JPS5990086A - Fast breeder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to fast breeder reactors.

[Technical background of the invention and its problems]

The primary cooling system of a conventional loop-type fast breeder reactor is constructed as shown in FIG. That is, the reference numeral I in the figure is this reactor vessel, and the upper opening IA of this reactor vessel 1 is closed by a shielding plug IB. A reactor core 2 is housed within this reactor vessel 1 . A primary coolant such as liquid sodium is contained within the reactor vessel 1, and this secondary coolant flows within the reactor core 2 from below to above.
Heated to high temperatures. The primary coolant heated to a high temperature is sent to the intermediate heat exchanger 4 through the primary coolant pipe 3 and is configured to exchange heat with the secondary coolant. The primary coolant that has undergone heat exchange in this intermediate heat exchanger 4 and has become low temperature passes through the primary coolant pipe 3f: the primary coolant pipe 3.
5, the pressure is increased by this secondary cooling pump 5, and the primary coolant is returned to the reactor pressure vessel 1 through the primary coolant pipe 3, and the secondary coolant is circulated through this path. It is configured. Note that the reference numeral 6 in the figure indicates the core upper mechanism. Further, the primary coolant pipe 3 is arranged substantially horizontally to prevent the primary coolant inside the reactor vessel I from flowing out in the event of a breakage. On the inner peripheral side of the reactor vessel I, an inner cylinder 10 is provided upright from the partition wall 1 with a gap.

This inner cylinder 10 is configured to promote active mixing of the coolant. An outlet nozzle I2 for outflowing the coolant is provided on the side wall of the reactor vessel 1, and flow holes 13 are arranged at equal intervals in the circumferential direction in the inner cylinder 10 at a position corresponding to the outlet nozzle I2. is formed. This flow hole Z3 is configured to ensure a coolant flow path during leakage in the reactor vessel l and when the liquid level drops during fuel exchange. The effective diameter of the flow hole 13 is determined so that only a little less than 10 inches of the total flow can flow during rated flow.

Generally, nuclear reactor equipment is equipped with a reactor safety system.
The reactor is configured to scram in the event of an emergency such as an earthquake to ensure safety. During this scram, control rods (not shown) are rapidly inserted into the reactor core 2 to stop the nuclear reaction in the reactor core 2 and stop the operation of the primary cooling pump 5. By the way, the nuclear reaction in the reactor core 2 is stopped instantaneously by the rapid insertion of the control rods, but the secondary coolant Ponzo 5 continues to operate due to inertia, so the secondary coolant flows into the reactor vessel I. do. The inflow of the primary coolant due to the inertia of the secondary coolant pump 5 has a small flow rate of about 10% of the rated operation, and continues for a relatively long time. The primary coolant that has flowed into the reactor vessel 1 flows upward within the reactor core 2 and flows out from the two sides of the reactor rb2.
Since the nuclear reaction inside reactor core 2 has already stopped, this -
The temperature of the secondary coolant does not rise even after passing through the core 2, and it flows out from the upper surface of the low-temperature, low-flow rate core 2. Therefore, this low-temperature primary coolant 8a has a higher density than the high-temperature primary coolant 8b that existed in the upper part of the reactor vessel 1 before the scram, and the flow rate from the two sides of the reactor core 2 is lower. The upward momentum is quickly canceled out and the coolant does not mix sufficiently with the high-temperature primary coolant 8b, but due to the density difference, it descends and accumulates in the lower part of the reactor vessel 1. A relatively clear boundary surface 9 is formed between the low-temperature primary coolant 8a and the high-temperature primary coolant 8b. This is called stratification. Then, the reactor core 2
As the low-temperature primary coolant 8a continues to flow out from the upper surface, this boundary surface 9 rises with time. Depending on the reactor system, this stratified flow phenomenon that begins in the reactor vessel may be maintained for a long time, and eventually this boundary surface 9 will reach the position of the primary coolant pipe 3, causing low-temperature fluid to flow inside this secondary coolant pipe. Primary coolant 8a
The high temperature primary coolant 8b flows out while being separated into layers.

The temperature difference between the low-temperature primary coolant 8a and the high-temperature primary coolant 8b generally reaches 300°C or more, and the density ratio between the two is 1.09 at 200°C and 500°C. Moreover, since liquid sodium is used as the secondary coolant and its heat transfer ability is extremely large, a large thermal gradient occurs near the interface 9 between the low-temperature primary coolant 8a and the high-temperature primary coolant 8b. Therefore, excessive thermal stress occurs in this portion due to the difference in thermal expansion, which causes a problem that adversely affects the structural integrity of the primary coolant pipe 3 including the reactor internals and the outlet nozzle. As mentioned above, in the case of the type in which the inner cylinder IO having the flow pole 13 is provided on the inner peripheral side of the reactor vessel l, when the above-mentioned stratified flow occurs, the coolant temperature as shown in Fig. 2 Show the distribution. In this case, the flow resistance of the flow hole 13 is relatively large, and therefore the boundary surface 9 rises even after passing through the entire flow hole I3. And boundary surface 9
Until it overflows from the upper end of the inner cylinder 10, the low-temperature coolant 8a flows out from the ball 13, and the annulus 14 between the reactor vessel I and the inner fJT 10 is filled with high-temperature coolant 8b. flows down and collects at the nozzle I2. At this time, the low-temperature coolant 8a and the Takahata coolant 8b do not mix loosely and flow in a stratified manner while remaining in a two-layer state, partly due to the fact that the flow itself is reduced. The force that causes stratified flow at the outlet nozzle Z2, straight pipe, L d? Stratified flow persists even in the primary coolant piping system, which is made up of basic elements such as heat and cheese. Therefore, in the case of secondary coolant piping, measures are taken to absorb thermal expansion at various points, such as by providing bent parts, while in the case of outlet nozzles 1θ, beams that support the heavy lifting of various pipings are used. As a result, it forms one end of
Even at rated flow, an excessive 1u1 reaction may occur, which is why the welded structure is rigid. Therefore, if thermal stress is generated due to stratified flow, strain will be generated and accumulated, and there is a risk of breakage.

