JP4374776B2

JP4374776B2 - Radioactive waste volume reduction device and operation method thereof

Info

Publication number: JP4374776B2
Application number: JP2000384676A
Authority: JP
Inventors: 明夫清水
Original assignee: Fuji Electric Holdings Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 2000-12-19
Filing date: 2000-12-19
Publication date: 2009-12-02
Anticipated expiration: 2020-12-19
Also published as: JP2002181994A

Description

【０００１】
【発明の属する技術分野】
本発明は、原子力施設内で発生する可燃性または難燃性の放射性廃棄物の減容装置、特に放射性廃棄物を加熱分解するとともに酸素をプラズマ加熱して酸化反応を促進して減容する装置、およびその運転方法に関する。
【０００２】
【従来の技術】
従来、この種の放射性廃棄物の減容処理には、バーナを利用した焼却法、不燃ガス中で高温に加熱して分解する熱分解法、過酸化水素を用いた酸化分解法等が使用され、あるいは適用が検討されている。
これらの減容処理法のうち、焼却法は、燃料燃焼炎で空気を高温にして樹脂を燃焼し、灰化減容する方法である。熱分解法は、ガス化成分と固体成分に分離し、放射性核種を含まないガス成分を焼却して減容するものである。また、酸化分解法は、過酸化水素と触媒を用いて樹脂成分を水と二酸化炭素に分解して分離し、減容するものである。この他、これらの方法とは趣を異にする方法として、低気圧下において酸素プラズマで樹脂を酸化分解し、灰化減容する方法の検討もなされている。また、特願2000−127020号に記載されているがごときプラズマ式燃焼処理方法も提案されている。
【０００３】
【発明が解決しようとする課題】
上記の減容処理法のうち、焼却法においては、適用が比較的線量の低い樹脂に限定されるという基本的な問題がある。また比較的線量の低い樹脂に適用する場合においても、樹脂が燃焼して発生するガスに加えて、高温空気を得るための燃料燃焼用バーナのからの燃焼排ガスが発生し、さらに不完全燃焼防止のための二次燃焼用の高温空気を導入することが必要となるため、処理装置全体から発生する排気ガス量は膨大となる。従って、この焼却法では大規模な排ガス処理装置を設置することが必要になるという問題がある。また、処理される樹脂が高カロリであるため、焼却炉の炉壁材が高温に曝されて損傷しやすく、頻繁に補修することが必要となるので、二次放射性廃棄物が多くなり、同時にメンテナンス費用も大きくなるという問題がある。
【０００４】
また、熱分解法においては、熱分解に伴って放射性核種を含有する多量のタール質成分のミストが発生するので、処理装置の後段に大容量のフィルタを備える必要があり、システムが大形化するという問題がある。また、前述のフィルタは目詰まりしやすく頻繁に交換する必要があるため、多量の二次放射性廃棄物が生じるとともに、多額のメンテナンス費用を要するという問題がある。
【０００５】
また、従来のプラズマ焼却法では、反応処理圧力を 0.001 MPa前後の比較的低い圧力に保持する必要があるため、処理能力を大きくするためには排気能力の大きな真空ポンプを使用する必要があり、この真空ポンプの排気能力によって処理能力が事実上制限されるという問題点があった。
また、特に可燃性放射性廃棄物などはかさ比重が小さいので、バッチ式の焼却炉では1度に多量に廃棄物を供給してもその処理重量は小さく、処理能力の向上が困難であった。
【０００６】
