JP5602241B2 - Surface decontamination method - Google Patents
Surface decontamination method Download PDFInfo
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- JP5602241B2 JP5602241B2 JP2012541479A JP2012541479A JP5602241B2 JP 5602241 B2 JP5602241 B2 JP 5602241B2 JP 2012541479 A JP2012541479 A JP 2012541479A JP 2012541479 A JP2012541479 A JP 2012541479A JP 5602241 B2 JP5602241 B2 JP 5602241B2
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
- G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
- G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/04—Treating liquids
- G21F9/06—Processing
- G21F9/12—Processing by absorption; by adsorption; by ion-exchange
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/28—Treating solids
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
- G21F9/28—Treating solids
- G21F9/30—Processing
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- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
- Cleaning By Liquid Or Steam (AREA)
- Apparatus For Disinfection Or Sterilisation (AREA)
- Treatment Of Water By Oxidation Or Reduction (AREA)
Description
本発明は、加圧水型原子炉の冷却剤循環路の部材の表面除染方法に関する。冷却剤循環路の主要部分は原子炉圧力容器であり、この原子炉圧力容器内に核燃料を含む燃料要素が配置されている。この原子炉圧力容器には、たいていは、それぞれ１つの冷却剤ポンプ及び１つの蒸気発生器を備えた複数の冷却ループが接続されている。 The present invention relates to a surface decontamination method for a member of a coolant circulation path of a pressurized water reactor. The main part of the coolant circulation path is a reactor pressure vessel, and a fuel element containing nuclear fuel is arranged in the reactor pressure vessel. The reactor pressure vessel is usually connected to a plurality of cooling loops each having one coolant pump and one steam generator.
２８８℃の範囲内の温度を有する加圧水型原子炉の出力運転の条件下で、例えば冷却ループの管系を構成する不銹性オーステナイトのＦｅＣｒＮｉ鋼、例えば蒸気発生の交換管を構成するＮｉ合金、及びその他の、例えば冷却剤ポンプ用に使用される、例えばコバルトを含有する、部材でさえ、水中で所定の溶解度を示す。上記の合金から溶け出した金属イオンは、冷却剤流と共に原子炉圧力容器に達し、この場所で、これらの金属イオンは、この箇所で生じる中性子線により部分的に放射性核種に変換される。これらの核種は、同様に、冷却剤流により全体の冷却剤系中に分散され、運転中に冷却剤系の部材の表面上に形成される酸化物層中に沈積する。運転時間の増加と共に、この沈積される放射性核種の量も増加するため、この冷却剤系の部材表面で放射能又は線量出力が増大する。この酸化物層は、部材のために使用される合金の種類に応じて、主成分として二価及び三価の鉄を有する酸化鉄、及び上述の鋼中に合金成分として存在する他の金属、特にクロム及びニッケル、の酸化物を含む。この場合、ニッケルは常に二価の形（Ｎｉ2+）で存在し、クロムは三価の形（Ｃｒ3+）で存在する。 Under the conditions of power operation of a pressurized water reactor having a temperature in the range of 288 ° C., for example, an austenitic austenitic FeCrNi steel that constitutes the tube system of the cooling loop, for example, an Ni alloy that constitutes a steam generating exchange tube, And even other components, such as those used for coolant pumps, for example containing cobalt, exhibit a certain solubility in water. The metal ions dissolved from the alloy reach the reactor pressure vessel along with the coolant flow, where these metal ions are partially converted to radionuclides by the neutron rays generated at this location. These nuclides are likewise dispersed in the entire coolant system by the coolant stream and deposited in the oxide layer that forms on the surface of the coolant system components during operation. As the operating time increases, so does the amount of radionuclide deposited, increasing the radioactivity or dose output at the surface of the coolant system components. Depending on the type of alloy used for the component, this oxide layer is composed of iron oxide having divalent and trivalent iron as the main component, and other metals present as alloy components in the steel described above, In particular, oxides of chromium and nickel are included. In this case, nickel is always present in the divalent form (Ni 2+ ) and chromium is present in the trivalent form (Cr 3+ ).
