JPH0431359B2 - - Google Patents
Info
- Publication number
- JPH0431359B2 JPH0431359B2 JP60218045A JP21804585A JPH0431359B2 JP H0431359 B2 JPH0431359 B2 JP H0431359B2 JP 60218045 A JP60218045 A JP 60218045A JP 21804585 A JP21804585 A JP 21804585A JP H0431359 B2 JPH0431359 B2 JP H0431359B2
- Authority
- JP
- Japan
- Prior art keywords
- oxide film
- metal
- water
- pure water
- component
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 37
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 27
- 229910052760 oxygen Inorganic materials 0.000 claims description 27
- 239000001301 oxygen Substances 0.000 claims description 27
- 229910052751 metal Inorganic materials 0.000 claims description 25
- 239000002184 metal Substances 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 21
- 239000000941 radioactive substance Substances 0.000 claims description 19
- 239000000498 cooling water Substances 0.000 claims description 11
- 238000010828 elution Methods 0.000 claims description 10
- 239000013078 crystal Substances 0.000 claims description 8
- 229910021645 metal ion Inorganic materials 0.000 claims description 8
- 229910017052 cobalt Inorganic materials 0.000 claims description 6
- 239000010941 cobalt Substances 0.000 claims description 6
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 6
- 230000003647 oxidation Effects 0.000 claims description 6
- 238000007254 oxidation reaction Methods 0.000 claims description 6
- 150000002739 metals Chemical class 0.000 claims description 5
- 230000001681 protective effect Effects 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052725 zinc Inorganic materials 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 2
- 229910052749 magnesium Inorganic materials 0.000 claims description 2
- 239000010935 stainless steel Substances 0.000 description 16
- 229910001220 stainless steel Inorganic materials 0.000 description 16
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 12
- 230000015572 biosynthetic process Effects 0.000 description 10
- 238000010586 diagram Methods 0.000 description 7
- 239000012857 radioactive material Substances 0.000 description 7
- 230000007797 corrosion Effects 0.000 description 6
- 238000005260 corrosion Methods 0.000 description 6
- 229910052742 iron Inorganic materials 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- 230000002285 radioactive effect Effects 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000000470 constituent Substances 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 238000004140 cleaning Methods 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 238000007654 immersion Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 229910001429 cobalt ion Inorganic materials 0.000 description 2
