JPS6138435B2 - - Google Patents
Info
- Publication number
- JPS6138435B2 JPS6138435B2 JP53026594A JP2659478A JPS6138435B2 JP S6138435 B2 JPS6138435 B2 JP S6138435B2 JP 53026594 A JP53026594 A JP 53026594A JP 2659478 A JP2659478 A JP 2659478A JP S6138435 B2 JPS6138435 B2 JP S6138435B2
- Authority
- JP
- Japan
- Prior art keywords
- corrosion products
- water
- hydrogen
- reactor
- corrosion
- 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
Links
- 238000005260 corrosion Methods 0.000 claims description 63
- 230000007797 corrosion Effects 0.000 claims description 63
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 37
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 36
- 239000001257 hydrogen Substances 0.000 claims description 36
- 229910052739 hydrogen Inorganic materials 0.000 claims description 36
- 230000002285 radioactive effect Effects 0.000 claims description 25
- 239000000498 cooling water Substances 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 22
- 238000009835 boiling Methods 0.000 claims description 2
- 239000000047 product Substances 0.000 description 53
- 238000001816 cooling Methods 0.000 description 21
- 239000000463 material Substances 0.000 description 10
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 7
- 239000007789 gas Substances 0.000 description 7
- 239000001301 oxygen Substances 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
- 238000011109 contamination Methods 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 4
- 230000007704 transition Effects 0.000 description 4
- 229910018916 CoOOH Inorganic materials 0.000 description 3
- 229910018661 Ni(OH) Inorganic materials 0.000 description 3
- 229910002640 NiOOH Inorganic materials 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 238000002347 injection Methods 0.000 description 3
- 239000007924 injection Substances 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 239000002826 coolant Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000003608 radiolysis reaction Methods 0.000 description 2
- 230000008929 regeneration Effects 0.000 description 2
- 238000011069 regeneration method Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910020599 Co 3 O 4 Inorganic materials 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 1
- 235000013980 iron oxide Nutrition 0.000 description 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000009392 mechanical decontamination Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 230000007480 spreading Effects 0.000 description 1
- 238000003892 spreading Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000009849 vacuum degassing Methods 0.000 description 1
- 229910006279 γ-NiOOH Inorganic materials 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
-
- 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