本発明は上記のごとき従来技術の問題点を考慮してなされたもので、本発明の目的は、排気系の真空ポンプの所要排気能力が従来のプラズマ式処理装置の真空ポンプに比べて大幅に低減され、あるいは、同容量でも処理速度が飛躍的に増大して、かつ連続的に処理可能となり、さらには、二次放射性廃棄物の発生も少なく、メンテナンス費も低減される放射性廃棄物の減容装置、ならびにその運転方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記の目的を達成するために、本発明においては、
原子力施設内で発生する可燃性または難燃性の放射性廃棄物の減容装置で、ほぼ鉛直に配された円筒形の処理容器と、その下端に配され処理容器と同軸円形で処理容器と嵌合されたヒーターと、被処理用の放射性廃棄物投入手段と、少なくとも一つの酸素導入手段と、少なくとも一つのプラズマ発生手段と、排気手段とを備えてなり、酸素導入手段によって処理容器の内部に酸素を導入し、プラズマ発生手段により酸素を高温に加熱するとともに、排気手段により排気して低気圧酸素雰囲気とし、放射性廃棄物投入手段によってヒーター上に投入した放射性廃棄物をヒーターにより加熱して加熱分解する放射性廃棄物の減容装置において、
（１）上記のプラズマ発生手段を、石英管とこの石英管に同軸に巻かれた誘導コイルを備えるものとし、石英管に酸素を供給し、誘導コイルに高周波電力を供給して酸素プラズマを発生する手段であり、酸素導入手段の少なくとも一つが、導入された酸素が処理容器内部において旋回流を形成するように構成された旋回流形成ノズルであるとともに、減容処理時の処理容器の内部の圧力が０．００５乃至０．０５ＭＰａ、好ましくは０．０１乃至０．０２ＭＰａに調整されて成るものとする。
【０００８】
（２）また、上記（１）において、放射性廃棄物を加熱するヒータの内径と処理容器のヒータに接する側面の外径をほぼ等しくし、かつこれらを連結して被処理物の放射性廃棄物がこぼれない構造とする。
（３）また、上記（１）または（２）において、酸素導入手段の少なくとも一つを、導入された酸素が処理容器の下端に連結されたヒーターの方向に向かう流れを形成する燃焼酸素供給ノズルとする。
【０００９】
（４）さらに上記（１）において、処理容器内部を排気する排気手段に連結される排気口を、旋回流形成ノズルにより形成された旋回ガス流の中心軸上の上方に設けることとする。
【００１０】
（５）また、上記（１）〜（４）において、処理容器と処理容器内部を排気する排気手段との間に高周波誘導結合型プラズマ式の２次燃焼室が設けられていることを特徴とする減容装置。
（６）また、上記（１）〜（５）において、処理容器の側壁に処理容器内部の温度を検知する温度監視センサを少なくとも一つ設けることとする。
【００１１】
（７）あるいは、上記（１）〜（５）において、装置の排気手段に排ガス中の酸素濃度を測定する酸素濃度測定手段を少なくとも一つ設けることとする。
（８）あるいは、上記（１）〜（５）において、装置の排気手段に排ガス中の二酸化炭素濃度を測定する二酸化炭素濃度測定手段を少なくとも一つ設けることとする。
【００１２】
（９）また、断続的に放射性廃棄物を投入しつつ、上記（１）〜（５）の減容装置を連続的に減容運転することとする。
（１０）また、温度監視センサで検知された温度が、上昇した後、下降に転じ、所定の温度レベルに低下したとき放射性廃棄物を投入する方法を用いて、上記（６）の減容装置を連続的に減容運転することとする。
【００１３】
（１１）また、酸素濃度測定手段によって検知された酸素濃度によって酸素導入手段により供給する酸素量を調整しつつ、上記（７）の減容装置を連続的に減容運転することとする。
（１２）また、二酸化炭素濃度測定手段によって検知された二酸化炭素ガス濃度が、上昇した後、下降に転じ、所定の濃度レベルに低下したとき放射性廃棄物を投入する方法を用いて、上記（８）の減容装置を連続的に減容運転することとする。
【００１４】