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910001347 Stellite Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- AHICWQREWHDHHF-UHFFFAOYSA-N chromium;cobalt;iron;manganese;methane;molybdenum;nickel;silicon;tungsten Chemical compound C.[Si].[Cr].[Mn].[Fe].[Co].[Ni].[Mo].[W] AHICWQREWHDHHF-UHFFFAOYSA-N 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
Classifications
-
- 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
Landscapes
- Chemical Treatment Of Metals (AREA)
- Monitoring And Testing Of Nuclear Reactors (AREA)
Description
〔産業上の利用分野〕
本発明は原子力プラントに係り、特に一次冷却
系配管のように、放射性物質が溶解している液と
接して使用される構造材に対する放射性物質の付
着抑制方法に関する。
〔従来の技術〕
BWRプラントの一次冷却糸に使用されている
配管、ポンプ、弁等はステンレス鋼及びステライ
ト等（以下構成部材の略称する）から構成されて
る。これらの金属は長時間使用されると腐蝕損傷
をうけ、構成金属元素が原子炉冷却水（以下冷却
水と略称する）中に溶出し、原子炉内に持ち込ま
れる。溶出金属元素は大半は燃料棒に付着し中性
子照射を受ける。その結果、60Co、58Co、51Cr、
54Mn等の放射性核種が生成する。これらの放射
性核種は再溶出してイオンあるいは不溶性固体成
分（以下、クラツドと称する）として浮遊する。
その一部は炉水浄化用の脱塩器等で除去される
が、残りは一次冷却系を循環しているうちに構成
部材表面に付着する。このため、構成部材表面に
おける線量率が高くなり、保守、点検を実施する
際の作業員の放射能被爆が問題となつている。
従つて、放射性物質の付着量を低減させるた
め、その源である前記金属元素の溶出を抑制する
方法が提案されている。例えば耐蝕性のよい材料
の使用あるいは酸素を給水系内に注入して構成部
材の腐蝕を抑制する方法等がある。しかし、いず
れの方法を用いても給水系をはじめとし、一次冷
却水系の構成部材の腐蝕を十分に抑制することは
できず、一次冷却水中の放射能物質を十分に低減
することはできないため、構成部材への放射能物
質の付着による表面線量率の増加がやはり問題と
して残つている。
また、構成部材に付着した放射性物質を除去す
る方法が検討され、実施されている。除去方法に
は(1)機械的洗浄、(2)電気分解による洗浄のほか、
(3)化学的洗浄がある。しかし、(1)、(2)の方法は構
成部材表面に強く密着した放射能物質の除去が困
難であり、また広い範囲を系統的に除染すること
ができない等の問題があるため、現状では(3)の方
法が広く用いられている。(3)の方法は酸溶液等の
薬剤を用いて化学反応により鋼表面の酸化皮膜を
溶解し、同皮膜中に存在する放射性物質を除去す
るものである。この方法の問題は一時的に線量率
を低減しても、構成部材を再び高い濃度の放射性
物質を溶解する液にさらした場合急速に再汚染さ
れることである。
そこで、構成物質表面に予め酸化皮膜を形成
し、放射性物質の付着を抑制する方法が、特開昭
55−121197号公報及び特開昭59−37498号公報等
で開示された。しかし、予め形成しておく酸化皮
膜の性状により放射性物質の付着挙動は著しく異
なつてくる。たとえば、放射性イオンの挙動は予
め形成しておいた酸化皮膜の荷電状態により異な
るし、また、放射性物質が溶解する液に浸漬した
のちに構成部材表面に新たに形成される酸化皮膜
の成長速度の既存の皮膜の性状により変わつてく
る。したがつて、構成部材を適用する液に最も適
した方法により酸化処理を行うことが必要であ
る。
〔発明が解決しようとする問題点〕
本発明は放射性物質を含む冷却水と接する原子
力発電プラント構成部材への放射性物質の付着量
を低減することにより、保守、点検を実施する際
の作業員の放射線被爆の問題を解決することにあ
る。
〔問題点を解決するための手段〕
本発明は、放射性物質を含む原子炉冷却水と接
触する原子力発電プラント構成部材への放射性物
質の付着を抑制するに当たり、該部材の接水面に
溶存酸素濃度を300〜500PPbとした200〜300℃の
高温純水によつて、構成部材を構成する金属の溶
出を低減しつつ、結晶粒径0.5μｍ以下の緻密で保
護性の高い酸化皮膜を形成させることにより、コ
バルトの構成部材への付着を防止することを特徴
とする。
冷却水に溶存する放射性核種はステンレス鋼の
腐蝕によつて表面に形成される酸化皮膜内にその
形成過程で取り込まれる。ところで、本発明者ら
の研究によると、放射性核種の付着速度は皮膜成
長速度と相関関係を示すので、皮膜成長を抑制す
ることは付着低減につながるであろうと推定され
た。
即ち、放射性核種の付着速度が皮膜の成長速度
と相関関係を示すのは、放射性核種の皮膜の成長
点で取り込まれるからである。したがつて、皮膜
の成長を抑制するとそれだけ放射性核種が取り込
まれる頻度が減少する、即ち取り込みが抑制され
るのである。冷却水環境下でのステンレス鋼の皮
膜量（ｍ）の増加は(9)式に示すように時間（ｔ）
の対数則によつて表される。
ｍ＝alog（bt＋１）
ここで、ａ及びｂは定数
すなわち、皮膜の成長とともにその成長速度は
小さくなる。したがつて、予め適当な非放射性の
酸化皮膜を形成しておけば放射性物質が溶存して
いる液へ浸漬したのちの新たな皮膜形成を抑制す
ることができ、ひいては皮膜形成時に多くみられ
る放射性物質の付着を抑制できる。
本発明者らは、放射性物質を溶存した原子炉冷
却水と接して使用される金属構成部材にあらかじ
め適当な非放射性の酸化皮膜を形成することによ
つて放射性物質の付着を抑制できる点に着目する
