JP2023105754A - Method for decontaminating contaminated metal member and method for manufacturing regenerated metal - Google Patents
Method for decontaminating contaminated metal member and method for manufacturing regenerated metal Download PDFInfo
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- 239000002184 metal Substances 0.000 title claims abstract description 139
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- 238000005498 polishing Methods 0.000 claims abstract description 165
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- 238000005202 decontamination Methods 0.000 claims abstract description 37
- 238000002844 melting Methods 0.000 claims abstract description 9
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- 239000012530 fluid Substances 0.000 claims description 7
- 238000005507 spraying Methods 0.000 claims description 3
- 230000002285 radioactive effect Effects 0.000 abstract description 2
- 230000003588 decontaminative effect Effects 0.000 description 21
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Abstract
Description
本発明は、汚染金属部材の除染方法及び再生金属の製造方法に関する。 The present invention relates to a method for decontaminating contaminated metal members and a method for producing recycled metal.
原子力施設で発生する放射性廃棄物は、その表面に放射性核種が付着していることがある。このような放射性廃棄物のうち、金属の部材については、表面の放射性核種を除去することで、再利用がし易くなることがある。金属部材の表面に付着した放射性核種の除去は、その付着状況に応じた除染方法を適用することが求められる。 Radioactive waste generated at nuclear facilities may have radionuclides attached to its surface. Among such radioactive wastes, metal members can be easily reused by removing radionuclides from their surfaces. To remove radionuclides adhering to the surface of metal members, it is required to apply a decontamination method according to the state of adhesion.
被処理物に研磨用粒子を高速で衝突させることで、前記被処理物の表面を研削して除染する装置が知られている（特開２０００－０７５０９５号公報）。この除染装置は、水ノズルから噴射される水と、蒸気ノズルから噴射される蒸気とで形成される超音速蒸気噴流に研磨用粒子を供給し、前記被処理物に前記研磨用粒子を高速で衝突させている。 There is known an apparatus that grinds and decontaminates the surface of an object to be treated by colliding abrasive particles with the object at high speed (Japanese Patent Application Laid-Open No. 2000-075095). This decontamination apparatus supplies abrasive particles to a supersonic steam jet formed by water ejected from a water nozzle and steam ejected from a steam nozzle, and blasts the abrasive particles onto the object to be processed at high speed. is collided with
前記公報所載の除染装置は、研磨用粒子としてセラミックス粒子を用いることで、研削能力が高く、研磨用粒子の再利用をすることができ、効率的な除染ができるとしている。前記除染装置は、前記超音速蒸気噴流を形成するためのノズルの構造が複雑であり、さらにセラミックス粒子を用いていること等から、低コストで簡易に除染をすることができないおそれがある。 The decontamination apparatus described in the above publication uses ceramic particles as the abrasive particles, so that it has a high grinding ability, the abrasive particles can be reused, and efficient decontamination is possible. The decontamination device has a complicated nozzle structure for forming the supersonic steam jet, and furthermore, ceramic particles are used. .
本発明の発明者らは、低コストで簡易に除染できる方法について検討した。Ｃｏ－６０等の放射性核種は、通常、金属表面に発生する錆などの酸化物の結晶体に取り込まれて存在し、この結晶体の性状によって付着状況が異なる。例えば、原子炉の冷却系を構成する配管、機器などの部材で使用されている金属の表面に付着している結晶体は、その金属表面が腐食して生成した酸化被膜であり、前記金属表面に均等に分布して強固に固着している。一方、他所で生成した腐食生成物が、例えば冷却水で運ばれて前記酸化被膜に付着することで堆積した結晶体は、不均一に分布して弱く付着している。すなわち、放射性核種は、均一に分布して前記金属表面に比較的強固に結合している固着物と、不均一に分布して前記固着物に比較的弱く結合している付着物に分類することができる。一般に、このような固着物、付着物を除染する方法は、化学的方法と機械的方法に分類されるが、放射性廃棄物の除染では、除染により発生する廃棄物が少ない方が有利とされている。前記機械的方法でも乾式ブラスト等の粒子を衝突させる方法は、前記固着物及び前記付着物の両方の除去に適用でき、かつ金属加工における前処理方法として広く利用されているため機材が容易に入手できる。よって、放射性金属の廃棄物を低コストで簡易に除染する方法として、粒子を衝突させる方法は適用性が高いとの結論に至った。 The inventors of the present invention have investigated a low-cost and simple decontamination method. Radionuclides such as Co-60 are usually present as they are incorporated into crystals of oxides such as rust generated on metal surfaces, and the state of adhesion differs depending on the properties of these crystals. For example, crystals adhering to the surface of metal used in members such as pipes and equipment that make up the cooling system of a nuclear reactor are oxide films formed by corrosion of the metal surface. are evenly distributed and strongly adhered to each other. On the other hand, crystals deposited by corrosion products produced elsewhere, for example, carried by cooling water and adhering to the oxide film, are non-uniformly distributed and adhere weakly. That is, radionuclides are classified into adherents that are uniformly distributed and are relatively strongly bound to the metal surface and adherents that are non-uniformly distributed and are relatively weakly bound to the aforesaid metallic surface. can be done. In general, methods for decontaminating such adherents and deposits are classified into chemical methods and mechanical methods, but in decontamination of radioactive waste, it is advantageous to generate less waste by decontamination. It is said that In the mechanical method, the method of colliding particles such as dry blasting can be applied to the removal of both the solid matter and the adhering matter, and is widely used as a pretreatment method in metal processing, so equipment is easily available. can. Therefore, it was concluded that the particle collision method is highly applicable as a low-cost and simple decontamination method for radioactive metal waste.
