JP2004020411A

JP2004020411A - Nuclear power plant and its operation method

Info

Publication number: JP2004020411A
Application number: JP2002176611A
Authority: JP
Inventors: Yoshihisa Saito; 斉藤　宣久; Yumiko Abe; 阿部　由美子; Kazuyoshi Kataoka; 片岡　一芳; Tadashi Yotsuyanagi; 四柳　端
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2002-06-18
Filing date: 2002-06-18
Publication date: 2004-01-22

Abstract

<P>PROBLEM TO BE SOLVED: To suppress migration and accumulation of radioactive corrosion products onto the surface of components outside a reactor. <P>SOLUTION: A nuclear power plant has a reactor 10 using water as coolant, a turbine 21 driven by steam supplied from the reactor, steam piping 26 introducing steam from the reactor to the turbine and water supply piping 23 for returning the coolant exhausted from the turbine. An injection device 31 for injecting oxidizing agent or reducing agent into the steam piping is provided. Also, an electric potential measuring device 34 for measuring corrosion potential is provided to the steam piping and a corrosion product removal device 35 may be provided downstream the injection device. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、冷却材として水を用いる原子炉で発生したエネルギーにより発電を行う原子力発電プラントおよびその運転方法に関する。
【０００２】
【従来の技術】
従来の軽水炉は、冷却水を炉内で沸騰させ発生した水蒸気により発電を行う沸騰水型原子炉と、炉内を加圧状態に保ち、蒸気発生器にて発生した蒸気により発電を行う加圧水型の２種に大別される。いずれの型もエネルギー効率は３０数％で近年の超臨界火力発電の４０数％以上というエネルギー効率には劣る。これに対し、軽水炉においても温度を３７４℃の臨界点以上に高め、エネルギー効率を４０数％に高めた超臨界圧原子炉の開発が検討されている（例えば、特開平８−３１３６６４号公報参照）。
【０００３】
超臨界圧原子炉のうち原子炉冷却材で直接タービンを駆動するワンススルータイプでは放射性腐食生成物の一部が、原子炉外へ移行し機器表面の線量を高め、プラント運転員または定期検査時における作業員の被爆を引き起こす可能性がある。
【０００４】
【発明が解決しようとする課題】
原子炉の冷却水中には機器を構成する金属材料から溶け出した微量の腐食生成物が存在する。この腐食生成物は燃料棒表面に付着して放射化された後再び放出され、放射性腐食生成物として冷却水中を浮遊している。超臨界圧原子炉のうち原子炉冷却材で直接タービンを駆動するワンススルータイプでは放射性腐食生成物の一部が、原子炉外へ移行し機器表面の線量を高め、プラント運転員または定期検査時における作業員の被爆を引き起こす可能性がある。
【０００５】
この腐食生成物をフィルタ等により物理的あるいは機械的に除去しようとした場合、圧力抵抗が生じプラントの効率を低下させる原因となる。本発明の目的はこのような課題を解決するものであって、原子炉外の機器または配管等の表面への放射性腐食生成物の移行および蓄積を抑制することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は上記目的を達成するものであって、請求項１に記載の発明は、冷却材として水を用いる原子炉と、その原子炉から供給される蒸気によって駆動されるタービンと、前記原子炉から前記タービンへ蒸気を導く蒸気配管と、前記タービンから排出された冷却材を再び前記原子炉へ戻す給水配管と、を有する原子力発電プラントであって、前記蒸気配管に酸化剤または還元剤の少なくとも一方を注入する注入装置を設けたこと、を特徴とする。
【０００７】
請求項１の発明によれば、原子力発電プラントの目標とする場所を腐食生成物が析出し難い状態とすることにより、原子炉外の機器または配管等の表面への放射性腐食生成物の移行および蓄積を抑制することができる。
【０００８】
また、請求項２に記載の発明は、請求項１に記載の原子力発電プラントおいて、前記蒸気配管に腐食電位を測定する電位測定装置を設けたこと、を特徴とする。請求項２の発明によれば、請求項１の発明による作用・効果が得られるほか、さらに精度よく目標とする原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積を抑制することができる。
【０００９】
また、請求項３に記載の発明は、請求項１または２に記載の原子力発電プラントおいて、前記蒸気配管の前記注入装置の下流側に前記冷却材中の腐食生成物を除去する腐食生成物除去装置を設けたこと、を特徴とする。請求項３の発明によれば、請求項１または２の発明による作用・効果が得られるほか、原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積をさらに抑制することができる。
【００１０】
また、請求項４に記載の発明は、請求項３に記載の原子力発電プラントおいて、前記腐食生成物除去装置内の腐食電位を測定する電位測定装置と、前記腐食生成物除去装置内に放射性腐食生成物を選択的に蓄積させるように前記腐食生成物除去装置内の腐食電位を腐食生成物除去装置外より低く制御するべく前記注入装置から注入する酸化剤または還元剤の少なくとも一方の量を制御する手段と、を有すること、を特徴とする。請求項４の発明によれば、請求項３の発明による作用・効果が得られるほか、原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積をさらに抑制することができる。
【００１１】
また、請求項５に記載の発明は、請求項３または４に記載の原子力発電プラントおいて、前記腐食生成物除去装置をはさんで前記蒸気配管の上流側と下流側に酸化剤を注入する酸化剤注入装置と還元剤を注入する還元剤注入装置とを設けたこと、を特徴とする。請求項５の発明によれば、請求項３または４の発明による作用・効果が得られるほか、原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積をさらに抑制することができる。
【００１２】
また、請求項６に記載の発明は、請求項１ないし５のいずれかに記載の原子力発電プラントにおいて、前記冷却材として水の一部が超臨界状態となっていること、を特徴とする。請求項６の発明によれば、請求項１ないし５のいずれかの発明による作用・効果が得られるほかに、次の効果がある。すなわち、超臨界圧炉では炉内に気液界面が存在せず、均一な流体としてタービン系へ移行するため、放射性腐食生成物がタービン系へ移行しやすいと考えられるが、本発明により、放射性物質によるタービン系機器の汚染が抑制され、安全な原子力プラントを提供できる。
【００１３】
また、請求項７に記載の発明は、冷却材として水を用いる原子炉と、その原子炉から供給される蒸気によって駆動されるタービンと、前記原子炉から前記タービンへ蒸気を導く蒸気配管と、前記タービンから排出された冷却材を再び前記原子炉へ戻す給水配管と、を有する原子力発電プラントの運転方法であって、前記蒸気配管に酸化剤または還元剤の少なくとも一方を注入し、前記タービンに流入する蒸気が、前記冷却材中の腐食生成物が溶けやすい状態に維持されるように、前記酸化剤または還元剤の注入量を制御すること、を特徴とする。
【００１４】
請求項７の発明によれば、原子力発電プラントの目標とする場所を腐食生成物が析出し難い状態とすることができ、原子炉外の機器または配管等の表面への放射性腐食生成物の移行および蓄積を抑制することができる。
【００１５】
また、請求項８に記載の発明は、冷却材として水を用いる原子炉と、その原子炉から供給される蒸気によって駆動されるタービンと、前記原子炉から前記タービンへ蒸気を導く蒸気配管と、前記タービンから排出された冷却材を再び前記原子炉へ戻す給水配管と、を有する原子力発電プラントの運転方法であって、前記蒸気配管に酸化剤または還元剤の少なくとも一方を注入し、前記蒸気配管を通る蒸気が前記タービンに流入する前に前記冷却材中の放射性腐食生成物を選択的に蓄積させるように前記酸化剤または還元剤の注入量を制御すること、を特徴とする。
【００１６】
請求項８の発明によれば、原子力発電プラントの目標とする場所を腐食生成物が析出し難い状態とすることができ、原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積を抑制することができる。
【００１７】
また、請求項９に記載の発明は、請求項７または８に記載の原子力発電プラントの運転方法において、前記蒸気配管における腐食電位を測定し、この腐食電位を所定の目標の範囲に近づけるべく前記酸化剤または還元剤の注入量を制御すること、を特徴とする。請求項９の発明によれば、請求項７または８の発明による作用・効果が得られるほか、さらに精度よく原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積をさらに抑制することができる。
【００１８】
また、請求項１０に記載の発明は、請求項７ないし９のいずれかに記載の原子力発電プラントの運転方法において、あらかじめ腐食生成物の電位−ｐＨ関係を表す電位−ｐＨ関係特性を用意し、前記蒸気配管の各部位ごとの温度と腐食電位とｐＨの値を用いて、前記電位−ｐＨ関係特性に基いて腐食生成物の安定形態を推定し、それによって、前記蒸気配管の各部位のうちの目標とする部位の腐食電位を他の部位より低くして前記冷却材中の放射性腐食生成物が蓄積するように前記酸化剤または還元剤の注入量を制御すること、を特徴とする。請求項１０の発明によれば、請求項７ないし９のいずれかの発明による作用・効果が得られるほか、原子炉外の機器等の表面への放射性腐食生成物の移行および蓄積をさらに抑制することができる。
