JP3838909B2 - Method for preventing corrosion of structural materials for liquid metal coolant - Google Patents

Method for preventing corrosion of structural materials for liquid metal coolant Download PDF

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JP3838909B2
JP3838909B2 JP2001388855A JP2001388855A JP3838909B2 JP 3838909 B2 JP3838909 B2 JP 3838909B2 JP 2001388855 A JP2001388855 A JP 2001388855A JP 2001388855 A JP2001388855 A JP 2001388855A JP 3838909 B2 JP3838909 B2 JP 3838909B2
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liquid metal
structural material
oxygen concentration
dissolved oxygen
coolant
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JP2003185787A (en
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尚志 延永
勤也 鎌田
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Mitsui Engineering and Shipbuilding Co Ltd
Mitsui E&S Holdings Co Ltd
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Mitsui Engineering and Shipbuilding Co Ltd
Mitsui E&S Holdings Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Description

【０００１】
【発明の属する技術分野】
本発明は、液体金属冷却材用構造材の腐食防止方法に関するもので、特に、液体金属と接触する構造材表面に液体金属に対して健全性を有する保護被膜を安定的、かつ、持続的に形成させる方法に関するものである。
【０００２】
【従来の技術】
液体金属は、熱や放射線に対して安定であり、また、熱伝導性が優れていることから冷却材として使用されている。その代表的な例が高速増殖炉の液体Ｎａ金属である。このような目的に用いられる金属は、主として、Ｎａ，Ｎａ−Ｋ，Ｌｉ，Ｂｉ，Ｐｂなどの低融点金属であるが、こうした液体金属を冷却材として使用する場合、液体金属による機器や配管などの構造材の腐食が問題となる。
【０００３】
液体金属による腐食は、水溶液などの腐食にみられる電気化学過程ではなく、金属元素の液体金属中への溶解が主原因である。したがって、冷却材として使われる液体金属がその熱回収のために、高温部と低温部を循環する場合、高温部で構造材から溶解した元素が低温部で過飽和となり析出する、いわゆる質量移動現象が生じる。
【０００４】
この質量移動は、繰り返され、機器、配管などの構造材は腐食され続け、低温部では不純物が析出し、小口径配管などの液体金属流路を閉塞させる恐れもある。溶解速度を支配するのは、高温部での不飽和度によるが、ループの構成、形状などの装置の状況、流量、温度、温度差、表面粗さ、不純物濃度などの多種多様な条件で左右される。中でも液体金属中の不純物、特に、溶解酸素濃度は、腐食現象および速度に大きく影響を及ぼすことが知られている。
【０００５】
高速増殖炉のＮａ冷却材の場合、Ｎａの酸化物標準生成自由エネルギー（酸素ポテンシャル）の絶対値は、鋼材の主要元素（Ｆｅ，Ｎｉ，Ｃｒ）や、一般的な合金元素の酸化物標準生成自由エネルギーの絶対値より大きい。すなわち、液体Ｎａと接触している構造材表面は還元され、Ｎａは酸化される傾向にある。
【０００６】
したがって、構造材の腐食条件は、本質的にそれら主要元素の液体Ｎａ中への溶解度によって決定される。構造材主要元素の液体Ｎａ中への溶解度は比較的小さいことが知られているが、液体Ｎａ中の溶解酸素濃度の増加とともに腐食速度が増大することが分かっている。構造材がステンレス鋼の場合、成分元素のＣｒ，Ｎｉが高温部で溶出し、低温部で析出する。そして、Ｎａ中の酸素濃度が高いとＣｒの溶出が促進されると言われている。
【０００７】
したがって、構造材の腐食防止は、液体金属冷却材の実用化にとって非常に重要となってくる。
【０００８】
従来の液体金属冷却材用構造材の腐食防止方法については、その方法の１つにコールドトラップ法がある。この方法は、金属液体中の不純物を除去する精製法の一種であり、不純物の溶解度が低温で小さくなる性質を利用して、金属液体中の酸素、炭素などの不純物を低温下でいろいろな化合物の形（反応生成物）で析出除去し、分離回収する方法である。Ｎａの場合、コールドトラップでＮａ中の溶解酵素濃度を１０ｐｐｍ以下程度まで低減でき、ステンレス鋼及びＦｅ，Ｃｒ，Ｎｉ，Ｃｏ，Ｍｏなどとの両立性を図っている。
【０００９】
また、別の方法として、ホットトラップ法がある。この方法は、コールドトラップで得られる純度よりも更に高い純度を得たい時に用いられ、高温で酸素等の不純物とよく結合する金属ゲッターに液体金属を通して、液体金属中の不純物を金属ゲッターと反応させてゲッター中に固定除去する方法である。例えば、液体Ｎａ中の酸素に対して、酸化ナトリウムよりも安定な酸化物を生成する金属として、Ｔｉ，Ｚｒ及びＴｉ−Ｚｒ合金などが用いられ、約６００℃の液体Ｎａ中の溶解酸素濃度を数ｐｐｍ以下に管理できている。
【００１０】
【発明が解決しようとする課題】
しかしながら、従来の液体金属冷却材用構造材の腐食防止方法は、液体金属中の溶解酸素濃度の上限を制御するものである。しかし、このような腐食防止方法は、液体金属の種類によっては以下のような不都合を生じる。
【００１１】
例えば、液体金属にＰｂ−Ｂｉを使用した場合、液体Ｐｂ−Ｂｉに対する構造材主要元素の溶解度が大きく、液体Ｐｂ−Ｂｉ中の溶解酸素濃度を減少させるだけでは構造材の腐食を防止することが困難であるという問題が生じる。すなわち、溶解酸素濃度が小さ過ぎても反って構造材の腐食を加速させるという問題がある。
【００１２】
上記の問題点を回避するため、構造材の溶解速度を減少させる方法として、インヒビターの添加により構造材表面に保護被膜を形成させる方法があるが、この場合、保護被膜が厚く成長し過ぎると膜剥がれや熱衝撃によるクラックが発生し、こうした部分を基点に局部的に腐食が進行するといった問題があった。したがって、Ｐｂ，Ｂｉのような構造材主要元素の溶解度が大きい液体金属の冷却材への適用は、従来技術では十分な腐食防止ができていなかった。