すなわち、本発明は、放射性核種で汚染された金属部材を低コストで簡易かつ効率的に除染する方法、及び再生金属を効率的に製造する方法を提供することを目的とする。 That is, an object of the present invention is to provide a low-cost, simple, and efficient decontamination method for metal members contaminated with radionuclides, and a method for efficiently producing recycled metal.
前記課題を解決する本発明の一態様は、放射性核種で汚染された金属部材の除染方法であって、前記金属部材の表面に研磨用の第一粒子を衝突させる研磨工程を備え、予め設定された研磨時間で前記研磨工程を終了する。 One aspect of the present invention for solving the above problems is a method for decontaminating a metal member contaminated with a radionuclide, comprising a polishing step of colliding first particles for polishing against the surface of the metal member, The polishing process is finished at the specified polishing time.
本発明の別の一態様は、前記除染方法によって放射性核種を除去した金属部材を溶融する工程を備える再生金属の製造方法である。 Another aspect of the present invention is a method for producing recycled metal, comprising the step of melting a metal member from which radionuclides have been removed by the decontamination method.
本発明の除染方法は、放射性核種で汚染された金属部材を低コストで簡易かつ効率的に除染することができる。本発明の再生金属の製造方法は、当該除染方法で除染された金属部材を用いることで、再生金属を効率的に製造することができる。 The decontamination method of the present invention can easily and efficiently decontaminate metal members contaminated with radionuclides at low cost. The method for producing recycled metal of the present invention can efficiently produce recycled metal by using the metal member decontaminated by the decontamination method.
本発明の一態様は、放射性核種で汚染された金属部材の除染方法であって、前記金属部材の表面に研磨用の第一粒子を衝突させる研磨工程を備え、予め設定された研磨時間で前記研磨工程を終了する。 One aspect of the present invention is a method for decontaminating a metal member contaminated with a radionuclide, comprising a polishing step of colliding first particles for polishing against the surface of the metal member, wherein the polishing time is set in advance. The polishing step ends.
当該除染方法は、放射性核種で汚染された金属部材に対し、その表面に研磨用の第一粒子を衝突させることによって研磨を行う。このため、簡易かつ低コストで汚染金属の除染をすることができる。また、当該除染方法は、所定の時間で前記研磨工程を終了するため、効率的に除染をすることができる。 The decontamination method polishes a metal member contaminated with a radionuclide by colliding the first particles for polishing with the surface of the metal member. Therefore, it is possible to decontaminate contaminated metals simply and at low cost. Moreover, since the said decontamination method complete|finishes the said grinding|polishing process in predetermined time, it can decontaminate efficiently.
前記研磨時間が４分以上であるとよい。このように研磨を短時間で行うことにより、より効率的な除染をすることができる。 The polishing time is preferably 4 minutes or more. By performing polishing in a short time in this manner, more efficient decontamination can be achieved.
前記研磨工程後の前記金属部材の表面における前記放射性核種の密度を測定する研磨後測定工程をさらに備え、前記研磨後測定工程における測定値が予め設定された研磨後閾値以上であると、前記研磨工程と前記研磨後測定工程とを繰り返すとよい。このようにすることで、除染の確実性を向上することができる。 Further comprising a post-polishing measurement step of measuring the density of the radionuclides on the surface of the metal member after the polishing step, wherein if the measured value in the post-polishing measurement step is equal to or greater than a preset post-polishing threshold value, the polishing is performed. It is preferable to repeat the step and the post-polishing measurement step. By doing so, the certainty of decontamination can be improved.
前記研磨工程前に前記金属部材の表面における前記放射性核種の密度を測定する研磨前測定工程と、前記研磨前測定工程における測定値が予め設定された研磨前閾値以上の前記金属部材の表面に、前記研磨工程の前に研磨用の第二粒子を衝突させる粗研磨工程とをさらに備えるとよい。前記研磨工程前の前記金属部材の表面における前記放射性核種の密度が高いと、前記所定時間での研磨によっても十分な除染ができないおそれがある。前記研磨工程前の前記放射性核種の密度が高い前記金属部材の表面には前処理として粗研磨を行うことで前記放射性核種の密度を低減させ、その後に前記研磨工程を行うことで除染の確実性をより向上することができる。 A pre-polishing measurement step of measuring the density of the radionuclide on the surface of the metal member before the polishing step; It is preferable to further include a rough polishing step of colliding second particles for polishing before the polishing step. If the density of the radionuclides on the surface of the metal member before the polishing step is high, there is a possibility that sufficient decontamination cannot be achieved even by polishing for the predetermined time. The surface of the metal member having a high density of radionuclides before the polishing step is subjected to rough polishing as a pretreatment to reduce the density of the radionuclides, and then the polishing step is performed to ensure decontamination. It is possible to further improve the performance.