この冷却剤系の検査措置、メンテナンス措置、修理措置及び解体措置を行なう前に、従業員の放射線負荷を低下させるために、それぞれの部材及びコンポーネントの放射線を低減する必要がある。この低減は、部材の表面上に存在する酸化物層を除染方法によってできる限り完全に除去することにより行われる。この種の除染の場合に、全体の冷却剤系又はこの冷却剤系から、例えばバルブによって、分離されている部材を、水性洗浄溶液で満たすか又はこの系の個々の部材をこの洗浄溶液を含む個別の容器中で処理する。この酸化物層は、例えば加圧水型原子炉の事例において、クロムを含有する部材の場合に、まず酸化処理され（酸化工程）、引き続き、この酸化物層が、酸性条件下で、いわゆる除染工程において、酸（この酸を、以後、除染酸又は汚染除去酸という）を用いて溶解される。この際に酸化物層から溶液中へ入り込んだ金属イオンを、この溶液をイオン交換器に通すことにより、この溶液から除去することができる。酸化工程の過剰な酸化剤は、還元工程において還元剤の添加により中和、即ち、還元される。除染工程でのこの酸化物層の溶解又は金属イオンの溶出は、従って酸化剤の不在で行われる。この過剰量の酸化剤の還元は独立した処理工程であってもよく、この場合、この洗浄溶液には、還元の目的のためだけに利用する還元剤、例えばアスコルビン酸、クエン酸又は過酸化水素、が過マンガン酸塩イオン及び軟マンガン鉱の還元のために添加される。この過剰量の酸化剤の還元は、しかしながら、除染工程の範囲内でも行なうことができ、この場合、更に、還元剤に加えて、酸化物層の溶解に作用する除染酸、又は、過剰量の酸化剤、例えば、何倍も使用された過マンガン酸塩イオン及びそこから生じる軟マンガン鉱を還元することができる酸、を使用する。上記の場合に、この溶液に、一方で過剰量の酸化剤を中和し且つ他方で酸化物を溶解するのに十分な量の除染酸が、添加される。一般に、十分な成果を達成するために、一連の処理「酸化工程−還元工程−除染工程」又は「酸化工程−還元を同時に行なう除染工程」が数回行われる。この場合、除染工程においては、常に、同じ除染酸又は除染酸の混合物が使用される。 Prior to performing this coolant system inspection, maintenance, repair, and dismantling, it is necessary to reduce the radiation of each member and component in order to reduce the radiation load on the employee. This reduction is performed by removing the oxide layer present on the surface of the member as completely as possible by the decontamination method. In the case of this type of decontamination, the parts which have been separated from the whole coolant system or from this coolant system, for example by means of valves, are filled with an aqueous cleaning solution or the individual parts of this system are filled with this cleaning solution. Process in a separate container containing. This oxide layer is first oxidized (oxidation process) in the case of a member containing chromium, for example in the case of a pressurized water reactor, and then this oxide layer is so-called decontamination process under acidic conditions. In No. 1, the acid is dissolved using an acid (hereinafter referred to as decontamination acid or decontamination acid). At this time, metal ions entering the solution from the oxide layer can be removed from the solution by passing the solution through an ion exchanger. Excess oxidizing agent in the oxidation step is neutralized, that is, reduced by adding a reducing agent in the reduction step. This dissolution of the oxide layer or the elution of metal ions in the decontamination process is thus carried out in the absence of an oxidizing agent. This reduction of excess oxidant may be a separate processing step, in which case the cleaning solution contains a reducing agent utilized only for reduction purposes, such as ascorbic acid, citric acid or hydrogen peroxide. Are added for the reduction of permanganate ions and soft manganites. This reduction of the excess amount of oxidant, however, can also be carried out within the scope of the decontamination process. In this case, in addition to the reducing agent, decontamination acid acting on the dissolution of the oxide layer or excess A quantity of oxidant is used, for example permanganate ions that have been used many times and acids that can reduce the soft manganese ore resulting therefrom. In the above case, a sufficient amount of decontamination acid is added to this solution on the one hand to neutralize the excess of oxidant and on the other hand dissolve the oxide. In general, in order to achieve sufficient results, a series of treatments “oxidation process-reduction process-decontamination process” or “oxidation process-decontamination process that simultaneously performs reduction” is performed several times. In this case, the same decontamination acid or a mixture of decontamination acids is always used in the decontamination step.
この酸化物層の酸化処理は必須である。何故ならば、酸化クロム（ＩＩＩ）及び特にスピネル型の三価のクロムを含有する混合酸化物は、除染のために使用される酸に難溶性であるからである。従って、この溶解性を高めるために、まずこの酸化物層を、Ｃｅ4+、ＨＭｎＯ4、Ｈ2Ｓ2Ｏ8、ＫＭｎＯ4等の酸化剤の水溶液、酸若しくはアルカリ液とＫＭｎＯ4との混合物、又はＯ3で、処理する。この処理の結果として、Ｃｒ（ＩＩＩ）はＣｒ（ＶＩ）に酸化され、これはＣｒＯ4 2-として溶解する。 The oxidation treatment of this oxide layer is essential. This is because mixed oxides containing chromium (III) oxide and especially spinel type trivalent chromium are sparingly soluble in the acid used for decontamination. Therefore, in order to increase the solubility, first the oxide layer, Ce 4+, mixture of HMnO 4, H 2 S 2 O 8, an aqueous solution of KMnO 4 or the like oxidizing agent, an acid or alkali solution and KMnO 4 Or with O 3 . As a result of this treatment, Cr (III) is oxidized to Cr (VI), which dissolves as CrO 4 2− .