【００１３】
そこで、本発明は、このような問題点を解決するもので、その目的とするところは、液体金属中の溶解酸素濃度を制御することにより、液体金属と接触する構造材表面に液体金属に対して健全性を有する保護皮膜を安定的、かつ、持続的に形成させ、構造材に対して高い腐食性を示す液体金属においても腐食を防止することが可能な液体金属冷却材用構造材の腐食防止方法を提供することにある。また、上記の問題解決ばかりでなく新たなデバイスの創造に寄与するところにある。
【００１４】
【課題を解決するための手段】
上記目的は、下記（１）〜（６）により達成される。すなわち、
（１） 本発明は、液体金属を収納して冷却を行う液体金属冷却材用構造材において、前記液体金属と接触する前記液体金属冷却材用構造材の表面に、少なくとも前記液体金属冷却材用構造材の構造元素からなる酸化被膜を形成させるとともに、前記液体金属中の溶解酸素濃度を１０ -7 mass ％〜１０ -5 mass ％の範囲に管理することにより、前記酸化被膜の安定性および持続性を維持することを特徴とする液体金属冷却材用構造材の腐食防止方法である。
【００１５】
（２） 本発明は、前記液体金属冷却材用構造材に溶解酸素濃度測定センサーと温度センサーとを配置し、前記溶解酸素濃度測定センサーの測定値と前記温度センサーの測定値から前記液体金属中の溶解酸素濃度を演算し、この演算で求めた液体金属中の溶解酸素濃度と予め設定した溶解酸素濃度とを比較して液体金属中の溶解酸素濃度を随時調整し、液体金属中の溶解酸素濃度を１０ -7 mass ％〜１０ -5 mass ％の範囲に管理することを特徴とする上記（１）記載の液体金属冷却材用構造材の腐食防止方法である。
【００１６】
（３） 前記液体金属が鉛（Ｐｂ）、ビスマス（Ｂｉ）、鉛−ビスマス合金（Ｐｂ−Ｂｉ）であることを特徴とする上記（１）記載の液体金属冷却材用構造材の腐食防止方法である。
【００１７】
（４）本発明は、前記液体金属の温度範囲が前記液体金属の融点〜６５０℃であることを特徴とする上記（１）、（２）又は（３）記載の液体金属冷却材用構造材の腐食防止方法である。
【００１８】
（５）本発明は、前記液体金属冷却材用構造材が低合金鋼、特殊鋼、炭素鋼であることを特徴とする上記（１）記載の液体金属冷却材用構造材の腐食防止方法である。
【００１９】
（６） 前記溶解酸素濃度測定センサーが固体電解質酸素センサーであることを特徴とする請求項２記載の液体金属冷却材用構造材の腐食防止方法である。
【００２２】
【発明の実施の形態】
以下、本発明の液体金属冷却材用構造材の腐食防止方法の実施の形態について説明する。本発明の液体金属冷却材用構造材の腐食防止方法においては、液体金属中の溶解酸素濃度を制御することにより、液体金属と接触する構造材表面に液体金属に対して健全性を有する保護被膜を安定的、かつ、持続的に形成させ、構造材に対して高い腐食性を示す液体金属においても腐食を防止する。
【００２３】
液体金属中の溶解酸素濃度は、溶解酸素濃度測定センサーの測定値と温度センサーの測定値から演算し、その演算した値をフィードバックし、溶解酸素濃度が予め設定された管理下限以下になった時、酸化処理により自動的に溶解酸素濃度を増加させ、そして、予め設定された管理上限以上になった時、還元処理により自動的に溶解酸素濃度を減少させることにより液体金属中の溶解酸素濃度を制御し、保護被膜を形成、維持させる。
【００２４】
次に、液体金属中の溶解酸素濃度と構造材の酸化被膜の関係に関して説明する。熱力学的観点、すなわち、酸化物の標準生成自由エネルギーの比較から、本発明に係る主な液体金属成分および構造材主要成分の酸化物の安定性の序列は、酸化ケイ素＞酸化クロム＞酸化モリブデン＞酸化鉄＞酸化鉛＞酸化ビスマスの順である。これを基に液体金属及び構造材主要成分と酸素との相互作用による腐食性について、液体金属中の溶解酸素濃度レベルにより大きくは次の３つの場合に分類される。すなわち、
（ａ） 液体金属の溶解酸素濃度レベルが十分に低く、鉄が酸化されないような条件では、液体金属化に鉄が溶解し、構造材の腐食は進行する。
【００２５】
（ｂ） 液体金属中の溶解酸素濃度レベルが高くなり、鉄が酸化されるような条件では、酸化鉄、酸化クロム、鉄クロム複合酸化物等の酸化被膜が生成され、これらの酸化被膜は液体金属中で安定な保護被膜となり腐食が防止される。
【００２６】
（ｃ） 液体金属中の溶解酸素濃度レベルが更に高くなり、鉛が酸化されるような条件では、酸化鉛のスラグが液体金属中に発生し、冷却機能の悪化、配管のプラグ等を生じる。更に酸化被膜が厚く成長し過ぎて膜剥がれや熱衝撃によるクラックが発生し易くなり、こうした部分を基点に局部腐食が進行する。
【００２７】
したがって、本発明の液体金属冷却材用構造材の腐食防止方法においては、基本的に上記（ｂ）の条件、すなわち、鉄は酸化されて、鉛は酸化されないような溶解酸素濃度に制御すればよいことになる。
【００２８】
本発明の液体金属冷却材用構造材の腐食防止方法における液体金属としては、Ｐｂ系金属、Ｂｉ系金属、Ｐｂ−Ｂｉ系合金が挙げられる。
【００２９】
つぎに、液体金属冷却材用構造材については、低合金鋼、特殊鋼、炭素鋼が挙げられる。特殊鋼の代表的なものとしては、Ｃｒ−Ｍｏ系鋼、フェライトあるいはマルテンサイト系Ｃｒ含有鋼、オーステナイト鋼が好ましい。Ｐｂ，Ｂｉに対するＮｉの溶解度が高いため、Ｎｉを多く含んだ鋼材は好ましくない。
【００３０】
溶解酸素濃度測定センサーとしては，固体電解質酸素センサーが使用される。
【００３１】
本発明で使用し得る固体電解質としては、イットリア（Ｙ2 Ｏ3 ) 添加ジルコニア（ＡｒＯ2 ）、カルシア（ＣａＯ）添加ジルコニア、酸化ガドリニウム（Ｇｄ2 Ｏ3 ) 添加ジルコニア、酸化スカンジウム（Ｓｃ2 Ｏ3 ) 添加ジルコニア、酸化イッテルピウム（Ｙｂ2 Ｏ3 ) 添加ジルコニア、トリア・イットリア（ＴｈＯ2 −Ｙ2 Ｏ3 ) 、ハフニア・イットリア（ＨｆＯ2 −Ｙ2 Ｏ3 ) などが挙げられる。
【００３２】
また、前記固体電解質センサーを構成する標準極には、Ｉｎ／Ｉｎ2 Ｏ3 、Ｐｂ／ＰｂＯ系、Ｂｉ／Ｂｉ2 Ｏ3 系、Ｓｎ／ＳｎＯ2 系、Ｇａ／Ｇａ2 Ｏ3 系等が挙げられ、標準極と液体金属のそれぞれに接続されるリード線は、Ｍｏ，Ｔａ，Ｉｒ，Ｏｓ，Ｗ，Ｃなどが挙げられる。
【００３３】
一方、温度センサーは、測温用熱電対や放射温度計等の接触式、非接触式タイプのものが挙げられる。測温用熱電対を使用する場合、固体電解質酸素センサーを組み込んだ一体型の酸素プローブで構成してもよい。
【００３４】
溶解酸素濃度は、固体電解質センサーの起電力測定値と温度センサーの測定値から決定することができる。
【００３５】
本発明の酸化処理の酸化剤としては、一つには、固体酸化剤で、これには使用液体金属である酸化鉛、酸化ビスマスの１種または２種を混合して用いることができる。また、本発明の固体酸化剤の形状、寸法等は、特に限定されず、例えば、形状に関しては、円柱状、角柱状、円筒状、平板状、ハニカム状、顆粒状、ペレット状、粉末状等のあらゆる形状のものが可能であり、その大きさもあらゆる大きさのものが可能である。二つには、気体酸化剤で、酸素ガス、Ａｒガス−酸素ガス、Ａｒガス−水蒸気の混合ガス等の酸化性ガスが挙げられる。本発明における酸化処理方法としては、基本的には前記酸化剤により液体金属中の溶解酸素濃度を増加させれば良く、具体的には、例えば、次の４つの酸化処理方法が挙げられる。すなわち、