【００１９】
また、請求項１１に記載の発明は、請求項７ないし１０のいずれかに記載の原子力発電プラントの運転方法において、前記冷却材として水の一部が超臨界状態となっていること、を特徴とする。請求項１１の発明によれば、請求項７ないし１０のいずれかの発明による作用・効果が得られるほかに、次の効果がある。すなわち、超臨界圧炉では炉内に気液界面が存在せず、均一な流体としてタービン系へ移行するため、放射性腐食生成物がタービン系へ移行しやすいと考えられるが、本発明により、放射性物質によるタービン系機器の汚染が抑制され、安全な原子力発電プラントの運転方法を提供できる。
【００２０】
【発明の実施の形態】
以下、本発明に係る原子力発電プラントの実施の形態を、図面を参照しながら説明する。ただし、同一または類似の部分には共通の符号を付し、重複説明は省略する。
【００２１】
図１により、本発明に係る原子力発電プラントの第１の実施の形態を説明する。原子炉１０は原子炉圧力容器１１内に収容され、原子炉圧力容器１１内に、核燃料を装荷した炉心１２と、その反応を制御する制御棒１３が内包されている。また、図示の例では、炉心１２の外側を囲むように炉水滞留部１４が形成されている。炉心１２で発生した高温・高圧の蒸気は原子炉圧力容器１１を出て、蒸気配管２６を通って蒸気タービン２１へ送られる。
【００２２】
蒸気タービン２１では、蒸気の熱エネルギーがタービンの回転の仕事に変換され、発電機（図示せず）が回転して発電される。ここで、蒸気は熱エネルギーを放出し、さらに復水器２２で凝縮して復水になる。復水器２２を出た復水は復水浄化装置で浄化され、加圧ポンプ２５で加圧され、給水加熱器２４で加熱され、給水配管２３を経て原子炉圧力容器１１へ戻される。
【００２３】
この実施の形態では、蒸気配管２６に注入装置３１が接続されている。注入装置３１は、酸化剤または還元剤を蒸気配管２６に注入するものであって、注入口から一定流量で注入することにより、腐食生成物を溶けやすい状態に保つことができる。高温水中の腐食生成物は酸化還元電位により溶解度が変化するが、その傾向は温度やｐＨによって変化するので、注入する酸化剤または還元剤の量は原子炉圧力容器１１内の腐食電位よりも原子炉圧力容器１１外の腐食電位を高く保つようにプラントごとに最適値が決定される。
【００２４】
ここで、注入装置３１で注入する酸化剤としては、例えば、酸素ガスや過酸化水素水が適当である。酸素ガスは、地球上に豊富に存在し、高温水中に溶解させ酸化剤として作用させることが容易な上、環境を汚染させることがないので酸化剤として有効である。また、過酸化水素は比較的安価であり、１５０℃以上に加熱すると熱分解により酸素と水になるので酸素注入と同等の効果を得ることができる上、環境を汚染させることがないので酸化剤として有効である。
【００２５】
また、注入装置３１で注入する還元剤としては、例えば、水素ガスやヒドラジンが適当である。水素は地球上に豊富に存在し、高温水中に溶解させ還元剤として作用させることが容易な上、環境を汚染させることがないので還元剤として有効である。また、ヒドラジンは容易に合成でき、高温水中に溶解させて還元剤として作用させることが容易な上、環境を汚染させることがないので還元剤として有効である。
【００２６】
本実施の形態では、蒸気タービン２１、復水器２２、加圧ポンプ２５、給水加熱器２４（これらを合わせて「タービン系機器」と呼ぶ）に入る前に腐食生成物を溶けやすい状態にしているため、タービン系機器への放射性物質の析出が抑制され、線量の上昇が抑えられている。
【００２７】
なお、図１に示す実施の形態では、注入装置３１を１箇所に設けているが、複数箇所に注入装置３１を設けることも可能である。この点は、他の実施の形態でも同様である。
【００２８】
次に、図２により、本発明に係る原子力プラントの第２の実施の形態を説明する。この実施の形態では、第１の実施の形態（図１）の構成要素に加え、酸化剤または還元剤の注入装置３１の下流側の蒸気配管２６に腐食電位測定装置３４が設置されている。腐食電位測定装置３４は、蒸気配管２６の途中に設けた電位測定セル３３と、この電位測定セル３３内に設置した電位測定用電極３２を含んでいる。腐食電位測定装置３４により、注入装置３１で注入された酸化剤または還元剤の効果を把握することができる。したがって、注入量を適正に調節することができる。
【００２９】
次に、図３により、本発明に係る原子力プラントの第３の実施の形態を説明する。この実施の形態では、第１の実施の形態（図１）の構成要素に加え、酸化剤または還元剤を注入する注入装置３１の下流側の蒸気配管２６に腐食生成物除去装置３５が設置されている。
【００３０】
本実施の形態では、この腐食生成物除去装置３５の上流側に酸化剤または還元剤の注入装置３１の注入口を設けており、これにより腐食生成物除去装置３５内の腐食電位を装置外より低くすることによって析出した微量の腐食生成物を腐食生成物除去装置３５で除去させることができる。なお、この腐食生成物除去装置３５は圧力損失を極力低く抑える構造とするのが望ましい。
【００３１】
次に、図４により、本発明に係る原子力プラントの第４の実施の形態を説明する。この実施の形態では、第３の実施の形態（図３）の構成要素に加え、腐食生成物除去装置３５に図２に示したのと同様の腐食電位測定装置３４が設置されている。ただし、ここでは電位測定用電極３２が、図２の電位測定セル３３内に設置される代わりに、腐食生成物除去装置３５内に設置されている。
【００３２】
この実施の形態によれば、第３の実施の形態（図３）と同様に腐食生成物除去装置３５で析出した微量の腐食生成物を除去させることができる。さらに、腐食生成物除去装置３５内の腐食電位を知ることにより、注入装置３１で注入する酸化剤または還元剤の量を適正にし、腐食生成物除去装置３５内の腐食電位を低くすることができる。
【００３３】
次に、図５により、本発明に係る原子力プラントの第５の実施の形態を説明する。この実施の形態では、蒸気配管２６に還元剤注入装置３６、腐食生成物除去装置３５、酸化剤注入装置３７が、上流側からこの順に直列に接続されている。腐食生成物除去装置３５には、第４の実施の形態（図４）と同様に、電位測定用電極３２を含む腐食電位測定装置３４が設置されている。
【００３４】
この実施の形態によれば、還元剤注入装置３６からの還元剤注入によって腐食電位を低く保ち、腐食生成物を析出させて腐食生成物除去装置３５における腐食生成物除去を行い、その後、タービン系における腐食生成物の析出を防ぐように、酸化剤注入装置３７からの酸化剤注入を行ない腐食電位を高くする操作が可能である。
なお、第５の実施の形態（図５）の変形例として、還元剤注入装置３６と酸化剤注入装置３７の配置を逆にした配置も可能である。
【００３５】
図６は、２８８℃の高温水中における代表的腐食生成物であるクロム（Ｃｒ）の安定形態を示す電位−ｐＨ図である。この図は、ＥＰＲＩレポート（ＥＰＲＩ　ＮＰ−３１３７）に記載された熱力学計算手法を用いて発明者らが計算して得たものである。この図から、電位とｐＨによりクロムの化学形態が変化することがわかる。
【００３６】
例えば、ｐＨが中性の場合に電位が＋０．２５Ｖ（ＳＨＥ；　Ｓｔａｎｄａｒｄ　Ｈｙｄｒｏｇｅｎ　Ｅｌｅｃｔｒｏｄｅ）を超えると溶解が始まり、ＣｒＯ_４ ^２−のイオンの形態が安定となることがわかる。したがって、この形で溶解している場合には還元剤である例えば水素ガスを注入することによりＣｒ_２Ｏ_３の形で析出し、逆にやや電位が低い状態でＣｒ_２Ｏ_３の形で存在する場合には、酸素等の酸化剤を注入するとＣｒＯ_４ ^２−のイオンの形態で溶解する。
【００３７】
したがって、一般に、対象となる部位の温度における電位−ｐＨ図を作成しておき、酸化剤または還元剤の注入により電位をコントロールし、原子炉圧力容器外機器の腐食電位を原子炉圧力容器内よりも高く保つことで、目標とする機器への腐食生成物の付着を抑制したり、逆に原子炉圧力容器内よりも腐食電位を低く制御することによって、除去装置内に析出させたりすることができる。
【００３８】
例えば、第５の実施の形態（図５）で、腐食生成物除去装置３５の上流側の還元剤注入装置３６から水素を注入し、腐食生成物除去装置３５内にＣｒを酸化物として析出させた後に、下流側の酸化剤注入装置３７にて酸素を注入し、Ｃｒを溶解させるようなシステムを構成することができる。これにより、タービン系におけるＣｒの析出を防ぐことができる。
【００３９】
上記各実施の形態の原子炉として、例えば、炉内の温度／圧力が３７４℃／２２．１ＭＰａ以上となる超臨界圧炉を適用することも可能である。超臨界圧炉では炉内に気液界面が存在せず、均一な流体としてタービン系へ移行するため、放射性腐食生成物がタービン系へ移行しやすいと考えられるが、本発明により、放射性物質によるタービン系機器の汚染が抑制され、より安全な原子力プラントを提供できる。
【００４０】
なお、超臨界圧状態では液体と気体の区別がなくなるが、本明細書では便宜的に、原子炉からタービンに供給される高温・高圧の作動流体を蒸気と呼び、タービンから排出されて原子炉に戻る比較的低温の作動流体を水と呼んでいる。
【００４１】
【発明の効果】
この発明によれば、原子力発電プラントにおいて、タービン系などの原子炉外の機器または配管等の表面への放射性腐食生成物の移行および蓄積を抑制することができる。これにより、放射性腐食生成物が原子炉外へ移行し機器表面の線量を高めるのを防止または抑制し、プラント運転員または定期検査時における作業員の被爆を抑制することができる。
【図面の簡単な説明】
【図１】本発明に係る原子力発電プラントの第１の実施の形態の概略系統を示す系統図。
【図２】本発明に係る原子力発電プラントの第２の実施の形態の概略系統を示す系統図。
【図３】本発明に係る原子力発電プラントの第３の実施の形態の概略系統を示す系統図。
【図４】本発明に係る原子力発電プラントの第４の実施の形態の概略系統を示す系統図。
【図５】本発明に係る原子力発電プラントの第５の実施の形態の概略系統を示す系統図。
【図６】クロムの安定形態を示す電位−ｐＨ図。
【符号の説明】
１０…原子炉、１１…原子炉圧力容器、１２…炉心、１３…制御棒、１４…炉水滞留部、２１…蒸気タービン、２２…復水器、２３…給水配管、２４…給水加熱器、２５…加圧ポンプ、２６…蒸気配管、２７…復水浄化装置、３１…注入装置、３２…電位測定用電極、３３…電位測定セル、３４…腐食電位測定装置、３５…腐食生成物除去装置、３６…還元剤注入装置、３７…酸化剤注入装置。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nuclear power plant that generates power using energy generated in a nuclear reactor that uses water as a coolant, and a method of operating the nuclear power plant.
