JPS6034716B2 - fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel assembly in which flow vents are provided at the upper and lower positions of the suber pad to prevent damage to the suber pad.

A conventional fast breeder reactor has a large number of fuel assemblies 1 each having a neck 38 or a P-stop 39 as shown in FIGS. 1 and 2, and a plunket arranged in a donut shape around the fuel assembly 1. It is composed of a fuel assembly 2 and a reflector 3 arranged around the outer periphery of the Plunket fuel assembly 2.

The plurality of fuel assemblies 1 are arranged to form one cylindrical body. These fuel assemblies 1, plunket fuel assemblies 2, and reflectors 3 are supported by a core support plate 4.
The core support plate 4 is composed of an upper support plate 4a and a lower support plate 4b. As shown in FIG. 3, the fuel assembly 1 includes a hexagonal cylindrical trumpet tube 5, a cylindrical entrance nozzle 6 fixed to the lower end of the trumpet tube 5, and an orderly arrangement in the trumpet tube 5. It consists of a large number of fuel pins 7, and a smooth pad 8 attached to or extruded from a part of the wall surface of the wrapper tube 5. The spacing pad 8 is composed of an upper spacing pad 8a and a middle spacing pad 8b. A plurality of orifice holes 9 are bored in the side surface of the entrance nozzle 6. The coolant flows through this orifice hole 9.
It enters the entrance nozzle 6 and flows upward in the trumpet tube 5. The fuel pin 7 has Pu02 and U02.
A reactor core part 7a containing a pellet, an upper shaft plunket part 7b located above and below this core part 7a and containing a U02 pellet, a lower shaft plunket part 7C, and the upper foundation plunket part 7b. It is composed of a plenum 7d provided above. The Plunkett fuel assembly 2 has the same shape as the fuel assembly 1, and has a core portion 7a of the fuel pin 7.
This is a plunkett version of By the way, the fuel assembly 1 and the Plunkett fuel assembly 2 configured in this way
Since the coolant flows upward between the reflector 3 and the reflector 3, there is a large temperature difference between the inside and outside of the trumpet tube 5, and the amount of thermal expansion of the inner and outer wall surfaces of the trumpet tube 5 differs. .

Therefore, thermal stress acts on the trumpet tube 5 and its wall surface, and stress concentration occurs particularly on the wall surface of the trumpet tube 5 in the upper and lower portions of the surface pad 8. Moreover, due to the curved deformation of the wrapper tube 5, it interacts with the adjacent wrapper tube 5 through the surface pad 8. The interaction due to the curved deformation is very large, and the wall surface of the stress concentration part is plastically deformed, causing damage to the smoothing pad 8. The present invention has been made in view of the above-mentioned circumstances, and it is possible to obtain a fuel assembly having a smooth pad within elastic deformation by removing the stress concentration part on the tube wall of the wrapper tube and reducing thermal stress in the smooth pad part. The purpose is to

An embodiment of the present invention will be described below with reference to the drawings.

It should be noted that parts having the same functional structure as that of the slave are given the same reference numerals and detailed description thereof will be omitted. Several holes (
A flow vent) 43 is provided.

The flow pent 43 is provided at the upper and lower ends of the base pad 8. In addition, in order to prevent interference with the flow pent of an adjacent fuel assembly, holes are bored on every other side of the wall of the hexagonal wrapper tube 5, as shown in FIG. Then, as shown in FIG. 6, the pipe wall of the adjacent fuel assembly 1 is used to
It is installed so as to cover the flow vent 43 of. Next, the effect will be explained.

The trumpet tube 5 is inserted from the orifice hole 9 of the entrance nozzle 6.
The coolant that has entered inside rises while cooling the lower shaft plunket portion 7C of the fuel pin 7 and the reactor core portion 7a. Reactor core 7a
The coolant that has risen to 100% has been heated to almost 100%. A portion of the heated coolant goes out of the wrapper tube 5 through the flow vents 43 at the upper and lower ends of the intermediate spacing pad 8b, and rises while heating the outer surface of the intermediate spacing pad 8b.
Most of the coolant cools the upper shaft planket portion 7b and rises further to reach the plenum 7d. A portion of the heated coolant goes out of the wrapper tube 5 through the flow vents 43 at the upper and lower ends of the upper spacer pad 8a, and rises while heating the outer surface of the upper spacer pad 8a. Most of the remaining coolant further rises and flows out of the wrapper tube 5. Therefore, the outer surface of the smoothing pad 8 is heated, the temperature difference between the inner and outer surfaces of the smoothing pad 8 is reduced, and the thermal stress acting on the wall surface of the smoothing pad 8 is suppressed by 4.0, and stress is concentrated in the wrapper tube around the smoothing pad 8. will no longer occur. Furthermore, since the flow vents 43 are provided at the upper and lower ends of the surface pad 8, an elastic structure is formed against the interaction caused by the curved deformation of the wrapper tube 5.
The strength of the smooth pad 8 against interaction is increased and plastic deformation is eliminated. In addition, the interaction is strong and the girl next door is smooth.
If the sapad 8 sinks in and blocks the flow path on the outside of the wrapper tube 5, and the pressure of the coolant on the outside rises too much, the flow vent 43 acts as a bypass and also works to prevent the pressure from rising. Thus, in the fuel assembly of the present invention, the subsurface pad functions sufficiently to provide a reactor core that is highly reliable and resistant to bending deformation.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the subordinate reactor core viewed from above, Figure 2 is a cross-sectional diagram of the subordinate reactor core, and Figure 3 is a conceptual diagram of a conventional fuel assembly.
FIG. 4 is a conceptual diagram showing an embodiment of the fuel assembly of the present invention;
FIG. 5 is a sectional view of FIG. 4 taken along the line V-V and viewed in the direction of the arrows, and FIG. 6 is an explanatory diagram showing the position of the flow vent in the core. 5...Trumpet pipe, 6...Entrance nozzle, 7...Fuel pin, 8...Subasa pad, 9...Orifice hole, 4
3...Flopent. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 A polygonal cylindrical lapper tube, an entrance nozzle for taking in the coolant attached to the lower part of the lapper tube, a large number of fuel pins arranged in an orderly manner inside the lapper tube, and a plurality of fuel pins attached to a part of the wall surface of the lapper tube. 1. A fuel assembly comprising extruded or extruded spacer pads, characterized in that flow vents are bored in the upper and lower wrapper tube walls of the spacer pads.