JP2005283181A - Operation method of residual heat removal system - Google Patents

Operation method of residual heat removal system Download PDF

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JP2005283181A
JP2005283181A JP2004094005A JP2004094005A JP2005283181A JP 2005283181 A JP2005283181 A JP 2005283181A JP 2004094005 A JP2004094005 A JP 2004094005A JP 2004094005 A JP2004094005 A JP 2004094005A JP 2005283181 A JP2005283181 A JP 2005283181A
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heat removal
residual heat
removal system
reactor
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JP4349956B2 (en
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Masahiko Tachibana
正彦 橘
Kazunari Ishida
一成 石田
Yoichi Wada
陽一 和田
Naoshi Usui
直志 碓井
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Hitachi 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

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Abstract

<P>PROBLEM TO BE SOLVED: To reduce the quantity of a radioactive nuclide in an oxide film generated on the pipe inner surface in a residual heat removal system. <P>SOLUTION: A hydrazine injection device is equipped with a hydrazine adjustment tank 23a and a hydrazine injection pipe 20. A hydrazine injection pump 25 and a flow adjustment valve 22a are provided on the hydrazine injection system pipe 20. The hydrazine injection pipe 20 is connected to a residual heat removal system pipe 4 in the residual heat removal system 12. A control rod is inserted into the core to reduce a reactor output, and when the reactor water temperature is lowered to about 150°C, operation of the residual heat removal system 12 is started. A part of reactor water in recirculation system pipe 2 is introduced into the residual heat removal system pipe 4. The flow adjustment valve 22a is opened, and the hydrazine injection pump 25 is driven. Hydrazine in the hydrazine adjustment tank 23a is added to the reactor water flowing in the residual heat removal system pipe 4 through the hydrazine injection pipe 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、残留熱除去系の運転方法に係り、特に、残留熱除去系配管内面酸化皮膜中に蓄積する放射性核種（特に58Ｃｏ，60Ｃｏ）に起因する作業員の被曝を抑制するのに好適な残留熱除去系の運転方法に関する。 The present invention relates to an operation method of a residual heat removal system, and in particular, to suppress exposure of workers due to radionuclides (particularly 58 Co, 60 Co) accumulated in an inner surface oxide film of the residual heat removal system pipe. The present invention relates to a method for operating a suitable residual heat removal system.

代表的な沸騰水型原子炉（以下、ＢＷＲと記す）の系統図を図１に示す。ＢＷＲでは、燃料で発生した熱を効率的に原子炉圧力容器内の冷却水に移して蒸気にするため、冷却水を再循環ポンプやインターナルポンプを動作させて強制循環する。原子炉内で発生した蒸気は、炉心上部に設けられたセパレータおよびドライヤで湿分を除去した後タービンへ送り、一部はタービン抽気として取り出され、高圧および低圧ヒータの熱源として利用するが、他の大部分の蒸気は発電に利用した後、復水器で凝縮されて水に戻る。復水器内で復水はほぼ完全に脱気され、その際、炉心での水の放射線分解によって発生した酸素および水素もほぼ完全に除去される。   A system diagram of a typical boiling water reactor (hereinafter referred to as BWR) is shown in FIG. In BWR, in order to efficiently transfer the heat generated in the fuel to the cooling water in the reactor pressure vessel to make steam, the cooling water is forcedly circulated by operating a recirculation pump or an internal pump. Steam generated in the reactor is sent to the turbine after moisture is removed by a separator and dryer provided at the top of the core, and part of it is taken out as turbine bleed and used as a heat source for high and low pressure heaters. Most of the steam is used for power generation, then condensed in a condenser and returned to water. In the condenser, the condensate is almost completely degassed, and oxygen and hydrogen generated by radiolysis of water in the core are almost completely removed.

復水は再び給水として原子炉圧力容器に供給されるが、その際、原子炉圧力容器での放射性腐食生成物の発生を抑制するため、復水中の金属不純物を除去する目的で復水全量を復水フィルターで処理し、海水リーク時のＣｌを炉内に持ち込ませないために復水脱塩器等で処理し、続いて多段の低圧および高圧ヒータで２００℃近くまで加熱される。一方、腐食生成物の発生は原子炉圧力容器内や再循環系等の接水部でも生じ、炉内を循環する放射性腐食生成物の源となるため、これらの主要な一次系構造材は腐食の少ないステンレス鋼や、ニッケル基合金などの高耐食鋼が使用されている。また、炭素鋼製の原子炉圧力容器はステンレス鋼で内面肉盛りされ、炭素鋼が直接炉水と接触する事を防いでいる。以上のような材料上の配慮に加えて、炉水の一部を炉水浄化装置によって浄化し、炉水中に生成する微量の金属不純物を積極的に除去している。   Condensate is supplied again to the reactor pressure vessel as feed water, and at that time, in order to suppress the generation of radioactive corrosion products in the reactor pressure vessel, the total amount of condensate is reduced for the purpose of removing metal impurities in the condensate. It is treated with a condensate filter and treated with a condensate demineralizer or the like in order to prevent Cl at the time of seawater leakage from being brought into the furnace, and then heated to nearly 200 ° C. with a multistage low-pressure and high-pressure heater. On the other hand, the generation of corrosion products also occurs in the reactor pressure vessel and the wetted parts such as the recirculation system, and it becomes a source of radioactive corrosion products circulating in the reactor. High-corrosion-resistant steel such as stainless steel and nickel-base alloy are used. Moreover, the reactor pressure vessel made of carbon steel is built up with stainless steel to prevent the carbon steel from coming into direct contact with the reactor water. In addition to the material considerations described above, a portion of the reactor water is purified by the reactor water purification device, and trace metal impurities generated in the reactor water are actively removed.

しかし、このような材料、および水質管理による腐食抑制対策にも関わらず、炉水中の極わずかな金属不純物の存在は避けられないため、一部の金属不純物は金属酸化物として燃料棒の沸騰表面に付着する。燃料棒表面に付着した金属元素は燃料から放射される中性子の照射を受けて原子核反応を起こし60Ｃｏ，58Ｃｏ，51Ｃｒ，54Ｍｎ等の放射性核種を生成する。これらの放射性核種は大部分が酸化物の形態で燃料棒表面に付着するが、一部は取り込まれている酸化物の溶解度に従って溶出して炉水中に再放出され、あるいはクラッドと呼ばれる不溶性固体として炉水中に再放出される。これらの放射性物質は炉水浄化系への通水によって除去されるが、炉水浄化系への通水は給水流量の約２％であり、常に炉水の全量が浄化される訳ではないため、炉水中にはわずかに放射性物質が残存する。これらの放射性物質は、炉水と共に再循環系等を循環する間に構造材接水部表面に蓄積する。このため、構造材表面から放射線が放射され、定検作業時の従事者の放射線被曝が生じる。作業被曝の量は各人毎に規定値を超えないように管理されている。そのため、配管への放射性核種付着を低減する様々な方法、及び配管への放射性核種付着の駆動力となる炉水放射性核種濃度を低減する様々な方法が検討されている。 However, in spite of such materials and corrosion control measures by water quality management, the presence of very slight metal impurities in the reactor water is unavoidable, so some metal impurities are metal oxides as boiling surfaces of the fuel rods. Adhere to. The metal element attached to the surface of the fuel rod is irradiated with neutrons emitted from the fuel and causes a nuclear reaction to generate radionuclides such as 60 Co, 58 Co, 51 Cr, and 54 Mn. Most of these radionuclides adhere to the fuel rod surface in the form of oxides, but some are eluted according to the solubility of the incorporated oxides and re-released into the reactor water, or as insoluble solids called cladding. Re-released into the reactor water. Although these radioactive substances are removed by passing water through the reactor water purification system, the passage through the reactor water purification system is about 2% of the feed water flow rate, and the total amount of reactor water is not always purified. Some radioactive material remains in the reactor water. These radioactive substances accumulate on the surface of the structural material wetted part while circulating in the recirculation system together with the reactor water. For this reason, radiation is radiated from the surface of the structural material, resulting in radiation exposure of workers during regular inspection work. The amount of work exposure is managed so that it does not exceed the prescribed value for each person. Therefore, various methods for reducing the attachment of radionuclide to the pipe and various methods for reducing the concentration of the reactor water radionuclide that becomes the driving force for the attachment of the radionuclide to the pipe have been studied.

放射性イオンは、配管表面の酸化皮膜の成長に伴って取り込まれる事が知られている。これまで、再循環系、或いは炉内構造物除染に関する除染技術は、以下に示すように種々の方法が提案されている。   It is known that radioactive ions are taken in along with the growth of an oxide film on the pipe surface. Up to now, various methods have been proposed as decontamination techniques related to recirculation systems or decontamination of in-furnace structures as shown below.

（１）鉄注入技術：非特許文献１には、原子炉運転中，炉水中にＦｅを添加し、炉水中に含まれるＮｉと反応させＮｉフェライトを形成し、フェライト結晶中にＣｏを固定化する技術が示されている。その結果、放射性核種の炉水中への溶出が抑制され、炉水中放射性核種濃度を低減でき、炉外、特に再循環系配管酸化皮膜に取り込まれる量を低減することにより作業員の被曝量を低減する。 (1) Iron injection technology: In Non-Patent Document 1, during reactor operation, Fe is added to the reactor water, reacted with Ni contained in the reactor water to form Ni ferrite, and Co is fixed in the ferrite crystal. Technology to do is shown. As a result, elution of radionuclides into the reactor water is suppressed, the concentration of radionuclides in the reactor water can be reduced, and the exposure to workers is reduced by reducing the amount taken into the oxide film outside the furnace, especially in the recirculation system. To do.

（２）化学除染：一部の高経年化プラントや配管線量率の高いプラントでは、除染が行われている再循環系配管に付着している鉄酸化物（皮膜）を、シュウ酸などの有機酸を還元剤として使用して鉄酸化物を還元溶解する事により、酸化皮膜と、皮膜中に取り込まれている放射性核種とを併せて除去し、再循環系配管酸化皮膜に取り込まれている放射性核種の量を低減する技術が特許文献１に記載されている。ただし、酸化皮膜を除去した配管表面では初期腐食速度が速く、放射性核種の取込速度も増大してしまうため、再付着防止策が必要となる。 (2) Chemical decontamination: In some aging plants and plants with a high pipe dose rate, iron oxide (film) adhering to the recirculation piping where decontamination is performed is removed by oxalic acid, etc. By reducing and dissolving the iron oxide using the organic acid as a reducing agent, the oxide film and the radionuclides incorporated in the film are removed together and taken into the recirculation piping oxide film. Patent Document 1 discloses a technique for reducing the amount of radionuclides present. However, since the initial corrosion rate is fast and the radionuclide uptake rate is increased on the pipe surface from which the oxide film has been removed, measures for preventing reattachment are necessary.

（３）Ｚｎ注入技術：亜鉛などの金属イオンを炉水中に共存させ、再循環系配管表面に
Ｚｎを含む緻密な酸化皮膜を形成させる事で、酸化皮膜中への60Ｃｏや58Ｃｏ等の放射性核種の取り込みを抑制する方法が、特許文献２及び特許文献３に記載されている。 (3) Zn implantation technology: By making metal ions such as zinc coexist in the reactor water and forming a dense oxide film containing Zn on the surface of the recirculation system, such as 60 Co and 58 Co in the oxide film. Methods for suppressing the uptake of radionuclide are described in Patent Document 2 and Patent Document 3.

（４）特許文献４には、原子炉運転中に炉水が通水される再循環系配管およびＲＷＣＵ系配管に対して一定条件で予備酸化皮膜を形成させる技術が記載されている。 (4) Patent Document 4 describes a technique for forming a pre-oxidized film under certain conditions on a recirculation system pipe and a RWCU system pipe through which reactor water is passed during the operation of a nuclear reactor.

（５）給水へのＯ2 注入：給水系の炭素鋼表面に不溶性鉄酸化物の皮膜を生成させ、炉心への鉄流入を抑止：国内ＢＷＲのほとんどで実施されている（非特許文献２）。 (5) O 2 injection into feed water: An insoluble iron oxide film is formed on the surface of carbon steel in the feed water system, and iron inflow into the core is suppressed: implemented in most domestic BWRs (Non-patent Document 2) .