[0002]
[Prior art]
Conventional light water reactors are a boiling water reactor that generates power using steam generated by boiling cooling water in the reactor, and a pressurized water reactor that generates power using steam generated by a steam generator while keeping the reactor pressurized. Are roughly divided into two types. Each type has an energy efficiency of 30% or more, which is inferior to the recent 40% or more of supercritical thermal power generation. On the other hand, the development of a supercritical reactor in which the temperature is raised to a critical point of 374 ° C. or higher and the energy efficiency is increased to over 40% also in light water reactors is being studied (for example, see Japanese Patent Application Laid-Open No. 8-313664). ).
[0003]
In the once-through type of supercritical reactors, in which the turbine is driven directly by the reactor coolant, some of the radioactive corrosion products migrate to the outside of the reactor to increase the dose on the equipment surface, and are used by plant operators or during periodic inspections. May cause workers to be exposed.
[0004]
[Problems to be solved by the invention]
In the cooling water of the nuclear reactor, there is a trace amount of corrosion products that have melted out of the metal material constituting the equipment. This corrosion product adheres to the fuel rod surface, is activated and released again, and floats in the cooling water as a radioactive corrosion product. In the once-through type of supercritical reactors, in which the turbine is driven directly by the reactor coolant, some of the radioactive corrosion products migrate to the outside of the reactor to increase the dose on the equipment surface, and are used by plant operators or during periodic inspections. May cause workers to be exposed.
[0005]
If an attempt is made to physically or mechanically remove this corrosion product using a filter or the like, pressure resistance is generated, which causes a reduction in plant efficiency. An object of the present invention is to solve such a problem, and an object of the present invention is to suppress the transfer and accumulation of radioactive corrosion products to the surface of equipment or piping outside a nuclear reactor.
[0006]
[Means for Solving the Problems]
The present invention achieves the above object, and the invention according to claim 1 includes a reactor using water as a coolant, a turbine driven by steam supplied from the reactor, and the reactor A steam pipe for guiding steam from the turbine to the turbine, and a water supply pipe for returning the coolant discharged from the turbine to the nuclear reactor again, wherein the steam pipe has at least an oxidizing agent or a reducing agent. An injection device for injecting one is provided.
[0007]
According to the first aspect of the present invention, the target location of the nuclear power plant is set in a state in which corrosion products are unlikely to precipitate, so that the transfer of radioactive corrosion products to the surface of equipment or piping outside the reactor and Accumulation can be suppressed.
[0008]
According to a second aspect of the present invention, in the nuclear power plant according to the first aspect, a potential measuring device for measuring a corrosion potential is provided in the steam pipe. According to the second aspect of the present invention, the operation and effect of the first aspect of the present invention can be obtained, and furthermore, the transfer and accumulation of radioactive corrosion products to the surface of the target equipment outside the reactor can be suppressed more accurately. be able to.
[0009]
According to a third aspect of the present invention, there is provided the nuclear power plant according to the first or second aspect, wherein a corrosion product in the coolant is removed downstream of the injection device in the steam pipe. A removing device is provided. According to the third aspect of the invention, the operation and effect of the first or second aspect of the invention can be obtained, and the transfer and accumulation of radioactive corrosion products to the surface of equipment and the like outside the reactor can be further suppressed. .
[0010]