Landscapes
- Preventing Corrosion Or Incrustation Of Metals (AREA)
- Structure Of Emergency Protection For Nuclear Reactors (AREA)
Description
本発明は、沸騰水型軽水炉原子力プラントにお
いて作業者を体外放射線被ばくから防護し、機器
の放射能汚染を防止する方法に関し、詳しくは、
原子力プラントの運転停止および再起動という運
転状態の過渡期において、冷却水中に水素を注入
することにより、放射性核種を含む構造材料の腐
食生成物の冷却水濃度を抑制する方法に関する。
原子力プラントにおいては、一般に冷却系の構
造材料の腐食生成物が生成する。この腐食生成物
は炉心において放射化された後、一部は冷却系全
体に拡散して蓄積する。この冷却系に蓄積した放
射化された腐食生成物（以下「放射性腐食生成
物」という）は、原子力プラントの作業者が受け
る放射線被ばくおよび機器の放射能汚染の主たる
原因になつている。したがつて、放射線被ばくか
ら防護し、放射能汚染を防止するためには、炉心
で生成する放射性腐食生成物の冷却系全体への拡
散を抑制する必要がある。
放射性腐食生成物の生成過程を説明すると、ま
ず、冷却水に接触する冷却系の構造材料が腐食
し、腐食生成物が該構造材料の表面に生成する。
この腐食生成物の一部が、冷却水中へ溶解し、又
は剥離して懸濁状態で移行し、冷却水とともに炉
心に入り、炉心を循環する過程で、一部は炉心内
の燃料被覆管やその他の機器の表面に析出、沈積
して蓄積する。炉心内に蓄積した腐食生成物は、
再び冷却水中へ移行し、かつまた蓄積を繰り返す
こともあるが、炉心において中性子照射を受けて
放射化され、放射性腐食生成物を生成するに至
る。かくして生成した放射性腐食生成物が冷却水
の循環によつて冷却系全体に拡散する。冷却水中
の放射性腐食生成物の含有量は、通常の化学分析
では検知できない程微量であるが、長期の運転期
間の間には冷却系内に多量に蓄積するに至り、放
射線被ばく、放射能汚染の原因になる。
従来、冷却系内に蓄積した放射性腐食生成物に
よる放射線被ばく等を軽減する方法として、定期
的な機械除染によつて、冷却系機器表面に蓄積し
た腐食生成物を剥離し、ろ過脱塩器により除去す
る方法が行われてきた。しかし、この方法で除染
できるのは、冷却系の限られた個所にすぎなかつ
た。
また、プラントの運転停止の期間を通じて冷却
水を真空脱または加熱脱気して、冷却水中の溶存
酸素を除去することにより、腐食生成物の生成を
抑制する方法が知られている。しかし、この方法
においては、腐食生成物を還元するために必要な
低濃度まで酸素の溶存量を減少させることは技術
的に困難であることから、ある程度腐食の進行を
緩和できるに止まる。
さらに、積極的な方法として、原子力プラント
の運転中においても、常時、冷却水中に水素を注
入する方法が知られている。この方法では、冷却
水中の水素濃度は高く保たれるので、冷却系の構
造材料の腐食は抑制され、生成した腐食生成物は
還元される。また、冷却水中の溶存酸素は水素に
より置換され、また水の放射線分解により生成し
た酸素は、2H2＋O2→2H2Oなる反応により水を
再生して減少する。この方法は、冷却系構造材料
の腐食生成物そのものの生成を抑制するので、放
射線被ばく、放射能汚染を防止する上で効果的で
あるばかりでなく、応力腐食割れ等の腐食による
障害を防止できるので、腐食に対する抜本的対策
と言える。しかし、常時水素を冷却水に注入する
ため、復水器から流出する、放射性ガス等を含ん
だガスから、莫大な量の過剰水素を、分離、回収
する複雑かつ特殊な排ガス処理装置が必要である
という欠点を有し、未だ採用されていない。
本発明は、原子力プラントの作業者の放射線被
ばく等の原因が特に冷却系全体に蓄積した放射性
腐食生成物に存することに着目し、前述のような
従来技術の欠点を解消すべくなされたものであ
る。
すなわち、本発明の目的は、たとえ腐食生成物
が炉心において放射化されても、炉心内に蓄積し
た放射性腐食生成物が溶解または剥離して炉水中
に移行し、冷却水中の放射性腐食生成物の濃度が
増加することを抑制することにある。さらにこの
放射性腐食生成物が、炉心外へ流出し、冷却系全
体に拡散することを抑制することにより、冷却系
に放射性腐食生成物が蓄積することを防ぎ、もつ
て原子力プラントの作業者の放射線被ばくから防
護し、機器の放射性汚染を防止することにある。
本発明の方法は、炉水の温度がｔ℃であるとき
に、原子力プラントの運転停止操作開始直前か
ら、再起動操作終了直後までの期間内に、冷却水
中に水素を注入することによつて前記の期間を通
じて炉水中の水素濃度を2exp（0.013t）cm3N.T.P.
／KgH2O以上に保持することを内容とするもので
ある。
さらに詳述すると、冷却水中への水素の注入
は、前記期間を通じて連続的に行つてもよく、ま
た断続的に行つてもよい。したがつて、ブラント
の運転停止期間中に、原子炉圧力容器の蓋を開け
ない場合は勿論、蓋を開ける場合であつても本発
明は実施することができる。蓋を開ける場合に
は、蓋を開ける直前から蓋を閉じた直後まで水素
の注入は中止することになろう。また、水素を注
入する際の状態は水素ガスとしてでもよく、水に
溶解した状態でもよい。さらに、水素の注入は、
炉水中の水素濃度を必要な値以上に保持すること
ができれば、炉水中へ直接行つてもよく、他の場
所で行つてもよい。通常は、第１図の例に示すよ
うに冷却水の再循環ループにおいて、再循環ポン
プの吐出側から注入を行うことが適切である。
本発明を、さらに詳しく説明すると、本発明の
成立は、第一に従来の原子力プラントの冷却系に
蓄積した腐食生成物中の、蓄積放射性核種に関す
る知見に基く。第一表に、従来の原子力発電所の
例を示す。
The present invention relates to a method for protecting workers from external radiation exposure and preventing radioactive contamination of equipment in a boiling water reactor nuclear power plant.