（ａ） ロッド状等の固体酸化剤を金属中に出し入れする。
【００３６】
（ｂ） 粉末状、顆粒状等の固定酸化剤を液体金属中に適量添加する。
【００３７】
（ｃ） 酸化処理装置の液体金属流路内に予めボール状、ペレット状、ハニカム状等の固体酸化剤を配置しておき、液体金属を固体酸化剤に接触させながら通過させる。
【００３８】
（ｄ） 液体金属中に気体酸化剤を注入する。
【００３９】
また、本発明の酸化処理の装置は特に限定されず、例えば、ロッド状等の固体酸化剤を液体金属中に出し入れするような方法であれば、出し入れする機構などを具備すればよい。また、気体酸化剤を注入するような場合には、流量計、供給バルブ等を具備すればよい。さらに、固体酸化剤を液体金属流路内に装入させておき、液体金属を通過する際に酸化させるような場合には、酸化処理装置自体に駆動系制御部品を具備しないでも酸化処理装置前後に配置したバルブの調整のみで酸化処理を制御することも可能である。
【００４０】
前記還元処理の還元剤としては、気体還元剤として水素ガス、Ａｒガス−水素ガス、Ａｒガス−水素ガス−水蒸気の混合ガス等の還元性ガスが挙げられる。また、固体還元剤として、炭素、Ａｌ，Ｚｒ，Ｔｉ，Ｍｇなどが挙げられる。なお、本発明の固体還元剤の炭素、Ａｌ，Ｚｒ，Ｔｉ，Ｍｇなどの形状、寸法などは、特に限定されるものではない。本発明の還元方法としては、基本的には、前記還元剤により液体金属中の溶解酸素濃度を減少させれば良く、具体的には、次の３つの還元処理方法が挙げられる。すなわち、
（ａ） ロッド状等の固体還元剤を金属中に出し入れする。
【００４１】
（ｂ） 還元処理装置の液体金属流路内に予めボール状、ペレット状、ハニカム状等の固体還元剤を配置しておき、液体金属を固体還元剤に接触させながら通過させる。
【００４２】
（ｃ） 液体金属中に気体酸化剤を注入する。
【００４３】
また、本発明の還元処理の装置は前記酸化処理の装置と同様に特に限定されず、処理方法等に応じて装置構成を決定すればよい。その場合、必要に応じて還元処理装置に駆動系制御部品等を具備して制御すればよい。また、液体金属中に気体還元剤を注入する場合は、還元処理で生成した水蒸気をループ外に放出させる機構を具備しておくことが好ましい。
【００４４】
次に、本発明の液体金属冷却材用構造材の腐食防止方法において、ループ系における酸化処理装置と還元処理装置の配置は、例えば、以下のような配置が挙げられる。すなわち、
（ａ） 主幹の液体金属ループラインの途中に直接酸化処理装置と還元処理装置を配置する。
【００４５】
（ｂ） 主幹の液体金属ループラインに溶解酸素濃度調整タンクを配置し、このタンクに酸化処理装置と還元処理装置を配置する。
【００４６】
（ｃ） 主幹の液体金属ループラインに分岐点を設けてそのバイパスラインに酸化処理装置と還元処理装置を配置する。
【００４７】
（ｄ） 主幹の液体金属ループラインに分岐点を設けてそのバイパスラインを酸化処理ラインと還元処理ラインの２つに分岐し、配置する。
【００４８】
また、本発明の液体金属冷却用構造材の腐食防止方法において、ループ系における溶解酸素濃度測定センサーと温度センサーの配置は、例えば、液体金属ループラインに直接挿入配置したり、液体金属ループラインに分岐点を設けて、そのバイパスラインに挿入配置することが挙げられる。さらに、複数の溶解酸素濃度測定センサーと温度センサーを配置することも可能であり、この場合、溶存酸素濃度の制御がし易くなる。
【００４９】
本発明において、液体金属の温度範囲は、使用する液体金属の融点〜６５０℃であることが好ましく、Ｐｂ系は、３３０℃〜５５０℃、Ｂｉ系及びＰｂ−Ｂｉ系は、３００℃〜５５０℃がより好ましい。温度が低すぎると、固体電解質酸素センサーによる起電力の測定が困難となり、極端な場合には測定不能となる。また、温度が高すぎると、構造材の腐食が激しくなり、腐食防止制御が困難となる。
【００５０】
なお、液体金属冷却用構造材の内部には、カバーガスを用いておくことが好ましい。カバーガスとしては、十分に水分を除去した高純度のＡｒガスなどの不活性ガスが好ましい。
【００５１】
【実施例】
以下、本発明の液体金属冷却材用構造材の腐食防止方法について具体的に説明する。図１は本発明の液体金属冷却材用構造材の腐食防止方法の実施に用いた液体金属中の酸素濃度制御装置の概略図である。
【００５２】
本装置を冷却材のループ系に装入配置する。液体金属１は、液体金属冷却材用構造材２内を矢印の方向に流れる。主幹である液体金属ループライン３には、バルブ４が配置されている。このバルブ４を迂回するように液体金属ループライン３は、途中で分岐し、液体金属ループライン３と、バイパスラインとしての酸化処理ライン５及び還元処理ライン９の３つのラインに分かれている。
【００５３】
酸化処理装置６は、バルブ７，バルブ８とともに酸化処理ライン５に配置され、再び、液体金属ループライン３に合流するようになっている。一方、還元処理装置１０は、バルブ１１，バルブ１２とともに還元処理ライン９に配置され、再び、液体金属ループライン３に合流するようになっている
溶解酸素濃度測定センサーとして固体電解質酸素センサー１３と、温度センサーとして測温用熱電対１５を用い、それぞれ、測定部が液体金属に浸るように液体金属ループライン３に挿入配置する。これら両センサー１３および１５は、バイパスライン５および９の下流側に配される。
【００５４】
固体電解質酸素センサー１３は、酸素濃度測定装置１４と接続し、測温用熱電対１５は、温度測定装置１６と接続している。酸素濃度測定装置１４と温度測定装置１６は、データ処理装置１７に接続され、得られた酸素濃度データと温度データをデータ処理装置１７で演算処理し、溶解酸素濃度を求める。そこで得られた制御信号をコントローラ１８に供給して、その制御信号に基づいて酸化処理装置６または還元処理装置１０および各ラインに配置したバルブ７，８、並びに１１，１２の開閉により、自動的に溶解酸素濃度を制御する。
【００５５】
図２は、上記酸化処理装置６の一実施の形態を示す概略図である。配管５に容器２０が配置され、容器２０内にはハニカム状の固体処理剤２１が装入されている。
【００５６】
図３は、本発明の還元処理装置１０の一実施の形態を示す概略図である。配管９に容器２３が配置され、容器２３内にガス導入口２４から還元ガス２７がコントローラにより制御可能なバルブ２６と流量計２５を介して導入できるようになっている。
【００５７】
図１、図２、図３を用いて、本発明の液体金属冷却材用構造材の腐食防止方法における溶解酸素濃度制御装置の動作を説明する。
【００５８】