その他にも、（６）オゾンを用いた除染技術（特許文献５）、（７）レーザーを用いた除染技術（特許文献６）、（８）キャビテーションを伴う高速水中水噴流を用いた除染技術除染（特許文献７）などが実機で適用、あるいは適用が検討されている。   In addition, (6) decontamination technology using ozone (Patent Document 5), (7) decontamination technology using laser (Patent Document 6), (8) decontamination using a high-speed submerged water jet with cavitation Dyeing technology decontamination (Patent Document 7) and the like are being applied or studied for use in actual machines.

以上の対策の結果、再循環系配管や炉水浄化系配管に対する対策は担保されている。   As a result of the above measures, measures against recirculation piping and reactor water purification piping are secured.

しかし、１９９０年のＩＣＲＰ勧告による職業被曝の線量限度が、それまでの５０mSv／年から、５０ｍＳｖ／年かつ１００ｍＳｖ／５年に規制された事で、被曝低減に対する要求が一層強くなった。さらに、改良標準前の原子力発電プラントでは、炉内構造物の予防保全策として腐食環境を緩和する水素注入が適用されているが、米国では水素注入によって炉水中放射性核種濃度が増大し、これに伴い配管線量が増大する事から、水素注入条件下での配管線量の上昇抑制技術は、従来技術のみでは不充分になりつつある。上記のような背景から、新たな被曝低減技術が求められている。   However, since the dose limit for occupational exposure according to the 1990 ICRP recommendation was regulated to 50 mSv / year and 100 mSv / 5 years from the previous 50 mSv / year, the demand for exposure reduction became stronger. Furthermore, in nuclear power plants prior to the improvement standard, hydrogen injection to mitigate the corrosive environment has been applied as a preventive maintenance measure for reactor internals. In the United States, hydrogen injection increases the concentration of radionuclides in the reactor water. As the piping dose increases, the technology for suppressing the increase in piping dose under hydrogen injection conditions is becoming insufficient with the conventional technology alone. From the background as described above, a new exposure reduction technique is required.

原子力発電プラントにおける主要な被曝源は、再循環系配管，炉水浄化系配管、及び残留熱除去系配管であり、ＢＷＲが建設された当初は再循環系配管が主な被曝源であった。しかし、これまでに、後述するような被曝低減対策が採られてきた事により、全被曝量における残留熱除去系配管の寄与率が相対的に増加した。特に、改良型沸騰水型原子炉（以下、ＡＢＷＲと記す）では、再循環系が無いため、炉水浄化系配管と残留熱除去系配管とが主要な被曝源となっている。そのため、残留熱除去系へのＣｏイオン付着機構を調べる研究も行われるようになった（非特許文献３）。   The main exposure sources in nuclear power plants are recirculation system piping, reactor water purification system piping, and residual heat removal system piping. At the beginning of BWR construction, recirculation system piping was the main exposure source. However, the contribution rate of the residual heat removal system piping in the total exposure dose has been relatively increased by taking measures for reducing exposure as described later. Particularly, in the improved boiling water reactor (hereinafter referred to as ABWR), since there is no recirculation system, the reactor water purification system piping and the residual heat removal system piping are the main exposure sources. For this reason, studies have been conducted to investigate the Co ion adhesion mechanism to the residual heat removal system (Non-patent Document 3).

ＢＷＲが発電を行っている通常運転中では、残留熱除去系は停止状態にある。ただし、１回／月程度の頻度でサプレッションチャンバー（以下、Ｓ／Ｐ）内の水を使用して残留熱除去系の動作確認試験が実施される。炉心への制御棒挿入による原子炉停止操作が開始されると、炉心温度を低下させるために残留熱除去系が使用される。２８０℃から１５０℃までは蒸気発生量が多いため、主蒸気系統から蒸気を復水器に送り、発生する蒸気の気化熱により原子炉を冷却する。１５０℃以下の温度では、気化熱による冷却効率が低下するため、炉水再循環系から分岐する残留熱除去系に通水することによって炉水を冷却する。冷却された炉水は、再循環系を経由するか、あるいは直接原子炉に戻る。１００℃以下の温度では、気化熱による冷却がほとんど不能となるため、残留熱除去系での冷却が主体となる。残留熱除去系は予備系統を有し、２系統以上を有する。複数の系統を、停止操作実施毎に交互に運転する。原子炉水を冷却する速度は、残留熱除去系熱交換器に通水する流量と、この熱交換器のバイパスライン流量をコントロールする事で調整する。   During the normal operation in which the BWR is generating power, the residual heat removal system is in a stopped state. However, an operation confirmation test of the residual heat removal system is performed using water in the suppression chamber (hereinafter referred to as S / P) at a frequency of about once / month. When the reactor shutdown operation by inserting control rods into the core is started, the residual heat removal system is used to lower the core temperature. Since the steam generation amount is large from 280 ° C. to 150 ° C., the steam is sent from the main steam system to the condenser, and the reactor is cooled by the heat of vaporization of the generated steam. At a temperature of 150 ° C. or lower, the cooling efficiency due to the heat of vaporization decreases, so the reactor water is cooled by passing water through the residual heat removal system branched from the reactor water recirculation system. The cooled reactor water passes through the recirculation system or returns directly to the reactor. At a temperature of 100 ° C. or lower, cooling by the heat of vaporization is almost impossible, so cooling in the residual heat removal system is the main. The residual heat removal system has a spare system and has two or more systems. A plurality of systems are operated alternately every time a stop operation is performed. The speed at which the reactor water is cooled is adjusted by controlling the flow rate of water passing through the residual heat removal system heat exchanger and the bypass line flow rate of this heat exchanger.

上記した（１）〜（８）の各従来技術では、原子炉停止時に炉水が通水される残留熱除去系については考慮されておらず、炉水中の放射性核種の付着抑制対策は残留熱除去系には及んでいない。そのため、原子炉停止時の残留熱除去系運用によって、残留熱除去系が放射性核種を含む炉水に接触する事で放射性核種の残留熱除去系配管内面への付着が起こり、定検などの作業時の被曝源となる。特に再循環系の無いＡＢＷＲでは、定検作業時の被曝に与える残留熱除去系の寄与が大きい。また、残留熱除去系は炭素鋼配管で構成されているため、除染によって過去に付着した放射性核種を含む酸化物を除去しても、原子炉運転中の残留熱除去系の保管時に配管表面に生成する腐食生成物が、残留熱除去系運用時の炉水中放射性核種の再付着を促進させてしまい、除染の効果を維持できない。   In each of the prior arts (1) to (8) described above, the residual heat removal system through which the reactor water is passed when the reactor is shut down is not considered, and the countermeasure for suppressing the attachment of radionuclides in the reactor water is the residual heat. It does not reach the removal system. For this reason, when the residual heat removal system is operated when the reactor is shut down, the residual heat removal system comes into contact with the reactor water containing the radionuclide, causing radionuclides to adhere to the inner surface of the residual heat removal system piping. It becomes a source of time exposure. Especially in ABWR without a recirculation system, the contribution of the residual heat removal system to the exposure during the regular inspection work is large. In addition, since the residual heat removal system is composed of carbon steel pipes, the surface of the pipes can be stored during storage of the residual heat removal system during reactor operation even if the oxides containing radionuclides adhering to the past are removed by decontamination. Corrosion products generated in this process promote the reattachment of radionuclides in the reactor water during the operation of the residual heat removal system, and the decontamination effect cannot be maintained.

そのため、近年では、わずかではあるが残留熱除去系を対象とした被曝低減技術が提案されている。これらは、残留熱除去系運用中に実施する技術と残留熱除去系保管時に実施する技術とに大別される。下記に残留熱除去系を対象とした被曝低減技術を示す。   Therefore, in recent years, an exposure reduction technique for a residual heat removal system has been proposed, albeit slightly. These are broadly divided into technologies implemented during operation of the residual heat removal system and technologies implemented during storage of the residual heat removal system. The exposure reduction technology for the residual heat removal system is shown below.

（９）残留熱除去系の低温投入：残留熱除去系配管内酸化皮膜生成速度低減により、酸化皮膜中に取り込まれる放射性核種の量を低減する。再循環系配管、及び炉水浄化系配管では、腐食による酸化皮膜の成長に伴って原子炉水中の放射性イオンが酸化皮膜中に取り込まれ、放射性核種の蓄積が生じる。従来は、残留熱除去系では運用開始時の原子炉水温度が１５０℃以下と低く、上記プロセスの寄与は小さく、放射性クラッドの付着が主体である考えられていた。しかしながら近年では、放射性イオン成分の寄与も大きく、放射性イオン成分の付着は主に炉水温度１３０℃以上で生ると考えられている。この考えに基づき、一部の国内プラントでは残留熱除去系の低温投入が行われ、残留熱除去系の投入温度を従来の１５０℃から１２０℃以下に下げる事で放射性核種の付着を抑制している（非特許文献３）。 (9) Low temperature introduction of residual heat removal system: Reduce the amount of radionuclide incorporated into the oxide film by reducing the rate of oxide film formation in the residual heat removal system pipe. In the recirculation system piping and the reactor water purification system piping, radioactive ions in the reactor water are taken into the oxide film as the oxide film grows due to corrosion, and radionuclides accumulate. Conventionally, in the residual heat removal system, the reactor water temperature at the start of operation is as low as 150 ° C. or less, the contribution of the above process is small, and it has been considered that the deposition of radioactive cladding is the main. However, in recent years, the contribution of the radioactive ion component is also large, and it is considered that the attachment of the radioactive ion component mainly occurs at a reactor water temperature of 130 ° C. or higher. Based on this idea, some domestic plants use low-temperature residual heat removal systems, and by reducing the temperature of the residual heat removal system from the conventional 150 ° C to 120 ° C or less, the adhesion of radionuclides is suppressed. (Non-patent Document 3).

（10）残留熱除去系保管環境改善：配管内面の４弗化エチレンコーティング(特許文献８)は、放射性核種の付着量を減じるため、配管内面に４弗化エチレンを被覆する技術である。特許文献９に記載された残留熱除去系配管流路面への酸化皮膜付与、保管水への腐食抑制剤添加、及び残留熱除去系配管流路面の酸化皮膜形成は、残留熱除去系保管時の鉄酸化物生成を抑制して残留熱除去系運用時の放射性核種付着，蓄積を抑制する技術である。キャビテーションを伴う高速水中水噴流による放射性核種除去（特許文献９）は、キャビテーションを伴う高速水中水噴流に放射性核種を除去した後の残留熱除去系配管の炉水と接触する表面を接触させる事によって配管内表面に酸化皮膜を形成させたり、キャビテーションを伴う高速水中水噴流を用いて炉水と接触する表面に蓄積した放射性核種を含む酸化物の除去を行うと同時に新たな酸化皮膜を形成させる技術である。 (10) Improvement of storage environment for residual heat removal system: Tetrafluoroethylene coating on the inner surface of the pipe (Patent Document 8) is a technique for coating the inner surface of the pipe with tetrafluoroethylene in order to reduce the amount of radioactive nuclides attached. The provision of an oxide film on the surface of the residual heat removal system pipe flow path, the addition of a corrosion inhibitor to the stored water, and the formation of an oxide film on the surface of the residual heat removal system pipe flow path described in Patent Document 9 are performed during storage of the residual heat removal system. This technology suppresses the formation and accumulation of radionuclides during operation of the residual heat removal system by suppressing iron oxide generation. Radionuclide removal by high-speed submerged water jet with cavitation (Patent Document 9) is achieved by bringing the surface in contact with the reactor water of the residual heat removal system piping after removing the radionuclide into the high-speed submerged water jet with cavitation. Technology to form an oxide film on the inner surface of the pipe or to remove oxides containing radionuclides accumulated on the surface in contact with the reactor water using a high-speed submerged water jet with cavitation and at the same time form a new oxide film It is.