According to a fourth aspect of the present invention, in the nuclear power plant according to the third aspect, a potential measuring device for measuring a corrosion potential in the corrosion product removing device, and a radioactive device in the corrosion product removing device. In order to selectively accumulate corrosion products, the amount of at least one of the oxidizing agent and the reducing agent to be injected from the injection device is controlled so that the corrosion potential in the corrosion product removal device is controlled to be lower than that outside the corrosion product removal device. And means for controlling. According to the invention of claim 4, the operation and effect of the invention of claim 3 can be obtained, and the transfer and accumulation of radioactive corrosion products to the surface of equipment outside the reactor can be further suppressed.
[0011]
According to a fifth aspect of the present invention, in the nuclear power plant according to the third or fourth aspect, an oxidizing agent is injected upstream and downstream of the steam pipe with the corrosion product removing device interposed therebetween. An oxidizing agent injection device and a reducing agent injection device for injecting a reducing agent are provided. According to the fifth aspect of the invention, the operation and effect of the third or fourth aspect of the invention can be obtained, and the transfer and accumulation of radioactive corrosion products on the surface of equipment outside the reactor can be further suppressed. .
[0012]
According to a sixth aspect of the present invention, in the nuclear power plant according to any one of the first to fifth aspects, a part of water as the coolant is in a supercritical state. According to the sixth aspect of the present invention, the following effects can be obtained in addition to the functions and effects of the first to fifth aspects of the present invention. In other words, in a supercritical pressure furnace, since there is no gas-liquid interface in the furnace and the gas is transferred to the turbine system as a uniform fluid, radioactive corrosion products are considered to be easily transferred to the turbine system. It is possible to provide a safe nuclear power plant in which contamination of turbine system equipment by substances is suppressed.
[0013]
Further, the invention according to claim 7 is a reactor using water as a coolant, a turbine driven by steam supplied from the reactor, a steam pipe for guiding steam from the reactor to the turbine, A water supply pipe returning the coolant discharged from the turbine to the nuclear reactor again, comprising: injecting at least one of an oxidizing agent and a reducing agent into the steam pipe; The injection amount of the oxidizing agent or the reducing agent is controlled so that the flowing steam is maintained in a state where the corrosion products in the coolant are easily dissolved.
[0014]
According to the invention of claim 7, the target location of the nuclear power plant can be set in a state in which corrosion products are unlikely to precipitate, and the radioactive corrosion products are transferred to the surface of equipment or piping outside the reactor. And accumulation can be suppressed.
[0015]
The invention according to claim 8 is a reactor using water as a coolant, a turbine driven by steam supplied from the reactor, and a steam pipe for guiding steam from the reactor to the turbine. A water supply pipe for returning the coolant discharged from the turbine to the nuclear reactor again, comprising: injecting at least one of an oxidizing agent and a reducing agent into the steam pipe; Controlling the injection amount of the oxidizing agent or the reducing agent so as to selectively accumulate radioactive corrosion products in the coolant before the steam passing through the turbine flows into the turbine.
[0016]
According to the invention of claim 8, the target location of the nuclear power plant can be set in a state where corrosion products are hardly deposited, and the transfer and accumulation of radioactive corrosion products on the surface of equipment and the like outside the nuclear reactor Can be suppressed.
[0017]
According to a ninth aspect of the present invention, in the method for operating a nuclear power plant according to the seventh or eighth aspect, the corrosion potential in the steam pipe is measured, and the corrosion potential is brought close to a predetermined target range. The injection amount of the oxidizing agent or the reducing agent is controlled. According to the ninth aspect of the invention, the operation and effect of the seventh or eighth aspect of the invention can be obtained, and the transfer and accumulation of radioactive corrosion products to the surface of equipment outside the reactor can be further accurately suppressed. be able to.
[0018]