除染工程での還元剤の存在により、酸化工程中で生じ、クロム酸塩として洗浄液中に存在するＣｒ（ＶＩ）は、再び、Ｃｒ（ＩＩＩ）に還元される。除染工程の終わりには、この洗浄液中に、Ｃｒ（ＩＩＩ）、Ｆｅ（ＩＩ）、Ｆｅ（ＩＩＩ）、Ｎｉ（ＩＩ）及びその他に、例えばＣｏ−６０等の、放射性同位体が存在する。これらの金属イオンは、この洗浄液からイオン交換体を用いて除去することができる。除染工程において頻繁に使用される除染酸は、シュウ酸である。何故ならば、このシュウ酸によって、部材表面から除去した酸化物層を溶解できるためである。 Due to the presence of the reducing agent in the decontamination process, Cr (VI) that is generated in the oxidation process and exists in the cleaning liquid as chromate is reduced again to Cr (III). At the end of the decontamination process, radioisotopes, such as Co-60, are present in the cleaning solution, such as Cr (III), Fe (II), Fe (III), Ni (II) and others. These metal ions can be removed from the cleaning liquid using an ion exchanger. A decontamination acid frequently used in the decontamination process is oxalic acid. This is because the oxide layer removed from the surface of the member can be dissolved by the oxalic acid.
しかしながら、シュウ酸は、Ｎｉ2+、Ｆｅ2+、Ｃｏ2+、Ｃｕ2+等の二価の金属イオンとの間で難溶性のシュウ酸塩沈殿物を生じ、このシュウ酸塩沈殿物が全体の冷却剤系に分散され、配管及びコンポーネント、例えば蒸気発生器、の内壁に沈着するという欠点がある。このため、これらの沈殿物が方法全体の遂行を困難にしている。溶液の種々の有機成分は、酸化剤による処理及びＵＶ照射によって、二酸化炭素及び水に変換され、それによりこの溶液から除去される。しかしながら、この沈殿物により、溶液は曇り、ＵＶ照射の有効性は、かなり低下してしまう。同様に、放射性核種の共沈が生じ、従って部材表面の再汚染が起こる。この再汚染の危険は、体積に対する表面積の割合の大きいコンポーネントの場合に、特に著しい。これには、特に、小さな直径を有する極めて多数の交換器管を有している蒸気発生器が該当する。シュウ酸を使用することの他の欠点は、シュウ酸塩沈殿物が濾過装置、例えばイオン交換器の前方に配置されたフィルター及び循環ポンプの多孔板又は保護フィルター、を閉塞しかねないことである。更なる欠点は、結局、上述の酸化工程及び除染工程からなる処理サイクルを繰り返すこと、つまり除染工程に引き続き新たな酸化工程を行なうこと、にある。先行する除染工程中でシュウ酸塩沈殿物が生じる場合に、相応する金属イオン、例えばシュウ酸ニッケル沈殿物の場合のＮｉ、は、イオン交換体を用いて洗浄液から除去することはできない。この結果、引き続く酸化工程で、この沈殿物のシュウ酸塩残基は、二酸化炭素と水とに酸化され、これにより酸化剤は消費されて役に立たなくなる。それに対して、このシュウ酸塩が溶液中に存在する場合、つまり、沈殿物の形で結合されていない場合、には、このシュウ酸塩は、例えば洗浄液をイオン交換体に通す前に、簡単で低コストの方法で、例えばＵＶ光を用いて、簡単に、破壊する、例えば二酸化炭素と水とに転換する、ことができる。要するに、シュウ酸塩沈殿物により生じる濁りが、例えば測光による、この方法の監視を損なうことが欠点である。 However, oxalic acid produces a slightly soluble oxalate precipitate with divalent metal ions such as Ni 2+ , Fe 2+ , Co 2+ , and Cu 2+. It has the disadvantage of being distributed over the entire coolant system and depositing on the inner walls of pipes and components such as steam generators. For this reason, these precipitates make it difficult to carry out the entire process. The various organic components of the solution are converted to carbon dioxide and water by treatment with an oxidant and UV irradiation, and thereby removed from the solution. However, this precipitate causes the solution to become cloudy and the effectiveness of UV irradiation is significantly reduced. Similarly, radionuclide co-precipitation occurs, thus causing recontamination of the member surface. This risk of recontamination is particularly significant for components with a high surface area to volume ratio. This applies in particular to steam generators with a very large number of exchanger tubes having a small diameter. Another disadvantage of using oxalic acid is that oxalate precipitates can block filtration devices such as filters placed in front of ion exchangers and perforated plates or protective filters of circulation pumps. . A further disadvantage is that, after all, the treatment cycle consisting of the above-mentioned oxidation process and decontamination process is repeated, that is to say that a new oxidation process is carried out following the decontamination process. If an oxalate precipitate occurs in the preceding decontamination process, the corresponding metal ions, such as Ni in the case of nickel oxalate precipitates, cannot be removed from the cleaning liquid using an ion exchanger. As a result, in the subsequent oxidation step, the oxalate residue of the precipitate is oxidized to carbon dioxide and water, thereby consuming the oxidant and making it useless. On the other hand, if the oxalate is present in the solution, i.e. not bound in the form of a precipitate, the oxalate can be easily removed, e.g. before passing the washing solution through the ion exchanger. In a low-cost way, it can easily be destroyed, for example converted into carbon dioxide and water, for example using UV light. In short, it is a disadvantage that the turbidity caused by the oxalate precipitate impairs the monitoring of this method, for example by photometry.
