Method for decommissioning and solidifying material

Abstract

To provide a method for decommissioning for accelerating processing of debris.SOLUTION: The method for decommissioning includes the following steps: (1) a sealing step of sealing a water leakage hole with a first solidifying material JC1 obtained by mixing jet concrete and a radiation absorber; (2) a solidifying material supplying step of supplying a second solidifying material JC2 obtained by mixing jet concrete and a radiation absorber, together with a crushing device E, into a reactor containment vessel 10; and (3) a crushing and mixing step of crushing debris D and mixing the crushed debris D with the second solidifying material JC2 by means of the crushing device E.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a decommissioning method. [Background technology]

[0002] When an accident occurs at a nuclear power plant or other facility, nuclear fuel may melt and fall, and then cool and solidify, creating debris. Traditionally, removing this debris has required a great deal of time, money, and effort (see, for example, Non-Patent Document 1). Additionally, debris removal work poses a risk of radiation exposure to operators. [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] "Fuel debris retrieval status," https: / / www.tepco.co.jp / decommission / progress / retrieval / Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a decommissioning method that speeds up the processing of debris.

[0005] The contents of the above "Background Art" and "Problem to be Solved by the Invention" indicate the opportunity (trigger) that led to the invention, and do not limit the technical scope of the invention, nor do they permit a limited interpretation of the technical scope of the invention (see 2005 (Gyo-Ke) No. 10042 and the Patent Office Examination Guidelines, Part II, Chapter 2, Section 2, 3.2.1 as of the filing date). [Means for solving the problem]

[0006] The present invention relates to a decommissioning method comprising the following steps: (1) A sealing process in which jet concrete and a radiation absorber are mixed, and the solidification time is set to a time TS1 that is longer than the time T1 required from immediately after the preparation of the first solidification material JC1 to the completion of pouring into the sealing location, but shorter than the time T2 required for the first solidification material JC1 to mix with the wastewater DW. (2) A solidification agent injection process in which jet concrete and a radiation absorber are mixed, and the solidification time is set to a time TS2 that is longer than the sum of the time T3 until the second solidification agent JC2 and the pulverizer E are completely injected into the containment vessel 10 and the time T4 from the time T3 until the pulverization and mixing process is completed, and shorter than the time T6 required for the pulverized debris D to settle downward. (3) A crushing and mixing process in which the debris D is crushed and mixed with the second solidification material JC2 by the powder device E. (4) A step of leaving the second solidification material JC2 to stand until it solidifies. to provide. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a decommissioning method that speeds up the processing of debris. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a schematic view of a nuclear reactor 1 in which a nuclear fuel meltdown accident occurred. [Figure 2] FIG. [Figure 3] FIG. 10 is a diagram showing a solidifying agent injection step. [Figure 4] FIG. 2 is a diagram showing a grinding and mixing process. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a decommissioning method according to one embodiment of the present invention will be described in detail with reference to the drawings. (Basic Concept) Conventionally, debris has been removed from nuclear reactors, processed, and disposed of. In addition, reactors that have experienced accidents in which nuclear fuel has melted cannot be reused and have been dismantled and disposed of. Furthermore, large amounts of waste water are generated during the debris removal process, and the disposal of this waste water containing nuclear material has also become a problem. As mentioned above, after an accident, the entire reactor is disposed of, and very little is reused. Therefore, even if the debris is separated and disposed of separately, it will still be transported to a management facility and left there until the radiation levels drop, so there is little need to separate the debris and other components. The present invention provides a method for solidifying the nuclear reactor where an accident has occurred, including all debris, and leaving it as is until the radiation dose decreases.

[0010] (Decommissioning method) (Structure of the reactor and debris) Fig. 1 is a cross-sectional view showing a schematic diagram of a nuclear reactor 1 in which a nuclear fuel meltdown accident occurred. As shown in Fig. 1, the nuclear reactor 1 comprises a reactor containment vessel 10, a pressure vessel 11 housed inside the reactor containment vessel 10 and containing nuclear fuel 12 therein, and a pressure suppression chamber 13 communicating with the inside of the reactor containment vessel 10. In the event of a nuclear fuel meltdown accident, cooling of the nuclear fuel 12 is hindered, and the high-temperature nuclear fuel 12 melts together with the nuclear fuel container and falls under its own weight, cools, and generates debris D. The debris D may also melt and fall to the bottom of the reactor containment vessel 10 and solidify. In this case, a part of the containment vessel 10 also melts, opening a hole that allows the cooling water W to leak out of the pressure suppression chamber 13, producing waste water DW. In addition, the material C at the bottom supporting the pressure vessel 11 deteriorates, producing deteriorated material RC.

[0011] (Decommissioning method) The decommissioning method of this embodiment includes the following steps. (1) Sealing process of sealing the leak hole with the first solidifying agent JC1 (2) A solidification agent injection step of injecting the second solidification agent JC2 and the pulverization device E into the containment vessel 10 (3) A crushing and mixing process in which the debris D is crushed and mixed with the second solidification material JC2 by the powder device E. (4) A step of leaving the second solidification material JC2 to stand until it solidifies.

[0012] Fig. 2 is a diagram showing the sealing step. As shown in Fig. 2, the first solidifying agent JC1 is poured into the chamber that houses the pressure suppression chamber 13, and is solidified to seal the water leakage hole.

[0013] Figure 3 is a diagram showing the solidifying agent injection step. As shown in Figure 3, first, the crushing device E is placed near the debris D. Next, the second solidifying agent JC2 is injected until the debris D is hidden.