（１３）また、高周波誘導結合型プラズマ式の２次燃焼室の圧力を 600 Pa 以上に設定して上記（５）の放射性廃棄物の減容装置を運転することとする。
（１４）また、（９）〜（１３）の運転に際して、処理容器の内部の圧力を0.005乃至 0.05 MPa 、好ましくは 0.01 乃至 0.02 MPa に調整して減容運転することとする。
【００１５】
前述のように、従来のプラズマ焼却法を用いた処理装置では、安定にプラズマを立てられる限界は、0.003 MPa 以下であり、反応処理圧力は 0.001 MPa前後に限られていた。
これに対して、本発明者による実験結果により、上記（１）のごとく、石英管内に酸素を導入し、この石英管に同軸に巻かれた誘導コイルに高周波電力を供給して酸素プラズマを発生するプラズマ発生手段、すなわち、トーチ型のプラズマ源を用いて、処理容器の内部に酸素プラズマの旋回流を導入することによって、酸素プラズマ加熱手段より導入された酸素プラズマの旋回流が追加加速され、処理容器の内部圧力が 0.03 MPa 以上の高い圧力であっても充分安定してプラズマを立てられることが明らかとなった。したがって、従来の約 10 倍の高い圧力で安定に高温酸素を供給して処理することが可能となり、酸素の供給ガス量が同一のとき排気系の真空ポンプの所要排気能力は約 1/10 で済むこととなった。また、これとは逆に、同一の排気能力の真空ポンプで約 10 倍の供給ガスを流す大量処理に対応できることとなった。また、供給ガス量を約 10 倍にすることができるので、同一処理量であれば処理速度は約 10 倍となり、処理時間が大幅に短縮される。
【００１６】
また、上記（２）のごとくとすれば、被処理物の漏出が防止される。
また、上記（３）のごとく燃焼酸素供給ノズルを組み込めば、ヒータ上部に投入された被処理物へと効果的に酸素が供給され、被処理物が燃焼される。
【００１７】
また、上記（４）のごとく処理容器内部を排気する排気手段に連結される排気口を配置すれば、旋回流に伴った巻き上がった微粒子はサイクロン作用によって分離離脱し落下する。また、上記（５）のごとく処理容器と処理容器内部を排気する排気手段との間に高周波誘導結合型プラズマ式の２次燃焼室を設ければ、排ガス中に含まれる微量の未燃焼ガスを燃焼させることができる。
【００１８】
また、上記（６）のごとく温度監視センサを設ければ、処理容器内部の燃焼状態の知見が得られる。したがって、上記（１０）のごとき効率的な減容運転が可能となる。また、上記（７）のごとく排ガス中の酸素濃度を測定する酸素濃度測定手段を設ければ処理容器内部の燃焼状態の知見が得られる。したがって、上記（１１）のごとき効率的な減容運転が可能となる。
【００１９】
また、上記（８）のごとく排ガス中の二酸化炭素濃度を測定する二酸化炭素濃度測定手段を設ければ、処理容器内部の燃焼状態の知見が得られる。したがって、上記（１２）のごとき効率的な減容運転が可能となる。
【００２０】
【発明の実施の形態】
以下、本発明を実施例を用いて説明する。
図１は、本発明の放射性廃棄物の減容装置の一実施例を示す構成図である。図において、１は金属製の円筒状の処理容器、２は、処理容器１の下端に気密に連結された被処理物加熱用のヒーターである。３は、処理用の放射性廃棄物を収納する被処理物収納用器で、被処理物を処理容器１の内部に投入するためのロードロック式投入口３１と被処理物収納用器の内部を真空廃棄するための排気装置３２が付設されている。また、４は、処理容器１の下端に連結されたヒーター２の方向へと酸素を導入する燃焼酸素供給ノズルであり、５は、処理容器１の内部に高温の酸素プラズマを供給するプラズマ発生手段、６は、処理容器１の内部において旋回流をなす様に酸素を導入する旋回流形成ノズルである。
【００２１】