このことを前提として、本発明の課題は、上記の欠点が改善された除染方法を提供することにある。 On the premise of this, an object of the present invention is to provide a decontamination method in which the above drawbacks are improved.
上記課題は、請求項１に記載の２つの段階を有する除染方法により解決される。 The above problem is solved by a decontamination method having two steps according to claim 1.
第１の段階では、酸化工程、還元工程及びそれに引き続く第１の除染工程を有する少なくとも１つの処理サイクルを実施する。この種の処理サイクルは、部材表面上での酸化物形成の規模及び種類に応じて、１回だけ又は数回実施することができる。酸化工程では、酸化物層中に含まれる三価クロムを六価クロムに変換させるのに十分な酸化力を有する酸化剤を含有する水性洗浄液で、この部材を処理する。既に上述したように、この工程により、部材上に存在する酸化物層の溶解性が高められる。還元工程では、還元剤を含有する溶液でこの部材を処理して、酸化工程からの過剰の酸化剤を還元する。第１の除染工程では、例えばシュウ酸の場合にそうであるような、溶液中に含まれる金属イオン、特にＮｉ（ＩＩ）、Ｆｅ（ＩＩ）、Ｃｏ（ＩＩ）及びＭｎ（ＩＩ）等の二価の金属イオン、との間で難溶性沈殿物を形成するということがない少なくとも１種の除染酸を、もっぱら又は優勢な割合で、つまり５０モル％よりも多くの割合で、含有する水溶液で、この部材を処理する。三価以上の酸との間でも難溶性沈殿物を形成しない除染酸を使用するのが有利であり、これには、問題の除染のために通常使用されている酸、例えばギ酸及びグリオキシル酸、が該当する。この方法によれば、特に難溶性のシュウ酸ニッケル沈殿物の形成が抑制される。除染工程の間に又は終わりに、この溶液は、その中に含まれる、酸化物層及び／又は部材の基材金属に由来する金属イオンの除去のためにイオン交換体に通される。 In the first stage, at least one treatment cycle having an oxidation process, a reduction process and a subsequent first decontamination process is performed. This type of treatment cycle can be performed only once or several times depending on the scale and type of oxide formation on the component surface. In the oxidation step, the member is treated with an aqueous cleaning solution containing an oxidizing agent having an oxidizing power sufficient to convert trivalent chromium contained in the oxide layer into hexavalent chromium. As already mentioned above, this step enhances the solubility of the oxide layer present on the member. In the reduction step, this member is treated with a solution containing a reducing agent to reduce excess oxidant from the oxidation step. In the first decontamination step, for example as in the case of oxalic acid, the metal ions contained in the solution, in particular Ni (II), Fe (II), Co (II) and Mn (II) etc. Contains at least one decontamination acid that does not form a sparingly soluble precipitate with the divalent metal ion, either exclusively or in a predominant proportion, ie in proportions greater than 50 mol%. The member is treated with an aqueous solution. It is advantageous to use decontamination acids that do not form sparingly soluble precipitates with trivalent or higher acids, which include acids commonly used for decontamination in question, such as formic acid and glyoxyl Acid. According to this method, the formation of a particularly insoluble nickel oxalate precipitate is suppressed. During or at the end of the decontamination process, this solution is passed through an ion exchanger for the removal of metal ions contained therein from the oxide layer and / or the base metal of the component.