前記粗研磨工程後の前記金属部材の表面に清掃用流体を吹き付ける清掃工程をさらに備えるとよい。前記粗研磨工程での研磨によって発生した前記放射性核種を含む粉塵が前記金属部材の表面に再付着することがある。前記粗研磨工程後に前記清掃工程を行うことで、再付着した粉塵を前記金属部材の表面から除去することができ、前記研磨工程による除染の効率性をより向上することができる。 It is preferable to further include a cleaning step of spraying a cleaning fluid onto the surface of the metal member after the rough polishing step. Dust containing the radionuclide generated by polishing in the rough polishing step may reattach to the surface of the metal member. By performing the cleaning step after the rough polishing step, reattached dust can be removed from the surface of the metal member, and the efficiency of decontamination by the polishing step can be further improved.
前記清掃用流体がエアであるとよい。エアで清掃することで、前記清掃工程を低コストで効率的に行うことができる。 The cleaning fluid may be air. By cleaning with air, the cleaning process can be performed efficiently at low cost.
本発明のさらに別の一態様は、前記除染方法で前記放射性核種を除去した金属部材を溶融する工程を備える再生金属の製造方法である。 Yet another aspect of the present invention is a method for producing recycled metal, comprising the step of melting the metal member from which the radionuclide has been removed by the decontamination method.
当該再生金属の製造方法は、簡易かつ効率的に除染された金属部材を溶融するため、再生金属を効率的に製造することができる。 Since the method for manufacturing the recycled metal melts the decontaminated metal member simply and efficiently, the recycled metal can be manufactured efficiently.
［発明を実施するための形態の詳細］
以下、本発明の実施の形態について詳説する。
[Details of the mode for carrying out the invention]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail.
＜再生金属の製造方法＞
本発明の一実施形態である再生金属の製造方法は、放射性核種を除去した金属部材を溶融する工程を備える。放射性核種を除去した金属部材を溶融する方法としては、特に限定されるものでなく公知の方法を採用することができ、例えば、加熱した炉に放射性核種を除去した金属部材を投入して溶解する方法が挙げられる。複数の金属部材を同時に溶解すれば均質で量の大きい素材にでき、冷却後に様々な金属製品に加工できる。
<Method for manufacturing recycled metal>
A method for manufacturing recycled metal, which is an embodiment of the present invention, comprises a step of melting a metal member from which radionuclides have been removed. The method of melting the metal member from which the radionuclide has been removed is not particularly limited, and a known method can be adopted. For example, the metal member from which the radionuclide has been removed is put into a heated furnace and melted. method. By simultaneously melting a plurality of metal members, it is possible to obtain homogeneous and large-volume materials, which can be processed into various metal products after cooling.
溶融した金属をサンプリングして放射能濃度を測定することが好ましい。このようにすることで、前記金属部材をより安全に再利用することができる。 Preferably, the molten metal is sampled to measure the radioactivity concentration. By doing so, the metal member can be reused more safely.
〔汚染金属の除染方法〕
当該放射性核種で汚染された金属の除染方法は、前記金属部材の表面に研磨用の第一粒子を衝突させる研磨工程を備え、予め設定された研磨時間で前記研磨工程を終了する。
[Method for decontamination of contaminated metals]
The method for decontaminating metal contaminated with the radionuclides includes a polishing step of colliding first particles for polishing against the surface of the metal member, and the polishing step is completed in a preset polishing time.
本実施形態における汚染金属の除染方法は、図１に示すように、前記研磨工程の前に前記金属部材の表面における前記放射性核種の密度を測定する研磨前測定工程と、前記研磨前測定工程における測定値が予め設定された研磨前閾値以上の前記金属部材の表面に、前記研磨工程の前に研磨用の第二粒子を衝突させる粗研磨工程と、前記粗研磨工程後の前記金属の表面に清掃用流体を吹き付ける清掃工程とをさらに備える。また、本実施形態における汚染金属の除染方法は、前記研磨工程後の前記金属部材の表面における前記放射性核種の密度を測定する研磨後測定工程とをさらに備える。 As shown in FIG. 1, the method for decontaminating contaminated metals in this embodiment comprises a pre-polishing measurement step of measuring the density of the radionuclides on the surface of the metal member before the polishing step, and the pre-polishing measurement step. a rough polishing step of colliding the second particles for polishing with the surface of the metal member whose measured value is equal to or higher than a preset pre-polishing threshold before the polishing step; and the surface of the metal after the rough polishing step. and a cleaning step of spraying a cleaning fluid on. Further, the method for decontamination of contaminated metals in the present embodiment further includes a post-polishing measurement step of measuring the density of the radionuclides on the surface of the metal member after the polishing step.
