JPH01265196A - Fuel assembly for fast breeder - Google Patents

Abstract

PURPOSE:To extremely decrease the propagation of a complete inlet closure accident even in the event of the outbreak of such accident by providing a mechanism to form a coolant flow passage at the time of the large-scale clogging of the coolant inflow port to the low-pressure plenum side of an entrance nozzle part. CONSTITUTION:The coolant inflow hole 10 opening to the low-pressure plenum 9 is formed to the bottom end part of the entrance nozzle part 5 and a spherical movable plug 11 is disposed in this hole 10. A movable plug stop 12 is disposed to the upper part of the movable plug 11. The movable plug 11 normally closes the inflow hole 10 by the coolant pressure from the high-pressure plenum side 8 flowing in from the coolant inflow hole 4. The pressure in the assembly drops below the pressure of the low-pressure plenum 9 and, therefore, the movable plug 11 is lifted when the coolant inflow hole 4 of the high-pressure plenum side 8 is completely closed by a certain cause. An a result, the inflow hole 10 is opened and since the coolant flow in from the low-pressure plenum 9, the propagation of the accident is prevented.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a fast breeder reactor fuel assembly used in a liquid metal cooled fast breeder reactor.

(Prior Art) Generally, a conventional fuel assembly for a fast breeder reactor is constructed as shown in FIG. That is, the fuel pins 1 are regularly arranged in a hexagonal lattice shape and housed in a trumpet tube 2 having a hexagonal horizontal cross section. Further, a handling head 3 is arranged at the upper end, and a handling head 3 is arranged at the lower end.
An entrance nozzle part 5 in which a coolant inflow hole 4 is formed is arranged.

As shown in FIG. 8, the entrance nozzle portion 5 is inserted into an opening in a support plate 6.7 located at the bottom of the reactor core. Coolant flows into the coolant inflow hole 4 from the high-pressure plenum 8 to cool the fuel pin 1 in the sock pipe 2.

Note that the lower part of the support plate 7 is a low pressure plenum 9.

Further, the structure of the entrance nozzle section is designed with consideration given to prevention of artificial occlusion, flow rate adjustment, prevention of erroneous loading, prevention of floating of aggregates, and the like.

(Problems to be Solved by the Invention) At present, there is some uncertainty in identifying the form or scale of the blockage accident as described above. For this reason, at present, the upper limit of blockage is assumed to be an accident where the entrance is completely blocked, which is an accident that exceeds the design standards, or an accident where the site is evaluated. However, in the conventional fast breeder reactor fuel assembly described above,
If such a complete blockage accident occurs, the flow of coolant within the assembly will almost stop, which may cause damage to the fuel pins.

The present invention was made in response to such conventional circumstances, and even in the event that a complete population blockage accident occurs, the ripple effects of the accident can be significantly alleviated, and safety is improved compared to the past. The present invention aims to provide a fuel assembly for a fast breeder reactor that can achieve the following.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a fuel assembly for a fast breeder reactor equipped with an entrance nozzle portion having a coolant inflow hole opening into a high-pressure plenum. The low-pressure plenum side of the entrance nozzle section is normally closed, but when the coolant inflow hole is largely blocked, it opens due to the difference between the reduced pressure inside the entrance nozzle section and the pressure of the low-pressure plenum, and the low-pressure It is characterized by the arrangement of a mechanism that forms a coolant flow path from the plenum side.

(Function) In the fuel assembly for a fast breeder reactor of the present invention having the above-mentioned configuration, the low-pressure plenum side of the entrance nozzle section is normally closed, but when the coolant inflow hole is large-scale blocked, the inside of the entrance nozzle section is lowered. A mechanism is arranged that opens due to the difference between the pressure of

Therefore, even if a total population blockage accident should occur, the ripple effects of the accident can be significantly reduced, and safety can be improved compared to the past.

(Example) Hereinafter, details of the present invention will be described with reference to the drawings.

1 and 2 show the main parts of a fuel assembly for a fast breeder reactor according to an embodiment of the present invention. At the lower end of the entrance nozzle part 5, a coolant inlet opens into a low pressure plenum 9. A hole 10 is formed, and a spherical movable stopper 11 is disposed in the coolant inflow hole 10. In addition, movable stopper 1
A movable stopper 12 is arranged on the upper part of the stopper 1 .
'In the fuel assembly for a fast breeder reactor of this embodiment having the above configuration, during normal operation, the movable plug 11 prevents the coolant from flowing in due to the pressure caused by the coolant from the high-pressure plenum 8 that flows in from the coolant inflow hole 4. The coolant inflow hole 10 is in a state of being pressed against the hole 10, and the coolant inflow hole 10 is closed.

On the other hand, as shown in FIG. 3, if the coolant inflow hole 4 on the high pressure plenum 8 side is completely blocked for some reason,
Since the pressure inside the assembly is lower than the pressure in the low pressure plenum 9, the movable stopper 11 is pushed up due to the pressure difference, the coolant inflow hole 10 is opened, and the coolant flows in from the low pressure plenum 9.