この還元工程及び除染工程は、既に説明したように、一緒に又は同時に実施することもできる。 This reduction step and decontamination step can also be performed together or simultaneously as already described.
第１の段階で、提案された方法で、難溶性沈殿物の形成の危険を生じることなしに、難溶性沈殿物の形成に関して危険な金属イオン、つまり特にＮｉ（ＩＩ）、Ｆｅ（ＩＩ）及びＣｏ（ＩＩ）、のかなりの部分を洗浄液から、ひいては除染すべき部材表面から除去することができる。今や、第２の段階において、特に酸化物層中に存在するＦｅ（ＩＩＩ）及びＦｅ（ＩＩ）を溶出させるために高効率のシュウ酸を問題なく使用できる、第２の除染工程を実施する可能性が提供される。何故ならば、この洗浄液中には、危険な二価のイオン、特にＮｉ（ＩＩ）、は、もはや存在しないか又は沈殿を引き起こす濃度では存在しないからである。本発明方法の場合、従って２つの異なる除染態様を適用し、その際、第１の態様又は第１の除染工程で難溶性のシュウ酸塩沈殿物を形成するイオンを除去し、次いで、残留するＦｅ（ＩＩＩ）、Ｆｅ（ＩＩ）イオン等を、酸化物溶解に関して効率の高いシュウ酸を用いて溶解させることができる。この場合、酸化物層からのＦｅ（ＩＩ）又はＦｅ（ＩＩＩ）の溶解のために第１の段階で添加された「危険でない」除染酸が有効であるか否かは重要でない。何故ならば、これは第２の段階で、シュウ酸を用いて有効な方法で、行なうことができるためである。 In the first stage, the proposed method does not pose a risk of the formation of sparingly soluble precipitates, but dangerous metal ions, in particular Ni (II), Fe (II) and A significant portion of Co (II) can be removed from the cleaning liquid and thus from the surface of the member to be decontaminated. Now, in the second stage, a second decontamination process is carried out, in which high-efficiency oxalic acid can be used without problems, in particular to elute Fe (III) and Fe (II) present in the oxide layer. The possibility is offered. This is because dangerous divalent ions, particularly Ni (II), are no longer present or present at concentrations that cause precipitation in the cleaning solution. In the case of the method according to the invention, therefore, two different decontamination aspects are applied, in which the ions forming the sparingly soluble oxalate precipitate in the first aspect or the first decontamination step are removed, Residual Fe (III), Fe (II) ions, etc. can be dissolved using oxalic acid, which is highly efficient with respect to oxide dissolution. In this case, it is immaterial whether the “non-hazardous” decontamination acid added in the first stage is effective for the dissolution of Fe (II) or Fe (III) from the oxide layer. This is because, in the second stage, this can be done in an effective manner using oxalic acid.
第２の除染工程では、シュウ酸だけを使用するのが有利である。しかしながら、１種以上の他の除染酸との混合物を使用することも考えられ、この場合、しかしながら、シュウ酸が優勢である、つまり、５０モル％以上存在する。 In the second decontamination step, it is advantageous to use only oxalic acid. However, it is also conceivable to use a mixture with one or more other decontaminating acids, in which case oxalic acid is predominant, ie 50 mol% or more is present.
従って、要約すれば、本発明方法は、除染の有効性を損なうことなく、難溶性沈殿物の形成を抑制するか又は少なくとも著しく低下させる可能性を提供する。 Therefore, in summary, the method of the present invention offers the possibility of suppressing or at least significantly reducing the formation of sparingly soluble precipitates without compromising the effectiveness of decontamination.
この方法は、第１の段階で、先ず、少なくとも１つの処理サイクルを実施し、引き続く第２の段階で、第２の除染工程を、前記の酸化なしに、部材表面に実施する、つまり、この部材の酸化物層をシュウ酸で処理するように、実施することができる。しかしながら、第２の段階において、酸化物層を、先ず、例えば上記の他の酸化剤で処理し、次いで、初めてこの酸化物層のシュウ酸による溶解を実施することも考えられる。この場合、勿論、同様に、上述のように、更に還元工程が必要である。 In the first stage, the method first carries out at least one treatment cycle, and in the second stage that follows, the second decontamination step is carried out on the component surface without said oxidation, i.e. This can be done by treating the oxide layer of this member with oxalic acid. However, in the second stage, it is also conceivable to treat the oxide layer first, for example with the other oxidants mentioned above, and then to dissolve this oxide layer with oxalic acid for the first time. In this case, of course, similarly, as described above, a further reduction step is required.
