JPH0151792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactor main vessel suitable for use in a tank-type fast reactor.

In a sodium cooled tank type fast reactor, a reactor core, a plurality of intermediate heat exchangers, and a plurality of primary side main circulation pumps are installed in the reactor main vessel.
Furthermore, a thermal shielding structure is installed inside the reactor main vessel to separate the high temperature primary sodium flowing out from the reactor core from the low temperature primary sodium flowing out from the intermediate heat exchanger, forming a core cooling path. There is. Conventionally, there have been several problems that must be solved in the manufacture of this nuclear reactor main vessel. One of these concerns transient changes in the temperature of the primary sodium flowing out from the core. In other words, during transient operations such as scramming a nuclear reactor, changes in density of primary sodium occur as the temperature changes from high temperature to low temperature in the hot plenum, which constitutes the flow path for primary sodium flowing out from the core. As a result, a so-called stratification phenomenon occurs in which low-density, high-temperature sodium remains in the upper part of the hot plenum, resulting in severe temperature changes in the primary sodium flowing into the intermediate heat exchanger. , which has the disadvantage of increasing the thermal shock inside the intermediate heat exchanger.

An object of the present invention is to provide a good tank-type nuclear reactor that does not suffer from the above-mentioned drawbacks by effectively suppressing the strategy-ication that occurs as a result of temperature changes in the primary sodium within the hot plenum.

The present invention confirms the strategy of the primary sodium flowing in the hot plenum through numerical experiments, and furthermore, the strategy increases the transient temperature change of the primary sodium flowing into the intermediate heat exchanger, It was confirmed theoretically that the thermal shock to the internal structure of the intermediate heat exchanger would be excessive, and as a means to suppress this strategy, the intermediate heat exchanger was covered with a cylinder, and the cylinder and the intermediate heat exchanger were By flowing high-temperature sodium into the upper part of the hot plenum and low-temperature sodium at the lower part of the hot plenum into an annulus-shaped flow path consisting of a It is characterized by alleviating the