まず、バルブ７，バルブ８，バルブ１１，バルブ１２を閉め、バルブ４を開けておく。上流から流入した液体金属１は、液体金属ループライン３を流れ、固体電解質酸素センサー１３と測温用熱電対１５に流入する。流入した液体金属１中の固体電解質酸素センサーの起電力と温度を測定し、酸素濃度測定装置１４と温度測定装置１６により数値化され、得られた溶解酸素濃度データと温度データをデータ処理装置１７に伝送する。そして、データ処理装置１７で演算処理され、溶解酸素濃度が求められる。さらに、データ処理装置１７で求められた溶解酸素濃度が判定され、その判定結果に基づいた制御信号をコントローラ１８に供給し、後記の制御の基となる。この判定結果は、連続的もしくは間欠的に行われ、監視される。
【００５９】
溶解酸素濃度が予め設定した管理限界下限付近になった場合、データ処理装置１７から酸化処理実行のＯＮ指令がコントローラ１８に伝送される。そして、コントローラ１８の制御信号でバルブが作動し、バルブ４が閉じ、バルブ７とバルブ８が開状態となる。
【００６０】
したがって、液体金属１は、酸化処理ライン５に導かれ、固体酸化剤２１と接触し、その際、酸化されながら通過する。そして、溶解酸素濃度が管理限界内の正常値に復帰した場合、データ処理装置１７から「正常」の指令がコントローラ１８に伝送され、コントローラ１８の制御信号でバルブが作動し、バルブ４が開き、バルブ７とバルブ８が閉状態となる。液体金属１は、液体金属ループライン３に導かれ、正常時のループモードに復帰する。
【００６１】
一方、溶解酸素濃度が予め設定した管理限界上限付近になった場合、管理限界下限の検知と同様に、固体電解質酸素センサー１３と測温用熱電対１５により溶解酸素濃度の管理限界上限を検知し、データ処理装置１７から還元処理実行のＯＮ指令がコントローラ１８に伝送される。そして、コントローラ１８の制御信号でバルブが作動し、バルブ４が閉じ、バルブ１１とバルブ１２が開状態となり、液体金属１は還元処理ライン９に導かれる。そして、コントローラ１８の制御信号でバルブ２６が作動し、還元ガス２７が容器２３内に導入され、液体金属１が還元される。
【００６２】
溶解酸素濃度が管理限界内の正常値に復帰した場合、データ処理装置１７から「正常」の指令がコントローラ１８に伝送され、コントローラ１８の制御信号でバルブが作動し、バルブ４が開き、バルブ１１とバルブ１２が閉状態となる。液体金属１は、液体金属ループライン３に導かれる。また、ガス供給がバルブ２６の作動により停止され、正常時のループラインに復帰する。
（実施例１）
本発明の液体金属冷却材用構造材の腐食防止方法として、液体金属としてＰｂ−Ｂｉ共晶合金を、また、液体金属冷却材用構造材として１８Ｃｒ−１Ｍｏ鋼を用い、流速０．５ｍ／ｓ、高温部５５０℃、低温部３５０℃の強制ループ装置での液体金属と構造材の健全性を評価した。
【００６３】
強制ループ装置内の溶解酸素濃度を増加させ、１０-5ｍａｓｓ％付近より多くなると、次第にスラグが析出し始め、低温部の構造材内部に付着し、流路を狭めた。スラグを分析したところ、酸化鉛が主成分であった。したがって、溶解酸素濃度の管理限界上限は、約１０-5ｍａｓｓ％で、これより多くなると、Ｐｂ−Ｂｉ液体金属の鉛の酸化物が生成され、健全性が維持できなかった。
【００６４】
一方、強制ループ装置内の溶解酸素濃度を減少させ、１０-7ｍａｓｓ％付近より少なくなると、次第にスラグが析出し始め、低温部の構造材内部に付着し、流路を狭めた。スラグを分析したところ、Ｆｅを主成分とした構造材の構成元素であった。
【００６５】
したがって、溶解酸素濃度の管理限界下限は、約１０-7ｍａｓｓ％で、これより少なくなると、Ｐｂ−Ｂｉ液体金属中に構造材の構成元素であるＦｅ，Ｃｒなどが溶解され、構造材表面には、安定な酸化被膜は生成されず、液体金属と構造材との健全性を維持されなかった。
【００６６】
これに対し、本発明の液体金属冷却材用構造材の腐食防止方法を用いて溶解酸素濃度を１０-7ｍａｓｓ％〜１０-5ｍａｓｓ％に管理すると、低温部でのプラグもなく、長期に亘って液体金属と構造材との健全性を維持することができた。試験終了後、構造材表面を分析したところ、鉄酸化物、鉄クロムスピネル酸化物、クロム酸化物、モリブデン酸化物等の酸化被膜が形成されていた。
【００６７】
【発明の効果】
以上述べたように、本発明によれば、液体金属中の溶解酸素濃度を制御することにより、液体金属と接触する構造材表面に液体金属に対して健全性を有する保護被膜を安定的、かつ、持続的に形成させることができる。構造材表面に保護被膜を形成、および維持させることにより、これまで使用することができなかった腐食性の高いＰｂ，Ｂｉ系の液体金属を冷却材に使用することができる。
【００６８】
これにより、従来、Ｎａ冷却材で問題とされた反応性（特に、水との反応性）の高さに関して、より化学的に不活性なＰｂ，Ｂｉ系が使用できるようになるなと、その適用範囲は極めて広い。
【図面の簡単な説明】
【図１】本発明の方法を実施する際に適用した液体金属中の酸素濃度制御装置の概略図である。
【図２】酸化処理装置の概略図である。
【図３】還元処理装置の概略図である。
【符号の説明】
１ 液体金属
２ 液体金属冷却材用構造材
３ 液体金属ループライン
４，７，８，１１，１２，２６ バルブ
５ 酸化処理ライン
６ 酸化処理装置
９ 還元処理ライン
１０ 還元処理装置
１３ 固体電解質酸素センサー
１４ 酸素濃度測定装置
１５ 測温用熱電対
１６ 温度測定装置
１７ データ処理装置
１８ コントローラ
２０，２３ 容器
２１ 固体処理剤
２４ ガス導入口
２５ 流量計
２７ 還元ガス[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing corrosion of a structural material for a liquid metal coolant, and in particular, stably and continuously a protective coating having soundness to the liquid metal on the surface of the structural material in contact with the liquid metal. It relates to a method of forming.
[0002]
[Prior art]
Liquid metal is used as a coolant because it is stable against heat and radiation and has excellent thermal conductivity. A typical example is liquid Na metal in a fast breeder reactor. Metals used for such purposes are mainly low melting point metals such as Na, Na-K, Li, Bi, and Pb. When such liquid metals are used as coolants, equipment and piping made of liquid metals, etc. Corrosion of the structural material becomes a problem.
