JPH034879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a fuel rod scale removal method and apparatus for removing scale mainly composed of Fe ₂ O ₂ attached to the surface of a fuel rod.

Technical background and problems thereof FIG. 1 shows a general water-cooled and water-moderated nuclear reactor, which will be explained below.

In the figure, reference numeral 1 denotes a reactor core disposed within a reactor pressure vessel 2. This reactor core 1 is surrounded by an annular shroud 3 and is located between an upper core lattice 4 and a lower core support plate 5. A plurality of fuel assemblies 6 and a reactor core 1 are removably supported on the
Each of the control rods 7 has a plurality of control rods 7 selectively inserted between the fuel assemblies 6 to control the reactivity of the fuel assemblies 6.

At the lower end of each fuel assembly 6, a nose-shaped piece 8 is provided which engages with a fuel support fitting incorporated in the lower core support plate 5.
are provided respectively, and the nose-like pieces 8 penetrate the lower core support plate 5 from above. This nose-shaped piece 8 is provided with an opening for communicating the inside of the fuel assembly 6 and the coolant supply chamber 9.

The coolant from the coolant supply chamber 9 is thus forced to flow upwardly into the fuel assembly 6 through the opening in the nose. A portion of the coolant turns into steam while rising above the fuel assembly 6, and is supplied to utilization devices such as the turbine 11 through the separation and drying chamber 10. The steam used in the utilization equipment is condensed in a condenser 12, and the condensate is returned to the reactor pressure system 2 as feed water via a pump 13.

The fuel assembly 6 includes a plurality of elongated fuel rods 16 supported between a lower tie plate 14 and an upper tie plate 15, as shown in FIG. This maintains the spacing and restrains lateral vibration.

As shown in FIG. 2, each fuel rod 16 is made of a cladding tube 20 whose upper and lower ends are sealed by an upper end plug 18 and a lower end plug 19, respectively, and pelletized fuel 21 disposed within the cladding tube 20. It is configured. The lower end plug 19 has a taper for alignment and support in a support cavity 22 formed in the lower tie plate 14, and the upper end plug 18 has an extension 23, which extends The portion 23 is aligned with the support cavity 24 in the upper tie plate 15.

Some of the support cavities 22 in the lower tie plate 14 are provided with threads for receiving fuel rods 16 having threaded lower end plugs 19. The extension 23 of the upper end plug 18 of the fuel rod 16 extends upward through a support cavity 24 in the upper tie plate 15, and a retaining nut 28 is screwed onto the tip thereof. This allows the upper and lower tie plates 14, 15 and the fuel rod 1 to
6 form one unit structure.

The fuel assembly 6 also includes a channel 26 having a square cross section as shown in FIG. It is connected to the upper tie plate 15 via a bolt 28 passing through the tie plate 27 . The channel 26 is slidably fitted to the upper and lower tie plates 14, 15 and the spacer 17 by removing the bolt 28, and can be easily attached and detached.

Although the configuration of the nuclear reactor, particularly the core 1 and the fuel assembly 6 is as described above, a large amount of cooling water is circulated between each fuel rod 16.

Such cooling water plays extremely important roles such as moderating neutrons and propagating generated heat, but it also circulates corrosion products (water scale) generated from internal reactor structures. . Fuel rods are the hottest of all reactor internals, and therefore absorb most of the limescale. For this reason, water scale accumulates on the surface of the fuel rod over time, which deteriorates the heat transfer coefficient and increases the surface temperature.

Furthermore, when a fuel assembly with a large amount of water scale deposited on the fuel rod surface is transported to a reprocessing plant and reprocessed, the adhering water scale has a high radiation dose, which may cause problems in processing and handling.

The most reliable way to eliminate these problems is to strictly control the quality of the cooling water to prevent scale from entering the reactor core, but the amount of scale released into the cooling water from internal reactor structures There are so many that it is almost impossible to remove them all.
For this reason, it is inevitable that water scale will adhere to the surface of the fuel rods.

Based on the above, the only way to solve the problem is to periodically remove the water scale that has adhered to the fuel rods, but since the water scale that has adhered to the fuel rods is exposed to a high radiation field, the radioactivity of the water scale is The levels are extremely high, and the scale removed must be recovered to reduce exposure and prevent the spread of contamination.