特開２０００−１０５２９５号公報JP 2000-105295 A 特開昭５８−７９６９１号公報JP 58-79691 A 特開２０００−１６２３８３号公報JP 2000-162383 A 特開昭６２−９５４９８号公報JP-A-62-95498 特開２００３−９８２９４号公報JP 2003-98294 A 特開平１１−１８３６９３号公報Japanese Patent Laid-Open No. 11-183893 特開２００２−１１６２９５号公報JP 2002-116295 A 特開平１０−２３２２９５号公報Japanese Patent Laid-Open No. 10-232295 特開２００２−２３６１９１号公報JP 2002-236191 A 植竹、他４名、日本原子力学会１９９７年秋の大会予稿集Ｌ３４Uetake, 4 others, Japan Atomic Energy Society Autumn Meeting Proceedings L34 防食技術、Ｖol.３２，Ｎo.５、２７６−２８５Anticorrosion technology, Vol.32, No.5, 276-285 植竹、他５名、日本原子力学会１９９９年秋の大会予稿集Ｊ５６Uetake and 5 others, Japan Atomic Energy Society Autumn Meeting Proceedings J56 表面、Ｖol.１６、Ｎo.３（１９７８）Surface, Vol. 16, No. 3 (1978)

残留熱除去系に着目した被曝低減方法は少なく、特に残留熱除去系通水中に着目した被曝低減方法は、前述した低温投入以外に考案されていない。前述の残留熱除去系を対象とした被曝低減に関する従来技術には、以下に示す課題がある。   There are few exposure reduction methods that focus on the residual heat removal system, and no exposure reduction method that focuses on the residual heat removal system water flow has been devised except for the low-temperature charging described above. The prior art related to exposure reduction for the residual heat removal system has the following problems.

残留熱除去系の低温投入は大きな効果を上げているものの、１５０℃以下では気化熱による冷却効率が低いため、残留熱除去系投入開始温度を下げると原子炉停止操作に要する時間が増大し、時間的な不利益を生じる。キャビテーションを伴う高速水中水噴流技術は、施工時に酸化皮膜が除去されるため、酸化皮膜に取り込まれている放射性核種を物理的に除去するため放射性核種除去効果は大きいが、残留熱除去系運転時に前述のように130℃以上で通水すると酸化皮膜が生成されるため、放射性核種が取り込まれる可能性がある。４弗化エチレンコーティング技術は、運転中及び保管中双方において放射性核種の付着を抑制するため、高い効果が得られるが、既に酸化皮膜中に取り込まれている放射性核種を除去する性質は有しておらず、他の除染技術との併用が必要となる。   Although the low temperature introduction of the residual heat removal system has a great effect, the cooling efficiency due to the heat of vaporization is low at 150 ° C. or lower, so lowering the residual heat removal system introduction start temperature increases the time required for the reactor shutdown operation, There is a time penalty. The high-speed submerged water jet technology with cavitation is effective in removing radionuclides because it physically removes radionuclides incorporated in the oxide film because the oxide film is removed during construction. As described above, when water is passed at 130 ° C. or higher, an oxide film is generated, and thus radionuclides may be taken in. The tetrafluoroethylene coating technology is highly effective because it suppresses the deposition of radionuclides during both operation and storage, but it has the property of removing radionuclides that have already been incorporated into the oxide film. Therefore, it is necessary to use in combination with other decontamination techniques.

残留熱除去系の保管水に腐食抑制剤としてヒドラジンを添加する方法（特許文献９）は、炉水に接する表面に蓄積した放射性核種を除去した後に、残留熱除去系を満たす水中に腐食抑制剤としてヒドラジンを添加する技術であって、他の除染技術との併用が必要である。   The method of adding hydrazine as a corrosion inhibitor to the stored water of the residual heat removal system (Patent Document 9) is a method of removing the radionuclide accumulated on the surface in contact with the reactor water and then submerging the corrosion inhibitor in water that satisfies the residual heat removal system. As a technique for adding hydrazine, it must be used in combination with other decontamination techniques.

また、特許文献９のヒドラジンの添加時期は、残留熱除去系に保管水として使用する炉水を満たす時のみであり、保管期間中、および残留熱除去系と原子炉圧力容器内を炉水が循環されている期間にはヒドラジンの添加を行わない。かつ、保管期間が終了して残留熱除去系に通水する直前に、残留熱除去系の系統内にメイクアップ水を通水して、残留熱除去系内のフラッシングを行うため、ヒドラジンを含有する保管水は炉水に混入されない。よって、当然ながら、残留熱除去系に通水している期間中には炉水中にヒドラジンは存在しない。従って、残留熱除去系を高温（炉水温度１５０℃）で通水を開始すると、鉄の水酸化物の脱離ピークは１００℃〜１７０℃にあるため（非特許文献４）脱水反応が進む。特許文献９に記載の発明は、主に残留熱除去系保管期間中における１００℃以下の条件での水酸化鉄の生成を伴う腐食を抑制する技術であって、結果として、高温（１５０℃）で通水を開始したとき、通水中の放射性核種の付着，蓄積を抑制できない。以上示したように、残留熱除去系内と原子炉圧力容器内とを炉水が循環するような期間中において、残留熱除去系への通水を高温（１５０℃）の状態で開始できて、かつ、通水中に、既に酸化皮膜中に取り込まれている放射性核種の除去能力と、新規に取り込まれる放射性核種の量を低減する効果とを併せ持つ技術は考案されていない。   In addition, hydrazine is added only in Patent Document 9 only when the reactor water used as the storage water is filled in the residual heat removal system, and the reactor water is kept in the residual heat removal system and the reactor pressure vessel during the storage period. No hydrazine is added during the circulation period. In addition, hydrazine is contained to flush makeup water into the residual heat removal system and flush the residual heat removal system immediately before passing through the residual heat removal system after the storage period is over. The stored water is not mixed into the reactor water. Therefore, of course, there is no hydrazine in the reactor water during the period when water is passed through the residual heat removal system. Therefore, when water flow is started in the residual heat removal system at a high temperature (reactor water temperature 150 ° C.), the dehydration peak of iron hydroxide is 100 ° C. to 170 ° C. (Non-Patent Document 4), and the dehydration reaction proceeds. . The invention described in Patent Document 9 is a technique for suppressing corrosion accompanied by the formation of iron hydroxide mainly under conditions of 100 ° C. or less during the storage period of the residual heat removal system, and as a result, high temperature (150 ° C.) When water flow is started at, the attachment and accumulation of radionuclides in the water flow cannot be suppressed. As described above, during the period in which the reactor water circulates in the residual heat removal system and the reactor pressure vessel, the water flow to the residual heat removal system can be started at a high temperature (150 ° C.). In addition, no technology has been devised that has both the ability to remove radionuclides already taken into the oxide film and the effect of reducing the amount of new radionuclides taken into the water.

従来技術よりも効率的に残留熱除去系を運用するためには、残留熱除去系の投入が150℃で可能であり、高分子樹脂を使用せず、放射性核種付着が生じる残留熱除去系運転時を対象とした被曝低減であり、既に酸化皮膜中に取り込まれている放射性核種の除去能力と、新規に取り込まれる放射性核種の量を低減する効果とを併せ持つ技術が要求される。   In order to operate the residual heat removal system more efficiently than the conventional technology, the residual heat removal system can be introduced at 150 ° C, and the operation of the residual heat removal system that causes radionuclide adhesion without using polymer resin There is a need for a technique that reduces exposure to time and has both the ability to remove radionuclides already incorporated into oxide films and the effect of reducing the amount of radionuclides newly incorporated.

本発明の目的は、残留熱除去系の配管内面に生成する酸化皮膜内の放射性核種の量を低減できる残留熱除去系の運転方法を提供することにある。   An object of the present invention is to provide a method for operating a residual heat removal system that can reduce the amount of radionuclide in an oxide film formed on the inner surface of a pipe of the residual heat removal system.

上記した目的を達成する本発明の特徴は、沸騰水型原子炉の炉水温度を低下する原子炉停止操作運転期間中で、残留熱除去系に１００℃以上１５０℃以下の炉水を通水する期間中に、残留熱除去系に還元性物質を添加することにある。   The feature of the present invention that achieves the above-described object is that reactor water at 100 ° C. or more and 150 ° C. or less is passed through the residual heat removal system during the reactor shutdown operation period in which the reactor water temperature of the boiling water reactor is lowered. During this period, a reducing substance is added to the residual heat removal system.

これにより、残留熱除去系を流れる炉水が還元性雰囲気となり、酸化皮膜の生成を抑制して、放射性核種の付着サイトを減じる事によって放射性核種の付着，蓄積を抑制して残留熱除去系全体の放射性核種量を減じる事ができる。炉水が還元性雰囲気となるため、既に残留熱除去系配管内面に生成している酸化皮膜を還元，溶解できる。これにより、酸化皮膜中に取り込まれている放射性核種を溶出させる事によって、残留熱除去系全体の放射性核種量を減じる事ができる。   As a result, the reactor water flowing through the residual heat removal system becomes a reducing atmosphere, suppresses the formation of oxide film, and reduces the deposition and accumulation of radionuclides by reducing the deposition sites of radionuclides, thereby reducing the entire residual heat removal system. The amount of radionuclide can be reduced. Since the reactor water becomes a reducing atmosphere, the oxide film already formed on the inner surface of the residual heat removal system pipe can be reduced and dissolved. As a result, the amount of radionuclide in the entire residual heat removal system can be reduced by eluting the radionuclide incorporated in the oxide film.

本発明は、残留熱除去系保管期間中の保管水に腐食抑制剤としてヒドラジンを添加する方法（特許文献９）とは異なり、残留熱除去系を流れる炉水温度が保管時よりも高温である１００℃以上１５０℃以下である期間中にヒドラジンを添加し、後述するように鉄酸化物の生成を抑制して放射性核種の付着，蓄積を抑制する技術である。   Unlike the method of adding hydrazine as a corrosion inhibitor to stored water during the residual heat removal system storage period (Patent Document 9), the temperature of the reactor water flowing through the residual heat removal system is higher than that during storage. In this technique, hydrazine is added during a period of 100 ° C. or more and 150 ° C. or less, and the formation of iron oxide is suppressed as described later, thereby suppressing the attachment and accumulation of radionuclides.

前述のように、特許文献９に記載の方法においてはヒドラジンを含有する保管水が炉内に流入する事は無く、残留熱除去系への通水時に新たなヒドラジン添加を行う記載は無いため、残留熱除去系へ炉水を通水する期間中には炉水中にヒドラジンが存在しない方法である。従って、炉水温度が１５０℃の時点で残留熱除去系に通水した場合、酸素を含有する炉水が流入し、残留熱除去系配管表面に放射性付着サイトである鉄酸化物を生成する。鉄の水酸化物の脱離ピークは１００℃〜１７０℃にあることから（非特許文献４）、高温（１５０℃）で残留熱除去系に通水した場合、鉄の水酸化物の脱水，フェライト化が促進され、残留熱除去系に炉水を通水している期間中には放射性核種の付着抑制効果は得られない。   As described above, in the method described in Patent Document 9, storage water containing hydrazine does not flow into the furnace, and there is no description of adding new hydrazine when water is passed to the residual heat removal system. This is a method in which hydrazine does not exist in the reactor water during the period when the reactor water is passed through the residual heat removal system. Therefore, when water is passed through the residual heat removal system at the time when the reactor water temperature is 150 ° C., the reactor water containing oxygen flows in, and iron oxide that is a radioactive adhesion site is generated on the surface of the residual heat removal system pipe. Since the desorption peak of iron hydroxide is between 100 ° C. and 170 ° C. (Non-patent Document 4), when water is passed through the residual heat removal system at a high temperature (150 ° C.), dehydration of iron hydroxide, Ferritization is promoted and the effect of suppressing radionuclide adhesion cannot be obtained during the period when the reactor water is passed through the residual heat removal system.