本実施形態における放射性核種で汚染された金属部材（汚染金属部材）とは、例えば、原子力施設の設備更新、廃止などに伴い撤去される配管、機器などである。具体的には、原子炉の冷却系を構成する配管、機器などであって、表面にＣｏ－６０等の放射性核種が付着し、再利用することが困難な金属を意味する。ここで再利用することが困難な金属とは、原子力事業所内で再利用する場合は、事業者が定める許容量を超える量の放射性核種が付着した金属であり、原子力事業所以外で再利用する場合は、法令で定める許容量を超える量の放射性核種が付着した金属である。 Metal members contaminated with radionuclides (contaminated metal members) in the present embodiment are, for example, pipes, equipment, and the like that are removed along with equipment renewal or decommissioning of nuclear facilities. Specifically, it means a metal that is difficult to reuse because it is a pipe, equipment, etc. that constitutes a cooling system of a nuclear reactor, and a radionuclide such as Co-60 adheres to its surface. Here, metals that are difficult to reuse refer to metals attached with radionuclides that exceed the permissible amount specified by the operator when reused within nuclear power plants, and are reused outside of nuclear power plants. In some cases, it is metal with attached radionuclides in amounts exceeding the permissible amount stipulated by law.
（研磨前測定工程）
研磨前測定工程では、研磨する前の汚染金属部材の表面における放射性核種の密度を測定する。放射性核種の密度を測定する方法としては、特に限定されるものでなく、例えば、公知のサーベイメータ等を用いる方法が挙げられる。
(Measurement process before polishing)
In the pre-polishing measurement step, the radionuclide density on the surface of the contaminated metal member before polishing is measured. The method for measuring the radionuclide density is not particularly limited, and examples thereof include a method using a known survey meter or the like.
前記研磨前測定工程では、研磨前閾値が設定される。前記研磨前閾値は、過去の実績、サンプルの採取などから任意の値が設定され、例えば、放射能濃度として１００［Ｂｑ／ｇ］とすることができる。前記汚染金属部材の表面における放射性核種の密度の測定値から算出される放射能濃度が前記研磨前閾値未満であれば、前記汚染金属部材に後述する研磨工程を施す。前記放射能濃度が前記研磨前閾値以上の前記汚染金属部材には後述する粗研磨工程を施す。放射能濃度［Ｂｑ／ｇ］は、前記汚染金属部材の表面における放射性核種の密度の測定値［Ｂｑ／ｃｍ２］に前記金属部材の板厚を乗じ、前記金属部材の密度で除することで算出する。 In the pre-polishing measurement step, a pre-polishing threshold is set. The pre-polishing threshold value is set to an arbitrary value based on past performance, sampling, etc., and can be set to 100 [Bq/g] as the radioactivity concentration, for example. If the radioactivity concentration calculated from the measured value of the radionuclide density on the surface of the contaminated metal member is less than the pre-polishing threshold, the contaminated metal member is subjected to a polishing step, which will be described later. The contaminated metal member having the radioactivity concentration equal to or higher than the pre-polishing threshold is subjected to a rough polishing step, which will be described later. The radioactivity concentration [Bq/g] is obtained by multiplying the measured value of the radionuclide density [Bq/cm 2 ] on the surface of the contaminated metal member by the thickness of the metal member and dividing by the density of the metal member. calculate.
一般的には、放射性核種は、金属部材（金属）の表面に付着し、その内部に取り込まれることもなく、放射化することもない。このため、金属部材を除染するための測定としては、その金属部材の表面における放射性核種の密度を測定することで足りると考えられる。このため、前記研磨前閾値、後述する研磨後閾値、及び後述する粗研磨後閾値は、放射能濃度［Ｂｑ／ｇ］で設定してもよく、放射性核種の密度［Ｂｑ／ｃｍ２］で設定してもよい。本実施形態では、一例として、前記研磨前閾値、後述する研磨後閾値、及び後述する粗研磨後閾値を放射能濃度［Ｂｑ／ｇ］で設定したものとして説明する。 In general, radionuclides adhere to the surface of a metal member (metal), are not taken into the interior thereof, and are not activated. Therefore, it is considered sufficient to measure the density of radionuclides on the surface of the metal member for decontamination of the metal member. Therefore, the pre-polishing threshold, the post-polishing threshold described later, and the post-rough polishing threshold described later may be set by the radioactivity concentration [Bq/g], or by the radionuclide density [Bq/cm 2 ]. You may In the present embodiment, as an example, the pre-polishing threshold, the post-polishing threshold described later, and the post-rough-polishing threshold described later are set by the radioactivity concentration [Bq/g].
前記研磨前閾値は、後述する研磨後測定工程における研磨後閾値に対する比で設定してもよい。具体的には、前記研磨後閾値に対する前記研磨前閾値の比を、例えば、１０として設定してもよい。つまり、前記研磨後閾値を１［Ｂｑ／ｇ］とした場合に、前記研磨前閾値をその１０倍である１０［Ｂｑ／ｇ］としてもよい。 The pre-polishing threshold may be set as a ratio to the post-polishing threshold in the post-polishing measurement step described below. Specifically, the ratio of the pre-polishing threshold to the post-polishing threshold may be set to 10, for example. That is, when the post-polishing threshold value is 1 [Bq/g], the pre-polishing threshold value may be 10 [Bq/g], which is 10 times that value.