[0003]
Corrosion caused by liquid metal is not due to the electrochemical process observed in corrosion of aqueous solution or the like, but mainly due to dissolution of metal elements in liquid metal. Therefore, when a liquid metal used as a coolant circulates between a high temperature part and a low temperature part for heat recovery, an element dissolved from the structural material in the high temperature part becomes supersaturated and precipitates in the low temperature part, so-called mass transfer phenomenon occurs. Arise.
[0004]
This mass transfer is repeated, and structural materials such as equipment and piping continue to be corroded, and impurities may precipitate in the low temperature part, which may clog liquid metal channels such as small-diameter piping. The dissolution rate is governed by the degree of unsaturation at the high temperature part, but depends on various conditions such as loop configuration and shape of the equipment, flow rate, temperature, temperature difference, surface roughness, impurity concentration, etc. Is done. Among them, it is known that impurities in the liquid metal, particularly dissolved oxygen concentration, greatly affect the corrosion phenomenon and the rate.
[0005]
In the case of fast breeder reactor Na coolant, the absolute value of the standard free energy (oxygen potential) of Na oxide is the standard oxide generation of the main elements of steel (Fe, Ni, Cr) and general alloy elements. Greater than the absolute value of free energy. That is, the surface of the structural material in contact with liquid Na is reduced, and Na tends to be oxidized.
[0006]
Therefore, the corrosion conditions of the structural material are essentially determined by the solubility of these main elements in liquid Na. Although it is known that the solubility of the structural element main element in liquid Na is relatively small, it has been found that the corrosion rate increases with increasing dissolved oxygen concentration in liquid Na. When the structural material is stainless steel, the component elements Cr and Ni are eluted at the high temperature portion and precipitated at the low temperature portion. And it is said that the elution of Cr is promoted when the oxygen concentration in Na is high.
[0007]
Therefore, the corrosion prevention of the structural material becomes very important for the practical application of the liquid metal coolant.
[0008]
As a conventional method for preventing corrosion of a structural material for a liquid metal coolant, one of the methods is a cold trap method. This method is a type of purification method that removes impurities in metal liquids. Utilizing the property that the solubility of impurities decreases at low temperatures, various compounds such as oxygen and carbon in metal liquids can be removed at low temperatures. In the form (reaction product), and then separated and recovered. In the case of Na, the concentration of dissolved enzyme in Na can be reduced to about 10 ppm or less by a cold trap, and compatibility with stainless steel, Fe, Cr, Ni, Co, Mo, and the like is achieved.
[0009]
Another method is a hot trap method. This method is used when it is desired to obtain a purity higher than that obtained by a cold trap. The liquid metal is passed through a metal getter that bonds well with impurities such as oxygen at a high temperature, and the impurities in the liquid metal are reacted with the metal getter. This is a method of fixing and removing in the getter. For example, Ti, Zr, Ti-Zr alloy, etc. are used as a metal which produces an oxide more stable than sodium oxide with respect to oxygen in liquid Na, and the dissolved oxygen concentration in liquid Na at about 600 ° C. is used. It can be managed to several ppm or less.
[0010]
[Problems to be solved by the invention]
However, the conventional method for preventing corrosion of the structural material for liquid metal coolant controls the upper limit of the dissolved oxygen concentration in the liquid metal. However, such a corrosion prevention method has the following disadvantages depending on the type of liquid metal.
[0011]
For example, when Pb-Bi is used for the liquid metal, the solubility of the main element of the structural material in the liquid Pb-Bi is large, and corrosion of the structural material can be prevented only by reducing the dissolved oxygen concentration in the liquid Pb-Bi. The problem of difficulty arises. That is, there is a problem that even if the dissolved oxygen concentration is too small, the corrosion of the structural material is accelerated.
[0012]
In order to avoid the above problem, there is a method of reducing the dissolution rate of the structural material by forming a protective film on the surface of the structural material by adding an inhibitor. In this case, if the protective film grows too thick, the film There was a problem that cracking due to peeling or thermal shock occurred, and corrosion progressed locally from such a point. Therefore, the application of the liquid metal coolant having a large solubility of the structural element main elements such as Pb and Bi to the coolant has not been able to sufficiently prevent the corrosion in the prior art.
[0013]
Therefore, the present invention solves such problems, and the object of the present invention is to control the dissolved oxygen concentration in the liquid metal so that the surface of the structural material in contact with the liquid metal is protected against the liquid metal. Corrosion of structural materials for liquid metal coolant that can form a protective film with high soundness and stability and can prevent corrosion even in liquid metals that exhibit high corrosiveness to structural materials It is to provide a prevention method. In addition to solving the above problems, it contributes to the creation of new devices.
[0014]
[Means for Solving the Problems]
The above object is achieved by the following (1) to (6) . That is,
(1) The present invention is the liquid metal coolant for structural material for cooling housing the liquid metal, the surface of the liquid metal coolant for structural materials in contact with the liquid metal, at least for the liquid metal coolant Rutotomoni to form an oxide film composed of structural elements of the structural material, by managing the range of dissolved oxygen concentration of 10 -7 mass% ~10 -5 mass% of the liquid metal, the stability of the oxide film and A method for preventing corrosion of a structural material for a liquid metal coolant, characterized by maintaining sustainability.
[0015]
(2) In the present invention , a dissolved oxygen concentration measurement sensor and a temperature sensor are arranged in the structural material for a liquid metal coolant , and the liquid metal is measured from the measured value of the dissolved oxygen concentration measurement sensor and the measured value of the temperature sensor. The dissolved oxygen concentration in the liquid metal is adjusted as needed by comparing the dissolved oxygen concentration in the liquid metal calculated in this calculation with the preset dissolved oxygen concentration. The method for preventing corrosion of a structural material for a liquid metal coolant according to the above (1), wherein the concentration is controlled in the range of 10 −7 mass % to 10 −5 mass % .
[0016]
(3) The method for preventing corrosion of a structural material for a liquid metal coolant according to the above (1), wherein the liquid metal is lead (Pb), bismuth (Bi), or a lead-bismuth alloy (Pb-Bi). It is.
[0017]
(4) The liquid metal coolant structural material according to (1), (2) or (3) above, wherein the temperature range of the liquid metal is the melting point of the liquid metal to 650 ° C. This is a corrosion prevention method.
[0018]
(5) The present invention is the method for preventing corrosion of a structural material for liquid metal coolant according to (1) above, wherein the structural material for liquid metal coolant is low alloy steel, special steel, or carbon steel. is there.
[0019]
(6) The method for preventing corrosion of a structural material for a liquid metal coolant according to claim 2, wherein the dissolved oxygen concentration measurement sensor is a solid electrolyte oxygen sensor.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention will be described. In the method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention, the protective film having soundness to the liquid metal on the surface of the structural material in contact with the liquid metal by controlling the dissolved oxygen concentration in the liquid metal Is formed stably and continuously, and corrosion is prevented even in a liquid metal exhibiting high corrosiveness to a structural material.
[0023]
When the dissolved oxygen concentration in the liquid metal is calculated from the measured value of the dissolved oxygen concentration measurement sensor and the measured value of the temperature sensor, the calculated value is fed back, and the dissolved oxygen concentration falls below the preset control lower limit. The dissolved oxygen concentration is automatically increased by the oxidation treatment, and the dissolved oxygen concentration in the liquid metal is decreased by automatically reducing the dissolved oxygen concentration by the reduction treatment when it exceeds the preset control upper limit. Control and form and maintain a protective coating.