According to a tenth aspect of the present invention, in the method for operating a nuclear power plant according to any one of the seventh to ninth aspects, a potential-pH relationship characteristic representing a potential-pH relationship of a corrosion product is prepared in advance, Using the values of the temperature, the corrosion potential and the pH of each part of the steam pipe, the stable form of the corrosion product is estimated based on the potential-pH relationship characteristics, whereby, among the parts of the steam pipe, And controlling the injection amount of the oxidizing agent or the reducing agent so that the corrosion potential of the target portion is lower than that of the other portions and radioactive corrosion products in the coolant accumulate. According to the tenth aspect, the operation and effect of any one of the seventh to ninth aspects can be obtained, and the transfer and accumulation of radioactive corrosion products to the surface of equipment outside the reactor are further suppressed. be able to.
[0019]
According to an eleventh aspect of the present invention, in the operating method of the nuclear power plant according to any one of the seventh to tenth aspects, a part of water as the coolant is in a supercritical state. And According to the eleventh aspect of the present invention, the following effects are obtained in addition to the effects and advantages of the seventh aspect of the present invention. In other words, in a supercritical pressure furnace, since there is no gas-liquid interface in the furnace and the gas is transferred to the turbine system as a uniform fluid, radioactive corrosion products are considered to be easily transferred to the turbine system. It is possible to provide a safe operation method of a nuclear power plant, in which contamination of turbine system equipment by substances is suppressed.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a nuclear power plant according to the present invention will be described with reference to the drawings. However, the same or similar parts are denoted by the same reference numerals, and redundant description will be omitted.
[0021]
Referring to FIG. 1, a first embodiment of a nuclear power plant according to the present invention will be described. The reactor 10 is accommodated in a reactor pressure vessel 11, and a reactor core 12 loaded with nuclear fuel and a control rod 13 for controlling the reaction are contained in the reactor pressure vessel 11. Further, in the illustrated example, a reactor water retaining portion 14 is formed so as to surround the outside of the reactor core 12. The high-temperature and high-pressure steam generated in the reactor core 12 exits the reactor pressure vessel 11 and is sent to the steam turbine 21 through the steam pipe 26.
[0022]
In the steam turbine 21, the heat energy of the steam is converted into the work of rotating the turbine, and a generator (not shown) rotates to generate electric power. Here, the steam releases heat energy, and is further condensed in the condenser 22 to be condensed. The condensate that has exited the condenser 22 is purified by the condensate purification device, pressurized by the pressurizing pump 25, heated by the feed water heater 24, and returned to the reactor pressure vessel 11 through the feed water pipe 23.
[0023]
In this embodiment, an injection device 31 is connected to the steam pipe 26. The injection device 31 is for injecting an oxidizing agent or a reducing agent into the steam pipe 26, and by injecting the oxidizing agent or the reducing agent at a constant flow rate from the injection port, the corrosion product can be maintained in a state in which it can be easily dissolved. The solubility of the corrosion product in the high-temperature water changes depending on the oxidation-reduction potential, but the tendency changes depending on the temperature and the pH. An optimum value is determined for each plant so as to keep the corrosion potential outside the furnace pressure vessel 11 high.
[0024]
Here, as the oxidizing agent injected by the injection device 31, for example, oxygen gas or hydrogen peroxide solution is appropriate. Oxygen gas is abundant on the earth, easily dissolved in high-temperature water to act as an oxidizing agent, and does not pollute the environment, and is therefore effective as an oxidizing agent. In addition, hydrogen peroxide is relatively inexpensive, and when heated to 150 ° C. or higher, is thermally decomposed into oxygen and water, so that the same effect as oxygen injection can be obtained. Is effective as
[0025]
As the reducing agent injected by the injection device 31, for example, hydrogen gas or hydrazine is appropriate. Hydrogen is abundant on the earth, is easily dissolved in high-temperature water to act as a reducing agent, and is effective as a reducing agent because it does not pollute the environment. In addition, hydrazine can be easily synthesized, easily dissolved in high-temperature water to act as a reducing agent, and is effective as a reducing agent because it does not pollute the environment.
