JP6132782B2 - Method for recovering molten nuclear fuel material - Google Patents

Description

  The present invention relates to a method for recovering nuclear fuel material melted at the time of an accident in a nuclear power plant.

  A nuclear power plant consists of a circulation cycle that goes back to the reactor again through the steam generator, high-pressure turbine, low-pressure turbine, condenser, feed water pump, feed water heater, and the steam generated by the steam generator. The generator is operated by driving the high-pressure turbine and the low-pressure turbine to generate electricity. Among nuclear power plants, boiling water nuclear power plants (BWR) boil circulating water in a nuclear reactor, and the nuclear reactor also serves as a steam generator.

  On the other hand, if the power supplied to the nuclear power plant is lost due to a major disaster or the like, the water supply to the nuclear reactor may stop and the nuclear fuel material loaded in the nuclear reactor may melt. When such a severe accident occurs, it is necessary to safely remove the molten nuclear fuel material from the reactor core after the reactor is cold stopped.

  As a means for recovering such molten nuclear fuel material, a means has been proposed in which molten nuclear fuel material deposited in the lower part of a nuclear reactor or a containment vessel is cut by a cutting tool and carried out of the reactor by a transfer device (Patent Document 1). .

JP 2013-19875 A

  Since the molten nuclear fuel material contains uranium 235, if it is handled carelessly during the recovery operation, there is a possibility that a fission chain reaction rarely occurs and the criticality is reached. For example, when the recovered molten nuclear fuel material is stored in a storage container, recriticality may occur due to the stored molten nuclear fuel material depending on the internal volume of the storage container. For this reason, strict recriticality management is required for the molten nuclear fuel material, such as limiting the internal volume of the storage container.

  On the other hand, a part of the molten nuclear fuel material is attached to a metal reactor structure such as a core shroud, a core support plate, and a control rod guide tube. At that time, if the molten nuclear fuel material is recovered together with the reactor structure in the containment vessel, the molten nuclear fuel material that requires recriticality management and the nuclear reactor structure that does not require recriticality management will coexist in the containment vessel. However, there is a problem that strict and highly accurate recriticality control cannot be performed on the molten nuclear fuel material.

  The present invention has been made to solve the above-mentioned problems, and by separating and recovering the molten nuclear fuel material and the reactor structure, it is possible to perform strict and highly accurate recriticality management for the molten nuclear fuel material. An object is to provide a method for recovering molten nuclear fuel material.

In order to solve the above-mentioned problem, a method for recovering a molten nuclear fuel material according to the present invention is a recovery of a molten nuclear fuel material that separates and recovers the molten nuclear fuel material and the reactor structure from a nuclear reactor structure to which the molten nuclear fuel material is adhered. In the method, the step of measuring the electrical conductivity of the recovery object, and when the electrical conductivity of the recovery object is less than a reference value, the recovery object is determined to be a molten nuclear fuel material, and the electrical conductivity is greater than the reference value A determination step for determining a nuclear reactor structure, a crushing step for crushing the molten nuclear fuel material by applying an impact load when the recovery target is determined to be a molten nuclear fuel material, and the crushed molten nuclear fuel material A recovery step of recovering.

  According to the present invention, rigorous and highly accurate recriticality management is performed on molten nuclear fuel material by separating and recovering the nuclear fuel material that requires recriticality management and the reactor structure that does not require recriticality management. It can be carried out.

The block diagram of the nuclear power plant which concerns on this embodiment. (A)-(c) is a figure which shows the collection | recovery operation example of the molten nuclear fuel material which concerns on 1st Embodiment. (A)-(c) is a figure which shows the collection | recovery operation example of the nuclear reactor structure which concerns on 1st Embodiment. (A)-(c) is a figure which shows the collection | recovery operation example of the molten nuclear fuel material which concerns on 2nd Embodiment.