The present invention relates to a method of suppressing the concentration of corrosion products of structural materials containing radionuclides in cooling water by injecting hydrogen into the cooling water during the transitional period of operating conditions such as shutdown and restart of a nuclear power plant. In nuclear power plants, corrosion products of the structural materials of the cooling system are generally produced. After these corrosion products are activated in the core, some of them diffuse and accumulate throughout the cooling system. Activated corrosion products accumulated in the cooling system (hereinafter referred to as "radioactive corrosion products") are the main cause of radiation exposure to nuclear plant workers and radioactive contamination of equipment. Therefore, in order to protect against radiation exposure and prevent radioactive contamination, it is necessary to suppress the diffusion of radioactive corrosion products generated in the reactor core throughout the cooling system. To explain the process of generating radioactive corrosion products, first, the structural material of the cooling system that comes into contact with the cooling water corrodes, and corrosion products are generated on the surface of the structural material.
A part of this corrosion product dissolves or separates into the cooling water and moves in a suspended state, enters the reactor core together with the cooling water, and in the process of circulating through the reactor core, some of it is transferred to the fuel cladding tubes and other parts inside the reactor core. Precipitates and accumulates on the surfaces of other equipment. Corrosion products accumulated in the reactor core are
It may migrate back into the cooling water and accumulate again, but it is activated by neutron irradiation in the reactor core, producing radioactive corrosion products. The radioactive corrosion products thus produced are spread throughout the cooling system by the circulation of the cooling water. The content of radioactive corrosion products in cooling water is so small that it cannot be detected by ordinary chemical analysis, but during long-term operation, a large amount accumulates in the cooling system, causing radiation exposure and radioactive contamination. It causes Conventionally, as a method to reduce radiation exposure due to radioactive corrosion products accumulated in the cooling system, periodic mechanical decontamination is used to peel off the corrosion products accumulated on the surface of the cooling system equipment, and a filtration demineralizer is used. A method of removing it has been used. However, this method could only decontaminate a limited number of parts of the cooling system. Furthermore, a method is known in which the generation of corrosion products is suppressed by removing dissolved oxygen in the cooling water by vacuum degassing or heating deaeration of the cooling water throughout the period when plant operation is stopped. However, in this method, it is technically difficult to reduce the amount of dissolved oxygen to the low concentration required to reduce corrosion products, and therefore the progress of corrosion can only be alleviated to a certain extent. Furthermore, as a proactive method, a method is known in which hydrogen is constantly injected into cooling water even during operation of a nuclear power plant. In this method, the hydrogen concentration in the cooling water is kept high, so corrosion of the structural materials of the cooling system is suppressed and the generated corrosion products are reduced. Further, dissolved oxygen in the cooling water is replaced by hydrogen, and oxygen generated by radiolysis of water is reduced by regenerating water through the reaction 2H 2 +O 2 →2H 2 O. This method suppresses the generation of corrosion products themselves in the cooling system structural materials, so it is not only effective in preventing radiation exposure and radioactive contamination, but also prevents damage caused by corrosion such as stress corrosion cracking. Therefore, it can be said to be a drastic measure against corrosion. However, because hydrogen is constantly injected into the cooling water, a complex and special exhaust gas treatment device is required to separate and recover a huge amount of excess hydrogen from the gas containing radioactive gases flowing out from the condenser. However, it has some drawbacks and has not been adopted yet. The present invention focuses on the fact that the cause of radiation exposure of nuclear plant workers lies in the radioactive corrosion products that accumulate in the entire cooling system, and has been made to eliminate the drawbacks of the prior art as described above. be. In other words, the object of the present invention is that even if the corrosion products are activated in the reactor core, the radioactive corrosion products accumulated in the reactor core are dissolved or separated and transferred to the reactor water, and the radioactive corrosion products in the cooling water are removed. The purpose is to suppress the increase in concentration. Furthermore, by suppressing these radioactive corrosion products from flowing out of the core and spreading throughout the cooling system, radioactive corrosion products can be prevented from accumulating in the cooling system, thereby increasing the radiation exposure of nuclear plant workers. The purpose is to protect against radiation exposure and prevent radioactive contamination of equipment. The method of the present invention involves injecting hydrogen into cooling water during a period from immediately before the start of a nuclear plant shutdown operation to immediately after the end of a restart operation when the reactor water temperature is t°C. Throughout the above period, the hydrogen concentration in the reactor water was reduced to 2exp (0.013t) cm3 NTP.