と同時に、60Co等の放射性物質の付着速度は予め
形成された酸化皮膜の形成条件に依存し、特に形
成時の200〜300℃の高温純水中の溶存酸素濃度が
300〜500ppbの場合、著しく小さくなることを見
出した。また、この高温純水中に鉄より標準電極
電位及び電気陰性度の低い金属（Al、Mn、Mg、
Ni、Zn）のイオンを添加することにより、酸化
物が微細化し保護性の高い酸化皮膜が形成され、
60Coの付着速度が低下することを見出した。
上記の方法により金属表面へのCo付着速度を
小さくできる酸化皮膜が形成される原理は次の通
りである。
高温水中の溶存酸素濃度は、脱気条件では
0PPm、空気飽和とすれば8PPmの範囲となり、
その間の調整は、酸素分圧の異なる混合ガスによ
つて可能である。酸化皮膜材料から金属が溶出す
る際に金属イオンとなり、水中の水酸基（OH-）
の結合した後に脱水して酸化物となる。溶存酸素
濃度が脱気に近い高温純水に金属が接する場合、
金属の電位は低電位側にシフトするため鉄を主体
とする母材金属の腐蝕による溶出反応が進行し易
くなる。しかし、溶出金属イオンと結合するため
の水分子（H2O）の双極子は金属の電位が低い
ために金属表面側にＯを配位しにくくなり
（OH-）や（O2-）が金属表面にわずかしか吸着
しない。すなわち酸化物は生成される数が限定さ
れ、金属溶出量が多いために個々の酸化物は大き
くなる。この機構により、低溶存酸素濃度の高温
純水中で形成される皮膜量は多いが表面が粗雑な
酸化物層となるのである。
一方、溶存酸素濃度が高い高温水は金属の電位
を比較的正電位側にシフトさせる。したがつて鉄
の溶出は抑制されるがステンレス鋼の構成元素の
一つであるクロムの溶出が増加する。H2O（水分
子双極子）は金属表面側にＯを配位し易くなり
（OH-）や（O2-）が金属表面に多数吸着する。
しかしステンレス鋼の主成分である鉄の溶出はす
くないため、酸化物の成長が少ない。従つて微細
な酸化物が多く生成し緻密は表面となる。
本発明者らは、高温純水中でステンレス鋼等の
構成部材を酸化処理する場合、300〜500PPbの溶
存酸素濃度にすれば、構成部材を構成する金属の
溶出を低減しつつ、最も保護性のつよい酸化皮膜
が形成できることを発見したのである。高温純水
の温度は、200〜300℃の範囲であるが、250℃以
上の場合により有効な酸化皮膜が形成され、特に
280〜300℃の範囲が好ましい。本発明方法を適用
できる構成部材としてはステンレス鋼の他、炭素
鋼、鉄基合金などがある。鉄基合金の高温水中の
腐食に注目した場合、溶存酸素濃度を上記300〜
500PPbとして酸化処理を行うと、緻密で保護性
のある酸化皮膜が形成されるため60Co等の放射性
物質の付着を抑制することが可能となる。
また鉄よりも電気陰性度及び標準電極電位の低
い金属イオンを高温水中に添加すると、金属表面
電位が、溶存酸素濃度が高い場合と同じ機構で高
くなることをも筆者らは発見した。したがつて、
本発明方法で酸化処理を行うなう場合に高温水に
これらの金属イオンのうち１種以上を添加してお
いてもよい。金属イオン濃度は5ppb以上で効果
があらわれ、高温水に溶ける量の限界が1000ppm
であるので、5ppb〜1000ppmの範囲で添加でき
る。
なお、本発明方法により形成される酸化皮膜の
最も高温純水側に形成される酸化物の結晶粒径は
0.5μｍ以下であつた。
第１図は、各溶存酸素濃度の288℃の純水中で
ステンレス鋼上に形成された酸化皮膜量の変化を
示す折線図であり、第２図イ，ロ，ハ及びニは前
記第１図中イ，ロ，ハ及びニの符号を付した点に
おける前記酸化皮膜の結晶構造を示すSEM観察
写真である。後に述べる表２の結果をも考慮する
と300〜500ppbの溶存酸素濃度において緻密で保
護性の高い酸化皮膜が形成されることがわかる。
図４にステンレス鋼の280℃高温純水中における
金属溶出量と酸化皮膜形成量との水中溶存酸素依
存性（150時間浸漬）を示す。図の場合にみられ
るように、還元性の雰囲気に近い脱気及び低溶存
酸素濃度では溶出量が皮膜形成量をしのぐ。しか
も、300PPbから500PPbの溶存酸素濃度では、酸
化皮膜表面結晶の粒径が0.5μｍ以下の緻密な皮膜
が形成される。500PPbをこえるころから溶存酸
素が溶液の酸化性を増加させることから溶出より
は皮膜形成が主となるものも、皮膜の形成が短時
間に粗い結晶を形成させることとなる。そこで、
500PPb以上の溶存酸素濃度で形成された皮膜は、
後の炉水温度（溶存酸素濃度約200PPb）に接す
ると剥離・溶解するため、結果的に金属溶出が増
加し、放射性物質付着抑制への効果は大きく期待
できない。
実施例 １
第１表の化学組成（重量％）を有する
JISSUS304ステンレス鋼を、溶存酸素濃度を調
整した288℃の純水（液体）中に浸漬し酸化処理
を施した。その後、3PPbのコバルト２価イオン
を含む288℃の加熱水中に300時間、上記の酸化処
理したステンレス鋼を浸漬させ、酸化皮膜の増加
量並びにコバルトの付着量を測定した。結果を第
２表に示す。本発明による酸化処理は、酸化皮膜
の増加量が低く、かつ、コバルトの付着量が抑制
されていることがわかる。
[Industrial Field of Application] The present invention relates to nuclear power plants, and particularly to a method for suppressing the adhesion of radioactive substances to structural materials used in contact with liquid in which radioactive substances are dissolved, such as primary cooling system piping. [Prior Art] Piping, pumps, valves, etc. used in the primary cooling line of a BWR plant are made of stainless steel, Stellite, etc. (hereinafter referred to as component members). When these metals are used for a long period of time, they are subject to corrosion damage, and the constituent metal elements are eluted into the reactor cooling water (hereinafter referred to as cooling water) and brought into the reactor. Most of the eluted metal elements adhere to the fuel rods and are irradiated with neutrons. As a result, 60 Co, 58 Co, 51 Cr,
