JPH0530237B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a tank-type fast breeder reactor, and in particular, the present invention relates to a tank-type fast breeder reactor, and in particular, to uniformize the temperature distribution based on convection of cover gas in an annular space formed in a roof slab. The present invention relates to a tank-type fast breeder reactor having a configuration suitable for preventing thermal deformation of upper core equipment and the like inserted into the reactor.

[Background of the invention]

Generally, in a tank-type fast breeder reactor, for example, as shown in FIG. has been done.

The roof slab 2 is equipped with various upper furnace equipment, such as an intermediate heat exchanger (hereinafter referred to as IHX) 6 that exchanges heat between the high temperature primary sodium 5 and the secondary sodium heated in the core 3, and a primary sodium A pump 7 for circulating in the reactor, a control rod driving device 8 for controlling the output of the reactor core 3, or a rotary plug 9 for positioning a fuel exchanger (not shown) at a predetermined position during fuel exchange. The upper device is inserted. In such a nuclear reactor structure, a plurality of annular spaces whose axes extend in the vertical direction are formed around the roof slab 2 and around each of the upper reactor equipment inserted into the roof slab 2. ing. That is, the annular space formed between the outer periphery of the heat shielding layer 14 of the roof slab 2 and the reactor vessel 1;
and an annular space formed between the roof slab 2 and the IHX 6, pump 7, control rod driving equipment 8, rotating plug 9, etc.

By the way, argon gas, which is an inert gas (does not react with sodium), is filled above the high temperature primary sodium in the hot pool 5.
It fills the space between the sodium liquid level and roof slab 2. This cover gas also flows into the annular space.

On the other hand, during rated operation, the primary sodium temperature of the hot pool 5 is generally about 500°C, and unless special consideration is taken, the lower surface of the roof slab 2 facing the hot pool 5 will be heated by the high temperature sodium of the hot pool 5, and the temperature of the primary sodium of the hot pool 5 will be about 500°C. Although the temperature rises to about 400℃, the temperature limit for electrical components such as various core instrumentation mounted on this roof slab 2 is about 70℃, so the lower part of the roof slab 2 and rotating plug 9 is A cooling means consisting of a cooling channel 13 using an inert gas, a heat shielding layer 14, etc. is provided.

Therefore, in the annular space formed in the roof slab 2, the lower part is high temperature and the upper part is low temperature, and given such a temperature distribution,
Rayleigh number Ra = (g〓ΔTL ³ )/(aν) where, g: Gravitational acceleration β: Body expansion coefficient of gas ΔT: Temperature difference between the upper and lower sides of the annular space L: Representative length of the annular space a: Temperature of the gas Conductivity ν: Natural convection occurs when the kinematic viscosity coefficient of the gas exceeds a certain value (this is called the critical Rayleigh number). Figure 2 shows an example of the flow situation of this natural convection. The high-temperature argon cover gas forms an upward flow 16 at one location 15 in the annular space, splits into two directions at the upper end of the annular space, and returns to the cover gas layer as a downward flow 18 at a position 17 in the circumferential direction opposite to this. The number of pairs of such convections is
It is determined by the relationship between the height and diameter of the annular space. In other words, convection occurs in a shape in which the rising and falling distance of the cover gas (the height of the annular space) and the horizontal movement distance of the convection at the top of the annular space are approximately equal. Roof slab 2
In the annular space formed by the IHX 6, pump 7, etc. that pass through the pump, a pair of natural convection flows as shown in FIG. 2 generally occur. In addition, when the diameter of the annular space is significantly larger than the height of the annular space, such as between the reactor vessel 1 and the roof slab 2, several pairs of natural convection occur. In this case, since the gas temperature on the upward flow 16 side is higher than the gas temperature on the downward flow 18 side, a temperature difference occurs in the circumferential direction of the annular space, and each component disposed in this annular space Heat deformation will occur.

