can also be applied to the boiling water reactor of the first or second embodiment.

[0083] <Other> The embodiments described above are merely examples of the implementation of the present invention, and the technical scope of the present invention should not be interpreted as being limited by these. In other words, the present invention can be implemented in various forms without departing from its technical concept or main characteristics.

[0084] For example, it is possible to adjust the pressure loss by changing the pipe diameter. [Explanation of symbols]

[0085] 101...Boiling water reactor 102...Reactor pressure vessel 103, 103a, 103b, 103c, 103d...Control rod drive mechanism 104,302,601…Scram piping 104a, 104c, 104d, 302a, 302c, 302d, 601a, 601c, 601d, 702a, 702c, 702d...1st scram piping 104b, 302b, 601b, 702b...Second scram piping 105…HCU room 106…HCU 201...Control rod 201a, 201c, 201d...Control rods (first control rods) 201b…Control rod (second control rod) 202...Reactor containment vessel 203...Shuttle valve 204…Scram valve 205…Scram piping 206...Pressurized cylinder 207…Accumulator 208…Piston 209…Plumbing 301...Upper grid plate 401,502,503...Dashed line 501,504…solid line 701, 701a, 701b, 701c, 701d...Orifice valve (flow rate adjustment part)

Claims

1. In a boiling water reactor having a plurality of first control rods and one or more second control rods having a mass greater than that of the first control rods, a plurality of the first control rods are connected to the same hydraulic control rod drive mechanism via a first scram pipe and one or more of the second control rods are connected to the same hydraulic control rod drive mechanism via a second scram pipe; The pressure loss in the first scram piping is made larger than the pressure loss in the second scram piping.

1. A boiling water reactor comprising:

2. 2. The boiling water reactor of claim 1, The number of bends in the first scram piping is greater than the number of bends in the second scram piping.

1. A boiling water reactor comprising:

3. 2. The boiling water reactor of claim 1, When the angle of the bend is defined as the angle formed by the bent portion, the angle of the bend provided in the first scram piping is acuter than the angle of the bend provided in the second scram piping.

1. A boiling water reactor comprising:

4. 2. The boiling water reactor of claim 1, When the angle of the bend is defined as the angle of bending based on a straight state, the sum of the angles of the bends of the first scram piping is greater than the sum of the angles of the bends of the second scram piping.

1. A boiling water reactor comprising:

5. 2. The boiling water reactor of claim 1, The length of the first scram piping is longer than the length of the second scram piping.

1. A boiling water reactor comprising:

6. 2. The boiling water reactor of claim 1, The flow rate of the scram water flowing through the first scram piping is less than the flow rate of the scram water flowing through the second scram piping.

1. A boiling water reactor comprising:

7. 7. The boiling water reactor of claim 6, At least one of the first scram piping and the second scram piping has a flow rate adjusting unit for adjusting the flow rate of the scram water.

1. A boiling water reactor comprising:

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