第１の除染工程では有機酸を使用するのが有利である。何故ならば、この有機成分は、それが炭素、水素及び酸素からなる限り、二酸化炭素と水とに変換され、それにより実質的に残留物なく除去することができる。何故ならば、二酸化炭素は、この溶液からガスとして出て行くからである。この有機成分の除去は、過酸化水素等の酸化剤が添加された溶液にＵＶ光を照射する、自体公知の方法で、行われる。もっぱら炭素、水素及び酸素だけからなる酸を使用するのが有利である。その結果、イオン交換体を用いて、そして、二次廃棄物（廃棄処理しなければならない付加的な交換材料）を生じさせながら、除去しなければならない窒素のような元素は、溶液中には残留しない。 It is advantageous to use an organic acid in the first decontamination step. This organic component can be converted to carbon dioxide and water, so long as it consists of carbon, hydrogen and oxygen, and thereby be removed substantially without residue. This is because carbon dioxide leaves the solution as a gas. This removal of the organic component is performed by a method known per se, in which a solution to which an oxidizing agent such as hydrogen peroxide is added is irradiated with UV light. Preference is given to using acids consisting exclusively of carbon, hydrogen and oxygen. As a result, elements such as nitrogen that must be removed using ion exchangers and producing secondary waste (additional exchange material that must be disposed of) are not in solution. Does not remain.
多くの国々、例えば日本では、除染処置の過程において、上述の種類のイオン交換体を、錯生成する酸又はこのような酸の錯体で、処理することは、許されない。従って、この場合、金属イオンとの間で錯化合物を形成しない酸を使用することが有利である。 In many countries, such as Japan, it is not permitted to treat the above-mentioned types of ion exchangers with complexing acids or complexes of such acids during the decontamination process. Therefore, in this case, it is advantageous to use an acid that does not form a complex compound with the metal ion.
第１の除染工程で、最大で２つの炭素原子を有する酸を使用するのが有利である。このような酸の二酸化炭素と水とへの分解は、３つ以上の炭素原子を有する酸の分解よりもより迅速に進行し、その結果、時間、エネルギー及び酸化剤を、最終的にコストを、節約することができる。 In the first decontamination step, it is advantageous to use an acid having a maximum of two carbon atoms. Such decomposition of acids into carbon dioxide and water proceeds more rapidly than decomposition of acids having 3 or more carbon atoms, resulting in time, energy and oxidant costs that are ultimately reduced. Can be saved.
第１の段階での除染工程のために、ＨＮＯ3、ＨＢＦ4及びＨ2ＳＯ4等の無機酸；ギ酸、酢酸、モノヒドロキシ酢酸及びジヒドロキシ酢酸等の錯生成しないモノカルボン酸；ＥＤＴＡ、ニトリロ三酢酸及びタルトロン酸等の錯生成酸；が適している。廃棄物回避の観点で有利なのは、ギ酸及びグリオキシル酸であり、この場合、第１の段階でグリオキシル酸だけを使用するときに、最良の除染係数が達成された。この酸は、金属イオン、特に酸化物層のニッケル、との間で、可溶性の塩を形成する。このような塩を含む溶液をカチオン交換体に通す場合、この金属イオンは留め置かれ、酸アニオンは溶液中に残留し、上述のように、後で、残留物なしに酸化分解することができる。例えば、窒素原子を含有するグリシン又は無機酸の場合には、これは該当しない。 For the decontamination process in the first stage, inorganic acids such as HNO 3 , HBF 4 and H 2 SO 4 ; non-complexed monocarboxylic acids such as formic acid, acetic acid, monohydroxyacetic acid and dihydroxyacetic acid; EDTA, nitrilo Complexing acids such as triacetic acid and tartronic acid are suitable. Advantageous in terms of waste avoidance are formic acid and glyoxylic acid, where the best decontamination factor was achieved when using only glyoxylic acid in the first stage. This acid forms a soluble salt with metal ions, particularly nickel in the oxide layer. When a solution containing such a salt is passed through a cation exchanger, the metal ions are retained and the acid anion remains in the solution and can later be oxidatively decomposed without residue as described above. . For example, this is not the case for glycine or inorganic acids containing nitrogen atoms.