これに対して、本発明は、残留熱除去系に炉水を通水する全期間を通じて炉水中にヒドラジンを存在させるため、後述するように鉄酸化物の生成を生じない腐食電位を保持して通水でき、これにより、残留熱除去系に炉水を通水している期間中における配管内面への放射性核種の付着を抑制する効果が得られる。また、ヒドラジンを添加した炉水が一旦炉内を流れた後に再度残留熱除去系を流れる構成を有しており、炉内を流れる際に照射を受けてヒドラジンと酸素との反応を促進する事が出来、これによっても鉄酸化物の生成が減じられるため、より効率的に新規に取り込まれる放射性核種の量を低減する効果が得られる。   In contrast, in the present invention, since hydrazine is present in the reactor water throughout the entire period of passing the reactor water to the residual heat removal system, a corrosion potential that does not produce iron oxide is maintained as described later. It is possible to pass water, thereby obtaining an effect of suppressing the attachment of the radionuclide to the inner surface of the pipe during the period when the reactor water is passed through the residual heat removal system. In addition, the reactor water to which hydrazine has been added once flows through the residual heat removal system after flowing through the reactor, and when it flows through the reactor, it is irradiated to promote the reaction between hydrazine and oxygen. This also reduces the amount of radionuclide that is newly incorporated more efficiently because the production of iron oxide is reduced.

以上から、本発明によれば、残留熱除去系への通水を１５０℃で開始でき、また、既に酸化皮膜中に取り込まれている放射性核種の除去能力と、新規に取り込まれる放射性核種の量を低減する効果とを併せて得ることができ、特許文献９のように他の除染工程を必要としない利点を有する。   From the above, according to the present invention, water flow to the residual heat removal system can be started at 150 ° C., and the radionuclide removal capability already incorporated in the oxide film and the amount of newly incorporated radionuclide And the effect of not requiring another decontamination step as in Patent Document 9.

発明者らは、前述した種々の従来技術を考慮して種々の検討を行った結果、残留熱除去系の配管内面に生成される酸化皮膜内における放射性核種の量を低減できる方法を新たに見出した。その検討結果を、以下に説明する。   As a result of various studies in consideration of the above-described various conventional techniques, the inventors have found a new method that can reduce the amount of radionuclides in the oxide film formed on the inner surface of the pipe of the residual heat removal system. It was. The examination results will be described below.

残留熱除去系に使用されている炭素鋼配管では、炉水浄化系配管と同様に、高温水中ではヘマタイトとマグネタイトに加えて原子炉水中に含まれるＮｉなどのイオンを取り込んだフェライトを生成する。一方、残留熱除去系の配管が原子炉運転中に晒されているような１００℃以下の低温水中では水酸化鉄が主な腐食生成物である。この条件で生成する水酸化鉄は藻状の形態で表面積が大きく、水中の各種イオンを吸着する性質がある。このため、原子炉停止操作が行われ残留熱除去系の運用が始まると、炉水中の放射性イオンの吸着が起こる。   In the carbon steel pipe used for the residual heat removal system, ferrite that takes in ions such as Ni contained in the reactor water in addition to hematite and magnetite is generated in high-temperature water, similarly to the reactor water purification system pipe. On the other hand, iron hydroxide is the main corrosion product in low-temperature water of 100 ° C. or lower where the residual heat removal system piping is exposed during the reactor operation. Iron hydroxide produced under these conditions has an algae-like form, a large surface area, and a property of adsorbing various ions in water. For this reason, when the reactor shutdown operation is performed and the operation of the residual heat removal system is started, the adsorption of radioactive ions in the reactor water occurs.

水酸化鉄は、約１００℃以上の条件で（化１）及び（化２）に示したような反応で脱水反応を起こし、ヘマタイトやマグネタイトを生じる。この時、脱水領域にＮｉ，Ｃｏおよびこれらの放射性イオンが吸着しているとこれらのＮｉやＣｏを含むフェライトが(化３)及び（化４）のように生じて、脱離し難くなる。この様子を図２に模式的に示す。残留熱除去系保管中に残留熱除去系配管（炭素鋼）内表面に生成した水酸化鉄に放射性Ｃｏイオンの吸着領域が生じ、残留熱除去系運用時に１００℃以上の温度に晒された際に脱水領域が生じ、この２つが重なった領域でＣｏフェライトが生じ、放射性Ｃｏイオンの蓄積が起こる。   Iron hydroxide undergoes a dehydration reaction in the reactions shown in (Chemical Formula 1) and (Chemical Formula 2) under conditions of about 100 ° C. or higher to produce hematite and magnetite. At this time, if Ni, Co and these radioactive ions are adsorbed in the dehydration region, ferrite containing these Ni and Co is generated as shown in (Chemical Formula 3) and (Chemical Formula 4), and it is difficult to desorb. This is schematically shown in FIG. When the residual area of heat removal system is stored, the adsorption region of radioactive Co ions is generated in the iron hydroxide formed on the inner surface of the residual heat removal system pipe (carbon steel), and it is exposed to a temperature of 100 ° C or higher during operation of the residual heat removal system. A dehydration region is generated in the region, and Co ferrite is generated in the region where the two are overlapped, and accumulation of radioactive Co ions occurs.

２Ｆｅ(ＯＨ)3 → Ｆｅ2Ｏ3 ＋ ３Ｈ2Ｏ …（化１）
Ｆｅ(ＯＨ)2 ＋ ２Ｆｅ(ＯＨ)3 → Ｆｅ3Ｏ4 ＋ ４Ｈ2Ｏ …（化２）
Ｎｉ2+ ＋ ２Ｆｅ(ＯＨ)3 → ＮｉＦｅ2Ｏ4 ＋ ２Ｈ2Ｏ ＋ ２Ｈ+ …（化３）
Ｃｏ2+ ＋ ２Ｆｅ(ＯＨ)3 → ＣｏＦｅ2Ｏ4 ＋ ２Ｈ2Ｏ ＋ ２Ｈ+ …（化４） 2Fe (OH) 3 → Fe 2 O 3 + 3H 2 O (chemical formula 1)
Fe (OH) 2 + 2Fe (OH) 3 → Fe 3 O 4 + 4H 2 O (chemical formula 2)
Ni 2+ + 2Fe (OH) 3 → NiFe 2 O 4 + 2H 2 O + 2H + (Chemical formula 3)
Co 2+ + 2Fe (OH) 3 → CoFe 2 O 4 + 2H 2 O + 2H + (Chemical Formula 4)

従って、残留熱除去系配管への放射性イオンの蓄積防止は、上記Ｃｏ取り込み経路のうち何れか１つ以上を抑制すれば達成できることになる。   Therefore, prevention of accumulation of radioactive ions in the residual heat removal system piping can be achieved by suppressing any one or more of the Co uptake paths.

そこで発明者らは、残留熱除去系投入時に残留熱除去系を流れる炉水中に還元性物質を添加して残留熱除去系配管内面に生成する酸化皮膜に取り込まれている放射性核種を酸化皮膜と共に炉水中に溶解し、かつ残留熱除去投入時に配管内面に生成する酸化皮膜の生成を抑制して放射性核種付着サイトを無くし、また、還元性物質添加と同時にＣｏよりも鉄酸化物中に取り込まれやすい物質を必要に応じて添加してフェライトに取り込まれる放射性核種の付着，蓄積を抑制し、又は酸化鉄及びオキシ水酸化鉄の放射性核種の吸着サイトを占有し易い物質を必要に応じて添加してフェライトに取り込まれる放射性核種の付着，蓄積を抑制し、又は鉄の腐食を抑制する効果を有する物質を必要に応じて添加して鉄酸化物の生成を抑制する事により放射性核種の付着，蓄積を抑制する事を特徴とする放射性核種付着抑制方法により達成される事を見出した（図３参照）。   Therefore, the inventors added a reducing substance to the reactor water flowing through the residual heat removal system when the residual heat removal system was introduced, and the radionuclide incorporated into the oxide film generated on the inner surface of the residual heat removal system pipe together with the oxide film. Suppresses the formation of oxide film that dissolves in the reactor water and forms on the inner surface of the piping when residual heat is removed, and eliminates radionuclide attachment sites. At the same time as reducing substances are added, it is incorporated into iron oxide rather than Co. If necessary, add a substance that tends to occupy the adsorption site of the radionuclide of iron oxide and iron oxyhydroxide. In this way, substances that have the effect of suppressing the deposition and accumulation of radionuclides incorporated into ferrite or suppressing the corrosion of iron are added as necessary to reduce the release of iron oxides. Adhesion sex nuclides found that is achieved by a method radionuclides adhesion prevention, characterized in that to suppress the accumulation (see FIG. 3).

以下、本発明の好ましい具体例について、説明する。   Hereinafter, preferred specific examples of the present invention will be described.

好ましくは、沸騰水型原子炉の炉水温度を低下する原子炉停止操作運転期間中で、残留熱除去系に１００℃以上１５０℃以下の炉水を通水する期間中に、残留熱除去系に還元性物質を添加する工程と、この還元性物質による放射性核種付着蓄積抑制効果を高める補完物質を残留除去系に添加する工程を有することが望ましい。   Preferably, in the reactor shutdown operation period in which the reactor water temperature of the boiling water reactor is lowered, the residual heat removal system is passed during the period in which the reactor water of 100 ° C. or more and 150 ° C. or less is passed through the residual heat removal system. It is desirable to have a step of adding a reducing substance to the residual removal system and a step of adding a supplementary substance that enhances the radionuclide adhesion accumulation suppressing effect of the reducing substance to the residual removal system.

高温水中でのＣｏの鉄酸化物への吸着挙動は、高ｐＨでヘマタイト（α−Ｆｅ2Ｏ3）へのＣｏ付着量が増加する(J. Nuc.Sci. Tech.，Ｖol.２３，Ｎo.１０，pp.９２６−９２７，Oct (１９８６)) 。しかしながら、上記の具体例では残留熱除去系内全体が還元性雰囲気に晒されるため、後述する（化６）に示すようにヘマタイトの還元が生じ、主にマグネタイトやフェライトが生成するか、さらに還元が進み溶解すると考えられる。炭素鋼に形成する酸化被膜はＦｅ酸化物のみ(Ｆｅ(ＯＨ)3，ＦｅＯＯＨ，Ｆｅ2Ｏ3，Ｆｅ3Ｏ4) であるから、酸化皮膜が形成するとすればＣｏはＣｏＦｅ2Ｏ4（コバルトフェライト）を形成すると考えられる。ＣｏＦｅ2Ｏ4は逆スピネル化合物で、Ｃｏは八面***置に配位する。 The adsorption behavior of Co to iron oxide in high-temperature water increases the amount of Co deposited on hematite (α-Fe 2 O 3 ) at high pH (J. Nuc. Sci. Tech., Vol. 23, No. .10, pp.926-927, Oct (1986)). However, in the above specific example, since the entire residual heat removal system is exposed to a reducing atmosphere, hematite is reduced as shown in (Chemical Formula 6) described later, and mainly magnetite and ferrite are generated or further reduced. Is considered to dissolve. Since the oxide film formed on carbon steel is only Fe oxide (Fe (OH) 3 , FeOOH, Fe 2 O 3 , Fe 3 O 4 ), if an oxide film is formed, Co is CoFe 2 O 4 (cobalt). Ferrite) is considered to be formed. CoFe 2 O 4 is an inverse spinel compound, and Co is coordinated to an octahedral position.

［Ｆｅ3+］ｔ［Ｃｏ2+，Ｆｅ3+］ｏ Ｏ4 …（化５） [Fe 3+ ] t [Co 2+ , Fe 3+ ] o O 4 (Chemical Formula 5)

ここで、［ ］ｏはスピネル化合物の八面***置を表し、［ ］ｔはスピネル化合物の四面***置を表す。   Here, [] o represents the octahedral position of the spinel compound, and [] t represents the tetrahedral position of the spinel compound.

従って、Ｃｏよりも八面***置に優先して配位する機能を有する補完物質を炉水中に含有させる事で、Ｃｏの取り込み量を抑制でき、また、既に取り込まれているＣｏとの置換が生じるため、付着，蓄積する放射性核種の量を抑制できる。   Therefore, by incorporating a supplementary substance having the function of preferentially coordinating the octahedral position over Co in the reactor water, the amount of Co uptake can be suppressed, and substitution with Co already taken in occurs. Therefore, the amount of radionuclide that adheres and accumulates can be suppressed.