Purpose of the invention The present invention was made in view of the current situation, and
The object of the present invention is to provide a method and apparatus for removing scale that can easily and completely remove scale that has adhered to the surface of a fuel rod.

Structure of the Invention The object of the present invention is to store a fuel assembly in a drying container, supply a gas supply system for drying gas to the drying container, a reactor water supply system for supplying reactor water, and a drying container. Connect at least the gas supply system of the scale collection system for collecting limescale that has fallen to the bottom of the container and the gas exhaust system for discharging the gas inside the drying container, and drying the surface of the fuel rod with gas to remove limescale adhering to the surface; a drying container for storing the fuel assembly; and a device connected to the drying container for blowing gas into the drying container. A gas supply line equipped with a heating device, a reactor water supply line connected to the drying container to supply reactor water therein, and a scale collection system to collect limescale that has fallen to the bottom of the drying container. This is achieved by providing at least a gas supply system out of a gas discharge system and a gas discharge system for discharging the gas in the drying container.

Embodiment of the Invention Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 3 and 4.

In FIG. 3, the scale removal device according to the present invention has a drying container 30 for drying the fuel assemblies in the fuel pool P, and the fuel assemblies 6, 6 are housed in this container 30. It has a built-in cylindrical channel box. A gas supply line 32 for feeding drying gas into the channel box is connected to the lower part of the container 30, and water scale attached to the surface of the fuel rods that have fallen to the bottom of the channel box 31 is removed from the reactor water. A scale collection line 33 for discharging the water together with the water is connected.

On the other hand, above the channel box 31,
The gas discharging action for discharging the contaminated gas that was supplied from the gas supply line 32 into the channel box and containing fine scale particles on the surface of the fuel rods, and the supply of gas from the gas supply line 32 were stopped. A combination line 34 is connected which performs both the reactor water supply function and the later supply of reactor water into the channel box.

The tip of the combined use path 34 is a first ejector 35
This first ejector 35 is provided in the middle of a first ejector operating system path 36 for suctioning contaminants in the combined system path 34. One end of this first ejector operating system path 36 is connected to a separation tube 37.
The other end is inserted into the water surface S of the fuel pool P.
A gas discharge line 3 is provided on the upper surface of the separation tube 37 to discharge contaminated gas therein.
8 are connected. On the other hand, a second ejector 39 is connected below the separation cylinder 37, and this second ejector 39 is provided on a second ejector operating system path 40, and this second ejector operating system path 40 is connected to the scale collection system. A connecting line 41a is provided between the second ejector operating line 40 and the combined use line 34.

The drying container 30 has a container body 41, as clearly shown in FIG.
2a, and this upper lid 42a can be opened and closed by an automatic opening/closing device 43. A support box 42 is placed at the bottom of the main body 41, and the channel box 31 is supported on the support box 42. The interior of this channel box is partitioned by a partition plate 31a, and fuel assemblies 6, 6 are housed in left and right chambers partitioned by the partition plate. The lower end of this fuel assembly 6 is a support box 42
The fuel assembly 6 is supported by cylindrical lower pedestals 44, 44 provided above, and the upper side surface of the fuel assembly 6 is prevented from inclining by guide springs 45, 45...45 provided on the channel box 31 and the partition plate 43. The guide spring 45 serves to guide the insertion of the fuel assembly 6 into the channel box.

The upper side wall of the channel box 31 is supported by a support plate 46, and the upper surface of the channel box is closed by an upper lid 47, to which the tip of the combined system 34 is connected via a bellows 48. Note that a thermometer 49 for measuring the temperature of the fuel assembly is provided on the upper part of the partition plate 43.
A monitor 50 is connected to the thermometer 49 as shown in FIG.

A gas supply line 32 is provided on the side of the support box 42.
An inclined plate 52 is provided at the bottom of the support box 42, and a discharge port 53 is opened in the side wall of the support box 42 where the downwardly inclined tip of this inclined plate 52 is located. There is. The scale that has fallen from the fuel assembly 6 is guided by the inclined plate 52 together with the reactor water and flows into the scale collection system passage 33 from the discharge port 53. Further, a vibration device 54 is installed below the inclined plate 52 in the support box 42 to give vibration to the support box 42 and the channel box 31 supported by the support box 42 to promote peeling off of scale on the fuel rods. ing.