[0024]
Next, the relationship between the dissolved oxygen concentration in the liquid metal and the oxide film of the structural material will be described. From the thermodynamic viewpoint, that is, from the comparison of the standard free energy of formation of oxides, the order of stability of oxides of the main liquid metal component and the main component of the structural material according to the present invention is silicon oxide> chromium oxide> molybdenum oxide. The order is> iron oxide> lead oxide> bismuth oxide. Based on this, the corrosivity due to the interaction between the main component of the liquid metal and the structural material and oxygen is roughly classified into the following three cases depending on the dissolved oxygen concentration level in the liquid metal. That is,
(A) Under conditions where the dissolved oxygen concentration level of the liquid metal is sufficiently low and the iron is not oxidized, the iron is dissolved in the liquid metallization, and the corrosion of the structural material proceeds.
[0025]
(B) Under conditions where the dissolved oxygen concentration level in the liquid metal becomes high and iron is oxidized, oxide films such as iron oxide, chromium oxide, and iron-chromium composite oxide are generated, and these oxide films are liquid. Corrosion is prevented by a stable protective film in metal.
[0026]
(C) Under conditions where the dissolved oxygen concentration level in the liquid metal is further increased and lead is oxidized, slag of lead oxide is generated in the liquid metal, resulting in deterioration of the cooling function, piping plugs, and the like. Furthermore, the oxide film grows too thick, and film peeling or cracking due to thermal shock is likely to occur, and local corrosion proceeds from such a point.
[0027]
Therefore, in the method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention, basically, the condition of (b) above, that is, a dissolved oxygen concentration such that iron is oxidized and lead is not oxidized is controlled. It will be good.
[0028]
Examples of the liquid metal in the method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention include a Pb-based metal, a Bi-based metal, and a Pb-Bi-based alloy.
[0029]
Next, low alloy steel, special steel, and carbon steel are mentioned about the structural material for liquid metal coolant. As a typical special steel, Cr-Mo steel, ferrite or martensitic Cr-containing steel, and austenitic steel are preferable. Since the solubility of Ni in Pb and Bi is high, a steel material containing a large amount of Ni is not preferable.
[0030]
A solid electrolyte oxygen sensor is used as a sensor for measuring dissolved oxygen concentration.
[0031]
Examples of the solid electrolyte that can be used in the present invention include yttria (Y 2 O 3 ) -added zirconia (ArO 2 ), calcia (CaO) -added zirconia, gadolinium oxide (Gd 2 O 3 ) -added zirconia, and scandium oxide (Sc 2 O 3). ) Added zirconia, ytterpium oxide (Yb 2 O 3 ) added zirconia, tria yttria (ThO 2 —Y 2 O 3 ), hafnia yttria (HfO 2 —Y 2 O 3 ) and the like.
[0032]
The standard electrode constituting the solid electrolyte sensor includes In / In 2 O 3 , Pb / PbO system, Bi / Bi 2 O 3 system, Sn / SnO 2 system, Ga / Ga 2 O 3 system and the like. Examples of the lead wire connected to the standard electrode and the liquid metal include Mo, Ta, Ir, Os, W, and C.
[0033]
On the other hand, examples of the temperature sensor include contact type and non-contact type types such as a thermocouple for temperature measurement and a radiation thermometer. When a thermocouple for temperature measurement is used, it may be constituted by an integrated oxygen probe incorporating a solid electrolyte oxygen sensor.
[0034]
The dissolved oxygen concentration can be determined from the electromotive force measurement value of the solid electrolyte sensor and the measurement value of the temperature sensor.
[0035]
As the oxidizing agent for the oxidation treatment of the present invention, one is a solid oxidizing agent, and one or two of lead oxide and bismuth oxide, which are liquid metals used, can be used as a mixture. Further, the shape, dimensions, etc. of the solid oxidizer of the present invention are not particularly limited. For example, the shape, columnar shape, prismatic shape, cylindrical shape, flat plate shape, honeycomb shape, granular shape, pellet shape, powder shape, etc. Any shape can be used, and any size can be used. The second is a gaseous oxidant, and examples thereof include an oxidizing gas such as oxygen gas, Ar gas-oxygen gas, and Ar gas-water vapor mixed gas. As the oxidation treatment method in the present invention, basically, the dissolved oxygen concentration in the liquid metal may be increased by the oxidant. Specifically, for example, the following four oxidation treatment methods may be mentioned. That is,
(A) A rod-like solid oxidizing agent is taken in and out of the metal.
[0036]
(B) An appropriate amount of a fixed oxidizing agent such as powder or granule is added to the liquid metal.
[0037]
(C) A solid oxidizer such as a ball shape, a pellet shape, or a honeycomb shape is disposed in advance in the liquid metal flow path of the oxidation treatment apparatus, and the liquid metal is allowed to pass while contacting the solid oxidizer.
[0038]
(D) Injecting a gaseous oxidant into the liquid metal.
[0039]
Further, the oxidation treatment apparatus of the present invention is not particularly limited. For example, a method for taking in and out a rod-like solid oxidizing agent into and out of the liquid metal may be provided. In addition, when a gaseous oxidant is injected, a flow meter, a supply valve, etc. may be provided. Further, in the case where the solid oxidant is charged in the liquid metal flow path and is oxidized when passing through the liquid metal, the oxidation treatment apparatus itself is not provided with a drive system control component before and after the oxidation treatment apparatus. It is also possible to control the oxidation treatment only by adjusting the valve arranged in the above.
[0040]
Examples of the reducing agent for the reduction treatment include reducing gases such as hydrogen gas, Ar gas-hydrogen gas, and Ar gas-hydrogen gas-water vapor mixed gas as gas reducing agents. Moreover, carbon, Al, Zr, Ti, Mg etc. are mentioned as a solid reducing agent. In addition, the shape, dimension, etc. of carbon, Al, Zr, Ti, Mg, etc. of the solid reducing agent of the present invention are not particularly limited. As the reduction method of the present invention, basically, the dissolved oxygen concentration in the liquid metal may be reduced by the reducing agent. Specifically, the following three reduction treatment methods may be mentioned. That is,
(A) A rod-like solid reducing agent is taken in and out of the metal.
[0041]
(B) A solid reducing agent such as a ball shape, a pellet shape, or a honeycomb shape is disposed in advance in the liquid metal flow path of the reduction processing apparatus, and the liquid metal is allowed to pass while contacting the solid reducing agent.
[0042]
(C) Injecting a gaseous oxidant into the liquid metal.
[0043]
Further, the reduction treatment apparatus of the present invention is not particularly limited like the oxidation treatment apparatus, and the apparatus configuration may be determined according to the treatment method and the like. In that case, the reduction processing apparatus may be provided with a drive system control component or the like as necessary. Moreover, when inject | pouring a gaseous reducing agent in a liquid metal, it is preferable to provide the mechanism in which the water vapor | steam produced | generated by the reduction process is discharge | released out of a loop.
[0044]
Next, in the method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention, the arrangement of the oxidation treatment apparatus and the reduction treatment apparatus in the loop system includes, for example, the following arrangement. That is,
(A) An oxidation treatment device and a reduction treatment device are arranged directly in the middle of the main liquid metal loop line.