54 Radioactive nuclides such as Mn are generated. These radionuclides are re-eluted and float as ions or insoluble solid components (hereinafter referred to as cladding).
A portion of it is removed by a demineralizer for purifying reactor water, but the rest adheres to the surfaces of structural members while circulating through the primary cooling system. For this reason, the dose rate on the surface of the component increases, and radiation exposure of workers during maintenance and inspection has become a problem. Therefore, in order to reduce the amount of adhesion of radioactive substances, methods have been proposed for suppressing the elution of the metal elements that are the source of the radioactive substances. For example, there are methods to suppress corrosion of structural members by using materials with good corrosion resistance or by injecting oxygen into the water supply system. However, no matter which method is used, it is not possible to sufficiently suppress corrosion of the components of the primary cooling water system, including the water supply system, and it is not possible to sufficiently reduce radioactive substances in the primary cooling water. Increased surface dose rates due to adhesion of radioactive materials to components still remain a problem. Additionally, methods for removing radioactive substances adhering to structural members have been studied and implemented. Removal methods include (1) mechanical cleaning, (2) electrolytic cleaning, and
(3) There is chemical cleaning. However, methods (1) and (2) have problems such as difficulty in removing radioactive substances that are tightly adhered to the surface of component parts, and the inability to systematically decontaminate a wide area. Method (3) is widely used. Method (3) uses chemicals such as acid solutions to dissolve the oxide film on the steel surface through a chemical reaction, and removes the radioactive substances present in the film. The problem with this method is that even if the dose rate is temporarily reduced, if the component is exposed again to a liquid that dissolves high concentrations of radioactive materials, it will quickly become recontaminated. Therefore, a method of forming an oxide film on the surface of the constituent materials in advance to suppress the adhesion of radioactive substances was developed in JP-A-Sho.