（粗研磨工程）
粗研磨工程では、前記研磨前測定工程における測定値が前記研磨前閾値以上の前記金属部材の表面に、研磨用の第二粒子を衝突させる。衝突させる方法としては、特に限定されるものではないが、本実施形態では、前記汚染金属部材の表面に第二粒子を用いた乾式ブラスト（ショットブラストともいわれる）を行う方法で説明する。前記粗研磨工程は、前記研磨工程の前処理である。前記研磨前閾値以上の汚染金属部材の表面に乾式ブラストを行うことで、前記金属部材の表面に付着した放射性核種を剥離して前記汚染金属部材の放射能濃度を低減する。例えば、前記研磨前閾値を１００［Ｂｑ／ｇ］に設定した場合、１００［Ｂｑ／ｇ］を超える汚染金属部材に粗研磨工程を行う。
(rough polishing process)
In the rough polishing step, the surface of the metal member whose measured value in the pre-polishing measuring step is equal to or greater than the pre-polishing threshold value is collided with the second particles for polishing. The collision method is not particularly limited, but in the present embodiment, a method of dry blasting (also called shot blasting) using second particles on the surface of the contaminated metal member will be described. The rough polishing step is a pretreatment for the polishing step. Dry blasting is performed on the surface of the contaminated metal member having the pre-polishing threshold value or more to remove the radionuclide adhering to the surface of the metal member and reduce the radioactivity concentration of the contaminated metal member. For example, when the pre-polishing threshold value is set to 100 [Bq/g], the rough polishing process is performed on the contaminated metal member exceeding 100 [Bq/g].
前記粗研磨工程に用いられる投射材（メディア）としての第二粒子は、後述する研磨工程で用いられる投射材としての第一粒子より粒径が大きいものが好ましい。このようにすることで、前記汚染金属部材の放射能濃度を比較的容易に前記研磨前閾値未満の範囲にすることができる。前記第二粒子は、前記第一粒子と略同一の粒径であって前記第一粒子より高い硬度を有するものとしてもよく、第一粒子と同一のものを用いてもよい。 The second particles as the projection material (media) used in the rough polishing step preferably have a larger particle size than the first particles as the projection material used in the later-described polishing step. By doing so, the radioactivity concentration of the contaminated metal member can be relatively easily reduced to a range less than the pre-polishing threshold. The second particles may have substantially the same particle size as the first particles and have a higher hardness than the first particles, or may be the same as the first particles.
前記粗研磨工程は、前記汚染金属の放射能濃度を再利用可能な範囲（例えば、１０［Ｂｑ／ｇ］以下）まで低減するために行うものではなく、前記汚染金属部材に研磨工程を施すことができる放射能濃度（例えば、１００［Ｂｑ／ｇ］以下）に低減するために行う。 The rough polishing step is not performed to reduce the radioactivity concentration of the contaminated metal to a reusable range (e.g., 10 [Bq/g] or less), but the contaminated metal member is subjected to a polishing step. is performed to reduce the radioactivity concentration (for example, 100 [Bq/g] or less).
前記粗研磨工程の終了は、予め粗研磨時間を設定し、この粗研磨時間の経過後に終了してもよいし、粗研磨後に前記金属部材表面の放射性核種の密度を測定する粗研磨後測定工程を設け、この測定値が予め設定した粗研磨後閾値（例えば、１００［Ｂｑ／ｇ］）以下になると終了するようにしてもよい。 The rough polishing step may be terminated after the rough polishing time has been set in advance, or the post-rough polishing measurement step of measuring the density of radionuclides on the surface of the metal member after rough polishing. may be provided, and the process may be terminated when this measured value becomes equal to or less than a preset post-rough polishing threshold value (for example, 100 [Bq/g]).
（清掃工程）
清掃工程では、前記粗研磨工程後の前記金属部材の表面に清掃用流体を吹き付ける。前記粗研磨工程では、研磨によって前記放射性核種を含む粉塵が発生し、この粉塵が前記金属部材の表面に再付着することがある。前記清掃工程を行うことで、再付着した粉塵を前記金属部材の表面から除去することができる。前記粉塵を除去することで、前記粗研磨工程による前記放射能濃度を低減することの確実性を向上することができる。
(Cleaning process)
In the cleaning step, a cleaning fluid is sprayed onto the surface of the metal member after the rough polishing step. In the rough polishing step, dust containing the radionuclide is generated by polishing, and this dust may reattach to the surface of the metal member. By performing the cleaning step, the reattached dust can be removed from the surface of the metal member. By removing the dust, it is possible to improve the certainty of reducing the radioactivity concentration by the rough polishing step.
前記清掃用流体としては、水等の液体を用いてもよいが、エアを用いることが好ましい。エアを用いた清掃工程としては、前記乾式ブラストがコンプレッサを用いるものであれば、前記粗研磨工程の終了後に前記乾式ブラストにおける投射材（第二粒子）の投入を停止して、前記コンプレッサのエアを前記金属部材の表面に吹き付けるとよい。前記乾式ブラストがコンプレッサを用いるものでない場合、別途コンプレッサ等のエア供給装置を準備し、このエア供給装置で前記金属部材の表面にエアを吹き付けるとよい。 As the cleaning fluid, a liquid such as water may be used, but it is preferable to use air. As a cleaning process using air, if the dry blasting uses a compressor, after the completion of the rough polishing process, the injection of the projection material (second particles) in the dry blasting is stopped, and the air of the compressor is removed. is preferably sprayed onto the surface of the metal member. If the dry blasting does not use a compressor, an air supply device such as a compressor may be separately prepared, and air may be blown onto the surface of the metal member by this air supply device.