/KgH 2 O or higher. More specifically, hydrogen may be injected into the cooling water continuously or intermittently throughout the period. Therefore, the present invention can be carried out not only when the lid of the reactor pressure vessel is not opened during the blunt operation period, but also when the lid is opened. When the lid is opened, hydrogen injection will be stopped from just before the lid is opened to immediately after the lid is closed. Further, hydrogen may be injected in the form of hydrogen gas or dissolved in water. Furthermore, hydrogen injection
As long as the hydrogen concentration in the reactor water can be maintained above the required value, it may be carried out directly into the reactor water or at another location. It is usually appropriate to inject the cooling water from the discharge side of the recirculation pump in the cooling water recirculation loop, as shown in the example of FIG. To explain the present invention in more detail, the establishment of the present invention is firstly based on knowledge regarding accumulated radionuclides in corrosion products accumulated in the cooling system of a conventional nuclear power plant. Table 1 shows examples of conventional nuclear power plants.
【表】【table】
【表】
第１表の例によると、60Coおよび58Coは放射能
濃度が大きく、かつ比較的半減期が長い核種であ
ることから、放射線の主要な源になつている。こ
の60Coおよび58Coは、放射化反応により59Coおよ
び58Niからそれぞれ生成する。なお、腐食生成物
の大部分は、放射能的には悪影響の小さい鉄の酸
化物であり、60Coや58Coは通常の比学分析では検
知できない程、微量であることがわかつている。
以上の知見により、炉心内で生成する放射性腐食
生成物のうち、特に問題になるのは、Coおよび
Niの腐食生成物であると言うことができる。
次に、本発明の成立は、炉水において生成、蓄
積している腐食生成物が、炉水中へ溶解し、また
は剥離して懸濁状態で移行する量は、原子力プラ
ントが定常運転されているときよりも、プラント
を停止する過程または再起動する過程という運転
状態の過渡期において最も増大するという知見に
基いている。第２図は、従来の原子力プラントに
おいて、Feを含む腐食生成物とCoを含む腐食生
成物について、炉水中濃度の経時変化を測定した
結果を示す。図中、ａはFeを含む腐食生成物の
相対濃度を、ｂはCoを含む腐食生成物の相対濃
度を表わす。この測定結果の場合、プラントの停
止および再起動の過程で、Feの濃度は定常運転
時に比較して、最高103倍以上になり、Coの濃度
は102倍以上になつている。このように、プラン
トの運転状態の過渡期においては、炉心内に蓄積
した腐食生成物の溶解、剥離が著しくなり、その
結果、放射性腐食生成物の冷却系全体への拡散も
活発になることがわかる。この原因としては、運
転状態の過渡期における、炉心内の熱的、化学
的、および機械的変化、並びに運転中行つている
冷却水の脱気を中止することによつて起る溶存酸
素の増加等があげられる。
したがつて、原子力プラントの運転停止および
再起動という過渡期の前後を通じて、炉水中の水
素濃度を一定値以上に保持することにより、効果
的に、炉心内に蓄積している放射性腐食生成物を
含む腐食生成物を還元し、金属として炉心構造材
料の表面に析出せしめ、冷却水中への溶解、剥離
を抑制することができ、また新たな腐食も抑制す
ることができる。
本発明者らは、さらに炉心、冷却系の構造材料
に使用されている金属の腐食生成物について熱力
学的に検討した結果、炉水中に水素を注入する方
法は、特にCoおよびNiに対して効果的であるこ
とを見出し、有効な炉水中水素濃度を求めるに至
つた。
すなわち、次の反応式(1)〜(4)に示すCoおよび
Niの腐食反応について、熱力学的平衡条件を、
向坊らが提出した方法（向坊、増田、前田、室示
戸、電気化学第34巻388〜396頁、1966年）によつ
て、推定した。ここに示した腐食生成物CoO，
Co（OH）2，NiOおよびNi（OH）2は、Co，Niの
腐食生成物中、水中でかなり広い安定領域を有す
るものである。
Co＋H2O＝CoO＋H2 (1)
１／２Co＋H2O＝１／２Co（OH）2＋１／２H2(2)
Ni＋H2O＝NiO＋H2 (3)
１／２Ni＋H2O＝１／２Ni（OH）2＋１／２H2(4)
次に、求めた熱力学的平衡条件から、CoO，
Co（OH）2，NiO、およびNi（OH）2のすべてを還
元することができる最小の水素分圧を、各温度に
ついて求め、さらにこの水素分圧と平衡状態にあ
る炉水中水素濃度を、ピー・コーエン著「ウオー
ター・クーラント・テクノロジイ・オブ・パワ
ー・リアクターズ」、ゴードン・アンド・プリー
チ・サイエンス第１版（1969）107頁（P.Cohen
“Water Coolant Technology of Pawer
Reactors”，Gordon＆Breach Sci，Pub １，
（1969），P107）に記載された次式により求め
た。
Ｓ＝８．４５×１０４ＰＨ２／Ｈ
（式中、Ｓは溶解度［cm3N.T.P.／KgH2O］、
PH2は水素分圧［Psi］、Ｈは水素分圧［Psi］と
水中モル分率に関して定まるヘンリーの定数を表
わす。）
このようにして求めた、CoおよびNiの腐食生
成物を還元するために必要な最小の水素分圧およ
