JPS607390A - Aggregate of nuclear fuel - 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 The present invention improves the flow resistance between the legs of the lower nozzle by changing the shape of the lower nozzle of the fuel assembly in order to increase the flow resistance flowing into the gap between the buckle plate and the core barrel in a nuclear reactor. It concerns a nuclear fuel assembly that is made up of large-scale lateral flow resistance.

In general, the fuel assembly 40 is roughly divided into a lower nozzle 1, fuel rods 2, a grid 3, and an upper nozzle 4, as shown in FIG. 1, and as shown in FIG. 2, the fuel assembly 40 is loaded into the core. In this state, the flow of primary coolant around the core flows into the reactor vessel 6 from the inlet nozzle 5, flows between the reactor vessel 6 and the core tank 7 in the lower υ, and in the flow direction at the lower blennium 8. and enters the core 11 through the holes in the lower core support plate 9 and the lower core plate 1o.

A portion of the secondary coolant flows through the lower nozzle 1 of the fuel assembly 40, as shown in FIG. 3, which is an enlarged view of section A in FIG.
Bypass flow flows through the inter-leg space 21 into the gap 25 between the lower end of the baffle plate 13 and the core barrel 7 as shown by the arrow 23, passes through the holes 12 in the former plate 14, and reaches the upper brenum 15. It will be 23. Here, the distance 100 between the lower end of the buckle plate 13 and the lower core plate 10 is about 4Qmm.

Figure 4 shows an example of the axial distribution of buckle plate differential pressure in a conventional plant.
The baffle plate differential pressure, which is the differential pressure between the side and the core 11 side, increases at the axial position of the grid 3 in the fuel assembly indicated by G, and the pressure difference between the baffle plate 13 and the core barrel 7 increases at F. As shown, the former plate 14 decreases in the axial position, resulting in a jagged shape in the axial direction, but the pressure loss at the inlet of the gap 250 between the baffle plate 13 and the core tank 7 side is greater than the pressure loss at the fuel assembly lower nozzle 1. Because it is small, it takes 1 time! +125
The overall side is positive.

FIG. 5 is an explanatory diagram showing the positional relationship between the buckle plate 13 and the fuel assembly 40, and FIG. 6 is an enlarged view of part B in FIG. Since the pressure is higher in the gap 25 between the plate 13 and the core barrel 7, the jet stream 30 flows into the core.

Figure 7 shows the relationship between the flow velocity of the jet stream flowing into the core from the buckle plate gap and the vibration of the fuel rods.
Where the flow velocity of the jet stream is sufficiently low, the vibration of the fuel rods is also small. Furthermore, when the flow velocity of the jet stream is increased to a certain extent, vibrations due to Karman vortices are first generated, but when the flow velocity is further increased, Karman vortex vibrations no longer occur.

If the flow velocity continues to increase, hydroelastic vibrations occur, which suddenly become more intense and cause damage to the fuel rods.

Therefore, in order to keep the flow velocity of the jet flow as low as possible and prevent fuel damage, it is effective to manage the buckle plate gap 24 sufficiently small or to reduce the buckle plate differential pressure. In order to prevent the plate gap 24 from increasing, the dimensions of the buckle plate gap 24 are measured during regular inspections, which is one of the causes of increased radiation exposure and prolongation of the regular inspection period.

The present invention has been made in view of the above-mentioned circumstances, and improves the shape of the conventional fuel assembly lower nozzle to increase the resistance to flow into the gap between the baffle plate and the core barrel. It is an object of the present invention to provide a nuclear fuel assembly in which the bypass flow is restricted so that the flow velocity of the jet flow does not increase even if the buckle plate gap increases.

FIG. 8 shows the relationship between the baffle plate differential pressure and the flow velocity of the jet stream 30 (FIG. 6), and the flow velocity of the jet stream increases monotonically as the baffle plate differential pressure increases. Figure 9 shows the relationship between the area of the lateral flow passage on the side surface of the lower nozzle of the fuel assembly adjacent to the baffle plate, that is, the area of the space 21 between the lower nozzle legs (Figure 3), and the differential pressure across the baffle plate. be.