For example, in the annular space formed between the reactor vessel 1 and the roof slab 2, several pairs of natural convection occur because the diameter is large compared to the height of the annular space. A fuel transfer chute and an intermediate heat exchanger for the direct core cooling system, which are located asymmetrically with respect to the center of the reactor vessel,
Regular convection does not necessarily occur due to the asymmetric reactor structure with respect to the center of the reactor vessel, such as rotating plugs installed eccentrically with respect to the center of the reactor core. Therefore, the temperatures at positions that differ by 180° in the annular space, that is, at the target positions, are not necessarily the same, and if you look at the entire reactor vessel, there is a high possibility that the temperature distribution will be uneven in the circumferential direction. This may cause thermal deformation of the furnace vessel.

In addition, in the case of relatively small-diameter upper reactor equipment such as the IHX 6, pump 7, control rod drive mechanism 8, and rotary plug 9 that penetrate the roof slab 2, thermal deformation in the annular space may occur at the part inserted into the reactor vessel. This is likely to be caused by contact with the equipment.

Note that natural convection is known to occur when the following items are satisfied at the same time.

(a) The gap width of the annular space is greater than or equal to a certain value.

(b) It is in a so-called unstable flow state, with high temperature at the bottom and low temperature at the top.

(c) The walls forming the annular space have thermal resistance.

Conventionally, a method of preventing the occurrence of natural convection has been considered by utilizing the item (a) and filling the annular space with metal mesh. However, in this case, it is necessary to take measures to prevent small pieces of mesh from falling into the reactor throughout the life of the plant, that is, even during rated operation and during maintenance by pulling out the IHX 6 and pump 7. This poses a problem in that the configuration becomes extremely complex.

On the other hand, as a method using paragraph (b),
There is one disclosed in No. 38695. That is, as shown in FIGS. 3 and 4, a plurality of convection prevention pieces 19 are provided in the vertical direction and the circumferential direction between the outer body and the outer casing of the device. However, it is considered difficult to apply such a convection prevention piece 19 to the annular space of the roof slab of a tank-type fast breeder reactor for the following reasons.

IHX and circulation pumps are designed so that they can be removed for maintenance in the event of a failure, but convection prevention plates such as those described above may become stuck to the roof slab due to adhesion of sodium mist in the argon cover gas. be.

In addition, the above-mentioned convection prevention plate is very effective when the gap width of the annular space is almost uniform, but in tank-type fast breeder reactors, IHX penetrates at two places: the roof slab and the core support structure. There is a possibility that the gap width of the annular space will be uneven due to the relative manufacturing error between the roof slab through-hole and the core support structure through-hole, and the convection prevention plate will not work effectively.

Furthermore, when small pieces of metal such as these are used in the reactor structure, it is necessary to prevent them from falling or getting mixed into the sodium. It is not desirable from a reliability point of view to install several convection prevention plates.

Note that even if natural convection occurs, it may be possible to generate several pairs of convection within the annular space to prevent thermal deformation of the device from occurring in one direction due to temperature differences.

A plan view of an example of a structure when this concept is applied to roof slab penetrating equipment such as IHX, pumps, and the upper core mechanism that is the control rod drive mechanism is shown in Figure 5. A partition plate 21 is attached to the roof slab 2 and the roof slab penetrating equipment 20 such as an IHX, a pump, and an upper core mechanism, and an attempt is made to divide what was originally intended to be a pair of convection into several pairs of convection. however,
In order to make it possible to pull out IHX, pumps, etc. during maintenance, it is necessary to install the partition plates with a slight distance from each other to prevent them from sticking due to long-term operation. If there is a gap between the plates, a pair of natural convection will occur (generally, the flow velocity of natural convection is low, so even if there is a considerable obstruction in the flow path, the pressure loss will be small and the flow will pass through the obstruction). The structure no longer holds true.

In addition, natural convection in the annular space between the reactor vessel and the roof slab originally occurs in several pairs, but as mentioned above, it is unlikely that symmetrical convection occurs in this area, and the Directional temperature differences may occur. Therefore, even if structural measures as shown in FIG. 5 are taken, the above-mentioned problems remain.

[Purpose of the invention]

The present invention was made in view of these circumstances, and provides a tank-type fast breeder reactor that can reliably prevent deformation of equipment due to natural convection of argon cover gas into the annular space formed in the roof slab. The purpose is to provide.