[0045]
(B) A dissolved oxygen concentration adjusting tank is arranged in the main liquid metal loop line, and an oxidation treatment apparatus and a reduction treatment apparatus are arranged in this tank.
[0046]
(C) A branch point is provided in the main liquid metal loop line, and an oxidation treatment device and a reduction treatment device are arranged in the bypass line.
[0047]
(D) A branch point is provided in the main liquid metal loop line, and the bypass line is branched into an oxidation treatment line and a reduction treatment line.
[0048]
In the method for preventing corrosion of a liquid metal cooling structural material according to the present invention, the dissolved oxygen concentration measurement sensor and the temperature sensor in the loop system may be arranged, for example, by being inserted directly into the liquid metal loop line or in the liquid metal loop line. For example, a branch point may be provided and inserted into the bypass line. Furthermore, it is possible to arrange a plurality of dissolved oxygen concentration measuring sensors and temperature sensors. In this case, the dissolved oxygen concentration can be easily controlled.
[0049]
In the present invention, the temperature range of the liquid metal is preferably from the melting point of the liquid metal to be used to 650 ° C, the Pb system is 330 ° C to 550 ° C, the Bi system and the Pb-Bi system are 300 ° C to 550 ° C. Is more preferable. If the temperature is too low, it is difficult to measure the electromotive force with the solid electrolyte oxygen sensor, and in an extreme case, measurement is impossible. On the other hand, if the temperature is too high, corrosion of the structural material becomes severe, and corrosion prevention control becomes difficult.
[0050]
A cover gas is preferably used inside the liquid metal cooling structural material. The cover gas is preferably an inert gas such as high-purity Ar gas from which moisture has been sufficiently removed.
[0051]
【Example】
Hereinafter, the method for preventing corrosion of the structural material for liquid metal coolant of the present invention will be described in detail. FIG. 1 is a schematic diagram of an apparatus for controlling oxygen concentration in liquid metal used in the implementation of the method for preventing corrosion of a structural material for liquid metal coolant of the present invention.
[0052]
The device is placed in a coolant loop system. The liquid metal 1 flows in the direction of the arrow in the liquid metal coolant structural material 2. A valve 4 is arranged in the liquid metal loop line 3 which is the main trunk. The liquid metal loop line 3 branches along the way so as to bypass the valve 4 and is divided into three lines: a liquid metal loop line 3, an oxidation treatment line 5 as a bypass line, and a reduction treatment line 9.
[0053]
The oxidation treatment device 6 is disposed in the oxidation treatment line 5 together with the valve 7 and the valve 8 and again joins the liquid metal loop line 3. On the other hand, the reduction treatment device 10 is disposed in the reduction treatment line 9 together with the valve 11 and the valve 12, and again, as a dissolved oxygen concentration measurement sensor that is joined to the liquid metal loop line 3, a solid electrolyte oxygen sensor 13; A thermocouple 15 for temperature measurement is used as a temperature sensor, and each is inserted and disposed in the liquid metal loop line 3 so that the measurement unit is immersed in the liquid metal. Both sensors 13 and 15 are arranged downstream of the bypass lines 5 and 9.
[0054]
The solid electrolyte oxygen sensor 13 is connected to an oxygen concentration measuring device 14, and the temperature measuring thermocouple 15 is connected to a temperature measuring device 16. The oxygen concentration measuring device 14 and the temperature measuring device 16 are connected to the data processing device 17, and the obtained oxygen concentration data and temperature data are processed by the data processing device 17 to obtain the dissolved oxygen concentration. The control signal obtained there is supplied to the controller 18, and based on the control signal, the oxidation processing device 6 or the reduction processing device 10 and the valves 7, 8 and 11, 12 arranged in each line are automatically opened and closed. The dissolved oxygen concentration is controlled.
[0055]
FIG. 2 is a schematic view showing an embodiment of the oxidation treatment apparatus 6. A container 20 is disposed in the pipe 5, and a honeycomb-shaped solid processing agent 21 is charged in the container 20.
[0056]
FIG. 3 is a schematic view showing an embodiment of the reduction treatment apparatus 10 of the present invention. A container 23 is disposed in the pipe 9, and a reducing gas 27 can be introduced into the container 23 from a gas introduction port 24 through a valve 26 and a flow meter 25 that can be controlled by a controller.
[0057]
The operation of the dissolved oxygen concentration control apparatus in the method for preventing corrosion of a structural material for a liquid metal coolant according to the present invention will be described with reference to FIGS.
[0058]
First, the valve 7, the valve 8, the valve 11, and the valve 12 are closed, and the valve 4 is opened. The liquid metal 1 flowing in from the upstream flows through the liquid metal loop line 3 and flows into the solid electrolyte oxygen sensor 13 and the thermocouple 15 for temperature measurement. The electromotive force and temperature of the solid electrolyte oxygen sensor in the inflowing liquid metal 1 are measured and digitized by the oxygen concentration measuring device 14 and the temperature measuring device 16, and the obtained dissolved oxygen concentration data and temperature data are converted into the data processing device 17. Transmit to. Then, it is processed by the data processor 17 to obtain the dissolved oxygen concentration. Further, the dissolved oxygen concentration determined by the data processing device 17 is determined, and a control signal based on the determination result is supplied to the controller 18 to be a basis for the control described later. This determination result is continuously or intermittently performed and monitored.
[0059]
When the dissolved oxygen concentration is near the preset control limit lower limit, an ON command for executing the oxidation treatment is transmitted from the data processing device 17 to the controller 18. Then, the valve is actuated by the control signal of the controller 18, the valve 4 is closed, and the valves 7 and 8 are opened.
[0060]
Accordingly, the liquid metal 1 is guided to the oxidation treatment line 5 and comes into contact with the solid oxidant 21 and passes while being oxidized. When the dissolved oxygen concentration returns to a normal value within the control limit, a “normal” command is transmitted from the data processing device 17 to the controller 18, the valve is operated by the control signal of the controller 18, the valve 4 is opened, Valve 7 and valve 8 are closed. The liquid metal 1 is guided to the liquid metal loop line 3 and returns to the normal loop mode.
[0061]
On the other hand, when the dissolved oxygen concentration is near the preset control limit upper limit, the control limit upper limit of the dissolved oxygen concentration is detected by the solid electrolyte oxygen sensor 13 and the thermocouple 15 for temperature measurement in the same manner as the detection of the control limit lower limit. Then, an ON command for executing the reduction process is transmitted from the data processing device 17 to the controller 18. Then, the valve is operated by the control signal of the controller 18, the valve 4 is closed, the valve 11 and the valve 12 are opened, and the liquid metal 1 is guided to the reduction treatment line 9. Then, the valve 26 is actuated by the control signal of the controller 18, the reducing gas 27 is introduced into the container 23, and the liquid metal 1 is reduced.
[0062]
When the dissolved oxygen concentration returns to a normal value within the control limit, a “normal” command is transmitted from the data processing device 17 to the controller 18, the valve is operated by the control signal of the controller 18, the valve 4 is opened, and the valve 11 And the valve 12 is closed. The liquid metal 1 is guided to the liquid metal loop line 3. Further, the gas supply is stopped by the operation of the valve 26, and the normal loop line is restored.