At this time, the movable stopper 11 is locked by the movable stopper 12.

If the pressure of the high-pressure plenum 8 is pH and the pressure of the low-pressure plenum 9 is PL, then in the vicinity of the entrance nozzle section 5, P H ρgh+ΔPb+P.

PL-pgh+ΔPb'+P.

However, ρ: Coolant density g: Gravitational acceleration h: Height from the inlet to the outlet of the assembly ΔPb, ΔPb': Pressure loss inside the core fuel assembly and blanket fuel assembly Po: Pressure at the outlet of the assembly ′ . Normally, ΔPb (=4.3kg/cj) >ΔP b' (
= 0.5kg/cj), but if the inlet is completely blocked on the high pressure side, Δpb-o will result, so the PH
<PL, and the coolant corresponding to ΔPb° flows in from the low pressure plenum 9. Although the amount of coolant inflow varies depending on the number of internal orifices and the pitch of the pin bundle part, from the relationship between the aggregate flow rate and the bundle part pressure drop shown in Table 1, it can be approximated as (W' /W)QC(△ P b'/ΔPb) 4 However, W, W': aggregate flow rate Δpb, ΔPb': bundle portion pressure loss is established.

(Left below) From Table 1, from the total pressure drop of 0.5 kg/cj, if the contribution of the orifice is excluded, the pressure drop in the core region and the flow rate reduction rate are:
0.43 kg/cJ, 0.34 in the first region, 0.395 kg/cJ, 0.34 in the second region, 0.30 kg/cd in the third region.

0.34, ensuring a flow rate of 35% of the steady state.

The graph in FIG. 4 shows the relationship between the coolant maximum temperature and the coolant flow rate ratio. As shown in the figure, at a flow rate ratio of 35%, the maximum coolant temperature is close to the boiling limit, so although intermittent dryout occurs, stable boiling heat removal is possible. On the other hand, the pressure of the low pressure plenum 9 is approximately o, 4 kg/c-
If the flow rate is increased, the coolant flow rate will be approximately 48% of the steady flow rate. In this case, the maximum temperature of the coolant is approximately 800° C., which is well below the boiling range.

That is, in the fast breeder reactor fuel assembly of this example,
Even if a complete inlet blockage accident occurs, a coolant flow rate of about 35% of the normal flow rate, which allows stable boiling heat removal, can be secured. Therefore, the ripple effects of an accident can be significantly reduced compared to the past. Furthermore, by slightly increasing the pressure in the low-pressure plenum 9, it becomes possible to stably cool the accident assembly with sufficient margin.

In the above embodiment, an example using a spherical movable stopper 11 has been described, but the present invention is not limited to such an embodiment. For example, as shown in FIG. 5 and FIG. A movable stopper 11 in the shape of two cones superimposed on each other.
a and a movable stopper 1 that matches the shape of this movable stopper 11a.
Of course, any shape such as 2a may be used.

[Effects of the Invention] As explained above, according to the fast breeder reactor fuel assembly of the present invention, even if a complete blockage accident occurs,
The ripple effects of accidents can be significantly reduced, and safety can be improved compared to conventional methods.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a longitudinal sectional view showing the main parts of a fuel assembly for a fast breeder reactor according to an embodiment of the present invention, FIG. 2 is a top view of FIG. 1, and FIG. 3 is a top view of FIG. Figure 1 is a vertical cross-sectional view showing the state of the fast breeder reactor fuel assembly at the time of a complete blockage accident, Figure 4 is a graph showing the relationship between the coolant flow rate ratio and the maximum coolant temperature, and Figure 5 is the graph showing the relationship between the coolant flow rate ratio and the maximum coolant temperature. FIG. 6 is a top view of FIG. 5, FIG. 7 is a side view of a conventional fast breeder reactor fuel assembly, and FIG. 7 is a vertical sectional view showing the main part of FIG. 7. FIG. 4...... Coolant inflow hole (high pressure plenum side) 5... Entrance nozzle section 8...・High pressure plenum 9...
・・・・・・・・・Low pressure plenum 10・・・・・・・・・
Coolant inflow hole (low pressure plenum side) 11...
・Movable stopper 12・・・・・・・・・Movable stopper applicant Applicant of Japan Atomic Energy Corporation
Toshiba Corporation Representative Patent Attorney Sasa Suyama - Closed group ratio (σ) Figure 4

Claims (1)

[Claims] (1) In a fast breeder reactor fuel assembly equipped with an entrance nozzle section in which a coolant inflow hole opening into a high-pressure plenum is drilled, the entrance nozzle section is provided on the low-pressure plenum side with a In the case of a large-scale blockage of the coolant inflow hole, a mechanism is provided that opens due to the difference between the reduced pressure in the entrance nozzle part and the pressure in the low pressure plenum, and forms a coolant flow path from the low pressure plenum side. Features of fuel assembly for fast breeder reactor.