It was disclosed in JP-A-55-121197 and JP-A-59-37498. However, the adhesion behavior of radioactive substances differs markedly depending on the properties of the oxide film formed in advance. For example, the behavior of radioactive ions differs depending on the charge state of the oxide film that has been formed in advance, and the growth rate of the oxide film that is newly formed on the surface of the component after being immersed in a liquid in which radioactive substances are dissolved. It varies depending on the properties of the existing film. Therefore, it is necessary to carry out the oxidation treatment using a method most suitable for the liquid to which the component is applied. [Problems to be Solved by the Invention] The present invention reduces the amount of radioactive materials adhering to nuclear power plant components that come into contact with cooling water containing radioactive materials, thereby reducing the burden on workers during maintenance and inspection. The aim is to solve the problem of radiation exposure. [Means for Solving the Problems] The present invention, in suppressing the adhesion of radioactive materials to nuclear power plant component members that come into contact with reactor cooling water containing radioactive materials, reduces the concentration of dissolved oxygen on the water-contact surfaces of the members. Using high-temperature pure water at 200 to 300℃ with 300 to 500PPb, a dense and highly protective oxide film with a crystal grain size of 0.5 μm or less is formed while reducing the elution of metals that make up the component parts. This feature prevents cobalt from adhering to structural members. Radioactive nuclides dissolved in the cooling water are incorporated into the oxide film formed on the surface of stainless steel during its formation process. By the way, according to the research conducted by the present inventors, since the adhesion rate of radionuclides shows a correlation with the film growth rate, it was estimated that suppressing the film growth would lead to a reduction in adhesion. That is, the reason why the deposition rate of the radionuclide shows a correlation with the growth rate of the film is that the radionuclide is taken in at the growth point of the film. Therefore, the more the growth of the film is suppressed, the more the frequency at which radionuclides are taken in decreases, that is, the uptake is suppressed. The increase in the amount of film (m) on stainless steel in a cooling water environment is shown by equation (9), as shown in equation (9).
It is expressed by the logarithmic law of m=alog(bt+1) Here, a and b are constants. That is, as the film grows, its growth rate decreases. Therefore, if a suitable non-radioactive oxide film is formed in advance, it is possible to suppress the formation of a new film after immersion in a solution containing dissolved radioactive substances, and in turn, the formation of a new film after immersion in a solution containing radioactive substances can be prevented. Adhesion of substances can be suppressed. The present inventors focused on the fact that adhesion of radioactive substances can be suppressed by forming an appropriate non-radioactive oxide film on metal components used in contact with reactor cooling water containing dissolved radioactive substances. At the same time, the deposition rate of radioactive substances such as 60 Co depends on the formation conditions of the pre-formed oxide film, especially when the dissolved oxygen concentration in high-temperature pure water at 200 to 300°C at the time of formation is
It was found that in the case of 300 to 500 ppb, it becomes significantly smaller. In addition, metals (Al, Mn, Mg,
By adding Ni, Zn) ions, the oxide becomes finer and a highly protective oxide film is formed.
It was found that the deposition rate of 60 Co decreased. The principle behind the formation of an oxide film that can reduce the rate of Co deposition on metal surfaces by the above method is as follows. The dissolved oxygen concentration in high-temperature water is
If it is 0PPm and air saturation, it will be in the range of 8PPm,
Adjustment between them is possible by using mixed gases with different oxygen partial pressures. When the metal is eluted from the oxide film material, it becomes metal ions and hydroxyl groups (OH - ) in the water.