び炉水中水素濃度を第２表に示す。[Table] According to the example in Table 1, 60 Co and 58 Co are nuclides with high radioactivity concentrations and relatively long half-lives, so they are major sources of radiation. These 60 Co and 58 Co are generated from 59 Co and 58 Ni, respectively, by an activation reaction. It should be noted that most of the corrosion products are iron oxides that have little radioactive effect, and it is known that 60 Co and 58 Co are so small that they cannot be detected by normal ratiometric analysis.
Based on the above findings, among the radioactive corrosion products generated in the reactor core, Co and
It can be said that it is a corrosion product of Ni. Next, the establishment of the present invention is based on the fact that the amount of corrosion products generated and accumulated in the reactor water that dissolves or detaches into the reactor water and transfers in a suspended state is limited to the amount that is generated and accumulated in the reactor water when the nuclear power plant is in steady operation. This is based on the knowledge that the increase is greatest during the transitional period of operating conditions, such as the process of shutting down or restarting the plant, rather than during the process of shutting down or restarting the plant. FIG. 2 shows the results of measuring changes over time in the concentrations of Fe-containing corrosion products and Co-containing corrosion products in reactor water in a conventional nuclear power plant. In the figure, a represents the relative concentration of corrosion products containing Fe, and b represents the relative concentration of corrosion products containing Co. In the case of these measurement results, during the process of stopping and restarting the plant, the concentration of Fe is at most 10 3 times higher than during steady operation, and the concentration of Co is 10 2 times higher. As described above, during the transition period of plant operating conditions, the dissolution and peeling of corrosion products accumulated in the reactor core becomes significant, and as a result, the diffusion of radioactive corrosion products throughout the cooling system becomes active. Recognize. The causes include thermal, chemical, and mechanical changes within the core during the transition period of operating conditions, as well as an increase in dissolved oxygen caused by stopping degassing of cooling water during operation. can be given. Therefore, by maintaining the hydrogen concentration in the reactor water above a certain value before and after the transition period of shutting down and restarting a nuclear power plant, radioactive corrosion products accumulated in the reactor core can be effectively removed. It is possible to reduce the contained corrosion products and precipitate them as metals on the surface of the core structural material, thereby suppressing dissolution into cooling water and peeling, and also suppressing new corrosion. The inventors further thermodynamically investigated the corrosion products of metals used in the structural materials of the reactor core and cooling system, and found that the method of injecting hydrogen into reactor water was particularly effective against Co and Ni. They found that this method was effective and determined the effective hydrogen concentration in reactor water. That is, Co and