[Purpose of the invention]

The present invention prevents the occurrence of excessive thermal stress in the outlet nozzle, especially its welded part, due to the temperature difference of the secondary coolant, and improves the health and safety of not only the outlet nozzle but also the entire plant. We hope to provide a fast breeder reactor that can do this.

[A chest of inventions]

The fast breeder reactor according to the present invention includes a reactor vessel which houses a reactor core and a coolant therein and has an opening at the top, a shield Zorag provided to close the opening, and a shield provided on the side wall of the reactor vessel. an outlet nozzle for outflowing coolant, a coolant outflow pipe connected to the outlet nozzle, and an inner cylinder provided with a gap on the inner circumferential side of the reactor vessel; This configuration includes a flow hole formed at a position corresponding to the nozzle, and a protruding pipe connected to the flow hole and disposed for flowing out the coolant.

Therefore, when stratified flow of coolant occurs in the inner cylinder, this stratified flow can be prevented from spreading to the outlet nozzle, especially to the connection between the outlet nozzle and the reactor vessel. , it is possible to greatly improve the health and safety of the entire plant as well as the outlet nozzle section.

[Embodiments of the invention]

An example of a stone according to the present invention will be explained with reference to FIGS. 3 to 5. FIG. 3 is a system diagram of the primary cooling system of a loop type fast breeder reactor. Reference numeral 101 in the figure is a reactor vessel,
The upper thirteenth opening of this reactor vessel 101 is closed by a shielding plug I01'H. A reactor core 102 is housed within this reactor vessel 101 . A primary coolant such as liquid sodium is stored in the reactor vessel 101, and this secondary coolant is contained in the reactor vessel 101.
The water flows inside from the bottom to the top and is heated to a high temperature. The primary coolant heated to a high temperature is then transferred to the primary coolant pipe 1'.
03 to an intermediate heat exchanger 104, which is configured to exchange heat with a secondary coolant. The primary coolant that has undergone heat exchange in this intermediate heat exchanger 8G 104 and has become low temperature is sent to the primary coolant pipe 105 through the primary coolant piping system o 3, and is pressurized by the secondary coolant pump 105. and the reactor pressure vessel 1 through the primary coolant pipe 103.
01, and the secondary coolant is configured to circulate through this path. In addition, the code 1 in the figure
06 is the core upper mechanism, and the above-mentioned primary coolant pipe 10
3 is arranged substantially horizontally in order to prevent the primary coolant in the reactor vessel zor from flowing out in the event of rupture.

There is a gap on the inner circumference side of the reactor vessel 202, and the inner cylinder 1
10 are provided. An outlet nozzle 112 for coolant outflow is formed on the side wall of the reactor vessel 101, and a coolant outflow pipe 113 is connected to this outlet nozzle 112. A flow hole 114 is formed in the inner cylinder 110. The number of flow holes 114 is the same as that of the outlet nozzle 11.
The number is the same as the number 2. And this flow hole 114
A protruding pipe 115 is connected to. The tip of this protruding pipe 115 passes through the outlet nozzle 11.2 and forms a coolant outflow pipe ZZ, ? It has reached inside. That is, the low temperature coolant flowing out through the flow hole 114 and the inner cylinder 11
The high-temperature coolant that flows over the upper end of 0 and flows down the annulus section 117 between the inner cylinder 11θ and the reactor vessel IOI is mixed with the coolant at the outlet nozzle 112 as in the conventional case. The configuration is such that the mixture is first mixed in the outflow pipe 113.

Conventionally, the number of flow holes 114 is generally greater than the number of outlet nozzles 112; for example, there are 48 flow holes 114 compared to three outlet nozzles l12. If this is applied to this embodiment, the outlet nozzle 11
Since there are three 2, there are also three flow holes 114. At this time, the ratio of the flow rate of coolant flowing out from the 70-hole 114 to the total flow rate during rated flow is constant considering the characteristics of the flow hole 114.

Therefore, if the size of the flow hole 114 before the change is d, the diameter iD when applied to this embodiment, and the respective jet flow rates are τ and ■, the following relationship holds true.