Ｎ2Ｈ4 ＋ ６Ｆｅ2Ｏ3 → ４Ｆｅ3Ｏ4 ＋ ２Ｈ2Ｏ ＋ Ｎ2 …（化６） N 2 H 4 + 6Fe 2 O 3 → 4Fe 3 O 4 + 2H 2 O + N 2 (Chemical formula 6)

残留熱除去系通水時に添加する還元性物質としては、ヒドラジン，カーボヒドラジド，ジイミド，酸化数が負の窒素を含む化合物，メタノール、及びＬ−アスコルビン酸のうちで、何れか１種以上を用いるとよい。   As a reducing substance to be added when water is passed through the residual heat removal system, one or more of hydrazine, carbohydrazide, diimide, a compound containing nitrogen having a negative oxidation number, methanol, and L-ascorbic acid are used. Good.

原子炉停止操作が開始され、前述のように原子炉水温度が１５０℃程度まで低下した時点で残留熱除去系が投入され、残留熱除去系内に炉水を通水させたとき、炉水中に含まれる60Ｃｏ，58Ｃｏなどの放射性核種も残留熱除去系に流入し、酸化皮膜内に取り込まれる事になる。そこで、水酸化鉄発生の原因である溶存酸素を低減させるため、及び既に生成している水酸化鉄を還元して除去するために、前述のように炉水中に還元性物質を加える。この還元性物質としては、ヒドラジンが好適である。 When the reactor shutdown operation is started and the reactor water temperature is lowered to about 150 ° C. as described above, the residual heat removal system is introduced, and when the reactor water is passed through the residual heat removal system, Radionuclide such as 60 Co and 58 Co contained in the gas flows into the residual heat removal system and is taken into the oxide film. Therefore, a reducing substance is added to the reactor water as described above in order to reduce dissolved oxygen that is the cause of iron hydroxide generation and to reduce and remove iron hydroxide that has already been generated. As this reducing substance, hydrazine is preferred.

ヒドラジンを加える事により、残留熱除去系配管表面への鉄酸化物の生成を抑制できる。つまり、放射性核種の付着サイトである鉄酸化物を減じる事が可能となる。また、図４に示すように、ヒドラジン添加により炉水ｐＨが高くなるため、残留熱除去系配管内面に生成している鉄酸化物が還元，溶解する。このとき、鉄酸化物に付着、或いは取り込まれている60Ｃｏ，58Ｃｏなどの放射性核種も同時に溶解する。また、鉄酸化物が新たに生成する事が抑制される。これにより、既に酸化皮膜内に取り込まれている放射性核種を除去すると同時に、放射性核種の付着サイトを除去するため新たな付着も抑制される事になる。 By adding hydrazine, it is possible to suppress the formation of iron oxide on the surface of the residual heat removal system pipe. That is, it is possible to reduce the iron oxide that is the attachment site of the radionuclide. Further, as shown in FIG. 4, since the reactor water pH is increased by the addition of hydrazine, the iron oxide generated on the inner surface of the residual heat removal system pipe is reduced and dissolved. At this time, radionuclides such as 60 Co and 58 Co adhering to or incorporated in the iron oxide also dissolve simultaneously. Further, new generation of iron oxide is suppressed. As a result, the radionuclide already taken in the oxide film is removed, and at the same time, the new nuclide is suppressed because the attachment site of the radionuclide is removed.

ヒドラジン以外にも、カーボヒドラジド，ジイミド，酸化数が負の窒素を含む化合物，メタノール，Ｌ−アスコルビン酸など、炉水を還元性雰囲気とする物質の残留熱除去系への添加によっても、鉄酸化物の生成を抑制できるため、放射性核種の蓄積量を減少する事が可能となる。   In addition to hydrazine, carbohydrazide, diimide, compounds containing nitrogen with a negative oxidation number, methanol, L-ascorbic acid, etc., can be added to the residual heat removal system using furnace water as a reducing atmosphere. Since the production of objects can be suppressed, the amount of accumulated radionuclides can be reduced.

前述の補完物質は、逆スピネル結晶物の八面***置に配位し易い２価金属イオンを含むイオン結合性物質である。   The aforementioned complementary substance is an ion-binding substance containing a divalent metal ion that easily coordinates to the octahedral position of the inverse spinel crystal.

前述のように、Ｃｏは逆スピネル化合物ＣｏＦｅ2Ｏ4となる。Ｃｏの八面***置への入り易さは、
Ｃｏ2+ ＜ Ｍｇ2+ ＜ Ｆｅ2+ ＜ Ｃｕ2+ ＜ Ａｌ3+ ＜ Ｎｉ2+ ＜ Ｍｎ3+ ＜ Ｃｒ3+ …（化７）
のように優先順位が存在する（J. inorg. Chem.，Ｖol.２９，pp.２７０１−２７１４.
(１９６７)）。従って、Ｃｏを放出させるためには、Ｃｏよりも逆スピネル結晶物の八面***置に入り易い機能を有する２価のイオンを含むイオン結合性物質を添加すればよい。 As described above, Co becomes the reverse spinel compound CoFe 2 O 4 . The ease of entering Co's octahedral position is
Co 2+ <Mg 2+ <Fe 2+ <Cu 2+ <Al 3+ <Ni 2+ <Mn 3+ <Cr 3+ ( Formula 7)
(J. inorg. Chem., Vol. 29, pp. 2701-2714.
(1967)). Therefore, in order to release Co, an ion-binding substance containing a divalent ion having a function that is easier to enter the octahedral position of the reverse spinel crystal than Co may be added.

また、補完物質として、酸化鉄、及びオキシ水酸化鉄の放射性核種の吸着サイトを占有し易い物質を用いることが望ましい。前述の機能を有する補完物質を添加する事により放射性核種よりも優先して酸化鉄，オキシ水酸化鉄の吸着サイトに吸着し、フェライト化が起こったとしても、残留熱除去系配管への放射性核種の蓄積を抑制できる。   In addition, it is desirable to use a substance that can easily occupy the adsorption sites of iron oxide and radionuclide of iron oxyhydroxide as a complementary substance. Addition of supplementary substances with the functions described above gives priority to the adsorption site of iron oxide and iron oxyhydroxide over the radionuclide, and even if ferritization occurs, the radionuclide to the residual heat removal system piping Can be suppressed.

また、補完物質としては、該補完物質と鉄とが溶液を介して接触している際に鉄の腐食量を減じる物質であることが望ましい。前記機能を有する物質を炉水に添加する事により、母材からのＦｅ溶出が抑制されて鉄酸化物の生成量が減じられるため、放射性核種吸着サイトが減じられ、放射性核種付着，蓄積量が減じられる。   Further, it is desirable that the supplementary substance is a substance that reduces the corrosion amount of iron when the supplementary substance and iron are in contact via a solution. By adding the substance having the above function to the reactor water, the elution of Fe from the base material is suppressed and the amount of iron oxide produced is reduced, so that the radionuclide adsorption sites are reduced, and the amount of radionuclide adhesion and accumulation is reduced. Reduced.

前述の逆スピネル結晶物の八面***置に配位し易い２価金属イオンを含むイオン結合性の物質として、Ｍｇ，Ｆｅ，Ｎｉのうち何れか一つ以上を用いるとよい。（化７）のうち、Ｃｕは炉内構造物の腐食電位を上昇させ、腐食を加速する可能性があるため除外して、２価イオンを抽出すると、逆スピネルの八面***置に配位し易い金属イオンはＭｇ2+，
Ｆｅ2+，Ｎｉ2+が好適である事が判る。これらを添加すると、Ｃｏ2+が放出され、かつ新たな取り込み量を抑制できる。 Any one or more of Mg, Fe, and Ni may be used as an ion-binding substance containing a divalent metal ion that easily coordinates to the octahedral position of the above-described reverse spinel crystal. Of (Chemical Formula 7), Cu increases the corrosion potential of the internal structure of the furnace and may accelerate the corrosion. Therefore, when excluding divalent ions, Cu is coordinated to the octahedral position of the reverse spinel. Easy metal ions are Mg 2+ ,
It can be seen that Fe 2+ and Ni 2+ are suitable. When these are added, Co 2+ is released and the amount of new uptake can be suppressed.

前述の酸化鉄、及びオキシ水酸化鉄の放射性核種の吸着サイトを占有し易い物質として、Ｍｇを用いるとよい。酸化鉄，オキシ水酸化鉄の吸着サイトを占有し易い金属として
Ｍｇが好適であり（日本科学会第６７回春季年会，ｐｐ６４５（１９９４））、Ｍｇ添加によりＣｏの吸着サイトを減じることができる。 Mg may be used as a substance that easily occupies the adsorption sites of the radionuclide of iron oxide and iron oxyhydroxide described above. Mg is suitable as a metal that easily occupies the adsorption sites of iron oxide and iron oxyhydroxide (The 67th Annual Meeting of the Japanese Society of Science, pp 645 (1994)), and the adsorption site of Co can be reduced by adding Mg. .

前述の鉄の腐食を抑制する物質として、Ｚｎ，Ａｌ，Ｍｇ、その他鉄よりも酸化還元電位が卑な元素を用いるとよい。鉄の腐食を抑制する働きを有する金属としてＺｎが好適である（Water Chemistry for Nuclear Reactor Systems 4, BNES, London (１９８６)）。Ｚｎ添加によって鉄の溶出が抑制され、その結果Ｃｏの吸着サイトである鉄酸化物の生成を減じられる。   As a substance that suppresses the corrosion of iron, Zn, Al, Mg, and other elements having a lower oxidation-reduction potential than iron may be used. Zn is suitable as a metal having a function of suppressing iron corrosion (Water Chemistry for Nuclear Reactor Systems 4, BNES, London (1986)). By adding Zn, elution of iron is suppressed, and as a result, the production of iron oxide which is an adsorption site of Co can be reduced.

これら補完物質を含む物質を添加する事により、ヒドラジンなどの還元性物質を添加しても除去しきれない鉄酸化物、及び生成を避けきれない鉄酸化物への60Ｃｏ，58Ｃｏの付着，取り込みを抑制でき、放射性核種付着，蓄積抑制効果を高める事ができる。 By adding substances containing these complementary substances, 60 Co, 58 Co adheres to iron oxides that cannot be removed even when reducing substances such as hydrazine are added, and iron oxides that cannot be generated. Uptake can be suppressed, and radionuclide adhesion and accumulation suppression effects can be enhanced.

前述の還元性物質を添加する位置は、好ましくは、再循環系配管から残留熱除去系への分岐点、または原子炉圧力容器から残留熱除去系への分岐点に至るまでの再循環系配管の任意位置である。これにより残留熱除去系全体に対してＣｏ蓄積抑制効果が得られる。   Preferably, the reductive substance is added at a position where the recirculation system pipe reaches the branch point from the recirculation system pipe to the residual heat removal system or the branch point from the reactor pressure vessel to the residual heat removal system. Is an arbitrary position. As a result, an effect of suppressing the accumulation of Co is obtained for the entire residual heat removal system.

上記した運転方法は、残留熱除去系を有する沸騰水型原子炉型、及び改良型沸騰水型原子炉を用いた原子力発電プラントにおいて、還元性物質調整タンクに接続された還元性物質注入配管と、補完物質調整タンクに接続された補完物質注入配管を残留熱除去系配管に接続し、原子炉停止操作時に、残留熱除去系投入（炉水通水）開始時に、還元性物質と補完物質を、残留熱除去配管内を流れる炉水に添加して残留熱除去を行うことが望ましい。   In the nuclear power plant using the boiling water reactor type having the residual heat removal system and the improved boiling water reactor, the above-described operation method includes a reducing substance injection pipe connected to the reducing substance adjustment tank, , Connect the supplementary substance injection pipe connected to the supplementary substance adjustment tank to the residual heat removal system pipe, and at the time of shutting down the reactor, at the start of the residual heat removal system (water flow through the reactor water) It is desirable to remove residual heat by adding to the reactor water flowing in the residual heat removal pipe.