After bonding, it dehydrates and becomes an oxide. When metal comes into contact with high-temperature pure water whose dissolved oxygen concentration is close to degassed,
Since the potential of the metal shifts to the lower potential side, the elution reaction due to corrosion of the base metal, which is mainly composed of iron, tends to proceed. However, because the potential of the metal is low, the dipole of the water molecule (H 2 O) that binds to the eluted metal ion becomes difficult to coordinate O to the metal surface, causing (OH - ) and (O 2- ) It only slightly adsorbs to metal surfaces. That is, the number of oxides produced is limited, and since the amount of metal eluted is large, each oxide becomes large. Due to this mechanism, a large amount of film is formed in high-temperature pure water with a low dissolved oxygen concentration, but an oxide layer with a rough surface is formed. On the other hand, high-temperature water with a high dissolved oxygen concentration shifts the potential of the metal toward a relatively positive potential. Therefore, the elution of iron is suppressed, but the elution of chromium, which is one of the constituent elements of stainless steel, increases. H 2 O (water molecule dipole) tends to coordinate O on the metal surface side, and a large number of (OH − ) and (O 2− ) are adsorbed on the metal surface.
However, since little iron, the main component of stainless steel, elutes, oxides grow less. Therefore, many fine oxides are generated and the surface becomes dense. The present inventors have found that when oxidizing structural members such as stainless steel in high-temperature pure water, a dissolved oxygen concentration of 300 to 500 PPb provides the best protection while reducing the elution of metals constituting the structural members. They discovered that a strong oxide film could be formed. The temperature of high-temperature pure water is in the range of 200 to 300℃, but a more effective oxide film is formed when the temperature is 250℃ or higher.
A range of 280 to 300°C is preferred. Components to which the method of the present invention can be applied include stainless steel, carbon steel, iron-based alloys, and the like. When focusing on corrosion of iron-based alloys in high-temperature water, the dissolved oxygen concentration should be set to 300~
When oxidized as 500PPb, a dense and protective oxide film is formed, making it possible to suppress the adhesion of radioactive substances such as 60 Co. The authors also discovered that when metal ions with lower electronegativity and standard electrode potential than iron are added to high-temperature water, the metal surface potential increases by the same mechanism as when the dissolved oxygen concentration is high. Therefore,
One or more of these metal ions may be added to the high temperature water when performing the oxidation treatment according to the method of the present invention. The effect appears when the metal ion concentration is 5ppb or higher, and the limit of the amount that can be dissolved in high temperature water is 1000ppm.
Therefore, it can be added in a range of 5 ppb to 1000 ppm. In addition, the crystal grain size of the oxide formed on the highest temperature pure water side of the oxide film formed by the method of the present invention is
It was 0.5 μm or less. Figure 1 is a line diagram showing the change in the amount of oxide film formed on stainless steel in pure water at 288°C with each dissolved oxygen concentration, and Figure 2 A, B, C, and D are line diagrams showing the changes in the amount of oxide film formed on stainless steel in pure water at 288°C at various dissolved oxygen concentrations. FIG. 2 is a SEM observation photograph showing the crystal structure of the oxide film at points marked with symbols A, B, C, and D in the figure. FIG. Considering the results in Table 2, which will be described later, it can be seen that a dense and highly protective oxide film is formed at a dissolved oxygen concentration of 300 to 500 ppb.
Figure 4 shows the dependence of the amount of metal eluted and the amount of oxide film formed on dissolved oxygen in stainless steel in 280°C high-temperature pure water (immersed for 150 hours). As seen in the figure, the amount of elution exceeds the amount of film formation when degassing is close to a reducing atmosphere and the dissolved oxygen concentration is low. Moreover, at a dissolved oxygen concentration of 300PPb to 500PPb, a dense film with a grain size of oxide film surface crystals of 0.5 μm or less is formed. Dissolved oxygen increases the oxidizing properties of the solution when it exceeds 500 PPb, so even if film formation is the main cause rather than elution, the film formation will result in the formation of coarse crystals in a short period of time. Therefore,
A film formed with a dissolved oxygen concentration of 500PPb or more is
If it comes into contact with the later reactor water temperature (dissolved oxygen concentration of about 200PPb), it will peel off and dissolve, resulting in an increase in metal elution, and it cannot be expected to be very effective in suppressing the adhesion of radioactive materials. Example 1 Having the chemical composition (wt%) shown in Table 1
JISSUS304 stainless steel was oxidized by immersing it in pure water (liquid) at 288°C with adjusted dissolved oxygen concentration. Thereafter, the oxidized stainless steel was immersed in heated water at 288°C containing divalent cobalt ions of 3PPb for 300 hours, and the amount of increase in the oxide film and the amount of cobalt deposited were measured. The results are shown in Table 2. It can be seen that in the oxidation treatment according to the present invention, the amount of increase in the oxide film is low and the amount of cobalt deposited is suppressed.