48d −τ=3DV・・・・・・・・・・・・
(A) Since the resistance is constant, assuming that the flow hole 114 is a pipe flow, 1υ2 =: 1 y2 ......
・・・・・・・・・・・・(B)D. Therefore, from these formulas (A) and (B),
, = 3.0 is obtained.

Therefore, in order to apply it to this embodiment, it is sufficient to make the diameter three times the diameter of the conventional flow hole 114.

The operation will be explained based on the above configuration. Outlet nozzle 1
12 and the reactor vessel 101 is covered all around with the high temperature coolant 108b that has flowed over the upper end of the inner cylinder 110 and flowed down the annulus portion 117. on the other hand,
The flow state within the protruding pipe 115 is considered to be either as shown in FIG. 6(A) or FIG. 6(B) depending on the timing of the stratified flow within the inner cylinder 220.

That is, when the boundary surface 109 is located below the flow hole I14, the high temperature coolant 108a flows throughout the inside of the protruding pipe 115. And the boundary surface 109
When the coolant 10 rises and reaches the position of the flow hole 114, the inside of the protruding pipe 115 is filled with high-temperature coolant 10, as shown in FIG. 6(A).
8b and the low temperature coolant 10B& are in a two-layer state. Then, as it rises further, as shown in Fig. 6 (B), the protruding pipe 1
The entire area inside 15 becomes a low-temperature coolant 108a. In any of these cases, the welded portion 11
The area near 6 is the high-temperature cooling 1 flowing down the annulus part 117.
'708 b. Therefore, unlike the conventional case (shown in FIG. 6(C)), the layered relationship below the exit nozzle 112 does not occur, and the exit nozzle 112
It is possible to reliably prevent the generation of thermal stress caused by the temperature difference between the parts and the like, and it is possible to prevent accidents such as breakage due to the accumulation of strain.

Next, another embodiment will be described with reference to FIG. That is, the tip of the protruding pipe 115 is closed. A plurality of jetting ports ZZ5A are formed on the upper surface side of the protruding pipe 115 located in the coolant outflow pipe 113, and the low-temperature coolant 108a flowing through the protruding pipe 115 is spouted upward. Therefore, the low-temperature coolant 108a and the high-temperature coolant 108b are reliably mixed in the coolant outflow pipe 113, and stratified flow in the coolant outflow pipe 113 can be prevented. It is also possible to maintain the integrity of the primary coolant piping. Note that the functions and effects of the outlet nozzle 112 are the same as those in the previous embodiment.

〔Effect of the invention〕

The fast breeder reactor according to the present invention includes a reactor vessel that houses a reactor core and a coolant therein and has an opening at the top, a shielding plug provided to close the opening, and a shielding plug provided on a side wall of the reactor vessel. an outlet nozzle for outflowing coolant, a coolant outflow pipe connected to the outlet nozzle, and an inner cylinder provided with a gap on the inner circumferential side of the reactor vessel; A flow hole formed in Inf corresponding to the nozzle and a protruding pipe connected to this flow hole and disposed up to the coolant pipe were formed into a structure OH1 (lq configuration).

Therefore, when stratified flow of coolant occurs in the inner cylinder, this stratified flow can be prevented from spreading to the outlet nozzle, especially the connection between the outlet nozzle and the reactor vessel. This has great effects, such as greatly improving the health and safety of not only the outlet nozzle but also the entire plant.

[Brief explanation of drawings]

1 and 2 are diagrams showing a conventional example, in which FIG. 1 is a schematic system diagram of a loop type fast breeder reactor, and FIG. 2 is a sectional view showing a state of stratified flow. Figures 3 to 5 are diagrams showing one embodiment of the present invention, in which Figure 3 is a schematic system diagram of a loop type fast breeder reactor, Figure 4 is a cross-sectional view of the vicinity of the protruding pipe, and Figure 5 is a perspective view. , FIGS. 6A, 6B, and 6C are cross-sectional views for explaining the effects, and FIG. 7 is a cross-sectional view showing another embodiment. 101... Reactor vessel, 101k... Upper opening of reactor vessel, IθZB... Shielding plug, IO2... Core, 110... Inner cylinder, ZZ, ? ...Outlet nozzle, 1
13... Coolant outflow pipe, l14... Flow hole,
115...Protruding piping. Issuto's agent Patent attorney Suzue Takehiko Hikoho 4 il Iku 5 Iku 6 (A)

Claims (2)

[Claims] (1) A reactor vessel containing a reactor core and coolant inside and having an opening at the top, a shielding plug provided to close the opening, and a coolant outflow provided on the side wall of the reactor vessel. an outlet nozzle, a coolant outflow pipe connected to the outlet nozzle, an inner cylinder provided with a gap on the inner peripheral side of the reactor vessel, and a position of the inner cylinder corresponding to the outlet nozzle. A fast breeder reactor comprising a flow hole formed therein and a protruding pipe connected to the flow hole and disposed up to the coolant pipe. (2) The fast breeder reactor according to claim 1, wherein the tip of the protruding pipe is closed and a plurality of jet ports are formed on the upper surface side located inside the coolant pipe. .