On the side surface of this lower nozzle, the flow path area facing the gap 100 between the lower end of the baffle plate 13 and the lower core plate 10 is reduced to reduce the pressure loss in this part, which is the entrance of the flow to the gap between the baffle plate and the core barrel. By increasing the size, the pressure in the gap 25 between the baffle plate 13 and the core barrel 7 is lowered as a whole, so the baffle plate differential pressure is reduced as shown in FIG. In FIG. 10, G indicates the grid of the fuel assembly, and F indicates the position of the former plate 14. Furthermore, if the flow passage area on the side surface of the lower nozzle is reduced from point B in Figure 9, the buckle plate differential pressure becomes negative, but in this case, the flow in the buckle plate gap is from the core 11 side to the gap 25 between the baffle plate and the core barrel. The jet flow is not a problem.

As mentioned above, in order to reduce the jet flow from the baffle plate gap, it is effective to reduce the differential pressure between the baffle plates, so the legs of the conventional lower nozzle are made of a thickness that does not cause any problems in terms of strength. The structure of the lower nozzle 1 between the legs 22 of the lower nozzle 1 shown in FIG. The purpose is to reduce the differential pressure across the baffle plates by intentionally increasing the lateral flow resistance.

~ A detailed explanation will be given below based on FIGS. 11 to 17.

FIG. 11 is a partially fragmented side view showing the ttrI structure of the lower nozzle of a fuel assembly according to an embodiment of the present invention, and FIG. 12 is a bottom view of the same. 17 and legs 18, the difference from the conventional structure is that the enclosure 17 has a space 21 between the legs shown in FIG.
The area of the bypass flow 23 is reduced to limit fAikmf of the bypass flow 23. Therefore, a flow passage hole 26 is bored in the enclosure 17, and the area of the 7h passage hole 26 and the slit 102 is set to be less than the numerical value explained below, and the flow passage hole 26 is formed by the baffle shown in FIG. Lower end of plate 13 and lower core plate 10
The height of the lower nozzle should be 4 from the lower end so that it is located within the distance between
It is placed below 0 rhymes.

FIG. 13 is a graph showing changes in the axial baffle plate differential pressure distribution when the transverse flow passage surface utk per lower nozzle side surface due to the flow passage hole 26 and the slit 102 is changed, and the horizontal axis is the baffle plate differential pressure (Between the baffle plate and core tank Q - core side, 1), the vertical axis represents the height ff1) from the lower core plate. Curve ■ indicates the current design point, flow path surface! R8,3
00mm? Then, the flow path area per side surface of the lower nozzle is decreased in numerical order. The area of curve ■ is 650 mm, which is about 1/13 of the area of curve ■, the area of curve C is 300 m, which is about half of that of curve ■, and the area of curve ■ is 3 minutes of curve ■. The amount of change in area is gradually decreasing from 2 to 200 to 2. On the other hand, when looking at the amount of change in the baffle plate differential pressure, the difference between curves ■ and ■ is small;
Alternatively, the difference between curves ■ and ■ is larger.

In order to further clarify this relationship, FIG. 14 shows a graph showing the relationship between the area per side surface of the lower nozzle at an axial height of 1 m and the buckle plate differential pressure. Here, the horizontal axis is the cross flow channel area per side surface of the lower nozzle (10” m
m"), and the vertical axis represents the buckle plate differential pressure (P/Po) when the differential pressure at the Po-6 point is taken as the differential pressure at the Po-6 point.

In FIG. 14, when the lower nozzle side flow passage area is decreased from the current design point C, a buff appears at first. That is, Q for which the present invention is effective is that the lower nozzle side flow passage area is equal to or less than point D, and the value of point D is 2.000 mrn2. For nozzle side flow passage areas smaller than 8 points, the baffle plate differential pressure becomes negative, but in this case, the flow flows from the core 11 side in Fig. 3 to jQ25 between the baffle plate and the core tank. Therefore, no jet flow is generated toward the fuel assembly 40, and therefore, the present invention is effective. As can be seen from FIG. 13, the axial differential pressure distribution moves approximately parallel to the area of the lower nozzle side surface flow path, so the relationship shown in FIG. 14 is approximately the same at any position 16 in the axial direction.