[0026]
In the present embodiment, before entering the steam turbine 21, the condenser 22, the pressurizing pump 25, and the feedwater heater 24 (these are collectively referred to as “turbine-based equipment”), the corrosion products are brought into a state in which they are easily melted. As a result, the deposition of radioactive substances on turbine equipment is suppressed, and the rise in dose is suppressed.
[0027]
In the embodiment shown in FIG. 1, the injection device 31 is provided at one place, but the injection device 31 can be provided at a plurality of places. This point is the same in other embodiments.
[0028]
Next, a second embodiment of the nuclear power plant according to the present invention will be described with reference to FIG. In this embodiment, in addition to the components of the first embodiment (FIG. 1), a corrosion potential measuring device 34 is installed in the steam pipe 26 downstream of the oxidizing or reducing agent injection device 31. The corrosion potential measuring device 34 includes a potential measuring cell 33 provided in the middle of the steam pipe 26 and a potential measuring electrode 32 installed in the potential measuring cell 33. The effect of the oxidizing agent or the reducing agent injected by the injection device 31 can be grasped by the corrosion potential measuring device 34. Therefore, the injection amount can be appropriately adjusted.
[0029]
Next, a third embodiment of the nuclear power plant according to the present invention will be described with reference to FIG. In this embodiment, in addition to the components of the first embodiment (FIG. 1), a corrosion product removal device 35 is installed in a steam pipe 26 downstream of an injection device 31 for injecting an oxidizing or reducing agent. ing.
[0030]
In the present embodiment, the injection port of the oxidizing or reducing agent injection device 31 is provided on the upstream side of the corrosion product removing device 35, and thereby the corrosion potential in the corrosion product removing device 35 can be adjusted from outside the device. By lowering the amount, a small amount of precipitated corrosion products can be removed by the corrosion product removal device 35. It is desirable that the corrosion product removing device 35 has a structure in which pressure loss is suppressed as low as possible.
[0031]
Next, a fourth embodiment of the nuclear power plant according to the present invention will be described with reference to FIG. In this embodiment, in addition to the components of the third embodiment (FIG. 3), a corrosion potential measurement device 34 similar to that shown in FIG. However, here, the potential measurement electrode 32 is provided in the corrosion product removal device 35 instead of being provided in the potential measurement cell 33 of FIG.
[0032]
According to this embodiment, a small amount of corrosion products deposited by the corrosion product removal device 35 can be removed as in the third embodiment (FIG. 3). Further, by knowing the corrosion potential in the corrosion product removing device 35, the amount of the oxidizing agent or reducing agent to be injected by the injection device 31 can be made appropriate, and the corrosion potential in the corrosion product removing device 35 can be reduced. .
[0033]
Next, a fifth embodiment of the nuclear power plant according to the present invention will be described with reference to FIG. In this embodiment, a reducing agent injection device 36, a corrosion product removal device 35, and an oxidizing agent injection device 37 are connected in series to the steam pipe 26 in this order from the upstream side. As in the fourth embodiment (FIG. 4), a corrosion potential measurement device 34 including a potential measurement electrode 32 is installed in the corrosion product removal device 35.
[0034]
According to this embodiment, the corrosion potential is kept low by injecting the reducing agent from the reducing agent injecting device 36, the corrosion product is precipitated, and the corrosion product is removed in the corrosion product removing device 35. In order to prevent the deposition of corrosion products in the above, an operation of injecting an oxidizing agent from the oxidizing agent injecting device 37 to increase the corrosion potential is possible.
As a modification of the fifth embodiment (FIG. 5), an arrangement in which the arrangement of the reducing agent injection device 36 and the oxidizing agent injection device 37 is reversed is also possible.
[0035]