この提案された方法の有効性を試すために、加圧水型原子炉の一次循環系からの試料を用いて試験を実施する（表１参照）。この試料を、容器中で１リットルの体積でかつ約９０℃の温度を有する洗浄液中に浸漬する。更に、上述のように、１つの除染方法では、酸化物層から溶け出した金属イオンを、イオン交換体を用いて、洗浄液から除去する。簡素化のために、この試験では、イオン交換を実施せず、それぞれの洗浄溶液を処理サイクル（酸化工程及び除染工程）の終わりに廃棄し、新たな洗浄液を使用した。次に記載する全ての方法では、酸性領域、約ｐＨ値２、で作業する。 In order to test the effectiveness of the proposed method, a test is carried out using samples from the primary circulation system of a pressurized water reactor (see Table 1). The sample is immersed in a cleaning solution having a volume of 1 liter and a temperature of about 90 ° C. in a container. Further, as described above, in one decontamination method, metal ions dissolved from the oxide layer are removed from the cleaning liquid using an ion exchanger. For simplicity, in this test, no ion exchange was performed and each cleaning solution was discarded at the end of the treatment cycle (oxidation and decontamination steps) and a new cleaning solution was used. All the methods described below operate in the acidic region, about pH value 2.
表１〜３による試料を用いて、それぞれ３つの処理サイクルを行なう３つの異なる方法態様を実施する。各処理サイクルは、１つの酸化工程及び１つの除染工程を有する。酸化物層の酸化のために、この試料を含む容器をＨＭｎＯ4溶液（濃度＝２４０ｐｐｍ）で満たす。作用時間は、それぞれ１６時間である。最初の２つのサイクルでは、除染工程のために、シュウ酸は使用せず、ギ酸及び／又はグリオキシル酸を使用する（表１〜３を参照）。それぞれの酸化工程の後で、過剰の酸化剤（ＨＭｎＯ4）を、相応する量の還元剤の添加により中和し、引き続き、それぞれ除染工程で使用された酸を添加する。除染工程での酸の作用時間は、それぞれ５時間である。 Using the samples according to Tables 1 to 3, three different method embodiments are carried out, each carrying out three treatment cycles. Each treatment cycle has one oxidation step and one decontamination step. For the oxidation of the oxide layer, the container containing this sample is filled with a HMnO 4 solution (concentration = 240 ppm). The working time is 16 hours each. In the first two cycles, oxalic acid is not used for the decontamination process, but formic acid and / or glyoxylic acid is used (see Tables 1-3). After each oxidation step, excess oxidant (HMnO 4 ) is neutralized by the addition of a corresponding amount of reducing agent, followed by the acid used in each decontamination step. The action time of the acid in the decontamination process is 5 hours each.
この試料について、それぞれ最初のＣｏ６０−ガンマ放射能及び除染工程の後に存在するＣｏ６０ガンマ放射能（ベクレル即ちＢｑ）を測定し、この全体の除染係数（ＤＦ）、つまり試料の最初の放射能の、サイクルの後に存在する放射能に対する、比率を決定する。この結果は、表４にまとめられている。 For this sample, the initial Co60-gamma activity and the Co60 gamma activity (becquerel or Bq) present after the decontamination step are measured, respectively, and this overall decontamination factor (DF), ie the initial activity of the sample. Of the radioactivity present after the cycle is determined. The results are summarized in Table 4.
この結果の評価では、一般に約１０の除染係数で既に十分であることを考慮しなければならない。このような係数は、第２サイクルの後に既に達成される。更に、グリオキシル酸が、除染又は酸化物層の溶解のために、特にこの第１の段階での複数の、有利には全ての、除染サイクルにおいてこの酸を用いて作用する場合に、最も有効であることが確認される。 In assessing this result, it should be taken into account that a decontamination factor of approximately 10 is generally sufficient. Such a factor is already achieved after the second cycle. Furthermore, glyoxylic acid is most suitable for decontamination or dissolution of the oxide layer, in particular when it acts with this acid in several, preferably all, decontamination cycles in this first stage. It is confirmed that it is effective.