Regarding the corrosion reaction of Ni, the thermodynamic equilibrium conditions are
It was estimated by the method proposed by Mukabo et al. (Mukabo, Masuda, Maeda, Murojido, Electrochemistry Vol. 34, pp. 388-396, 1966). The corrosion product CoO shown here is
Among the corrosion products of Co and Ni, Co(OH) 2 , NiO and Ni(OH) 2 have a fairly wide stability range in water. Co+H 2 O=CoO+H 2 (1) 1/2Co+H 2 O=1/2Co(OH) 2 +1/2H 2 (2)
Ni+H 2 O=NiO+H 2 (3) 1/2Ni+H 2 O=1/2Ni(OH) 2 +1/2H 2 (4)
Next, from the thermodynamic equilibrium conditions obtained, CoO,
The minimum hydrogen partial pressure that can reduce all of Co(OH) 2 , NiO, and Ni(OH) 2 is determined for each temperature, and the hydrogen concentration in the reactor water that is in equilibrium with this hydrogen partial pressure is determined as follows: "Water Coolant Technology of Power Reactors" by P. Cohen, Gordon and Preach Science, 1st edition (1969), p. 107 (P. Cohen
“Water Coolant Technology of Power
Reactors”, Gordon & Breach Sci, Pub 1,
(1969), page 107). S=8.45×10 4 PH 2 /H (wherein, S is solubility [cm 3 NTP/KgH 2 O],
PH 2 represents hydrogen partial pressure [Psi], and H represents Henry's constant determined with respect to hydrogen partial pressure [Psi] and the molar fraction in water. ) Table 2 shows the minimum hydrogen partial pressure and hydrogen concentration in reactor water required to reduce Co and Ni corrosion products, thus determined.
【表】
本発明において限定した炉水中水素濃度の臨界
値、2exp（0.013t）（［cm3N.T.P／KgH2O］，ｔ
℃）は、第２表に得られた最小の必要水素濃度に
対し、若干の余裕を見込んで選択された値であ
る。
なお、冷却系で生成すると考えられるCoの腐
食生成物として、他にβ−CoOOH，CoOOH
（），CoOOH（），Co3O4等があり、またNiの
腐食生成物としては、他にα−NiOOH，β−
NiOOH，γ−NiOOH，Ni3O2（OH）4，4Ni
（OH）2・NiOOH等があるが、これらはそれぞれ
Co（OH）2およびNi（OH）2よりも強い酸化条件
において安定して存在するものであるから、本発
明の条件においては還元される。
かくして、本発明の効果として、炉水中の水素
濃度は増加し、かつこれによつてもたらされる酸
素の溶解度の低下と、反応式2H2＋O2→2H2Oで
示される水の再成反応のために、酸素濃度が低下
する結果、炉水に接する金属の自然電極電位は卑
へ移行し、この金属材料の腐食は抑制され、また
腐食生成物は還元される。したがつて、炉心構造
材料の表面に蓄積した腐食生成物の還元、および
炉水中に溶解している腐食生成物の構造材料表面
への析出が促進される。この効果は、放射能的に
最も問題となるCoおよびNiについて著しいが、
他の金属元素に対しても同様に現われるものであ
る。
さらに、炉水の放射線分解によつて生ずる過酸
化水素の増加も、反応式H2＋H2O2→2H2Oで示さ
れる水の再成反応によつて抑制されるので、腐食
は抑制されることになる。
このようにして、原子力プラントの運転停止お
よび再起動の過渡期に活発になる蓄積腐食生成物
の溶解または剥離による炉水中への移行は抑制さ
れ、結局、放射性腐食生成物の冷却系全体への拡
散を防止することができ、ひいてはプラント作業
者の放射線被ばく等を抑制することができる。
また、本発明の利点として、注入した水素の過
剰分を分離、回収するために、複雑かつ特殊な排
ガス処理装置は不要である。水素の気相／液相の
分配比（重量）は、温度低下により著しく増大す
る。例えば、炉水温度が運転中の290℃から、運
転停止中の40℃へ低下すると、分配比は、160か
ら６×105へ増大する。他方、本発明に係る必要
水素濃度は、80［cm3N.T.P／KgH2O］から３［cm3
N.T.P／KgH2O］へ減少する。したがつて、分配
比の増大は、必要水素濃度の減少を著しく上まわ
ることになるが、プラントの停止および再起動に
際しては一般に炉水温度が低下していて、原子炉
からタービン等の炉外へ蒸気の送り出しがないの
で、この期間における必要な水素注入量は、運転
時に水素注入を行う場合に比し少ないため、特殊
な排ガス処理装置を特に設ける必要はないのであ
る。[Table] Critical value of hydrogen concentration in reactor water limited in the present invention, 2exp (0.013t) ([cm 3 NTP/KgH 2 O], t