FIG. 6 is a potential-pH diagram showing a stable form of chromium (Cr), which is a typical corrosion product in high-temperature water at 288 ° C. This figure was obtained by the inventors using the thermodynamic calculation method described in the EPRI report (EPRI NP-3137). From this figure, it can be seen that the chemical form of chromium changes depending on the potential and the pH.
[0036]
For example, when the pH is neutral, if the potential exceeds +0.25 V (SHE; Standard Hydrogen Electrode), dissolution starts, and the form of the CrO ₄ ^2- ion becomes stable. Therefore, when dissolved in this form, it is precipitated in the form of Cr ₂ O ₃ by injecting, for example, hydrogen gas as a reducing agent, and conversely exists in the form of Cr ₂ O ₃ at a slightly lower potential. In this case, when an oxidizing agent such as oxygen is injected, it dissolves in the form of CrO ₄ ^2- ions.
[0037]
Therefore, in general, a potential-pH diagram at the temperature of a target site is prepared, the potential is controlled by injecting an oxidizing agent or a reducing agent, and the corrosion potential of the equipment outside the reactor pressure vessel is adjusted from the inside of the reactor pressure vessel. By keeping it high, it is possible to suppress the adhesion of corrosion products to the target equipment, or conversely, to deposit it in the removal equipment by controlling the corrosion potential lower than that in the reactor pressure vessel. it can.
[0038]
For example, in the fifth embodiment (FIG. 5), hydrogen is injected from the reducing agent injection device 36 upstream of the corrosion product removal device 35, and Cr is precipitated as an oxide in the corrosion product removal device 35. After that, a system can be configured such that oxygen is injected by the oxidizing agent injection device 37 on the downstream side to dissolve Cr. Thereby, precipitation of Cr in the turbine system can be prevented.
[0039]
As the nuclear reactor of each of the above embodiments, for example, a supercritical pressure reactor in which the temperature / pressure inside the reactor is 374 ° C./22.1 MPa or more can be applied. In supercritical pressure furnaces, there is no gas-liquid interface in the furnace, and the transition to the turbine system as a uniform fluid is expected, so radioactive corrosion products are likely to migrate to the turbine system. It is possible to provide a safer nuclear power plant in which contamination of turbine equipment is suppressed.
[0040]
In the supercritical pressure state, there is no distinction between liquid and gas.However, in this specification, for the sake of convenience, the high-temperature and high-pressure working fluid supplied to the turbine from the reactor is referred to as steam, and is discharged from the turbine to the reactor. The relatively cold working fluid that returns to is called water.
[0041]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, in a nuclear power plant, transfer and accumulation | storage of the radioactive corrosion product to the surface of equipment, piping, etc. outside a nuclear reactor, such as a turbine system, can be suppressed. Thereby, it is possible to prevent or suppress the radioactive corrosion products from moving out of the reactor and increase the dose on the surface of the equipment, thereby suppressing the exposure of the plant operator or the operator during the periodic inspection.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a schematic system of a first embodiment of a nuclear power plant according to the present invention.
FIG. 2 is a system diagram showing a schematic system of a second embodiment of the nuclear power plant according to the present invention.
FIG. 3 is a system diagram showing a schematic system of a third embodiment of the nuclear power plant according to the present invention.
FIG. 4 is a system diagram showing a schematic system of a fourth embodiment of the nuclear power plant according to the present invention.
FIG. 5 is a system diagram showing a schematic system of a fifth embodiment of the nuclear power plant according to the present invention.
FIG. 6 is a potential-pH diagram showing a stable form of chromium.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Reactor, 11 ... Reactor pressure vessel, 12 ... Reactor core, 13 ... Control rod, 14 ... Reactor water retention part, 21 ... Steam turbine, 22 ... Condenser, 23 ... Water supply piping, 24 ... Feedwater heater, 25 ... Pressure pump, 26 ... Steam pipe, 27 ... Condensate purification device, 31 ... Injection device, 32 ... Electrode measurement electrode, 33 ... Electrical potential measurement cell, 34 ... Corrosion potential measurement device, 35 ... Corrosion product removal device , 36: reducing agent injection device, 37: oxidizing agent injection device.