本発明によれば、残留熱除去系運用時に通水する炉水を還元性水質に保持でき、金属の腐食を抑制でき、酸化物を還元溶解できる。その結果、残留熱除去系通水時に炉水と接触する配管内表面に蓄積した放射性核種を除去でき、かつ酸化皮膜から放出した放射性核種の再付着を抑制して残留熱除去系に炉水を通水できるので、残留熱除去系配管への放射性核種の蓄積を抑制する事ができる。また、残留熱除去系の投入温度を１５０℃に出来る。その結果、定険時等の作業員の被ばく量を低減でき、原子炉を効率的に冷却できる。   ADVANTAGE OF THE INVENTION According to this invention, the reactor water passed at the time of residual heat removal type | system | group operation | movement can be hold | maintained to a reducing water quality, a metal corrosion can be suppressed, and an oxide can be reduced and dissolved. As a result, it is possible to remove radionuclides that have accumulated on the pipe inner surface that comes into contact with the reactor water when passing through the residual heat removal system, and to suppress the reattachment of radionuclides released from the oxide film, and to supply the reactor water to the residual heat removal system. Since water can be passed, accumulation of radionuclides in the residual heat removal system piping can be suppressed. In addition, the charging temperature of the residual heat removal system can be set to 150 ° C. As a result, it is possible to reduce the exposure amount of workers at the time of a fixed period and the like, and to cool the reactor efficiently.

本発明の実施例を、図面に基づいて説明する。   Embodiments of the present invention will be described with reference to the drawings.

本発明の好適な一実施例である実施例１の残留熱除去系の運転方法を、図１を用いて説明する。本実施例は、ＢＷＲ停止操作中に残留熱除去系内を流れる炉水にヒドラジンを添加する例である。図１はＢＷＲの残留熱除去系の構成を示している。   A method for operating the residual heat removal system according to the first embodiment which is a preferred embodiment of the present invention will be described with reference to FIG. In this embodiment, hydrazine is added to the reactor water flowing in the residual heat removal system during the BWR stop operation. FIG. 1 shows the configuration of a BWR residual heat removal system.

沸騰水型原子力発電プラントは、原子炉格納容器５内に設置された、沸騰水型原子炉を構成する原子炉圧力容器１を有する。原子炉圧力容器１は、２系統の再循環系を有する。これらの再循環系は、原子炉圧力容器１に連絡された再循環系配管２、及び再循環系配管２に設置された再循環ポンプ３を有する。沸騰水型原子力発電プラントはＡ系，Ｂ系の二系統の残留熱除去系１２を備える。これらの残留熱除去系１２は、再循環ポンプ３の上流側で再循環系配管２に一端が接続され、再循環ポンプ３の下流側で再循環系配管２に他端が接続される残留熱除去系配管４をそれぞれ有する。残留熱除去系配管４は再循環系配管２から分岐していると言える。開閉弁６，７，残留熱除去系ポンプ８，熱交換器（冷却装置）９及び開閉弁１１が、この順序で上流側より、それぞれの残留熱除去系配管４に設置される。腐食電位測定装置３０が開閉弁１１の下流側で残留熱除去系配管４に設置される。バイパス弁１０を設けたバイパス配管１３が、熱交換器９をバイパスするように残留熱除去系配管４に接続される。残留熱除去系配管４は炭素鋼製の配管である。   The boiling water nuclear power plant has a reactor pressure vessel 1 that constitutes a boiling water reactor installed in a reactor containment vessel 5. The reactor pressure vessel 1 has two recirculation systems. These recirculation systems include a recirculation system pipe 2 connected to the reactor pressure vessel 1 and a recirculation pump 3 installed in the recirculation system pipe 2. The boiling water nuclear power plant includes two systems of residual heat removal systems 12 of A system and B system. The residual heat removal system 12 has one end connected to the recirculation system pipe 2 on the upstream side of the recirculation pump 3 and the other end connected to the recirculation system pipe 2 on the downstream side of the recirculation pump 3. Each has a removal system pipe 4. It can be said that the residual heat removal system pipe 4 is branched from the recirculation system pipe 2. The on-off valves 6 and 7, the residual heat removal system pump 8, the heat exchanger (cooling device) 9 and the on-off valve 11 are installed in the respective residual heat removal system pipes 4 from the upstream side in this order. A corrosion potential measuring device 30 is installed in the residual heat removal system pipe 4 on the downstream side of the on-off valve 11. A bypass pipe 13 provided with a bypass valve 10 is connected to the residual heat removal system pipe 4 so as to bypass the heat exchanger 9. The residual heat removal system pipe 4 is a pipe made of carbon steel.

ヒドラジン注入装置は、ヒドラジン調整タンク２３ａ，ヒドラジン調整タンク２３ａに接続されたヒドラジン注入系配管２０を備える。ヒドラジン注入ポンプ２５及び流量調整バルブ２２ａがヒドラジン注入系配管２０に設けられる。ヒドラジン注入系配管２０は、それぞれの残留熱除去系１２の残留熱除去系配管４に連絡される。   The hydrazine injection device includes a hydrazine adjustment tank 23a and a hydrazine injection system pipe 20 connected to the hydrazine adjustment tank 23a. A hydrazine injection pump 25 and a flow rate adjustment valve 22 a are provided in the hydrazine injection system pipe 20. The hydrazine injection system pipe 20 is connected to the residual heat removal system pipe 4 of each residual heat removal system 12.

発電を行う沸騰水型原子力発電プラントの通常運転では、原子炉圧力容器１内の炉水は、再循環ポンプ３の運転により加圧されて原子炉圧力容器１内の炉心（図示せず）に供給される。この炉水は、炉心内で過熱されて蒸気となる。蒸気は、図示されていないが、主蒸気配管を通ってタービンに送られ、タービンを回転させる。タービンに連結された発電機が回転することによって電気が発生する。タービンから吐出された蒸気は復水器で凝縮されて水となる。この水は給水ポンプで加圧されて原子炉圧力容器１内に供給される。   In normal operation of a boiling water nuclear power plant that generates power, the reactor water in the reactor pressure vessel 1 is pressurized by the operation of the recirculation pump 3 and is applied to the core (not shown) in the reactor pressure vessel 1. Supplied. This reactor water is superheated in the core and becomes steam. Although not shown, the steam is sent to the turbine through the main steam pipe to rotate the turbine. Electricity is generated when a generator connected to the turbine rotates. The steam discharged from the turbine is condensed by the condenser to become water. This water is pressurized by a feed pump and supplied into the reactor pressure vessel 1.

沸騰水型原子力発電プラントの運転を停止するとき、すなわち、原子炉の運転を停止するとき、炉心内に制御棒を挿入して原子炉出力を減少させる。原子炉出力の低下に伴い、炉水の温度は低下する。炉水温度が１５０℃程度まで降下すると、残留熱除去系１２の運転が開始される。すなわち、開閉弁６，７及び１１が開き、残留熱除去系ポンプ８が駆動される。再循環系配管２内を流れている炉水の一部が、Ａ系及びＢ系の残留熱除去系１２の各残留熱除去系配管４に導入される。この炉水は、熱交換器９で冷却されて温度が低下され、再循環系配管２を通って原子炉圧力容器１内に戻される。熱交換器９への炉水の供給量は、バイパス弁１０及び開閉弁１１の開度によって調節される。   When the operation of the boiling water nuclear power plant is stopped, that is, when the operation of the reactor is stopped, a control rod is inserted into the core to reduce the reactor output. As the reactor power decreases, the temperature of the reactor water decreases. When the reactor water temperature falls to about 150 ° C., the operation of the residual heat removal system 12 is started. That is, the on-off valves 6, 7 and 11 are opened, and the residual heat removal system pump 8 is driven. A part of the reactor water flowing in the recirculation system pipe 2 is introduced into each residual heat removal system pipe 4 of the A system and B system residual heat removal system 12. The reactor water is cooled by the heat exchanger 9 and the temperature is lowered, and then returned to the reactor pressure vessel 1 through the recirculation system pipe 2. The amount of reactor water supplied to the heat exchanger 9 is adjusted by the opening degree of the bypass valve 10 and the on-off valve 11.

残留熱除去系１２の運転に先立ち、ヒドラジン調整タンク２３ａ内に、予め所望濃度に調整したヒドラジン溶液を満たし、不活性ガス配管２４を通じてヒドラジン調整タンク
２３ａ内を不活性ガスでバブリングし、ヒドラジン溶液を脱気しておく。残留熱除去系配管４へ炉水を供給し始めると同時に、流量調整バルブ２２ａを開き、ヒドラジン注入ポンプ２５を駆動する。このため、ヒドラジン調整タンク２３ａ内のヒドラジンが、ヒドラジン注入系配管２０を通して各残留熱除去系配管４内を流れる炉水に添加される。ヒドラジンの濃度は、炭素鋼の腐食電位実測結果に基づき調整する。腐食電位測定装置３０により、残留熱除去系配管４を構成する炭素鋼の炉水と接触する状態での腐食電位測定を行う。測定された炭素鋼の腐食電位が−０.６Ｖvs.ＳＨＥ以下となるように、残留熱除去系配管４内の炉水に添加するヒドラジン添加量を調整する。腐食電位−０.６Ｖvs.ＳＨＥ以下でＦＡＣによる減肉量が増大する事が知られている(“Redox Conditions Effect on Flow
Accelerated Corrosion：Inflluence of Hydrazine and Oxigen”，Water Chemistry in Nuclear Reactors Systems，２２−２６ April ２００２)。残留熱除去系１２を運転してヒドラジンの残留熱除去系配管４内への添加を開始すると、残留熱除去系配管４の炭素鋼の腐食電位が徐々に低下する。そのため、残留熱除去系配管４内に流れる炉水中に添加するヒドラジン濃度は、流量調整バルブ２２ａを調整して徐々に低濃度にしてゆき、炭素鋼の腐食電位が−０.６Ｖvs.ＳＨＥ以下となるように連続的に調整を行う。このとき、炉水の水質基準は原子炉停止時の基準が適用され、定常運転中より制約は少なくなる。ヒドラジンを添加することにより水質が変動する可能性があるが、停止時の水質基準内で添加を行うことができる。 Prior to the operation of the residual heat removal system 12, the hydrazine adjustment tank 23a is filled with a hydrazine solution adjusted to a desired concentration in advance, and the hydrazine adjustment tank 23a is bubbled with an inert gas through an inert gas pipe 24, so that the hydrazine solution is supplied. Degas. Simultaneously with the start of supplying the reactor water to the residual heat removal system pipe 4, the flow rate adjustment valve 22a is opened and the hydrazine injection pump 25 is driven. For this reason, hydrazine in the hydrazine adjustment tank 23 a is added to the reactor water flowing in each residual heat removal system pipe 4 through the hydrazine injection system pipe 20. The concentration of hydrazine is adjusted based on the actual measurement result of the corrosion potential of carbon steel. The corrosion potential measurement device 30 performs the corrosion potential measurement in a state where the corrosion potential measurement device 30 is in contact with the carbon steel reactor water constituting the residual heat removal system pipe 4. The amount of hydrazine added to the reactor water in the residual heat removal system pipe 4 is adjusted so that the measured corrosion potential of the carbon steel is −0.6 V vs. SHE or less. It is known that the amount of thinning due to FAC increases when the corrosion potential is -0.6 V vs. SHE or less ("Redox Conditions Effect on Flow
Accelerated Corrosion: Inflluence of Hydrazine and Oxigen ", Water Chemistry in Nuclear Reactors Systems, 22-26 April 2002). When the residual heat removal system 12 is operated and the addition of hydrazine into the residual heat removal system pipe 4 is started, the residual The corrosion potential of the carbon steel in the heat removal system piping 4 gradually decreases, so the hydrazine concentration added to the reactor water flowing in the residual heat removal system piping 4 is gradually decreased by adjusting the flow rate adjustment valve 22a. Continue to adjust so that the corrosion potential of the carbon steel is -0.6 V vs. SHE or less.At this time, the water quality standard of the reactor water is applied when the reactor is shut down. Although the water quality may be changed by adding hydrazine, the addition can be performed within the water quality standards at the time of stoppage.