[Summary of the invention]

In the tank-type fast breeder reactor of the present invention, a roof slab that closes off the reactor vessel from above has an annular space whose axis is directed vertically, and a cover gas inside the reactor vessel is introduced from below into this annular space. The temperature difference in the circumferential direction of the annular space caused by the convection formed when the cover gas flows into the annular space from below rises, flows in the circumferential direction, and then descends. In order to generate the gas symmetrically with respect to the axis of the annular space, a gas descending section for lowering the cover gas is provided.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 6 and 7. Note that this example was carried out targeting the annular space around the IHX.
Since there are many commonalities in the case where the present invention is applied around other upper reactor equipment and the case where it is applied to the annular space around the roof slab, descriptions thereof will be omitted.

As shown in FIG. 6, the outer shell 30 of the IHX6 is immersed in high temperature primary sodium in a hot pool. For this reason, heat is transmitted upward through the outer shell in the axial direction by conduction, and unless some measure is taken, the temperature reaches the flange portion 31 at the upper end of the outer shell.
Normally, the outer shell 3 of IHX6 is
A cooling pipe 32 is provided inside the shell 30 to cool the outer shell 30 and the flange 31.
Furthermore, at the lower end of the annular space, a mist intrusion prevention mechanism 33, such as a seal using a bellows or a sodium reservoir, is installed to prevent sodium mist from entering the annular space and adhering to the IHX 6 or the roof slab. Measures such as a sodium dam to trap and seal are taken.

In such an annular space, as mentioned above,
Generally, a pair of natural convection tends to occur, but
In this embodiment, as shown in FIG. 7, the plate thickness of the outer shell 30 of the IHX is thickened outward at several locations at equal intervals along the circumferential direction, and a plurality of protrusions along the vertical direction protrude into the annular space. 34 is formed. In order to satisfy the purpose of the present invention, such a protrusion 34 (in other words, a thick wall portion) should have a width of at least 2 in the circumferential direction.
More than one location is required.

According to this configuration, the outer body 30 of IHX6
is cooled from the inside, and the surface temperature of the outer shell 30 is determined by the thermal resistance from the cooling pipe 32 to the outer surface of the outer shell 30 of the IHX 6 in contact with the annular space. It is low, and becomes high at the protrusion portion 34. Therefore, within the annular space, the argon gas becomes an upward flow at the protrusion 34 and a downward flow at the concave section 35, but these upward and downward flows are symmetrical within the annular space with respect to its axis. This prevents the IHX6 from tilting in one direction due to thermal deformation and therefore does not impair its functionality. In addition, in a configuration where unevenness exists in the annular space as in this example, it becomes easy to regulate the convection position not only by thermal boundary conditions but also by the shape, which makes it possible to maintain stable convection. There is also the advantage of being able to obtain

It should be noted that from the viewpoint of reducing the stress generated in the outer shell 30 of the IHX6, it is preferable that the number of the protrusions 34 and the grooves 35 be as large as possible so as to reduce the temperature difference in the circumferential direction.
In order to obtain stable convection at a predetermined position, it is better to have as few as possible. According to a trial calculation based on the operating temperature conditions and structural dimensions of a typical tank-type reactor structure, in order to suppress the stress generated in the IHX outer shell to about 1/2 to 1/3 of the yield stress, it is necessary to It has been confirmed that the number of sets is preferably about 4 to 8.

According to the embodiments described above, thermal deformation of the IHX 6 is prevented, and the size of the seal between the IHX 6 and the core support structure can be reduced. Especially in the case of a bellows seal, the amount of sodium leakage can be reduced. In addition, it does not cause thermal deformation of the circulation pump.
Galling of the circulation pump can be reliably prevented.

In the above-mentioned embodiment, the heat drop portion in the annular space is formed into a protrusion 34 that protrudes into the annular space, but the present invention is not limited to such a structure, and various other means can be used. .

