JPH02284096A - Reactor shutdown device - Google Patents

Abstract

PURPOSE:To improve the responsiveness of the device to an abnormal temp. rise of coolants and to allow a sure scram by specifying the total aperture area of the coolant outflow holes provided in the upper part of an introducing pipe to the area larger than the sectional area of the flow passage in the introducing pipe. CONSTITUTION:The introducing pipe 7' which introduces the coolants 21a, 21b flowing out of a lower guide pipe 12 of a control rod provided in the reactor core 11 and a lower guide pipe 13 of a fuel assembly into an upper guide pipe 2 is integrally provided at the bottom end of the pipe 2. The coolant outflow holes 15a, 15b which discharge the coolants 21a, 21b flowing into the pipe 2 are provided in the upper part of a pipe 7'. Since the total aperture area of the holes 15a, 15b is set larger than the sectional area (pid<2>/4, d is the bore of the pipe 7') of the flow passage of the pipe 7', the flow resistance near the inlets of the holes 15a, 15b decreases to assure the smooth outflow of the coolants 21a, 21b flowing into the pipe 7' from the holes 15a, 15b. The generation of back flow in the pipe 7' and the generation of the stagnating part of the coolants 21a, 21b near the bottom end of the extension pipe 7 are, therefore, obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a reactor shutdown device for a fast breeder reactor.

(Prior technology) In fast breeder reactors that use liquid metal such as liquid sodium as a coolant, control rods are used to control the reactor's output and to absorb neutrons inside the reactor to perform an emergency shutdown of the reactor. be done.

This control rod houses a number of neutron absorption bins in a trumpet tube, and supports the upper and lower ends of the neutron absorption bins with lattice plates.A handling head is formed at the top of the trumpet tube. Then, such control rods are inserted into or withdrawn from the reactor core by a control rod drive mechanism to control the output of the nuclear reactor. Additionally, if the operating state of the reactor becomes transient, control rods are inserted into the reactor core to shut down the reactor.

During such a scram, it is necessary to shut down the reactor quickly and reliably. For this reason, fast breeder reactors are provided with a reactor shutdown device separate from the control rod drive mechanism for emergency shutdown of the reactor during scram.

A variety of control rod drive mechanisms and reactor shutdown devices have been proposed for fast breeder reactors. Among them, the control rods are attracted by magnets, and during scram, the control rods are separated from the magnets and allowed to fall by gravity into the reactor core. It is believed that this system has four advantages over other systems in terms of its structural simplicity and the fact that no mechanical action is required to disconnect the control rods.

This magnetic reactor shutdown system consists of an upper guide pipe inserted into the reactor vessel through a through hole of a shielding plug, an introduction pipe connected to the lower end of this upper guide pipe, and an inside of this introduction pipe and upper guide pipe. The control rod has an extension tube that is movable in the axial direction, and a Cucumber point electromagnet that is installed at the lower end of the extension tube. The structure is such that it is attracted to the rod and magnetically connected to the control rod.

FIG. 4 is a cross-sectional view showing the lower part of a conventional nuclear reactor shutdown system, and FIG. 5 is a view taken along the line ■-■ in FIG. 4. In FIGS. 4 and 5, reference numeral 41 denotes an L-portion guide tube, and within this guide tube 41 is provided an extension tube 42 having a Cucumber point electromagnet 43 at its lower end so as to be movable in the axial direction. A control rod 44 is magnetically connected to the Cucumber point electromagnet 43 and moves together with the extension tube 42.

Furthermore, an introduction pipe 48 is integrally provided at the lower end of the upper guide pipe 41 to introduce coolant from a control rod lower guide pipe 46 and a fuel assembly lower guide pipe 47 provided in the reactor core 45. . A coolant outflow hole 49 is provided in the upper part of the introduction pipe 48, and the coolant flowing into the introduction pipe 48 flows out through the coolant outflow hole 49.

In addition, a plurality of thermocouples 50 are provided in the introduction pipe 48 and supported by a measurement line porous support 51, and these thermocouples 50 are used to connect the control rod/lower guide pipe 46 and the fuel assembly lower guide pipe 47. It measures the outlet temperature of the coolant flowing out.

According to the reactor shutdown system configured as described above, the coolant 52a that has ascended within the control rod lower guide pipe 46 and the coolant 52b that has ascended within the fuel assembly lower guide pipe 47 are mixed within the introduction pipe 48. The coolant then rises inside the introduction pipe 48 and flows out from the coolant outflow hole 49. At this time, when the temperature of the coolant flowing into the introduction pipe 48 rises abnormally by 4 degrees and becomes below the cucumber point temperature of the cucumber point electromagnet 43, the cucumber point electromagnet 43 loses its magnetism and the control rod 44 Adsorption power disappears. As a result, the control rod 44 separates from the Cucumber point electromagnet 43 and falls into the reactor core 45 due to gravity, causing an emergency shutdown of the reactor.