ヒドラジンを添加した炉水は、残留熱除去系配管４内を流れて残留熱除去系１２から流出し、ヒドラジンを含有したまま原子炉圧力容器１に戻される。ヒドラジンが分解せずに残留したとしても、ステンレス鋼は還元環境でクロム酸化物皮膜が除去されることは無く、還元されない（非特許文献２）事から、構造材料の耐食性を劣らせない。残留して炉内に流入したヒドラジンは炉心で放射線の照射を受けて、最終的には、酸素存在下では水，窒素に分解し、酸素が存在しない場合は、窒素，水素，アンモニアが生成する。一部のプラントでは、復水器に銅系合金を使用しており、復水中にアンモニアが存在すると、酸素の共存下で腐食により生じたＣｕ2+イオンが、可溶性のアンモニア錯体を形成するため、アンモニアを極力存在させない事が望まれる。そのためにも、ヒドラジン注入を停止するまでの期間中、前述の添加濃度調整を連続して行う。 The reactor water to which hydrazine has been added flows through the residual heat removal system pipe 4 and flows out of the residual heat removal system 12, and is returned to the reactor pressure vessel 1 while containing hydrazine. Even if the hydrazine remains without being decomposed, the stainless steel does not remove the chromium oxide film in a reducing environment and is not reduced (Non-Patent Document 2), so the corrosion resistance of the structural material is not deteriorated. The hydrazine that remains and flows into the furnace is irradiated with radiation in the core, and eventually decomposes into water and nitrogen in the presence of oxygen, and in the absence of oxygen, nitrogen, hydrogen, and ammonia are produced. . In some plants, copper-based alloys are used in the condenser, and when ammonia is present in the condensate, Cu 2+ ions generated by corrosion in the presence of oxygen form soluble ammonia complexes. It is desirable that ammonia should not exist as much as possible. Therefore, the aforementioned addition concentration adjustment is continuously performed during the period until the hydrazine injection is stopped.

以上の操作を、残留熱除去系１２への通水中連続して行い、通水停止と同時にヒドラジン注入も停止する。   The above operation is continuously performed in the water passing through the residual heat removal system 12, and the hydrazine injection is stopped simultaneously with the water passing stop.

この実施形態では、還元性雰囲気となるため残留熱除去系配管４内面の酸化皮膜は還元され、放射性核種は酸化皮膜内から放出される。   In this embodiment, since it becomes a reducing atmosphere, the oxide film on the inner surface of the residual heat removal system pipe 4 is reduced, and the radionuclide is released from the oxide film.

本発明の他の実施例である実施例２の残留熱除去系の運転方法を、図５を用いて説明する。本実施例は、沸騰水型原子炉の運転停止操作（原子炉出力低下操作）中に、残留熱除去系１２内を流れる炉水に、ヒドラジン、及び補完物質としてのＭｇ(ＯＨ)2 を添加するものである。炉水浄化装置２７が、開閉弁１１よりも下流側で残留熱除去系配管４に設置される。 The operation method of the residual heat removal system of Example 2 which is another Example of this invention is demonstrated using FIG. In this embodiment, hydrazine and Mg (OH) 2 as a supplementary substance are added to the reactor water flowing in the residual heat removal system 12 during the shutdown operation (reactor power reduction operation) of the boiling water reactor. To do. A reactor water purification device 27 is installed in the residual heat removal system pipe 4 on the downstream side of the on-off valve 11.

本実施例は、実施例１と同様にヒドラジン注入装置を有しており、さらに補完物質注入装置を設けている。補完物質注入装置は、補完物質調整タンク２３ｂ、及び補完物質調整タンク２３ｂに接続された補完物質注入配管２１を備える。流量調整バルブ２２ｂ及び補完物質注入ポンプ２６が補完物質注入配管２１に設置される。補完物質注入配管２１は、それぞれの残留熱除去系１２の残留熱除去系配管４に連絡される。補完物質調整タンク
２３ｂ内には、所望濃度のＭｇ(ＯＨ)2 溶液が満たされている。本実施例における他の構成は、実施例１と同じである。 This embodiment has a hydrazine injection device as in the first embodiment, and further includes a supplementary substance injection device. The supplementary substance injection apparatus includes a supplementary substance adjustment tank 23b and a supplementary substance injection pipe 21 connected to the supplementary substance adjustment tank 23b. A flow rate adjusting valve 22 b and a supplementary substance injection pump 26 are installed in the supplementary substance injection pipe 21. The supplementary substance injection pipes 21 are connected to the residual heat removal system pipes 4 of the respective residual heat removal systems 12. The supplementary substance adjustment tank 23b is filled with a Mg (OH) 2 solution having a desired concentration. Other configurations in the present embodiment are the same as those in the first embodiment.

沸騰水型原子力発電プラントの運転を停止する際、すなわち、原子炉出力の出力が低下して１５０℃程度まで降下したとき、実施例１と同様に、残留熱除去系１２の運転が開始され、開閉弁６，７及び１１が開く。これによって、原子炉圧力容器１内の炉水が再循環系配管２を介して残留熱除去系配管４に供給される。流量調整バルブ２２ａを開いてヒドラジン注入ポンプ２５を駆動することによって、ヒドラジン調整タンク２３ａ内のヒドラジンを、ヒドラジン注入系配管２０を介してそれぞれの残留熱除去系１２の各残留熱除去系配管４内に注入する。また、流量調整バルブ２２ｂを開いて補完物質注入ポンプ２６を駆動することによって、補完物質調整タンク２３ｂ内のＭｇ(ＯＨ)2 溶液を、補完物質注入配管２１を通してそれぞれの残留熱除去系１２の残留熱除去系配管４内に注入する。残留熱除去系配管４の運転に先立ち、補完物質調整タンク２３ｂ内に、予め所望濃度に調整したＭｇ(ＯＨ)2 溶液を満たし、不活性ガス配管２４を通して補完物質調整タンク２３ｂ内を不活性ガスでバブリングして脱気しておく。 When the operation of the boiling water nuclear power plant is stopped, that is, when the output of the reactor power decreases to about 150 ° C., the operation of the residual heat removal system 12 is started as in Example 1, The on-off valves 6, 7 and 11 are opened. As a result, the reactor water in the reactor pressure vessel 1 is supplied to the residual heat removal system pipe 4 via the recirculation system pipe 2. By opening the flow rate adjustment valve 22a and driving the hydrazine injection pump 25, the hydrazine in the hydrazine adjustment tank 23a is converted into the residual heat removal system pipes 4 of the respective residual heat removal systems 12 via the hydrazine injection system pipes 20. Inject. In addition, by opening the flow rate adjusting valve 22b and driving the supplementary substance injection pump 26, the Mg (OH) 2 solution in the supplementary substance adjustment tank 23b passes through the supplementary substance injection pipe 21 and remains in each residual heat removal system 12. Inject into the heat removal system piping 4. Prior to the operation of the residual heat removal system pipe 4, the supplementary substance adjustment tank 23 b is filled with a Mg (OH) 2 solution adjusted to a desired concentration in advance, and the inert substance pipe 24 is filled with the inert gas inside the supplementary substance adjustment tank 23 b. Bubbling and degassing.

ヒドラジン及びＭｇ(ＯＨ)2 溶液はほぼ同時に各残留熱除去系配管４内を流れる炉水に注入される。ヒドラジン注入により、残留熱除去系内酸化皮膜に取り込まれている放射性核種を溶出し、残留熱除去系配管４内面での鉄酸化物成長は抑制されると共に、残留熱除去系１２内に炉水と共に放射性イオンが流れ込んでも、放射性イオンの蓄積に必要なフェライトの材料となる水酸化鉄が配管内面に存在しないため、放射性核種の付着は抑制される。また、Ｍｇは、Ｃｏよりもフェライトの八面***置に配位し易いので、溶出したＣｏが再度鉄酸化物内に取り込まれる事を抑制できる。 The hydrazine and Mg (OH) 2 solution are injected into the reactor water flowing through each residual heat removal system pipe 4 almost simultaneously. By injecting hydrazine, the radionuclide incorporated in the oxide film in the residual heat removal system is eluted, and iron oxide growth on the inner surface of the residual heat removal system pipe 4 is suppressed, and the reactor water enters the residual heat removal system 12. At the same time, even when radioactive ions flow in, since iron hydroxide, which is a ferrite material necessary for accumulation of radioactive ions, does not exist on the inner surface of the pipe, the attachment of radionuclides is suppressed. Moreover, since Mg is more easily coordinated to the octahedral position of ferrite than Co, it is possible to suppress the eluted Co from being taken into the iron oxide again.

ヒドラジンとＭｇを添加した炉水は、残留熱除去系配管４内を流れた後、再循環系配管２に戻るが、再循環系配管２への接続点上流側に炉水浄化装置２７を設け、炉水浄化装置２７に炉水を通水した後に再循環系配管２に接続する。炉水浄化装置２７に炉水を通水することで、溶出した放射性核種の原子炉圧力容器１内への持ち込み量を減じることが出来る。また、炉水浄化装置２７に炉水を通水することで、残留熱除去系配管４で反応せずに残留したヒドラジンとＭｇを分解、あるいは捕集して、浄化された水を原子炉圧力容器１内に送水できる。その他の構成は第１の実施形態と同様である。   The reactor water to which hydrazine and Mg have been added flows through the residual heat removal system pipe 4 and then returns to the recirculation system pipe 2. A reactor water purification device 27 is provided upstream of the connection point to the recirculation system pipe 2. Then, the reactor water is passed through the reactor water purification device 27 and then connected to the recirculation pipe 2. By passing the reactor water through the reactor water purification device 27, it is possible to reduce the amount of radionuclides that have been eluted into the reactor pressure vessel 1. Further, by passing the reactor water through the reactor water purification device 27, the residual hydrazine and Mg remaining without reacting in the residual heat removal system pipe 4 are decomposed or collected, and the purified water is supplied to the reactor pressure. Water can be fed into the container 1. Other configurations are the same as those of the first embodiment.

本発明の他の実施例である実施例３の残留熱除去系の運転方法を、図６を用いて説明する。本実施例は、原子炉圧力容器１に接続された残留熱除去系配管４を複数系統有する改良型沸騰水型原子炉を用いた原子力発電プラントにおいて、原子炉停止操作中に残留熱除去系配管４内を流れる炉水にヒドラジンと、補完物質としてＭｇＯを添加する例である。   A method for operating the residual heat removal system according to the third embodiment which is another embodiment of the present invention will be described with reference to FIG. In this embodiment, in a nuclear power plant using an improved boiling water reactor having a plurality of residual heat removal system pipes 4 connected to the reactor pressure vessel 1, the residual heat removal system pipes during the reactor shutdown operation. 4 is an example of adding hydrazine and MgO as a supplementary substance to the reactor water flowing in the reactor 4.

再循環系が設けられていないため、それぞれの残留熱除去系１２の残留熱除去系配管４の両端は、原子炉圧力容器１に直接接続されている。本実施例も、実施例２と同様に、ヒドラジン注入装置及び補完物質注入装置を備えている。それらの残留熱除去系配管４には、残留熱除去系１２の運転時に、ヒドラジン注入装置のヒドラジン注入系配管２０を介してヒドラジンが、補完物質注入装置の補完物質注入配管２１を介して所望濃度のＭｇＯのエタノール溶液が注入される。補完物質調整タンク２３ｂ内には所望濃度のＭｇＯのエタノール溶液が満たされている。ＭｇＯは、水には溶けないが、エタノール溶液に溶解する。   Since no recirculation system is provided, both ends of the residual heat removal system pipe 4 of each residual heat removal system 12 are directly connected to the reactor pressure vessel 1. As in the second embodiment, this embodiment also includes a hydrazine injection device and a complementary substance injection device. In these residual heat removal system pipes 4, during the operation of the residual heat removal system 12, hydrazine is added via the hydrazine injection system pipe 20 of the hydrazine injection device to a desired concentration through the supplementary substance injection pipe 21 of the supplementary substance injection device. A solution of MgO in ethanol is injected. The supplementary substance adjustment tank 23b is filled with an ethanol solution of MgO having a desired concentration. MgO does not dissolve in water, but dissolves in an ethanol solution.