The gas supply line 32 includes a first fan 55 for supplying gas, a first on-off valve 56, a receiver tank 57 for stabilizing the gas sucked by the fan 55, and a second on-off valve. 58
A heater 59 is also provided for heating the pipe line. Further, the first ejector operating system path 3
6 includes a first pump 60 and this first pump 60;
A third on-off valve 61 is provided in the vicinity of the second pump 62 , and a second pump 62 is provided in the second ejector operating system path 40 .
and a fourth on-off valve 63. A connecting line 41a branching from the middle between the second pump 62 and the fourth on-off valve 63 to the combined line 34 includes:
A fifth on-off valve 64 is provided, and the combined system 3
A sixth opening/closing valve 6 is provided on the first ejector 35 side of 4.
5 is provided.

Further, on the gas discharge line 38 connected to the upper end of the separation cylinder 37, in order from the separation cylinder 37 side, a seventh on-off valve 67, a steam separator 68, a paper filter 69 made of glass wool, and a second fan 70 are arranged.
is provided. and the scale collection system path 33
A scale collecting device 71 is connected to the device 71.
consists of a cyclone 72, a cyclone collection tank 73, a third pump 74, and a back filter 75, and the reactor water that has passed through the filter 75 is discharged into the fuel pool P.

Note that an eighth on-off valve 76 is provided on the scale collection system path 33, and a ninth on-off valve 77 is provided on the second ejector operating system path 40 near this valve, and all the above-mentioned valves are normally closed. be.

Next, the operation of the present invention will be explained.

The drying container 30 is provided in a fuel pool,
The upper cover 42a of the main body 41 is opened by operating the automatic opening/closing device 43, and the channel box 3 is opened.
The upper lid 47 of 1 is opened, the fuel assembly 6 is placed on the lower pedestal 44 while being guided by the guide spring 45, and then the upper lids 42a and 47 are closed.

When the preparation work is thus completed, the first and second open/close valves 56 and 58 on the gas supply line 32 are opened, and the eighth opening/closing valve 76 on the scale collection line 33 is opened. Then, the first fan 55 is rotated to send cold air into the support box 42. Then, the reactor water in the channel box 31 is forced out by dry gas and flows into the scale collection device 71 through the scale collection line 33. The scale contained in the reactor water is collected in a cyclone collection tank 73, and the reactor water from which the scale has been removed is discharged into the fuel pool by the action of a pump 74 whose drive is regulated by the controller C. Through this operation, the reactor water in the drying container is purified and released into the fuel pool. When the reactor water remaining in the channel box is returned to the fuel pool, the eighth opening/closing valve 76 is closed.

At the same time, the sixth opening/closing valve 65 on the combined system 34 is opened, and the third opening/closing valve 61 on the first ejector operating system 36 is opened to drive the first pump 60 and operate the first ejector 35. . As a result, the first ejector 35 becomes a negative pressure, and the drying gas in the channel box 31 is sucked by the first ejector 55 through the combined system 34, mixes with reactor water, and flows into the separation cylinder 37. . At this time, the seventh opening/closing valve 67 on the gas exhaust line 38 is opened and the second fan 70 is driven. Thereby, the gas in the separation tube 37 is purified through the steam/water separator 68 and the pepper filter 69, and is then discharged to the outside.

After the above work is completed, the heater 59 on the gas supply line 32 is activated, the tube is heated by the coil 59a, and the heated gas is transferred to the channel box 31.
to be sent within. This heated gas causes the fuel assembly 6 to
The drying process is accelerated. Note that the above-described operation continues even during this heated gas supply, and the gas sucked in from the first fan 55 dries the fuel rods in the channel box, and then passes through the combined system 34 and is sucked into the first ejector 35. The gas is mixed with reactor water and injected into the separation tube 37, and the gas separated in the separation tube 37 is discharged to the outside through the gas exhaust line 38. That is, the gas containing fine particles of limescale inside the channel box is purified as it passes through the separation tube 37 and the gas discharge line 38.