[0014] Fig. 4 is a diagram showing the pulverizing and mixing process. As shown in Fig. 4, after the second solidifying agent JC2 is poured into the containment vessel 10 to the extent that the debris D is hidden, the pulverizing device E is started and the second solidifying agent JC2 and the pulverized debris D are mixed.

[0015] Thereafter, the mixture is left standing as a standing step.

[0016] The reactor 1 in which the debris D has been pulverized and solidified by the second solidification agent JC2 is left stationary and managed until the radiation dose decreases.

[0017] (Solidifying agent) Both the first hardening agent JC1 and the second hardening agent JC2 are mixtures obtained by mixing jet concrete with a radiation absorber. It is desirable to mix the jet concrete and radiation absorber in the ratio up to the upper limit at which the mixture can solidify, but if the amount of DEBRIDGER D is small, it is possible to reduce the amount of radiation absorber. The upper limit at which the mixture can solidify varies depending on the jet concrete product.

[0018] Jet concrete is a type of concrete that hardens in a shorter time than regular concrete, and the following products have been published, for example: Super Jet Concrete (manufactured by Onoda Chemico Co., Ltd.) Denka Super Concrete (manufactured by Denka Co., Ltd.) Jet concrete (manufactured by Sumitomo Osaka Cement Co., Ltd.)

[0019] The first hardening agent JC1 and the second hardening agent JC2 can be one or more types of jet concrete selected from these jet concretes. The hardening time of the first hardening agent JC1 and the second hardening agent JC2 can be adjusted by increasing or decreasing the amount of setter added, which is an agent that adjusts the hardening time.

[0020] The solidification time of the first solidification agent JC1 is set to a time TS1 that is longer than the time T1 required from immediately after the preparation of the first solidification material JC1 until the completion of pouring into the sealing location, but shorter than the time T2 required for the first solidification agent JC1 to mix with the waste water DW.

[0021] The solidification time of the second solidification agent JC2 is set to a time TS2 that is longer than the time T5 obtained by adding the time T3 until the second solidification agent JC2 and the pulverization device E are completely introduced into the reactor containment vessel 10 and the time T4 from after the time T3 has elapsed until the pulverization and mixing process is completed, and is shorter than the time T6 required for the pulverized debris D to settle downward.

[0022] The radiation absorber can be a powder mixture of so-called control rod materials or so-called moderator materials. Examples of such materials include boron carbide, cadmium alloy, indium, silver, and hafnium, and one or more of these materials can be used. Discarded control rods can also be used as a powder. In addition to these, powders of substances that suppress radiation, such as lead compounds, can also be added.

[0023] (Powdering device) The powder device E can be either a chemical type or a mechanical type.

[0024] The chemical pulverizer E includes explosives such as TNT, a time-detonator set to a time TE longer than time T3 and shorter than time T4, and a container that seals these against the solidified material JC2. When multiple pulverizers E are used, the time TE is set so that they detonate at slightly different times.

[0025] The mechanical crushing device E includes a blade for crushing the debris D and a motor for driving the blade.

[0026] (Effects of decommissioning methods) As described above, the decommissioning method of this embodiment includes the following steps. (1) A sealing process in which jet concrete and a radiation absorber are mixed, and the solidification time is set to a time TS1 that is longer than the time T1 required from immediately after the preparation of the first solidification material JC1 to the completion of pouring into the sealing location, but shorter than the time T2 required for the first solidification material JC1 to mix with the wastewater DW. (2) A solidification agent injection process in which jet concrete and a radiation absorber are mixed, and the solidification time is set to a time TS2 that is longer than the sum of the time T3 until the second solidification agent JC2 and the pulverizer E are completely injected into the containment vessel 10 and the time T4 from the time T3 until the pulverization and mixing process is completed, and shorter than the time T6 required for the pulverized debris D to settle downward. (3) A crushing and mixing process in which the debris D is crushed and mixed with the second solidification material JC2 by the powder device E. (4) A step of leaving the second solidification material JC2 to stand until it solidifies.

[0027] Therefore, it is possible to provide a decommissioning method that speeds up the disposal of debris.

[0028] Furthermore, since the first solidification agent JC1 and the second solidification agent JC2 are mixtures of jet concrete and a radiation absorber, there is an effect of being able to prevent nuclear fission reactions from occurring after solidification. [Explanation of symbols]

[0029] 1 nuclear reactor 10 Reactor containment vessel 11 Pressure vessels 12 Nuclear fuel 13 Pressure Suppression Chamber D Debris DW waste water E. Crushing device JC1 First solidifying agent JC2 Secondary Hardener RC degraded material W Cooling water

Claims

1. A decommissioning method that includes the following steps: (1) A sealing process in which jet concrete and a radiation absorber are mixed and the water leakage hole is sealed with a first solidifying agent whose solidification time is set to a time TS1 that is longer than the time T1 required from immediately after preparation until the radiation absorber is completely poured into the sealing location and shorter than the time T2 required for the first solidifying agent to mix with the waste water. (2) A solidification agent injection process in which the jet concrete and the radiation absorber are mixed, and a second solidification agent and the pulverization device are injected into the containment vessel, the solidification time of which is set to a time TS2 that is longer than a time T5 obtained by adding a time T3 until the injection of a pulverization device for pulverizing debris into the containment vessel is completed and a time T4 from the time T3 until the pulverization and mixing process is completed, and shorter than a time T6 required for the pulverized debris to sink downward. (3) A crushing and mixing step of crushing the debris and mixing the crushed debris with the second solidification material by the powder device. (4) A step of leaving the second solidification material to stand until the second solidification material is solidified.

2. The first solidification agent of claim 1 .

3. The second solidification agent of claim 1 .

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