（研磨工程）
研磨工程では、前記粗研磨工程を施した汚染金属部材の表面、及び前記研磨前測定工程における測定値が前記研磨前閾値未満であった汚染金属の表面に、研磨用の第一粒子を衝突させる。衝突させる方法としては、例えば、前記汚染金属部材の表面に乾式ブラストを行う。前記汚染金属部材の表面に乾式ブラストを行うことで、前記表面に付着した放射性核種を除去して前記汚染金属部材の放射能濃度を再利用可能な範囲まで低減する。
(polishing process)
In the polishing step, first particles for polishing are caused to collide with the surface of the contaminated metal member subjected to the rough polishing step and the surface of the contaminated metal whose measured value in the pre-polishing measurement step is less than the pre-polishing threshold value. . As a method of colliding, for example, dry blasting is performed on the surface of the contaminated metal member. Dry blasting the surface of the contaminated metal member removes the radionuclide adhering to the surface and reduces the radioactivity concentration of the contaminated metal member to a reusable range.
前記第一粒子としては、特に限定されるものでなく、例えば、鉄系、アルミニウム系、ガラス系、ドライアイスなどを用いることができ、中でも金属粒子が好ましい。前記第一粒子の粒径としては、特に限定されるものでなく、例えば、０．３ｍｍ以上２．０ｍｍ以下の粒子を用いることができる。 The first particles are not particularly limited, and for example, iron-based, aluminum-based, glass-based, dry ice, etc. can be used, and among them, metal particles are preferable. The particle size of the first particles is not particularly limited, and, for example, particles having a size of 0.3 mm or more and 2.0 mm or less can be used.
前記研磨工程は、予め設定した研磨時間が経過すると終了する。前記研磨時間は、過去の実績などから任意に設定することができる。 The polishing process ends when a preset polishing time elapses. The polishing time can be arbitrarily set based on past performance.
前記研磨時間は４分以上であることが好ましい。前記研磨時間の下限としては、５分が好ましく、６分がより好ましい。前記研磨時間の上限としては、特に限定されるものでないが、例えば１２分であり、１０分が好ましく、８分がより好ましい。前記研磨時間が前記下限に満たないと、十分な除染ができないおそれがある。前記研磨時間が前記上限を超えると、除染の効率性が低下するおそれがある。 The polishing time is preferably 4 minutes or longer. The lower limit of the polishing time is preferably 5 minutes, more preferably 6 minutes. The upper limit of the polishing time is not particularly limited, but is, for example, 12 minutes, preferably 10 minutes, and more preferably 8 minutes. If the polishing time is less than the lower limit, there is a possibility that sufficient decontamination cannot be achieved. If the polishing time exceeds the upper limit, the efficiency of decontamination may decrease.
前記研磨工程及び前記粗研磨工程は、前記汚染金属部材をブラストチャンバ等の室内で行う。この室内に粒子回収ノズル等を設け、前記第一粒子及び前記第二粒子を回収して前記研磨工程及び前記粗研磨工程で再利用するとよい。原子炉冷却用伝熱管の内面などを研磨する場合は、前記配管の一方の端部から前記第一粒子又は前記第二粒子を衝突させ、前記配管の他方の端部から前記第一粒子又は前記第二粒子を回収するとよい。 The polishing step and the rough polishing step are performed on the contaminated metal member in a room such as a blast chamber. A particle recovery nozzle or the like may be provided in this chamber to recover the first particles and the second particles and reuse them in the polishing step and the rough polishing step. When polishing the inner surface of a reactor cooling heat transfer tube or the like, the first particles or the second particles are caused to collide from one end of the pipe, and the first particles or the second particles are applied from the other end of the pipe. The second particles may be recovered.
（研磨後測定工程）
研磨後測定工程では、前記研磨工程後の前記金属部材の表面における放射性核種の密度を測定する。放射性核種の密度を測定する方法としては、特に限定されるものでなく、例えば、公知のサーベイメータ等を用いる方法が挙げられる。
(Measurement process after polishing)
In the post-polishing measurement step, the density of radionuclides on the surface of the metal member after the polishing step is measured. The method for measuring the radionuclide density is not particularly limited, and examples thereof include a method using a known survey meter or the like.