For example, in the case shown in FIGS. 8 and 9, heat is generated by cooling pipes 32 buried at intervals in the circumferential direction near the surface of the outer shell 30 of the IHX6, which is a member forming the inner circumferential wall of the annular space. This is what constitutes the descending section.

Even with such a configuration, it is possible to form the high temperature part 40 and the low temperature part 39 in the annular space formed around the IHX 6, and it is possible to prevent thermal deformation of the equipment. High reliability can be achieved because the parts can be set actively and directly.

In addition, in the case shown in FIGS. 10 and 11, cooling pipes 32 are arranged in the circumferential direction at a constant radius on the outer shell 30 of the IHX 6, and the cooling pipes 32 are insulated at regular intervals on the surface side of the cooling pipes 32. By arranging the material 36, a heat drop portion is formed within the annular space.

Even with such a configuration, the same effects as in the embodiment described above can be achieved, and in this case, there is an advantage that the piping configuration of the cooling pipe 32 can be simplified.

In addition, in the above embodiments, the heat drop part was formed by the member forming the inner circumferential wall of the annular space, but it may be formed by the member forming the outer circumferential wall or both of it and the inner circumferential wall constituent member. Of course.

〔Effect of the invention〕

As described in detail in the above embodiments, according to the tank-type fast breeder reactor according to the present invention, a temperature difference is generated symmetrically in the circumferential direction in the annular space formed in the roof slab based on the convection of the cover gas. Since the heat drop section is provided, it is possible to reliably prevent thermal deformation of the roof slab itself or various upper core equipment, which is an excellent effect in terms of safety measures.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing a tank-type FBR reactor.
Figure 2 is an explanatory diagram showing the flow situation of natural convection, Figure 3
4 is a schematic diagram showing a conventional example, FIG. 4 is a detailed configuration diagram thereof, FIG. 5 is a schematic diagram showing another conventional example, FIG. 6 is a sectional view of essential parts showing an embodiment of the present invention, and FIG. The figure is a sectional view taken along the - line in Fig. 6, Fig. 8 is a sectional view showing main parts of another embodiment of the present invention, and Fig. 9 is a sectional view taken along the - line in Fig. 8.
10 is a cross-sectional view of a main part showing still another embodiment, and FIG. 11 is a cross-sectional view taken along the line -- of FIG. 10. 1... Reactor vessel, 2... Roof slab, 3...
... Core, 6, 7, 8 ... Core upper mechanism, 32 ...
Cooling pipe, 34... protrusion, 36... insulation material.

Claims (1)

[Claims] 1. An annular space whose axis is directed in the vertical direction is formed in a roof slab that thermally shields the upper part of the reactor vessel from the inside and closes it from the outside, and atoms are introduced into this annular space from below. In a tank-type fast breeder reactor into which cover gas flows into the reactor vessel, the temperature in the circumferential direction in the annular space is based on the convection formed by the rise, circumferential flow, and descent of the cover gas flowing into the annular space. 1. A tank-type fast breeder reactor, characterized in that it is provided with a gas descending section for cover gas which causes a difference symmetrically with respect to the axis of an annular space. 2. The gas descending section includes a cooling pipe arranged circumferentially at a constant radius inside one or both of the members forming the inner peripheral wall or the outer peripheral wall of the annular space, and the member forming the inner peripheral wall or the outer peripheral wall. The tank type fast breeder reactor according to claim 1, characterized in that the tank type fast breeder reactor is a plurality of vertically extending protrusions projecting into the annular space from one or both of the above. 3. A patent claim characterized in that the gas descending section is a cooling pipe disposed at intervals in the circumferential direction near the surface of either or both of the members forming the inner circumferential wall or the outer circumferential wall of the annular space. A tank type fast breeder reactor according to item 1. 4. The gas descending section consists of a cooling pipe disposed circumferentially at a constant radius on either or both of the members forming the inner circumferential wall or the outer circumferential wall of the annular space, and a cooling pipe arranged circumferentially at intervals on the surface side of this cooling pipe. 2. A tank-type fast breeder reactor according to claim 1, characterized in that the tank-type fast breeder reactor is formed by a heat insulating material arranged in a manner that the reactor is insulated.