℃) is a value selected with some allowance for the minimum required hydrogen concentration obtained in Table 2. In addition, other corrosion products of Co that are thought to be generated in the cooling system include β-CoOOH and CoOOH.
(), CoOOH (), Co 3 O 4, etc., and corrosion products of Ni include α-NiOOH, β-
NiOOH, γ-NiOOH, Ni 3 O 2 (OH) 4 , 4Ni
(OH) 2・NiOOH etc., but each of these
Since it exists stably under stronger oxidizing conditions than Co(OH) 2 and Ni(OH) 2 , it is reduced under the conditions of the present invention. Thus, as an effect of the present invention, the hydrogen concentration in the reactor water increases, and the resulting decrease in oxygen solubility and the water regeneration reaction shown by the reaction formula 2H 2 + O 2 → 2H 2 O occur. As a result, the oxygen concentration decreases, and as a result, the natural electrode potential of metals in contact with reactor water shifts to less noble, corrosion of this metal material is suppressed, and corrosion products are reduced. Therefore, the reduction of the corrosion products accumulated on the surface of the core structural material and the precipitation of the corrosion products dissolved in the reactor water on the surface of the structural material are promoted. This effect is remarkable for Co and Ni, which are the most radiologically problematic, but
Similar phenomena appear for other metal elements. Furthermore, the increase in hydrogen peroxide caused by radiolysis of reactor water is suppressed by the water regeneration reaction shown by the reaction formula H 2 + H 2 O 2 →2H 2 O, so corrosion is suppressed. That will happen. In this way, the migration of accumulated corrosion products into the reactor water through dissolution or flaking, which becomes active during the transition period between shutdown and restart of nuclear power plants, is suppressed, and eventually radioactive corrosion products are transferred to the entire cooling system. Diffusion can be prevented, and radiation exposure of plant workers can be suppressed. Further, as an advantage of the present invention, a complicated and special exhaust gas treatment device is not required in order to separate and recover the excess amount of injected hydrogen. The gas phase/liquid phase distribution ratio (weight) of hydrogen increases significantly as the temperature decreases. For example, when the reactor water temperature decreases from 290° C. during operation to 40° C. during shutdown, the distribution ratio increases from 160 to 6×10 5 . On the other hand, the required hydrogen concentration according to the present invention ranges from 80 [cm 3 NTP/KgH 2 O] to 3 [cm 3
NTP/KgH 2 O]. Therefore, the increase in the distribution ratio will significantly exceed the decrease in the required hydrogen concentration, but when the plant is shut down and restarted, the temperature of the reactor water is generally low, and there is Since no steam is sent to the engine, the required amount of hydrogen injection during this period is smaller than when hydrogen is injected during operation, so there is no need to provide a special exhaust gas treatment device.