(Problem to be Solved by the Invention) By the way, in such a conventional reactor shutdown device, the coolant 52b (usually at 500 to 550°C) flowing out from the fuel assembly lower guide pipe 47 is transferred from the control rod lower guide pipe 46. higher than the exit temperature (usually 400°C) of the coolant 52b flowing out;
The flow speed is also fast. Therefore, the static pressure of the coolant 52a flowing out from the control rod lower guide tube 46 decreases, and the flow of the coolant in the introduction tube 48 changes from the higher static pressure side to the lower static pressure side, that is, the control rod lower guide tube 46. The low temperature coolant 52a flowing out from the lower guide pipe 46 flows toward the high temperature coolant 52b flowing out from the fuel assembly lower guide pipe 47. Then, it is reversed at the upper part of the introduction pipe 48 and flows backward in the introduction pipe 48 or remains near the lower end of the extension pipe 42.

In this way, backflow may occur within the introduction pipe 48 or the extension pipe 4
Conventionally, the reason why a stagnation part occurs near the lower end of the coolant outlet hole 49 is that the opening area of the coolant outlet hole 49 is only about the same as the opening of the control rod lower guide tube 46; This is because the flow resistance near the inlet is large and contraction occurs here.

Therefore, in the conventional method, even if the temperature of the coolant flowing into the introduction pipe 48 rises abnormally, the cucumber point electromagnet 43 reaches the cucumber-JL humidity temperature due to the retention part generated near the lower end of the extension pipe 42, and the control rod 44 There was a problem in that it took a considerable amount of time to lose its adsorption power.

The present invention has been made in view of these points, and an object of the present invention is to provide a nuclear reactor shutdown device that has good responsiveness to abnormal temperature rises of the coolant and can reliably scram the reactor. shall be.

[(1) Construction of the invention] (Means for solving the problem) In order to achieve the above object, the present invention provides a method for detecting the inside of the reactor vessel through a through hole provided in a shielding plug that closes the upper opening of the reactor vessel. an upper guide pipe inserted into the upper guide pipe, an introduction pipe connected to the lower end of the upper guide pipe, a coolant outflow hole provided at the upper part of the introduction pipe, and a coolant outlet provided in the upper guide pipe so as to be movable in the axial direction. a control rod lower guide tube provided below the extension tube; a fuel assembly lower guide tube disposed around the control rod lower guide tube; and a do end of the extension tube. A nuclear reactor shutdown device comprising a Cucumber point electromagnet magnetically connected to the control rods according to the temperature of the coolant flowing out from the control rod lower guide pipe and the fuel assembly lower guide pipe, wherein the coolant The total opening area of the outflow hole is set to be greater than or equal to the cross-sectional area of the flow path in the introduction pipe.

(Function) In the present invention, by making the total opening area of the coolant outflow hole equal to or larger than the flow path cross section fs2 in the inlet pipe, the flow resistance near the inlet of the coolant outflow hole is reduced, and the coolant flowing into the inlet pipe is The coolant can flow out smoothly from the coolant outflow hole.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 show one embodiment of the present invention, and FIG. 1 is a sectional view showing a schematic configuration of a nuclear reactor shutdown device. In the figure, 1 is a shielding plug that closes the upper opening of a reactor vessel (not shown), and this shielding plug 1 is provided with a through hole 3 for inserting an upper guide tube 2 into the reactor vessel. It is being Further, a housing 5 of a control rod drive mechanism for driving the control rod 4 up and down is installed on the shielding plug 1, and a lower flange 6 for supporting the upper guide tube 2 is provided at the lower part of the housing 5.

An extension tube 7 is provided inside the guide tube 2 so as to be movable in the axial direction. A nut 8 is fixed to the upper part of the extension tube 7, and a screw shaft 9 driven by a motor (not shown) installed at the top of the housing 5 is screwed into the nut 8. Further, at the lower part of the extension tube 7, a cucumber point electromagnet 10 is provided, which is formed by winding a coil around a rod-shaped cucumber J and a magnetic material. The two chains of the control rod 4 are attracted to this Cucumber point electromagnet 10, and are moved in the axial direction together with the extension tube 7 by rotation of the screw shaft 9.

On the other hand, at the lower end of the upper guide tube 2, there is an introduction tube 14 for introducing the coolant flowing out from the control rod lower guide tube 12 and the fuel assembly lower guide tube 13 provided in the core 11 into the upper guide tube 2. It is integrated. At the upper part of the introduction pipe 14, coolant outflow holes 15a and 15b are provided for allowing the coolant that has flowed into the upper guide pipe 2 to flow out, as shown in FIG. When the inner diameter of the introduction pipe 14 is d, the opening surface ft12A of these coolant outflow holes 15a and 15b is 2.
A≧πd2/4 ・・・・・・(1) A≧πd2/8
・・・・・・(2) It has become.