【表】【table】
【表】
＊溶存酸素濃度
実施例 ２
前述の第１表の化学組成（重量％）を有する
JISSUS304ステンレス鋼を、溶存酸素濃度を調
整した288℃の純水（液体）中に浸漬し酸化処理
を施した。その時にAI、Mn、Ni、Zn、を金属
イオンとして添加した。その後、3PPbのコバル
ト２価イオンをふくむ288℃の加熱水中に300時
間、上記の酸化処理を施したステンレス鋼を浸漬
させ、酸化皮膜の増加量並びにコバルトの付着量
を測定した。結果を第３表に示す。本発明による
酸化処理は、酸化皮膜の増加量が低く、かつ、コ
バルトの付着量が抑制されていることがわかる。[Table] *Example 2 of dissolved oxygen concentration Having the chemical composition (wt%) shown in Table 1 above
JISSUS304 stainless steel was oxidized by immersing it in pure water (liquid) at 288°C with adjusted dissolved oxygen concentration. At that time, AI, Mn, Ni, and Zn were added as metal ions. Thereafter, the stainless steel subjected to the above oxidation treatment was immersed in heated water at 288°C containing divalent cobalt ions of 3PPb for 300 hours, and the amount of increase in the oxide film and the amount of cobalt deposited were measured. The results are shown in Table 3. It can be seen that in the oxidation treatment according to the present invention, the amount of increase in the oxide film is low and the amount of cobalt deposited is suppressed.
以上の説明から明らかなように、本発明は簡便
な手段によつてプラント構成部材への放射性物質
の付着を抑制できる。又、その応用範囲も広く、
特に原子力発電プラントに使用されるステンレス
鋼をはじめとする構成部材に適用して線量率の上
昇を抑え、従事者の被爆を低減するのに好適であ
り、実用価値が高く、工業的にきわめて有意義な
ものである。
As is clear from the above description, the present invention can suppress adhesion of radioactive substances to plant constituent members by simple means. In addition, its application range is wide,
It is particularly suitable for application to stainless steel and other structural members used in nuclear power plants to suppress increases in dose rates and reduce radiation exposure for workers, and has high practical value and is extremely meaningful industrially. It is something.
第１図は本発明の原理となつた酸化皮膜量の変
化を示す折線図、第２図イ，ロ，ハ及びニは前記
第１図中イ，ロ，ハ及びニの符号を付した点にお
ける前記酸化皮膜の結晶構造を示すSEM写真、
第３図は本発明を実施するための沸騰水型原子力
発電プラントの系統図、第４図は給水加熱器の仮
設循環ラインの系統図、及び第５図はステンレス
鋼の280℃高温純水中における金属溶出量と酸化
皮膜形成量との水中溶存酸素濃度依存性（150時
間浸漬）を示す図である。
１……原子炉、２……再循環系、３……再循環
ポンプ、４……原子炉浄化系、５……炉水浄化
器、６……タービン、７……復水器、８……復水
浄化装置、９……給水加熱器、１０……給水系、
１１……蒸気系、１２，１２″……酸素注入バル
ブ、１３……真空ポンプ、１４……排気塔、１５
……ポンプ、１６……タンク、１７……蒸気吹込
ライン、１８……蒸気ブローライン、１９……酸
素注入ライン、２０……バイパスライン、２１…
…循環ライン、２２……主蒸気隔離弁、２３……
ヒータチユーブ。
Fig. 1 is a line diagram showing changes in the amount of oxide film, which is the principle of the present invention, and Fig. 2 A, B, C, and D are points marked with A, B, C, and D in Fig. 1 above. SEM photograph showing the crystal structure of the oxide film in
Figure 3 is a system diagram of a boiling water nuclear power plant for implementing the present invention, Figure 4 is a system diagram of a temporary circulation line for a feed water heater, and Figure 5 is a system diagram of a 280°C high-temperature pure water made of stainless steel. FIG. 3 is a diagram showing the dependence of the amount of metal eluted and the amount of oxide film formed on the dissolved oxygen concentration in water (150 hours of immersion). 1... Nuclear reactor, 2... Recirculation system, 3... Recirculation pump, 4... Reactor purification system, 5... Reactor water purifier, 6... Turbine, 7... Condenser, 8... ... Condensate purification device, 9 ... Feed water heater, 10 ... Water supply system,
11...Steam system, 12,12''...Oxygen injection valve, 13...Vacuum pump, 14...Exhaust tower, 15
... pump, 16 ... tank, 17 ... steam blow line, 18 ... steam blow line, 19 ... oxygen injection line, 20 ... bypass line, 21 ...