第１図は、本発明において冷却水中に水素を注
入する方法の一例を示した概念図である。第２図
は、従来の原子力プラントにおいて、Feを含む
腐食生成物およびCoを含む腐食生成物の炉水中
濃度の経時変化を測定した結果を示す図であり、
図中ａはFeを含む腐食生成物に関し、ｂはCoを
含む腐食生成物に関する曲線である。第１図中、
番号を付した要素は次のとおりである。
１……原子炉、２……再循環系を除いた部分
で、通常の機器を具備した冷却系、３……再循環
ループ、４……再循環ポンプ、５……水素貯蔵タ
ンク、６……水素ガス置換用ガスタンク。
FIG. 1 is a conceptual diagram showing an example of a method of injecting hydrogen into cooling water in the present invention. FIG. 2 is a diagram showing the results of measuring changes over time in the concentration of corrosion products containing Fe and corrosion products containing Co in reactor water in a conventional nuclear power plant.
In the figure, a is a curve for a corrosion product containing Fe, and b is a curve for a corrosion product containing Co. In Figure 1,
The numbered elements are as follows. 1... Nuclear reactor, 2... Cooling system except for the recirculation system and equipped with normal equipment, 3... Recirculation loop, 4... Recirculation pump, 5... Hydrogen storage tank, 6... ...Gas tank for hydrogen gas replacement.
Claims (1)
水の温度がｔ℃であるとき、原子力プラントの運
転停止操作開始直前から、再起動操作終了直後ま
での期間内に、冷却水中に水素を注入することに
より、前記期間を通じて炉水中の水素濃度を
2exp（0.013t）cm3N.T.P.／KgH2O以上に保持する
ことを特徴とする原子力プラントの冷却水中の放
射性腐食生成物濃度を抑制する方法。1. In a boiling water light water reactor nuclear power plant, when the temperature of the reactor water is t°C, by injecting hydrogen into the cooling water during the period from immediately before the start of the shutdown operation to immediately after the end of the restart operation of the nuclear plant. , the hydrogen concentration in the reactor water throughout the above period.
A method for suppressing the concentration of radioactive corrosion products in cooling water of a nuclear power plant, characterized by maintaining the concentration at or above 2exp (0.013t) cm 3 NTP/KgH 2 O.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2659478A JPS54126894A (en) | 1978-03-10 | 1978-03-10 | Suppression of concentration of radioactive corrosion products in cooling water of nuclear power plant |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2659478A JPS54126894A (en) | 1978-03-10 | 1978-03-10 | Suppression of concentration of radioactive corrosion products in cooling water of nuclear power plant |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS54126894A JPS54126894A (en) | 1979-10-02 |
| JPS6138435B2 true JPS6138435B2 (en) | 1986-08-29 |
Family
ID=12197850
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2659478A Granted JPS54126894A (en) | 1978-03-10 | 1978-03-10 | Suppression of concentration of radioactive corrosion products in cooling water of nuclear power plant |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS54126894A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS61104298A (en) * | 1984-10-26 | 1986-05-22 | 日本原子力事業株式会社 | Radioactivity accumulation reducer for nuclear reactor primary cooling system |
| JP4434436B2 (en) * | 2000-06-12 | 2010-03-17 | 株式会社東芝 | Operation method of boiling water nuclear power plant |
| US10229761B2 (en) * | 2012-12-21 | 2019-03-12 | Ge-Hitachi Nuclear Energy Americas Llc | Startup/shutdown hydrogen injection system for boiling water reactors (BWRS), and method thereof |
-
1978
- 1978-03-10 JP JP2659478A patent/JPS54126894A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS54126894A (en) | 1979-10-02 |
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