残留熱除去系配管４の運転に先立ち、補完物質調整タンク２３ｂ内に、予め所望濃度に調整したＭｇＯのエタノール溶液を満たし、不活性ガス配管２４を通じて補完物質調整タンク２３ｂ内を不活性ガスでバブリングして脱気しておく。残留熱除去系配管４へ炉水を通水し始めると同時に、流量調整バルブ２２ｂを開き、補完物質注入ポンプ２６を運転して残留熱除去系配管４の配管内に流れる炉水中にＭｇＯ溶液を添加する。   Prior to the operation of the residual heat removal system pipe 4, the supplementary substance adjustment tank 23 b is filled with an MgO ethanol solution adjusted to a desired concentration in advance, and the inside of the supplementary substance adjustment tank 23 b is bubbled with an inert gas through the inert gas pipe 24. Then degas. At the same time that the reactor water starts to flow into the residual heat removal system pipe 4, the flow rate adjustment valve 22 b is opened and the supplementary substance injection pump 26 is operated to put the MgO solution into the reactor water flowing into the residual heat removal system pipe 4. Added.

ヒドラジン注入により、残留熱除去系内酸化皮膜に取り込まれている放射性核種を溶出し、配管内面での鉄酸化物成長は抑制されると共に、残留熱除去系内に炉水と共に放射性イオンが流れ込んでも、放射性イオンの蓄積に必要なフェライトの材料となる水酸化鉄が配管内面に存在しないため、放射性核種の付着は抑制される。Ｍｇは、Ｃｏよりもフェライトの八面***置に配位し易いので、溶出したＣｏが再度鉄酸化物内に取り込まれる事を抑制できる。   By injecting hydrazine, the radionuclides incorporated in the oxide film in the residual heat removal system are eluted, and iron oxide growth on the inner surface of the piping is suppressed. Even if radioactive ions flow into the residual heat removal system along with the reactor water, Since iron hydroxide, which is a ferrite material necessary for accumulation of radioactive ions, does not exist on the inner surface of the pipe, adhesion of radionuclides is suppressed. Since Mg is more easily coordinated to the octahedral position of ferrite than Co, it is possible to prevent the eluted Co from being taken into the iron oxide again.

ヒドラジンとＭｇＯを添加した炉水は、残留熱除去系配管４内を流れた後、原子炉圧力容器１内に戻るが、原子炉圧力容器への接続点の上流側に炉水浄化装置２７を設け、炉水浄化装置２７に炉水を通水した後に原子炉圧力容器１に接続する。炉水浄化装置２７に炉水を通水することで、溶出した放射性核種の原子炉圧力容器１内への持ち込み量を減じることが出来る。また、炉水浄化装置２７に炉水を通水することで、残留熱除去系配管４内で反応せずに残留したヒドラジンとＭｇを分解、あるいは捕集して浄化された水を原子炉圧力容器１内に送水できる。   The reactor water to which hydrazine and MgO have been added flows in the residual heat removal system pipe 4 and then returns to the reactor pressure vessel 1, but the reactor water purification device 27 is installed upstream of the connection point to the reactor pressure vessel. It is provided and connected to the reactor pressure vessel 1 after passing the reactor water through the reactor water purification device 27. By passing the reactor water through the reactor water purification device 27, it is possible to reduce the amount of radionuclides that have been eluted into the reactor pressure vessel 1. In addition, by passing the reactor water through the reactor water purification device 27, the hydrazine and Mg remaining without reacting in the residual heat removal system pipe 4 are decomposed or collected, and the purified water is removed from the reactor pressure. Water can be fed into the container 1.

Ｍｇの他に、Ｚｎ，Ｍｎ，Ｎｉ，Ｆｅ，Ａｌのうち何れか一つ以上を含有するイオン結合性物質を添加しても同様の効果が得られる。   The same effect can be obtained by adding an ion binding substance containing any one or more of Zn, Mn, Ni, Fe, and Al in addition to Mg.

本発明の好適な一実施例である実施例１の残留熱除去系の運転方法を適用する残留熱除去系の構成図である。It is a block diagram of the residual heat removal system which applies the operating method of the residual heat removal system of Example 1 which is one preferred embodiment of the present invention. Ｃｏが炭素鋼に吸着して蓄積する過程の模式的説明図である。It is typical explanatory drawing of the process in which Co adsorb | sucks and accumulate | stores in carbon steel. 本発明の概要と原理を模式的に示した図である。It is the figure which showed the outline | summary and principle of this invention typically. 還元性物質として炉水にヒドラジンを添加した時におけるヒドラジン濃度と炉水のｐＨとの関係を示す特性図である。It is a characteristic view which shows the relationship between the hydrazine density | concentration when adding hydrazine to a reactor water as a reducing substance, and the pH of a reactor water. 本発明の他の実施例である実施例２の残留熱除去系の運転方法を適用する残留熱除去系の構成図である。It is a block diagram of the residual heat removal system which applies the operating method of the residual heat removal system of Example 2 which is another Example of this invention. 本発明の他の実施例である実施例３の残留熱除去系の運転方法を適用する残留熱除去系の構成図である。It is a block diagram of the residual heat removal system which applies the operating method of the residual heat removal system of Example 3 which is another Example of this invention.

符号の説明Explanation of symbols

１…原子炉圧力容器、２…再循環系配管、３…再循環ポンプ、４…残留熱除去系配管、５…原子炉格納容器、６，７，１１…開閉弁、８…残留熱除去系ポンプ、９…熱交換器、１０…バイパス弁、１２…残留熱除去系、２０…ヒドラジン注入系配管、２１…補完物質注入配管、２２ａ，２２ｂ…流量調整バルブ、２３ａ…ヒドラジン調整タンク、２３ｂ…補完物質調整タンク、２４…不活性ガス配管、２５…ヒドラジン注入ポンプ、２６…補完物質注入ポンプ、２７…炉水浄化装置、３０…腐食電位測定装置。   DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Recirculation system piping, 3 ... Recirculation pump, 4 ... Residual heat removal system piping, 5 ... Reactor containment vessel, 6, 7, 11 ... Open / close valve, 8 ... Residual heat removal system Pump: 9 ... Heat exchanger, 10 ... Bypass valve, 12 ... Residual heat removal system, 20 ... Hydrazine injection system pipe, 21 ... Complementary substance injection pipe, 22a, 22b ... Flow rate adjustment valve, 23a ... Hydrazine adjustment tank, 23b ... Complementary substance adjustment tank, 24 ... inert gas piping, 25 ... hydrazine injection pump, 26 ... supplementary substance injection pump, 27 ... reactor water purification device, 30 ... corrosion potential measuring device.

Claims (12)

沸騰水型原子炉の炉水温度を低下する原子炉停止操作運転期間中で、残留熱除去系に
１００℃以上１５０℃以下の炉水を流動させる期間中に、残留熱除去系内に還元性物質を添加する工程を有することを特徴とする残留熱除去系の運転方法。 During the reactor shutdown operation period during which the reactor water temperature of the boiling water reactor is lowered, during the period in which the reactor water of 100 ° C. or more and 150 ° C. or less flows through the residual heat removal system, the reductive property is reduced in the residual heat removal system. A method for operating a residual heat removal system comprising a step of adding a substance. 沸騰水型原子炉の炉水温度を低下する原子炉停止操作運転期間中で、残留熱除去系に
１００℃以上１５０℃以下の炉水を流動させる期間中に、残留熱除去系内に還元性物質を添加する工程と、前記還元性物質による放射性核種付着蓄積抑制効果を増大させる補完物質を前記残留除去系内に添加する工程を有することを特徴とする残留熱除去系の運転方法。 During the reactor shutdown operation period during which the reactor water temperature of the boiling water reactor is lowered, during the period in which the reactor water of 100 ° C. or more and 150 ° C. or less flows through the residual heat removal system, the reductive property is reduced in the residual heat removal system. A method for operating a residual heat removal system, comprising: a step of adding a substance; and a step of adding a supplementary substance that increases an effect of suppressing accumulation of radionuclide by the reducing substance into the residual removal system. 前記還元性物質は、ヒドラジン，カーボヒドラジド，ジイミド，酸化数が負である窒素を含有する化合物，メタノール及びＬ−アスコルビン酸のうちで、１種以上を含む請求項１記載の残留熱除去系の運転方法。   2. The residual heat removal system according to claim 1, wherein the reducing substance includes one or more of hydrazine, carbohydrazide, diimide, a compound containing nitrogen having a negative oxidation number, methanol, and L-ascorbic acid. how to drive. 前記還元性物質は、ヒドラジン，カーボヒドラジド，ジイミド，酸化数が負である窒素を含有する化合物，メタノール及びＬ−アスコルビン酸のうちで、１種以上を含む請求項２記載の残留熱除去系の運転方法。   3. The residual heat removal system according to claim 2, wherein the reducing substance includes one or more of hydrazine, carbohydrazide, diimide, a compound containing nitrogen having a negative oxidation number, methanol, and L-ascorbic acid. how to drive. 前記補完物質は、Ｃｏ２＋イオンよりも逆スピネル結晶物の八面***置に配位し易い２価金属イオンを含むイオン結合性物質である請求項２または請求項４に記載の残留熱除去系の運転方法。 5. The residual heat removal system according to claim 2, wherein the complementary material is an ion-binding material containing a divalent metal ion that is more easily coordinated to an octahedral position of the reverse spinel crystal than the Co 2+ ion. how to drive. 前記補完物質は、Ｃｏ２＋イオンよりも酸化鉄、及びオキシ水酸化鉄の放射性核種の吸着サイトを占有し易い物質である請求項２または請求項４に記載の残留熱除去系の運転方法。 The operation method of the residual heat removal system according to claim 2 or 4, wherein the supplementary substance is a substance that occupies an adsorption site of radionuclide of iron oxide and iron oxyhydroxide more than Co 2+ ions. 前記補完物質は、鉄と溶液を介して接触している際に鉄の腐食量を減じる物質請求項２または請求項４に記載の残留熱除去系の運転方法。   The operating method of the residual heat removal system according to claim 2 or 4, wherein the supplementary substance is a substance that reduces the corrosion amount of iron when it is in contact with iron through a solution. 前記逆スピネル結晶物の八面***置に配位し易い２価金属イオンを含むイオン結合性物質は、Ｍｇ，Ｆｅ，Ｎｉのうち何れか一つ以上を含む請求項５記載の残留熱除去系の運転方法。   6. The residual heat removal system according to claim 5, wherein the ion-binding substance including a divalent metal ion that is easily coordinated to an octahedral position of the inverse spinel crystal material includes at least one of Mg, Fe, and Ni. how to drive. 前記酸化鉄、及びオキシ水酸化鉄の放射性核種の吸着サイトを占有し易い物質は、Ｍｇである請求項６記載の残留熱除去系の運転方法。   The operation method of the residual heat removal system according to claim 6, wherein the substance that easily occupies the adsorption sites of the radionuclide of iron oxide and iron oxyhydroxide is Mg. 前記補完物質と鉄とが溶液を介して接触している際に鉄の腐食量を減じる補完物質は、Ｚｎ，Ａｌ，Ｍｇ、その他鉄よりも酸化還元電位が卑な元素である請求項７記載の残留熱除去系の運転方法。   The supplementary substance that reduces the corrosion amount of iron when the supplementary substance and iron are in contact with each other through a solution is Zn, Al, Mg, or another element having a lower redox potential than iron. Operation method of residual heat removal system. 前記還元性物質を添加する位置は、原子炉圧力容器から残留熱除去系への分岐点に至るまでの再循環系配管の任意位置、及び炉水が残留熱除去系に向かう分岐点のうち何れかである請求項１または請求項２に記載の残留熱除去系の運転方法。   The reductive substance may be added at any position of the recirculation system piping from the reactor pressure vessel to the branch point to the residual heat removal system, or the branch point where the reactor water heads to the residual heat removal system. The operating method of the residual heat removal system according to claim 1 or claim 2. 前記補完物質を添加する位置は、原子炉圧力容器から残留熱除去系への分岐点に至るまでの再循環系配管の任意位置、及び炉水が残留熱除去系に向かう分岐点のうち何れかである請求項２に記載の残留熱除去系の運転方法。   The position where the supplementary substance is added is any one of the recirculation system piping from the reactor pressure vessel to the branch point to the residual heat removal system, and the branch point where the reactor water goes to the residual heat removal system. The operating method of the residual heat removal system according to claim 2.
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