Claims

A reactor using water as a coolant, a turbine driven by steam supplied from the reactor, a steam pipe for guiding steam from the reactor to the turbine, and a coolant discharged from the turbine again. A water supply pipe returning to the reactor, comprising:
Providing an injection device for injecting at least one of an oxidizing agent or a reducing agent into the steam pipe,
A nuclear power plant characterized by the following.

The nuclear power plant according to claim 1, wherein a potential measuring device for measuring a corrosion potential is provided in the steam pipe.

3. The nuclear power plant according to claim 1, further comprising a corrosion product removing device that removes a corrosion product in the coolant downstream of the injection device in the steam pipe. 4. Nuclear power plant.

The nuclear power plant according to claim 3,
A potential measuring device for measuring a corrosion potential in the corrosion product removing device,
An oxidizing agent injected from the injection device to control the corrosion potential in the corrosion product removal device to be lower than outside the corrosion product removal device so as to selectively accumulate radioactive corrosion products in the corrosion product removal device; Or means for controlling at least one amount of the reducing agent,
A nuclear power plant comprising:

5. The nuclear power plant according to claim 3, wherein an oxidizing agent is injected into the upstream and downstream sides of the steam pipe with the corrosion product removing device interposed therebetween, and reduction is performed by injecting a reducing agent. 6. And an agent injection device,
A nuclear power plant characterized by the following.

The nuclear power plant according to any one of claims 1 to 5, wherein a part of water is in a supercritical state as the coolant.

A reactor using water as a coolant, a turbine driven by steam supplied from the reactor, a steam pipe for guiding steam from the reactor to the turbine, and a coolant discharged from the turbine again. A water supply pipe returning to the nuclear reactor, and a method for operating a nuclear power plant having
Injecting at least one of an oxidizing agent or a reducing agent into the steam pipe, so that the steam flowing into the turbine is maintained in a state in which corrosion products in the coolant are easily melted. A method for operating a nuclear power plant, comprising controlling an injection amount.

A reactor using water as a coolant, a turbine driven by steam supplied from the reactor, a steam pipe for guiding steam from the reactor to the turbine, and a coolant discharged from the turbine again. A water supply pipe returning to the nuclear reactor, and a method for operating a nuclear power plant having
An oxidizing agent or a reducing agent is injected into the steam line, and the oxidizing agent is configured to selectively accumulate radioactive corrosion products in the coolant before steam flowing through the steam line flows into the turbine. Alternatively, a method for operating a nuclear power plant, comprising controlling an injection amount of a reducing agent.

The method for operating a nuclear power plant according to claim 7 or 8, wherein a corrosion potential in the steam pipe is measured, and an injection amount of the oxidizing agent or the reducing agent is controlled so that the corrosion potential approaches a predetermined target range. A method for operating a nuclear power plant, characterized in that:

The method for operating a nuclear power plant according to any one of claims 7 to 9,
A potential-pH relationship characteristic representing the potential-pH relationship of the corrosion product is prepared in advance, and the temperature, corrosion potential and pH value of each part of the steam pipe are used to perform corrosion based on the potential-pH relationship characteristic. Estimate the stable form of the product so that the corrosion potential of the target portion of each section of the steam pipe is lower than that of the other sections so that radioactive corrosion products in the coolant accumulate. Controlling an injection amount of the oxidizing agent or the reducing agent.

The method for operating a nuclear power plant according to any one of claims 7 to 10, wherein a part of water as the coolant is in a supercritical state.