After the fuel assembly 6 in the channel box 31 is heated for an appropriate time, the first and second fans 55,
70, and while stopping the pump 60, the first
2nd, 3rd, 8th, 6th, 7th opening/closing valve 56,
58, 61, 65, 67 are closed and the first fan 55
Stop the flow of gas inhaled from the At this time, the fifth and eighth on-off valves 64 and 76 are opened, and the second pump 62 is driven to discharge reactor water from the upper part of the channel box 31 to the fuel assembly 6 via the connection line 41a and the combined line 34. The discharged reactor water has already been peeled off from the fuel rods by drying with heated gas, and the scale that has fallen to the bottom of the support box 42 is passed through the scale collection system passage 33 to the scale collection device 7.
Transport it within 1.

When this reactor water injection step is completed, the fifth on-off valve 64 that was opened during the reactor water injection step is closed, and the fourth and ninth on-off valves 63 and 77 are opened. Then, the reactor water is sent to the second ejector 39, and the reactor water mixed with limescale in the separation cylinder 37 is sucked and sent to the scale collecting device 71, where it is cleaned and returned to the fuel pool.

The method and apparatus according to the present invention are carried out by such a cycle, and in particular, in order to effectively remove limescale adhering to the fuel assembly,
After a short period of rapid drying, reactor water is radiated to the fuel assembly to temporarily soak it with reactor water, and then the cycle of short period of rapid drying can be repeated several times. In this way, the peeling effect is increased due to the disturbance of furnace watering and drying.

Note that cold air may be used instead of heated gas for drying, but heated gas has a greater peeling effect. Also,
The channel box 31 is provided inside the container body 41, and is isolated from the reactor water in the fuel pool by a double structure, so a completely sealed structure can be achieved, and the gas is not diffused throughout the container body 41, allowing it to be efficiently assembled into fuel assemblies. This will improve drying efficiency.
Furthermore, if the vibration device 54 is driven as necessary, the fuel assembly will vibrate, increasing the scale removal effect. Then, the peeled scale is smoothly guided to the discharge port by the inclined plate 52. In addition to this,
Fine limescale mixed in the gas is removed from the gas exhaust system path 38.
After being cleaned by the action of the reactor water, it is discharged to the outside, and limescale mixed in the reactor water is cleaned by the limescale collecting device 71 and then returned to the fuel pool.

Effects of the Invention Since the present invention is constructed as described above, it is possible to safely and reliably remove water scales attached to the surfaces of fuel rods within a fuel pool without dispersing the scales within the fuel pool or into the atmosphere. It has the effect of being able to do it.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram inside the pressure vessel, FIG. 2 is a longitudinal sectional view of the fuel assembly, and FIG. 3 is a system diagram according to the present invention.
FIG. 4 is a longitudinal sectional view of the drying container according to the present invention. 30...Drying container, 31...Channel box,
32... Gas supply system path, 33... Scale collection system path, 34
...combined system path, 35...first ejector, 36...first
Ejector operating system path, 39...Second ejector, 4
0...Second ejector operating system path, 54...Vibration device,
71...Lake scale collection device.

Claims (1)

[Claims] 1. A dryer comprising a drying container for storing a fuel assembly installed in a fuel pool isolated from reactor water, and a heating device connected to the drying container and provided outside the drying container. A gas supply line for blowing gas into the container; a reactor water supply line connected to the drying container for supplying reactor water therein; A scale collection system line for collecting scales contained in the reactor water together with the reactor water; The drying container has a cylindrical body; A water stain on a fuel rod characterized by having a dry container channel box that is housed in the main body and can be housed in a sealed state with the fuel assembly, and a vibrator for giving vibration to the channel box at the bottom of the channel box. removal device. 2 A guide spring is provided in the channel box to guide the insertion of the fuel assembly into the channel box, and an inclined inclined catcher is provided at the bottom of the channel box to collect limescale that has fallen from the fuel rods. 2. The fuel rod scale removing device according to claim 1, further comprising a collecting plate, and the scale collecting system path is exposed at the tip of the inclined collecting plate.