1 and 2 show a known tank-type nuclear reactor main vessel to which the present invention is applied. The main vessel 1 houses a roof slab 2 that isolates the inside of the reactor from the outside world and mounts structures, a plurality of intermediate heat exchangers 7, a plurality of primary main circulation pumps 8, and a reactor core 5. . The core 5 is supported by a core support structure 3. Additionally, a core upper mechanism 6 is installed, which is comprised of control rods and the like that control the output of the reactor. A hot plenum 9 that accommodates high-temperature sodium flowing out from the reactor core 5 and a cold plenum 1 that accommodates low-temperature sodium flowing out from the intermediate heat exchanger.
0 by a heat shield structure 4. The primary sodium flowing out from the core is transferred to intermediate heat exchangers 7 and 1.
After once ascending through the annular unit composed of the secondary sodium induction cylinder 18, the primary sodium flows into the heat transfer tube group 19 through the primary sodium inflow window 13, and flows down while giving heat to the secondary sodium flowing inside the heat transfer tubes. It flows out into the Kort plenum 10 through the outflow window 14. This primary sodium is supplied to the primary main circulation pump 8.
It is sent to the reactor core 5. On the other hand, after the secondary sodium flows down the downcomer pipe 15, it flows into the secondary lower plenum 1.
6, the heat is distributed to a plurality of heat transfer tubes. The secondary sodium distributed in each heat exchanger tube rises while receiving heat from the primary sodium, and rises to the secondary side upper plenum 17.
and is sent to the steam generator system from the secondary outlet nozzle 23. FIG. 3 shows the flow of primary sodium in the hot plenum 9 when the reactor power suddenly decreases and the primary sodium changes from high temperature to low temperature. That is, when the reactor power rapidly decreases, the temperature of the primary sodium at the reactor core outlet also changes from high temperature to low temperature. At this time, the sodium flow condition in the hot plenum 9 is such that high-temperature sodium with low density stays in the upper part near the free liquid level 11, and a secondary flow 21 is generated, as shown by the arrow in the figure. On the other hand, low-temperature sodium flowing out of the core flows into the intermediate heat exchanger 7 along the primary sodium main stream 20 without being sufficiently mixed within the hot plenum. Therefore, a severe cold shock due to the primary sodium is applied to the intermediate heat exchanger 7, and unnecessary thermal stress is generated in the internal structure of the intermediate heat exchanger. Furthermore, an uneven sodium temperature distribution occurs downward from the free liquid level 11, and temperature distribution also occurs in the intermediate heat exchanger 7, the upper furnace mechanism 6, and the primary main circulation pump 8, causing unnecessary thermal stress. do. The object of the present invention is to provide a tank-type nuclear reactor main vessel that is suitable for preventing the stratification that causes the above-mentioned drawbacks. FIG. 4 shows an embodiment of the present invention. That is, the heat shielding structure 4 divides the inside of the main reactor vessel into a hot plenum 9 and a cold plenum 10 having a free liquid level 11.
and a roof slab 2 for closing the upper part of the main container.
and an intermediate heat exchanger 7 which penetrates the roof slab 2 and has a primary sodium inflow window 13 opening into the hot plenum 9 below the free liquid level 11 and a primary sodium outflow window 14 opening into the cold plenum 10; In a nuclear reactor comprising a primary sodium induction cylinder 18 surrounding the outer periphery of the primary sodium inflow window 13 of the intermediate heat exchanger 7 with a gap A maintained, the primary sodium induction cylinder 18 extends from below to above the lower end of the primary sodium induction cylinder 18. The outer periphery of the primary sodium induction cylinder 18 is surrounded by a strategy cation prevention cylinder 22 fixedly held on the heat shielding structure 4 while maintaining a gap B, and the strategy cation prevention cylinder 22 is shielded from heat. Fluid inlets 26 and 27 in the hot plenum 9 are provided at a portion near the structure 4 and at a portion above that portion. This strafication prevention cylinder 22 is fixed by welding to pedestals 24 arranged at approximately equal intervals in the circumferential direction, and the pedestals 24 are fixed to the heat shielding structure 4 by welding to provide fixed support. be done. Horizontal protruding spacers 25 are welded to the stratification prevention cylinder 22 at approximately equal intervals in the circumferential direction so that the gap B forming the flow path is maintained.

In such a configuration, the high temperature sodium that remains near the free liquid level 11 flows through the upper inlet 2.
6 into the gap B, relatively low-temperature sodium enters from the inlet 27, and both high and low-temperature sodium are merged and mixed at the lower end of the primary sodium induction cylinder 18, and the temperature is homogenized. Sodium rises in the gap A, becomes more uniform in temperature during the rising process, and finally flows into the primary sodium inflow window 13.

The effects of the present invention will be explained using a model shown in FIG. The main stream 20 of sodium, the area where the mixed flow 23 exists, and the area where the secondary flow 21 exists in the hot plenum 9 in FIG. 3 are the main stream in FIG. 6, respectively.
It corresponds to Q _a , mixed region V _a , and dead water region V _b . Furthermore, in FIG. 6, a bypass flow Q _b is also considered in which the flow at the core exit flows into the intermediate heat exchanger without being mixed in the hot plenum. According to a simplified physical model of the flow within this hot plenum, the energy balance in the mixing zone is given by the following equation.

ρCdθ _a /dt=ρQ _a (θ _p −θ _a )...(1) However, initial condition; θ _a (O)=0...(2) Inlet temperature; θ _p ...(3) Equation (1) The solution is given by the following equation.

θ _a /θ _b = 1−e ^-Qat/Qb (4) On the other hand, the balance of total flow rate is expressed by the following equation.

Q=Q _a +Q _b (5) Moreover, the relationship between the total volume V, the dead water area V _b , and the mixing area V _a is given by the following equation.