Furthermore, a plurality of thermocouples 16 are arranged within the introduction pipe 14 at predetermined intervals in the circumferential direction of the introduction pipe 14, as shown in FIG. Each of these thermal lightning pairs 16 is supported by a measurement line porous support 17, and the temperature of the coolant flowing inside the measurement line porous support 17 is measured by a total of Δ? 1. Note that a large number of through holes 18 are provided on the side surface of the measurement line porous support 17 so that the coolant that has flowed in can efficiently flow out. Further, a cylindrical neutron shield 19 is provided at the upper part of the upper guide tube 2 with its outer surface in close contact with the inner surface of the upper guide tube 2, and this neutron shield 19 and the extension tube 14 are connected by a bellows 20. This isolates the sodium atmosphere inside the reactor vessel from the control rod drive upper mechanism.

In the nuclear reactor shutdown device configured as described above, when the temperature of the coolant flowing into the upper guide pipe 2 from the inlet pipe 14 rises abnormally and reaches the cucumber point jAA degree of the cucumber point electromagnet 10 or higher, the cucumber point electromagnet is activated. Since the magnet 10 loses its magnetic force, the control rod 4 that was attracted to the cucumber point 71 magnet 10
falls due to gravity, causing an emergency shutdown of the reactor.

Moreover, in this embodiment, the coolant outflow hole 15a.

The total opening area of 15b for two people is the flow path cross-sectional area of introduction pipe 14 B (
-πd2/4) or less, the flow resistance near the coolant outflow holes 15a and 15b becomes small, and the flow resistance from the control rod lower guide pipe 12 and the fuel assembly lower guide pipe 13 to the inlet pipe 14 is reduced. The coolant flowing into the coolant outlet hole 15a
, 15b.

Therefore, the coolant outflow hole 15a is closed as in the conventional case.

The coolant flows into the introduction pipe 14 without causing a backflow in the introduction pipe 14 due to the flow resistance near the inlet of the extension pipe 15b, and without creating a stagnation part of the coolant near the upper end of the extension pipe 7. Since the Cucumber point electromagnet 10 reaches the Cucumber point lH degrees in a short time when the temperature of the reactor increases abnormally, the scram response of the nuclear reactor shutdown system can be improved.

In the above embodiment, two coolant outlet holes 15a and 15b were provided at the upper part of the introduction pipe 14, but the number of coolant outlet holes is three.
The number of coolant outflow holes may be one or more, and the same effect can be obtained as long as the total opening area of all the coolant outflow holes is greater than or equal to the flow path cross-sectional area of the introduction pipe 14.

[Effects of the Invention] As explained above, the present invention provides an upper guide tube inserted into the reactor vessel through a through hole provided in a shielding plug that closes the opening of the -L portion of the reactor vessel; An introduction pipe connected to the lower end of the pipe, a coolant outflow hole provided at the upper part of the introduction pipe, an extension pipe movable in the axial direction within the upper guide pipe, and an extension pipe provided below the extension pipe. A control rod lower guide tube provided, a fuel assembly lower guide tube provided around the control rod lower guide tube, a control rod lower guide tube provided at the lower end of the extension tube, and the fuel assembly lower guide tube provided at the lower end of the extension tube. In a nuclear reactor shutdown device having a Cucumber point electromagnet magnetically connected to a control rod according to the temperature of the coolant flowing out from the lower body guide pipe, the total opening area of the coolant outflow hole is defined as the flow path in the introduction pipe. The cross-sectional area is greater than or equal to the cross-sectional area. Therefore, the coolant that has flowed into the introduction pipe can be smoothly flowed out from the coolant outlet hole in the upper part of the introduction pipe, and a reactor shutdown device with excellent scram response can be provided.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a cross-sectional view showing the schematic structure of a nuclear reactor shutdown device, FIG. 2 is a cross-sectional view showing the lower part of the device, and FIG. is ■−■ in Figure 2
4 is a sectional view showing the lower part of a conventional nuclear reactor shutdown device, and FIG. 5 is a view taken along the line V--■ in FIG. 4. DESCRIPTION OF SYMBOLS 1... Shielding plug, 2... Upper guide pipe, 3... Through hole, 412. υj rod, 5...housing, 7...
・Extension tube, 8... Nut, 9... Screw shaft, 1
0... Cucumber point electromagnet, 11... Reactor core, 12.
... Control rod lower guide tube, 13... Fuel assembly lower guide tube, 14... Extension tube, 15a, 15b... Coolant outflow hole, 16... Thermal lightning pair. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 4 Figure 5

Claims (1)

[Claims] an upper guide tube inserted into the reactor vessel through a through hole provided in a shielding plug that closes an upper opening of the reactor vessel;
An introduction pipe connected to the lower end of the upper guide pipe, a coolant outflow hole provided at the upper part of the introduction pipe, an extension pipe movable in the axial direction within the upper guide pipe, and the extension pipe. a control rod lower guide tube provided below, a fuel assembly lower guide tube provided around the control rod lower guide tube, and a control rod lower guide tube provided at the lower end of the extension tube; In a nuclear reactor shutdown device having a Cucumber point electromagnet magnetically connected to a control rod according to the temperature of the coolant flowing out from the fuel assembly lower guide pipe, the entire opening area of the coolant outflow hole is set within the introduction pipe. A nuclear reactor shutdown device characterized in that the flow passage cross-sectional area is greater than or equal to .