前記研磨後測定工程では、研磨後閾値が設定される。前記研磨後閾値は、前記金属を溶融することができる値が設定され、例えば、１０［Ｂｑ／ｇ］とすることができる。前記金属部材の表面における放射性核種の密度の測定値から算出される放射能濃度が前記研磨後閾値未満であれば、前記金属部材を前記溶融工程に供する。前記放射能濃度が前記研磨後閾値以上であると、前記金属部材に再び前記研磨工程を施す。前記金属部材は、再び前記研磨工程を行った後に、再び前記研磨後測定工程を行い、前記金属部材の放射能濃度が前記研磨後閾値未満になるまで繰り返す。このようにすることで、前記金属部材における除染の確実性を向上できる。 In the post-polishing measurement step, a post-polishing threshold is set. The post-polishing threshold is set to a value at which the metal can be melted, and can be set to 10 [Bq/g], for example. If the radioactivity concentration calculated from the radionuclide density measurements on the surface of the metal member is less than the post-polishing threshold, the metal member is subjected to the melting step. When the radioactivity concentration is equal to or higher than the post-polishing threshold, the metal member is subjected to the polishing step again. After the metal member undergoes the polishing step again, the post-polishing measurement step is repeated until the radioactivity concentration of the metal member becomes less than the post-polishing threshold value. By doing so, the certainty of decontamination of the metal member can be improved.
前記研磨後閾値は、前記研磨前測定工程における研磨前閾値に対する比で設定してもよい。具体的には、前記研磨前閾値に対する前記研磨後閾値の比を、例えば、１／１０として設定してもよい。つまり、前記研磨前閾値を１０［Ｂｑ／ｇ］とした場合に、前記研磨後閾値をその１／１０である１［Ｂｑ／ｇ］としてもよい。 The post-polishing threshold may be set as a ratio to the pre-polishing threshold in the pre-polishing measurement step. Specifically, the ratio of the post-polishing threshold to the pre-polishing threshold may be set as 1/10, for example. That is, when the pre-polishing threshold value is 10 [Bq/g], the post-polishing threshold value may be 1/10 of 1 [Bq/g].
＜利点＞
当該汚染金属の除染方法は、乾式ブラストで汚染金属部材の表面を研磨するため、低コストで簡易に除染をすることができ、前記研磨を所定の時間で終了することで、効率的に汚染金属部材の除染をすることができる。例えば、目標値（前記研磨後閾値）を０．１［Ｂｑ／ｇ］とした場合、除染した結果が０．１［Ｂｑ／ｇ］以下であれば目標は達成される。よって、前記汚染金属部材の初期の放射能濃度の高低に関わらず、システマチックに行う工程と位置づければ、計画的な除染方法として活用できる。また、当該再生金属の製造方法は、当該除染方法で除染された金属部材を用いるため、再生金属を効率的に製造することができる。
<Advantages>
In the method for decontaminating contaminated metals, since the surface of the contaminated metal member is polished by dry blasting, decontamination can be easily performed at low cost. Contaminated metal members can be decontaminated. For example, when the target value (the post-polishing threshold value) is 0.1 [Bq/g], the target is achieved if the decontamination result is 0.1 [Bq/g] or less. Therefore, regardless of the level of the initial radioactivity concentration of the contaminated metal member, if it is positioned as a process to be systematically performed, it can be utilized as a planned decontamination method. Moreover, since the method for manufacturing the recycled metal uses the metal member decontaminated by the decontamination method, the recycled metal can be efficiently manufactured.
［その他の実施形態］
上述の実施形態は、本発明の構成を限定するものではない。従って、前記実施形態は、本明細書の記載及び技術常識に基づいて前記実施形態各部の構成要素の省略、置換又は追加が可能であり、それらは全て本発明の範囲に属するものと解釈されるべきである。
[Other embodiments]
The above-described embodiments do not limit the configuration of the present invention. Therefore, in the embodiment, the components of each part of the embodiment can be omitted, replaced, or added based on the description of the present specification and common general technical knowledge, and all of them are interpreted as belonging to the scope of the present invention. should.
前記粗研磨工程及び清掃工程は、必須の構成ではない。すなわち、全ての汚染金属部材を研磨工程のみで除染するようにしてもよい。この場合、前記研磨後測定工程における測定値が前記研磨後閾値以上の汚染金属部材は、再度前記研磨工程を行うとよい。 The rough polishing step and the cleaning step are not essential components. That is, all contaminated metal members may be decontaminated only by the polishing process. In this case, the contaminated metal member whose measured value in the post-polishing measurement step is equal to or greater than the post-polishing threshold value is preferably subjected to the polishing step again.
また、前記研磨後測定工程も必須の構成ではない。すなわち、前記研磨工程を行った汚染金属部材の全部を、放射性核種の密度を測定することなく溶融に供してもよい。この場合、前記研磨前測定における測定値が前記研磨前閾値以上であるものについては、前記粗研磨工程を行うとよい。 Also, the post-polishing measurement step is not an essential configuration. That is, all of the contaminated metal members subjected to the polishing step may be subjected to melting without measuring the radionuclide density. In this case, it is preferable to perform the rough polishing step for those whose measured values in the pre-polishing measurement are equal to or greater than the pre-polishing threshold value.