V=V _a +V _b (6) The temperature (θ) at the inlet of the intermediate heat exchanger can be obtained from the following energy balance equation.

Qθ=Q _a θ _a +Q _b θ _p (7) Therefore, the dimensionless intermediate heat exchanger outlet temperature θ ^* can be obtained by the following equation.

θ ^* =1−Q _a /Qe ^-Qa/QV/Vat* ...(8) However, θ ^* = (θ _p −θ) / (θ _p −θ _a (O)) ...(9) t ^* = V/Q FIG. 7 shows the results of determining the intermediate heat exchanger inlet temperature using the volume V _a of the mixing region as a parameter when Q _a /Q _b =1 in equation (8). As the dead water region V _b becomes larger due to the strategy, that is, the mixing region V _a becomes smaller, the temporal change in the intermediate heat exchanger inlet temperature θ ^* becomes larger, and thermal shock tends to increase. In the present invention, as shown in FIG. 5, a stratification prevention cylinder 22 having a gap B and upper and lower inflow ports 26 and 27 is installed around the outer periphery of the primary sodium induction cylinder 18, so that the buoyancy The high-temperature sodium that has risen due to the influence of is sucked in from the upper part of the cylinder 22 mentioned above and mixes with the low-temperature sodium flowing in from the lower part of the cylinder 22, so the condition of V _a /V = 1.0 in Fig. 7 can be created. , thermal shock to the internal structure of the intermediate heat exchanger 7 can be reduced.

According to the present invention, the high-temperature sodium that stays in the upper part of the hot plenum and the low-temperature sodium that flows in the lower part of the hot plenum can be mixed and flowed into the intermediate heat exchanger during excessive plant operation, so that the thermal shock applied to the intermediate heat exchanger is can be made smaller.

[Brief explanation of drawings]

Figure 1 is a side view showing the schematic structure inside the main vessel of a tank-type fast reactor, Figure 2 is a sectional view taken along line A-A in Figure 1, and Figure 3 shows the sodium flow situation in the hot plenum during plant transition. 4 is a side view showing one embodiment of the present invention, and FIG. 5 is a side view showing an embodiment of the present invention.
Fig. 6 is a simplified diagram of the hot plenum to explain the effects of the present invention, and Fig. 7 shows the dead water area caused by strategy cation. FIG. 3 is a diagram showing the influence on the intermediate heat exchanger inlet temperature. 1... Main vessel, 2... Roof slab, 3... Core support structure, 4... Heat shielding structure, 5... Core, 6... Core upper mechanism, 7... Intermediate heat exchanger,
8...Primary main circulation pump, 9...Hot plenum, 10...Cold plenum, 11...Free liquid level, 12...Auxiliary heat exchanger, 13...Primary sodium inflow window, 14...Primary sodium Outflow window, 1
5...Downcomer pipe, 16...Secondary side lower plenum, 1
7...Secondary side upper plenum, 18...Cylinder for primary sodium induction, 19...Heat transfer tube group, 23...2
Next outlet nozzle.

[Claims]

1 A method for repairing a nuclear reactor in the event that a fault occurs in the pressure pipe of a pressure tube reactor that interferes with the operation of the reactor, in which the method is used to repair a nuclear reactor near the water drum of the inlet pipe connected to the faulty pressure pipe. After cutting the outlet pipe at appropriate points near the steam drum and plugging the end of the inlet pipe on the water drum side and the outlet pipe end on the steam drum side at the cut points, the pressure pipe that caused the trouble was removed. pulling out the pressure pipe by disconnecting it from the inlet pipe and outlet pipe connected thereto at the pressure pipe lower extension part and the pressure pipe upper riser pipe vertical part, respectively;
A pressure pipe type characterized in that a radiation shielding plug pipe having a reciprocating coolant flow path communicating with the outside and shielding plugs located near both ends thereof is inserted and installed in place of the pulled out pressure pipe. How to repair a nuclear reactor.