Hereinafter, embodiments of a method for recovering a molten nuclear fuel material according to the present invention will be described with reference to the drawings.
[First Embodiment]
A method for recovering molten nuclear fuel material according to the first embodiment will be described with reference to FIGS.

(Constitution)
In a boiling water reactor (BWR), a pressure vessel 4 is accommodated in a containment vessel 3, and a core 1 loaded with a plurality of fuel assemblies is installed on a core support plate 2 in the pressure vessel 4. . If the nuclear fuel material of the fuel assembly is melted in a severe accident, the molten nuclear fuel material 5 may adhere to the core support plate 2, the lower part of the pressure vessel 4, or the lower part of the containment vessel 3, as shown in FIG. In addition, the molten nuclear fuel material 5 may adhere to a control rod guide tube, a core shroud, or the like (not shown).
In the present embodiment, an example in which the molten nuclear fuel material 5 attached to the core support plate 2 is recovered will be described, but it is needless to say that the present invention can be applied to cases where it adheres to other nuclear reactor structures.

  As shown in FIGS. 2 and 3, the recovery device used in the recovery method of the present embodiment includes a crushing tool 7 that repeatedly applies an impact load to an object to be recovered, a molten nuclear fuel material 5 crushed by the crushing tool 7, and A recovery tool 8 that recovers the core support plate 2 cut by the cutting tool 12, a lifting device 10 with a crushing tool 7, a recovery tool 8, or a cutting tool 12 attached to the tip, and a crane 9 that drives and controls the lifting device 10. And an image pickup device 11 that is attached to the tip of the lifting device 10 and includes a TV camera or the like for picking up an object to be crushed and an object to be collected, and a container 6 that contains the crushed molten nuclear fuel material 5.

  The crushing tool 7 includes, for example, a tool blade capable of repeatedly applying an impact load to the molten nuclear fuel material 5 or a tool blade having a sharp tip, and the tool blade by electromagnetic force, hydraulic pressure or air pressure. A reciprocating drive device (not shown).

A tool such as a grab bucket is used as the recovery tool 8 for recovering the crushed molten nuclear fuel material 5a.
The crushing tool 7, the recovery tool 8, and the cutting tool 12 may be detachably mounted on the tip of the lifting device 10, but may be mounted on a dedicated lifting device 10.

(Function)
The present embodiment is characterized in that the molten nuclear fuel material 5 is collected separately from the core support plate 2 that is a nuclear reactor structure.

  In this fractional collection, when the object to be recovered is the molten nuclear fuel material 5, the molten nuclear fuel material 5 is solidified after the uranium oxide is once melted. Therefore, it is hard and brittle like ceramics and is repeatedly impacted by the crushing tool 7. When the object to be recovered is the core support plate 2 while being crushed into small pieces by the load, the core support plate 2 is made of metal, and therefore, a part of the core support plate 2 that is plastically deformed by the crushing tool 7 is used. .

<Separation and crushing process>
First, the lifting / lowering device 10 equipped with the crushing tool 7 is lowered onto the core support plate 2 to which the molten nuclear fuel material 5 adheres, and an impact load is repeatedly applied to the collection object by the crushing tool 7 (FIG. 2 (a)). . Then, the appearance shape of the recovery object after the impact load is applied is observed by the imaging device 11. If the recovery object is crushed, it is determined as the molten nuclear fuel material 5, and if no crushing is observed, the core support plate 2. Is determined. In this case, if the impact load at which the molten nuclear fuel material 5 is crushed is obtained in advance, the molten nuclear fuel material 5 can be selectively crushed more clearly by applying the obtained impact load.

<Recovery process>
Next, the crushed molten nuclear fuel material 5a is collected by the collection tool 8 (FIG. 2B) and stored in the container 6 (FIG. 2C).
In this way, since only the molten nuclear fuel material 5 is stored in the container 6, recriticality management can be performed with high accuracy, and the occurrence of recriticality can be reliably prevented.

