JPS5925200B2 - Fuel assembly with measurement line - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a fuel assembly with measurement lines installed in a nuclear reactor to continuously examine the behavior of core fuel, and in particular, after use, the fuel assembly and the drive unit are separated. In particular, the present invention relates to a fuel assembly with a measurement wire having a cutting mechanism for cutting the measurement cable.

In addition to designing the core fuel assembly loaded in the fast reactor core, the core fuel (P uo2+U
It is necessary to continuously know the amount of fission product (FP) gas generated from O2), the flow rate of coolant, and the temperature of each part of the fuel pin. has not been put into practical use in Japan, and the recently devised fuel assembly with measurement wires is a fuel assembly with measurement wires that incorporates a measurement device into the loading section of the core fuel assembly.
Each measurement of core fuel is being carried out.

This fuel assembly with a measurement line consists of a fuel section incorporating a fuel pin containing UO2 and PuO2 at the tip of a measurement cable/tube, and a drive section that moves this fuel section up and down during fuel exchange.

The measurement cables and tubes coming out of the fuel section pass through the neutron shield cable penetration in the drive section and are connected to measuring instruments installed outside the reactor.

Since the measuring section of this fuel assembly with a measuring line has a short life, it is necessary to replace it with a new fuel assembly with a measuring line every 2 to 3 years.

However, in a fuel assembly with measurement wires, the driving part and the fuel part incorporating fissile material are integrated, so if it is handled as one unit using the method described above, the cask that will be delivered during maintenance for radiation protection will be removed. becomes thicker, heavier, and more difficult to handle.

Additionally, handling operations are restricted due to radiation dose.

The present invention provides a fuel assembly with a measuring line that can reduce the weight of the cask and improve workability by separating the fuel part and the drive part of the fuel assembly with a measuring line during maintenance of the fuel assembly with a measuring line. The purpose is to obtain fuel assemblies.

The present invention will be described in detail below with reference to the drawings of one embodiment.

In FIG. 1, a reactor core structure 2 in which a reactor fuel assembly, a neutron shield, a control rod, etc. are installed is attached to the lower part of the inside of a reactor vessel 1.

At the top of this is a shield plug 3 which is the lid of the reactor vessel 1.
is installed.

The shield plug 3 is provided with a through hole, and the drive section 4 passes through the through hole, and the integrated sample section 5 is inserted into the loading section of the core fuel assembly.

FIG. 2 shows a detailed diagram of this fuel assembly with measurement lines.

A plurality of fuel pins 8 are provided inside the sample portion 5 of the fuel assembly with measurement lines, and the sample portion fuel 7 is installed at an arbitrary location on the fuel pins 8.

Further, an end plug 9 is provided on the upper part of the fuel pin 8, and
A P gas measurement tube 10 and a neutron detector 11 are provided at each fuel pin 8.

In order to check the relationship between the coolant flow rate of the fuel pin 8 and the temperature of each part, a plurality of flowmeters 12 and temperature measurement sensors 13 are installed in the axial direction of the fuel pin 8. .

The above-mentioned pipe 10 and measurement cable 20 pass through the cutter guide 15 that connects the drive unit 4 and the fuel unit 5 from inside the handling head 14 above the fuel unit 5, and are provided inside the drive unit 4. It is connected by a shielded cable penetration 16 and taken out of the furnace.

The fuel section 5 is suspended from the drive section 4 by a finger 17 attached to the tip of the cutter guide 15.

The vertical movement during fuel exchange is performed by a swing crane (not shown) installed inside the containment vessel.

Since this vertical movement is a large stroke, a long bellows 21 is used as the pressure boundary of the reactor vessel 1.

When a fuel assembly with a measuring line has reached the end of its life after being used for a certain period of time, the bundle 18 attached to the upper part of the drive unit 4 lowers the outer extension pipe 22 to the inner extension pipe 23 that is integrated with the cutter guide 15. , because the cutter 19 fixed to the tip of the outer extension tube 22 descends, the measurement cable 2
0 and the pipe 10 are cut, and the measurement cable 20 and the pipe 10 connecting the drive part 4 and the fuel part 5 are separated.

Furthermore, when the finger 17 suspending the fuel section 5 is attached to the drive section, the pin 25 that holds the finger 17 is located outside the center of gravity of the finger, so the finger 17 is always open (
latched) state.

For this reason, after the cutting operation, the guide 24 attached to the top of the cutter simultaneously descends and presses the finger 17 from the outside, so that the finger 17 is
9 completely enters the inside from the outer circumferential surface, and the fuel part 5 is no longer suspended and is completely separated.

FIG. 3 shows a detailed view of the cutting and delatching portion caused by the vertical relative movement of the tips of the inner and outer extension tubes 22 and 23.

Next, the effects of the above device will be described.

The shear/delete mechanism is as shown in Figures 2 and 3.
A bundle 18 provided on the upper part of the drive unit 4 connects the outer extension tube 22.
The mechanism is such that the operation of cutting the measurement cable 20, etc., and the delatching operation of separating the fuel part 5 can be performed by the - movement only by this downward movement.

Therefore, since the simple downward motion of the extension pipe is directly used as a shear cutting force and a delatching action, there is no need to add a rotary cutting mechanism or a delatching mechanism of the side structure, and the overall structure is extremely simple and reliable. As soon as it lifts up, it becomes very easy to operate.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 and 5.

In FIG. 4, a cutter 19 is attached to the tip of the inner extension tube 23, a cutter guide 15 is provided on the outer extension tube 22, and the inner extension tube 23 is lowered to perform a cutting operation.

FIG. 5 shows a case where the cutter guide 15 is attached to the fuel section 5, and the operation is similar to that shown in FIG. 4.

As explained above, according to the present invention, since the driving part and the sample part are separated, the shielding thickness of the maintenance cask is thin (which makes it easy to carry out work due to its light weight when transporting it with a crane, trolley, etc.). As the working time is shortened, the amount of neutron and r-ray exposure of workers is reduced.

In addition, since the mechanism is such that the outer extension tube is lowered using a bundle, etc., and the measurement cable, etc. is cut only by this downward movement, unlike a rotary cutting mechanism, etc., the rotation is required to convert from linear to rotational in Na. There is no need to provide a conversion mechanism, and the overall structure is extremely simple and reliable.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the state in which the fuel assembly with measurement lines of the present invention is installed in a nuclear reactor, Fig. 2 is a vertical cross-sectional view of the fuel assembly with measurement lines shown in Fig. 1, and Fig. 3 is A vertical cross-sectional view showing the cutting/delatching mechanism of the outer extension tube in Figure 2, Figures 4 and 5.
This figure is a longitudinal sectional view showing another embodiment of the cutting/delatching mechanism section of FIG. 3. 4... Drive section, 5... Fuel section, 15.
...Cut guide, 17...Finger, 19...Curved cutter, 20...Measuring cable.

Claims (1)

[Claims] 1. A fuel part housing a fuel pin, a drive part connected to the fuel part via a latch mechanism, and a measurement cable connected to the fuel pin and led out to the outside through the inside of the drive part. In the fuel assembly with a measurement wire, the drive section is composed of a double pipe including an inner pipe and an outer pipe, and the measurement cable is inserted through a hole provided at the bottom of one of these pipes to wire the measurement cable. A fuel assembly with a measurement line, characterized in that a cutter is disposed at the bottom of the other tube so that the measurement cable can be cut by relative driving of these tubes.