Example 1
As a method for preventing corrosion of a structural material for liquid metal coolant of the present invention, Pb—Bi eutectic alloy is used as the liquid metal, 18Cr-1Mo steel is used as the structural material for the liquid metal coolant, and a flow rate of 0.5 m / s. The soundness of the liquid metal and the structural material in the forced loop device at the high temperature part 550 ° C. and the low temperature part 350 ° C. was evaluated.
[0063]
When the dissolved oxygen concentration in the forced loop apparatus was increased and increased from around 10 −5 mass%, slag gradually started to deposit and adhered to the inside of the structural material in the low temperature part, narrowing the flow path. When slag was analyzed, lead oxide was the main component. Therefore, the upper limit of control of the dissolved oxygen concentration is about 10 −5 mass%, and if it exceeds this, lead oxide of Pb—Bi liquid metal was generated, and the soundness could not be maintained.
[0064]
On the other hand, when the dissolved oxygen concentration in the forced loop device was decreased and became less than around 10 −7 mass%, slag gradually started to deposit and adhered to the inside of the structural material in the low temperature portion, narrowing the flow path. When slag was analyzed, it was a constituent element of a structural material mainly composed of Fe.
[0065]
Therefore, the lower limit of control of the dissolved oxygen concentration is about 10 −7 mass%, and when it is less than this, Fe, Cr, etc., which are constituent elements of the structural material, are dissolved in the Pb—Bi liquid metal, and the structural material surface However, a stable oxide film was not generated, and the soundness of the liquid metal and the structural material was not maintained.
[0066]
On the other hand, when the dissolved oxygen concentration is controlled to 10 −7 mass% to 10 −5 mass% by using the method for preventing corrosion of the structural material for liquid metal coolant according to the present invention, there is no plug in the low temperature part, and the long term It was possible to maintain the soundness of the liquid metal and the structural material. When the surface of the structural material was analyzed after the test was completed, an oxide film such as iron oxide, iron chromium spinel oxide, chromium oxide, molybdenum oxide was formed.
[0067]
【The invention's effect】
As described above, according to the present invention, by controlling the dissolved oxygen concentration in the liquid metal, a protective film having soundness against the liquid metal can be stably formed on the surface of the structural material in contact with the liquid metal, and Can be formed continuously. By forming and maintaining a protective coating on the surface of the structural material, highly corrosive Pb and Bi based liquid metals that could not be used can be used as the coolant.
[0068]
As a result, with regard to the high reactivity (especially the reactivity with water) that has been a problem with conventional Na coolant, a more chemically inert Pb, Bi system can be used. The range of application is extremely wide.
[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for controlling the oxygen concentration in a liquid metal applied when carrying out the method of the present invention.
FIG. 2 is a schematic view of an oxidation treatment apparatus.
FIG. 3 is a schematic view of a reduction processing apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Liquid metal 2 Structure material for liquid metal coolant 3 Liquid metal loop lines 4, 7, 8, 11, 12, 26 Valve 5 Oxidation treatment line 6 Oxidation treatment device 9 Reduction treatment line 10 Reduction treatment device 13 Solid electrolyte oxygen sensor 14 Oxygen concentration measuring device 15 Thermocouple 16 for temperature measurement Temperature measuring device 17 Data processing device 18 Controller 20, 23 Container 21 Solid processing agent 24 Gas inlet 25 Flow meter 27 Reducing gas

Claims (6)

液体金属を収納して冷却を行う液体金属冷却材用構造材において、前記液体金属と接触する前記液体金属冷却材用構造材の表面に、少なくとも前記液体金属冷却材用構造材の構造元素からなる酸化被膜を形成させるとともに、前記液体金属中の溶解酸素濃度を１０ -7 mass ％〜１０ -5 mass ％の範囲に管理することにより、前記酸化被膜の安定性および持続性を維持することを特徴とする液体金属冷却材用構造材の腐食防止方法。In the structural material for liquid metal coolant that cools by storing the liquid metal, the surface of the structural material for liquid metal coolant that comes into contact with the liquid metal includes at least a structural element of the structural material for liquid metal coolant Rutotomoni to form an oxide film, by managing the concentration of dissolved oxygen of the liquid metal in the range of 10 -7 mass% ~10 -5 mass% , to maintain the stability and persistence of the oxide layer A method for preventing corrosion of a structural material for a liquid metal coolant. 前記液体金属冷却材用構造材に溶解酸素濃度測定センサーと温度センサーとを配置し、前記溶解酸素濃度測定センサーの測定値と前記温度センサーの測定値から前記液体金属中の溶解酸素濃度を演算し、この演算で求めた液体金属中の溶解酸素濃度と予め設定した溶解酸素濃度とを比較して液体金属中の溶解酸素濃度を随時調整し、液体金属中の溶解酸素濃度を１０ -7 mass ％〜１０ -5 mass ％の範囲に管理することを特徴とする請求項１記載の液体金属冷却材用構造材の腐食防止方法。 A dissolved oxygen concentration measurement sensor and a temperature sensor are arranged in the structural material for the liquid metal coolant, and the dissolved oxygen concentration in the liquid metal is calculated from the measurement value of the dissolved oxygen concentration measurement sensor and the measurement value of the temperature sensor. The dissolved oxygen concentration in the liquid metal obtained by this calculation is compared with the preset dissolved oxygen concentration, and the dissolved oxygen concentration in the liquid metal is adjusted as needed, and the dissolved oxygen concentration in the liquid metal is adjusted to 10 −7 mass %. The method for preventing corrosion of a structural material for a liquid metal coolant according to claim 1, wherein the corrosion resistance is controlled within a range of 10 −5 −5 mass % . 前記液体金属が鉛（Ｐｂ）、ビスマス（Ｂｉ）、鉛−ビスマス合金（Ｐｂ−Ｂｉ）であることを特徴とする請求項１記載の液体金属冷却材用構造材の腐食防止方法。2. The method for preventing corrosion of a structural material for a liquid metal coolant according to claim 1, wherein the liquid metal is lead (Pb), bismuth (Bi), or a lead-bismuth alloy (Pb-Bi). 前記液体金属の温度範囲が前記液体金属の融点〜６５０℃であることを特徴とする請求項１、２又は３記載の液体金属冷却材用構造材の腐食防止方法。        4. The method for preventing corrosion of a structural material for liquid metal coolant according to claim 1, wherein a temperature range of the liquid metal is a melting point to 650 [deg.] C. of the liquid metal. 前記液体金属冷却材用構造材が低合金鋼、特殊鋼、炭素鋼であることを特徴とする請求項１記載の液体金属冷却材用構造材の腐食防止方法。        2. The method for preventing corrosion of a structural material for liquid metal coolant according to claim 1, wherein the structural material for liquid metal coolant is low alloy steel, special steel, or carbon steel. 前記溶解酸素濃度測定センサーが固体電解質酸素センサーであることを特徴とする請求項２記載の液体金属冷却材用構造材の腐食防止方法。3. The method for preventing corrosion of a structural material for liquid metal coolant according to claim 2, wherein the dissolved oxygen concentration measuring sensor is a solid electrolyte oxygen sensor.
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