<Recovery of reactor structure>
On the other hand, when the recovery object is determined to be the core support plate 2 (FIG. 3A), a cutting tool 12 made of, for example, a rotary saw is attached to the tip of the lifting device 10 to cut the core support plate 2. (FIGS. 3B and 3C). The cut core support plate 2a is unloaded by the recovery tool 8 and stored in a container (not shown) different from the container 6 storing the molten nuclear fuel material 5.

  Note that the core structure such as the core support plate 2 and the control rod guide tube to which the molten nuclear fuel material 5 adheres becomes an obstacle to the recovery operation of the molten nuclear fuel material 5 deposited under the pressure vessel 4 or under the containment vessel 3. In some cases or when the reactor is dismantled, it is cut and collected as appropriate.

(effect)
According to the present embodiment, the molten nuclear fuel material that requires recriticality management and the reactor structure that does not require recriticality management are separated by simple means, and each is collected in different containers to obtain molten nuclear fuel material. On the other hand, strict and highly accurate recriticality management can be performed.

[Second Embodiment]
A method for recovering molten nuclear fuel material according to the second embodiment will be described with reference to FIG.
In the second embodiment, the molten nuclear fuel material 5 is an insulator and has low electrical conductivity. On the other hand, the core structure such as the core support plate 2 is made of metal and has high electrical conductivity. It is characterized in that it is determined whether the recovery object is a molten nuclear fuel material 5 or a reactor structure.

  First, a pair of electrodes 13 is attached to the tip of the lifting device 10, and the current between the electrodes 13 is measured by bringing the electrode 13 into contact with the collection object while confirming the collection object with the imaging device 11 (FIG. 4 (a)). )). If the value is below the reference value, it is determined as the molten nuclear fuel material 5, and if it is above the reference value, it is determined as the core support plate 2.

The electrode 13 is preferably a needle-like electrode with a sharp tip in order to ensure contact with the object.
The crushing process, cutting process, and recovery process after discriminating the molten nuclear fuel material 5 or the core support plate 2 are the same as in the first embodiment (FIGS. 4B and 4C).

According to the second embodiment, in addition to the effects of the first embodiment, the molten nuclear fuel material 5 or the nuclear reactor structure can be more easily separated.
Although the BWR plant has been described in the first and second embodiments, it is needless to say that this molten fuel material recovery method can also be applied to a PWR plant, a fast breeder reactor, or a reprocessing facility.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, combinations, replacements, and changes can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Core support plate (reactor structure), 3 ... Containment vessel, 4 ... Pressure vessel, 5 ... Molten nuclear fuel material, 6 ... Container, 7 ... Crushing tool, 8 ... Recovery tool, 9 ... Crane, DESCRIPTION OF SYMBOLS 10 ... Elevating device, 11 ... Imaging device, 12 ... Cutting tool, 13 ... Electrode.

Claims (3)

In the method for recovering a molten nuclear fuel material, the molten nuclear fuel material and the nuclear reactor structure are separated and recovered from a nuclear reactor structure to which the molten nuclear fuel material is attached.
A step of measuring the electrical conductivity of the recovery object; and when the electrical conductivity of the recovery object is below a reference value, the recovery object is determined to be a molten nuclear fuel material, and the electrical conductivity is above the reference value A determination step for determining a nuclear reactor structure, a crushing step for applying an impact load to the molten nuclear fuel material when the recovery target is determined to be a molten nuclear fuel material, and a recovery for recovering the crushed molten nuclear fuel material And a method for recovering molten nuclear fuel material. Method for recovering molten nuclear fuel material according to claim 1 Symbol placement collection object, characterized in that it further comprises a recovery step of recovering by cutting the reactor structure when it is determined that the reactor structure. 3. The method for recovering molten nuclear fuel material according to claim 2, wherein the recovered molten nuclear fuel material and the reactor structure are stored in different containers.

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