上記の、本発明による方法に従った試験では、有機酸の例として、グリオキシル酸及びギ酸を使用した。しかしながら、この第１の段階の除染工程のためには、無機酸も適している。この有効性を証明するために、上記の試料に相当するサイズの、加圧水型原子炉の一次循環系からの試料を、酸化工程及び除染工程からなる１つのサイクルにかける試験を実施する。６００ｍｌの洗浄液の体積及び約９５℃の温度で、先ず、試料上に存在する酸化物層の酸化を、ＨＭｎＯ4（３００ｐｐｍ）で、２０時間の期間で実施する。この段階の後に存在する残りの酸化剤を、過酸化水素及び硝酸からなる混合物で中和するが、その際、前者は酸化工程でＨＭｎＯ4から形成される軟マンガン鉱（ＭｎＯ2）を溶解させるために必要である。引き続き、５時間の除染を行い、この場合に、既に溶液中に含まれる硝酸（ＨＮＯ3）が、除染酸として、つまり、試料上に存在する酸化物層の溶解のために、作用する。この除染工程の後に、試料のガンマ放射能は、２．１８Ｅ＋４Ｂｑの値に低下する。この試料の初めの放射能６．８８Ｅ＋４Ｂｑと比較して、これは、３．１６の除染係数を意味する。 In the tests according to the method according to the invention described above, glyoxylic acid and formic acid were used as examples of organic acids. However, inorganic acids are also suitable for this first stage decontamination process. In order to prove this effectiveness, a test is performed in which a sample from the primary circulation system of a pressurized water reactor having a size corresponding to the above sample is subjected to one cycle consisting of an oxidation step and a decontamination step. First, the oxidation of the oxide layer present on the sample is carried out with HMnO 4 (300 ppm) over a period of 20 hours, with a volume of 600 ml of cleaning solution and a temperature of about 95 ° C. The remaining oxidant present after this stage is neutralized with a mixture of hydrogen peroxide and nitric acid, where the former dissolves soft manganese ore (MnO 2 ) formed from HMnO 4 in the oxidation process. Is necessary for. Subsequently, decontamination is carried out for 5 hours. In this case, nitric acid (HNO 3 ) already contained in the solution acts as decontamination acid, that is, for dissolution of the oxide layer present on the sample. . After this decontamination step, the gamma activity of the sample is reduced to a value of 2.18E + 4Bq. Compared to the initial radioactivity of 6.88E + 4Bq for this sample, this means a decontamination factor of 3.16.
Claims (10)
− 第１の段階では、酸化工程、還元工程及びそれに引き続く第１の除染工程を有する少なくとも１つの処理サイクルを実施し、その際、
−− 前記酸化工程では、前記部材を、前記酸化物層中に含まれる三価クロムを六価クロムに変換させる酸化剤を含有する水溶液で、処理し、
−− 前記還元工程では、前記部材を、前記酸化工程からの過剰量の酸化剤を還元する還元剤を含有する水溶液で、処理し、
−− 前記第１の除染工程では、前記部材を、前記水溶液中に含まれる金属イオンとの間で難溶性沈殿物を形成しない少なくとも１種の除染酸を、５０モル％よりも多くの割合で、含有する水溶液で、処理し、そして
−− 前記溶液を、前記酸化物層又は前記部材の基材金属に由来する、前記溶液中に含まれる金属イオンの除去のために、イオン交換体に通し、
− 第２の段階では、前記部材を、除染酸としてシュウ酸を５０モル％よりも多くの割合で含有する水溶液で、処理する第２の除染工程を有する少なくとも１回の処理サイクルを実施する。 A method of chemically decontaminating a surface having an oxide layer of a metal member of a primary circulation system of a pressurized water reactor, which is divided into two stages and configured as follows.
-In the first stage, carrying out at least one treatment cycle comprising an oxidation step, a reduction step and a subsequent first decontamination step,
-In the oxidation step, the member is treated with an aqueous solution containing an oxidizing agent that converts trivalent chromium contained in the oxide layer into hexavalent chromium,
-In the reduction step, the member is treated with an aqueous solution containing a reducing agent that reduces an excessive amount of the oxidizing agent from the oxidation step,
- In the first decontamination step, the member, at least one decontamination acid does not form a sparingly soluble precipitate with the metal ions contained in the aqueous solution, more than 50 mole% at a rate of, an aqueous solution containing, processed, and - the solution, said also oxide layer from the substrate metal of the member, for removal of metal ions contained in the solution, ion Through the exchanger,
-In the second stage, the member is subjected to at least one treatment cycle having a second decontamination step of treating the member with an aqueous solution containing oxalic acid as a decontamination acid in a proportion of more than 50 mol%. To do.
Formic acid or characterized by the use of glyoxylic acid A method according to claim 6.
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2010
- 2010-12-01 EP EP10795259A patent/EP2417606B1/en not_active Not-in-force
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- 2010-12-01 JP JP2012541479A patent/JP5602241B2/en not_active Expired - Fee Related
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| CA2755288A1 (en) | 2011-06-09 |
| EP2417606B1 (en) | 2013-02-20 |
| EP2417606A1 (en) | 2012-02-15 |
| ZA201106436B (en) | 2012-08-29 |
| JP2013513098A (en) | 2013-04-18 |
| DE102009047524A1 (en) | 2011-06-09 |
| KR20120057568A (en) | 2012-06-05 |
| CN102405500A (en) | 2012-04-04 |
| US20120138086A1 (en) | 2012-06-07 |
| WO2011067271A1 (en) | 2011-06-09 |
| TW201131581A (en) | 2011-09-16 |
| ES2404895T3 (en) | 2013-05-29 |
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