...Circulation line, 22...Main steam isolation valve, 23...
heater tube.
Claims (1)
属からなる構成部材が前記冷却水にさらされる前
に予め前記構成部材表面に酸化皮膜を形成し放射
能を低減する方法において、前記構成部材を、溶
存酸素濃度を300〜500PPbとした200〜300℃の高
温純水に接し、構成部材を構成する金属の溶出を
低減しつつ、結晶粒径0.5μｍ以下の緻密で保護性
の高い酸化皮膜を形成させることにより、コバル
トの構成部材への付着を防止することを特徴とす
る原子力プラントの放射能低減方法。 ２ 高温純水に、Al、Mn、Mg、Ni、Znからな
る金属イオンの群から選ばれた１種以上を添加す
ることを特徴とする特許請求の範囲第１項記載の
原子力プラントの放射能低減方法。 ３ 高温純水に含まれる金属イオンの濃度が
5PPb〜1000PPbであることを特徴とする特許請
求の範囲第２項記載の原子力プラントの放射能低
減方法。[Claims] 1. A method for reducing radioactivity by forming an oxide film on the surface of a component made of metal that comes into contact with reactor cooling water containing radioactive substances before the component is exposed to the cooling water. , the component is brought into contact with high-temperature pure water at 200 to 300°C with a dissolved oxygen concentration of 300 to 500 PPb to reduce the elution of the metals that make up the component, and to form a dense and protective crystal grain with a crystal grain size of 0.5 μm or less. A method for reducing radioactivity in a nuclear power plant, characterized by preventing cobalt from adhering to structural members by forming an oxide film with high oxidation. 2. Radioactivity of a nuclear power plant according to claim 1, characterized in that one or more selected from the group of metal ions consisting of Al, Mn, Mg, Ni, and Zn is added to high-temperature pure water. Reduction method. 3 The concentration of metal ions contained in high-temperature pure water is
The method for reducing radioactivity in a nuclear power plant according to claim 2, characterized in that the radioactivity is 5PPb to 1000PPb.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60218045A JPS6279396A (en) | 1985-10-02 | 1985-10-02 | Radioactivity reducing method of nuclear power plant |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60218045A JPS6279396A (en) | 1985-10-02 | 1985-10-02 | Radioactivity reducing method of nuclear power plant |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6279396A JPS6279396A (en) | 1987-04-11 |
| JPH0431359B2 true JPH0431359B2 (en) | 1992-05-26 |
Family
ID=16713782
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP60218045A Granted JPS6279396A (en) | 1985-10-02 | 1985-10-02 | Radioactivity reducing method of nuclear power plant |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6279396A (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5860296A (en) * | 1981-10-07 | 1983-04-09 | 株式会社東芝 | Method of removing cobalt of light water reactor |
-
1985
- 1985-10-02 JP JP60218045A patent/JPS6279396A/en active Granted
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5860296A (en) * | 1981-10-07 | 1983-04-09 | 株式会社東芝 | Method of removing cobalt of light water reactor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6279396A (en) | 1987-04-11 |
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