FIG. 15 is a perspective view showing another embodiment of the present invention, in which the flow passage hole in the enclosure 17 is eliminated and a slit 102 is provided at the bottom of the enclosure, but in this case, the flow per side of the lower nozzle is Road surface impact can be adjusted by adjusting the slit height.

FIG. 16 is a perspective view showing another embodiment of the present invention, which is functionally equivalent to FIG. 11, but in this case, a sliding side plate 19 is inserted between the legs 220. is fixed with bolt 20.

In the case of this structure, it is possible to remove the side plate 19, and it is possible to remove and load the side plate 19 at positions other than those in contact with the baffle plate.

FIG. 17 is a perspective view showing another embodiment of the present invention, which has a structure in which a removable side plate 19 is attached between legs 22 with bolts 20 in the same way as in FIG. It has a structure of 9.

As explained in detail above, according to the present invention, the influence of the jet flow from the baffle plate gap on the fuel rods becomes negligibly small, so there is no need to measure the dimensions of the buckle plate gap during regular inspections. This has the effect of shortening the inspection period and reducing the amount of radiation exposure.

[Brief explanation of the drawing]

Figure 1 is a front view of a conventional nuclear fuel assembly, Figure 2 is an explanatory diagram showing the flow of primary coolant around the core when fuel assemblies are loaded into the core, and Figure 3 is Figure 2. Enlarged view of part A,
Figure 4 is a graph of the axial distribution of baffle plate differential pressure in a conventional plant, Figure 5 is a cross-sectional view showing the positional relationship between the baffle plate and the fuel assembly, Figure 6 is an enlarged view of part B in Figure 5, 7
The figure is a graph showing the relationship between the flow velocity of the jet flow flowing into the core from the baffle plate gap and the vibration of the fuel rod. Figure 8 is a graph showing the relationship between the baffle plate differential pressure and the flow velocity of the jet flow.
The figure is a graph showing the relationship between the lower nozzle side flow passage area of the fuel assembly adjacent to the baffle plate and the baffle plate differential pressure.
Figure 0 is a graph of the axial distribution of the baffle plate differential pressure when the flow path area on the side surface of the lower nozzle is set to the following value, and Figure 11 is a part showing the structure of the lower nozzle of a fuel assembly, which is an embodiment of the present invention. A fragmented side view, Fig. 12 is a bottom view of the same, Fig. 13
The figure is a graph showing the change in differential pressure distribution on the axial baffle plate when the lateral flow channel area per side surface of the lower nozzle is changed. Figure 14 is the area per side surface of the lower nozzle at an axial height of 1 m. FIG. 15 is a perspective view showing the lower nozzle structure of a fuel assembly according to another embodiment of the present invention, and FIGS. 16 and 17 are perspective views of the embodiment on the same side. This is a diagram of R1. 1...Lower nozzle, 17...Encrosia, 19
... Side plate, 18.22 ... Leg, 26 ... Channel hole,
40...Fuel assembly, Patent applicant Mitsubishi Atomic Crab Industry Co., Ltd. Agent Patent Attorney Tosa Hideaki Fuji (Sof) Shikofc Bu7 Meiichi Sea 20 N.22 Octopus A2 Buff 2 Shifin L U//Sekida Sefu 2 Hot Ba□Tsufnom≠Uke,! /E (1 la / 4 mills 1 o 15 (2

Claims (1)

[Scope of Claims] (1) In a nuclear reactor in which a fuel assembly having four sides is loaded in a lower nozzle, in order to prohibit or suppress cross flow of coolant between the lower nozzle legs of the fuel assembly, In addition to providing an enclosure or side plate between the lower nozzle legs, the cross flow flow area in the lower nozzle section is set to 200mm2 or less per surface, and the height of flow path 9 from the lower end of the lower nozzle is set to 40mm or less. Characteristic nuclear fuel assembly. (2) The nuclear fuel assembly according to claim (1), characterized in that the enclosure does not have flow passage holes. (3) The nuclear fuel assembly according to claim (1), characterized in that the enclosure has flow passage holes. (The nuclear fuel assembly according to claim (1), characterized in that the 41m+11 plate has flow passage holes, can be removed between the legs, and is fixed in a sliding manner. (5) Side plate The nuclear fuel assembly according to claim 1, wherein the nuclear fuel assembly has a passage hole and is removably fixed between the legs.