［実施例］
原子炉の冷却水と長期間接触した熱交換器の伝熱管を用いて本発明の除染方法の効果を検証した。前記伝熱管は、同一の汚染状態のＵ字管が複数存在するため、除染条件を変化させた比較評価が可能である。７本の前記伝熱管を異なる研磨時間で除染し、各Ｕ字部分に残留する放射能濃度の結果を図１に示す。
[Example]
The effect of the decontamination method of the present invention was verified using the heat transfer tubes of the heat exchanger that were in contact with the cooling water of the nuclear reactor for a long period of time. Since there are a plurality of U-shaped heat transfer tubes with the same contamination state, it is possible to perform comparative evaluation under different decontamination conditions. Seven heat transfer tubes were decontaminated at different polishing times, and the results of the radioactivity concentration remaining in each U-shaped portion are shown in FIG.
前記７本の伝熱管における前記Ｕ字部分の除染前の放射能濃度は、いずれも略１００［Ｂｑ／ｇ］であった。前記７本の伝熱管それぞれの前記研磨工程における研磨時間を０分、７分、９分、１２分、１４分、１６分及び１８分とした。研磨工程を行った６本の前記伝熱管における前記Ｕ字部分に残留する放射能濃度は１０［Ｂｑ／ｇ］に収束した。図１を見ると、前記研磨工程を一定時間以上行っても、放射能濃度が低下しないことが分かる。この原因は、乾式ブラストによって対象物表面の凹凸の凸部を削り落すことにより金属表面に付着する結晶体及びこの結晶体中の放射性核種は除去されるが、凹部に放射性核種が残るためと考えられる。前記研磨工程後の金属表面は、光沢があり結晶体が残留しているようには見えないが、放射性核種は、質量が微量でも有意な放射能量があり、例えば、Ｃｏ－６０の場合、質量は２．３９×１０－１４ｇで、１Ｂｑの放射能量がある。このため、前記研磨工程における第一粒子（投射材）が到達することのできない凹部に残留する結晶体の影響により一定レベルの放射能濃度が残留し、前記研磨時間を延長しても放射能濃度を低減することができないと考えられる。以上のことから、前記伝熱管に対する研磨時間は、例えば５分と設定することができる。 The radioactivity concentration before decontamination of the U-shaped portions of the seven heat transfer tubes was approximately 100 [Bq/g]. The polishing time in the polishing process for each of the seven heat transfer tubes was 0, 7, 9, 12, 14, 16, and 18 minutes. The concentration of radioactivity remaining in the U-shaped portion of the six heat transfer tubes subjected to the polishing process converged to 10 [Bq/g]. It can be seen from FIG. 1 that the radioactivity concentration does not decrease even if the polishing process is performed for a certain period of time or more. The reason for this is thought to be that although the crystals adhering to the metal surface and the radionuclides in these crystals are removed by scraping off the convexities on the surface of the object by dry blasting, the radionuclides remain in the concave portions. be done. The metal surface after the polishing step is shiny and does not appear to have any crystals remaining, but the radionuclide has a significant amount of radioactivity even if the mass is very small. is 2.39×10 −14 g and has a radioactivity of 1 Bq. For this reason, a certain level of radioactivity concentration remains due to the influence of the crystals remaining in the concave portions where the first particles (projection material) cannot reach in the polishing step, and the radioactivity concentration remains even if the polishing time is extended. cannot be reduced. From the above, the polishing time for the heat transfer tubes can be set at, for example, 5 minutes.
本発明の除染方法は、低コストで簡易かつ効率的に金属表面の放射性核種を除去することができるため、原子力施設の設備更新、廃止などに伴い撤去される金属部材の再利用に好適に利用できる。 The decontamination method of the present invention can easily and efficiently remove radionuclides on metal surfaces at low cost, so it is suitable for reusing metal members that are removed due to equipment renewal or decommissioning of nuclear facilities. Available.
Claims (7)
前記金属部材の表面に研磨用の第一粒子を衝突させる研磨工程を備え、
予め設定された研磨時間で前記研磨工程を終了する汚染金属部材の除染方法。 A method for decontaminating a metal member contaminated with a radionuclide,
A polishing step of colliding the first particles for polishing against the surface of the metal member,
A method for decontaminating a contaminated metal member, wherein the polishing process is completed in a preset polishing time.
前記研磨後測定工程における測定値が予め設定された研磨後閾値以上であると、前記研磨工程と前記研磨後測定工程とを繰り返す請求項１又は請求項２に記載の汚染金属部材の除染方法。 Further comprising a post-polishing measurement step of measuring the density of the radionuclides on the surface of the metal member after the polishing step,
3. The method of decontaminating a contaminated metal member according to claim 1, wherein the polishing step and the post-polishing measurement step are repeated when the measured value in the post-polishing measurement step is equal to or greater than a preset post-polishing threshold value. .
前記研磨前測定工程における測定値が予め設定された研磨前閾値以上の前記金属部材の表面に、前記研磨工程の前に研磨用の第二粒子を衝突させる粗研磨工程と
をさらに備える請求項１、請求項２又は請求項３に記載の汚染金属部材の除染方法。 A pre-polishing measurement step of measuring the density of the radionuclides on the surface of the metal member before the polishing step;
2. A rough polishing step of colliding second particles for polishing before the polishing step with the surface of the metal member whose measured value in the pre-polishing measuring step is equal to or greater than a preset pre-polishing threshold value. A method for decontaminating a contaminated metal member according to claim 2 or 3.
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