このうち、プラズマ発生手段５は、図２に示した横断面図に見られるように、二重の石英管５ａの間に冷却水を流して冷却し、石英管５ａの内部で 30 l/minの軸方向ガスと 20 ｌ/minの旋回ガスを形成するよう石英管５ａの一端に設けられたフランジより酸素が導入されている。この石英管５ａの外側には水冷式の誘導コイル５ｂが石英管５ａと同軸に５ターン巻かれており、この誘導コイル５ｂに 13.56 MHzの高周波電力を供給することによって石英管５ａの内部の酸素がプラズマ化され、約 2 kW の電力が供給される。高周波電力が直接酸素ガスを加熱するので他にエネルギーロスが少なく、効率よく高温酸素を生成することができる。図２に見られるように、このプラズマ発生手段５は石英管５ａの中心軸が処理容器１の中心軸を外れた外周近傍となるよう連結されており、プラズマ発生手段５で生じた約 2000 ℃の高温の酸素プラズマが処理容器１の内部に旋回流として導入され、被処理物の酸化反応の促進に寄与する。
【００２２】
処理容器１は、上端の排気口７に連結された排気系によって排気され、所定の圧力に維持される。本実施例の減容装置では、排気速度 80 m³/hのドライポンプ９が組み込まれており、処理容器１の内部圧力が 0.02 MPa となるようにコンダクタンスバルブ１０を用いて制御されている。
なお、処理容器１内で酸化反応が行われている場合、処理容器１内にはガス流による被処理物の小片や粒状の放射性核種を含んだ物質が舞い上がる。このため、図１に示した処理容器１の天井部分に周辺から旋回ガスを流す酸素供給口を配置して、サイクロン効果によって排気口７の付近には粒状物質は取り込まないよう工夫されている。しかしながら排気口７からの未燃焼ガス成分の流出を皆無にすることはできないので、図１に示したごとく、排気口７と排気系との間に高周波誘導結合型プラズマ式の２次燃焼室１１が設けられている。この２次燃焼室１１では、未燃焼ガスや酸素ガスがプラズマ中の電子と衝突し活性化して酸化反応をさせる仕組みになっている。電子に衝突されてイオン化する分子の寿命は 1μｓ程度であるので、この２次燃焼室１１内の排ガス速度を 1 m/s、イオン化率を０.０１％とすれば、プラズマ長がほぼ 10 mmですべての分子が平均１回プラズマ化することになる。したがって、この２次燃焼室１１内にプラズマ長が数十 mmのプラズマを発生させることによって、容易に 99 ％以上の分子をイオン化させることができる。イオン化した未燃焼ガスと酸素は容易に酸化反応を起こすので、この２次燃焼室１１を通すことによって排ガスをほぼ完全燃焼させることができる。
【００２３】
なお、図１に示した実施例の構成では、処理容器１の上端のサイクロンで分離できなかった微粒子を後段に設置したサイクロン８で捕集するシステムが採用されている。このサイクロン８の後段には、前述のようにドライポンプ９が配され、処理容器１を排気している。ドライポンプ９から排出される排気ガスには、放射性核種移行率として10^-6程度の低濃度放射性物質が含まれるので、ドライポンプ９の後段にはこれらの粒子状の核種を完全にフィルタリングするための図示しない可燃性プレフィルタとＨＥＰＡフィルタが組み込まれている。また、被処理物２０にイオウや窒素原子が含まれている場合には、酸化反応によりSO_XやNO_Xが発生するため、排ガスの無害化装置として小型のスクラバを介して大気に放出するシステムが採用される。
【００２４】
本構成の放射性廃棄物の減容装置において、処理容器１の下端に連結されたヒーター２を約 500℃に加熱しておき、ロードロック式投入口３１を開けて被処理物収納容器３に収納された可燃性・難燃性の被処理物２０を約 1l 処理容器内のヒーター２の上に投入する。投入された被処理物２０は、ヒーター２の上で可燃性ガスを放出し、酸素ガスと混合され、上記のプラズマ発生手段５より供給される高温酸素プラズマの助けを借りて完全燃焼が進行する。時間とともに徐々に可燃ガス放出量が増え、図１中に点線で示したごとき主酸化反応領域２１が上方へと拡大する。さらに時間が経過し、燃焼が進行して燃焼量が減少すると、可燃ガスの放出量も減少し、主酸化反応領域２１が下方へと後退する。
【００２５】
このため、図３に示したごとく、処理容器１の壁面に温度監視センサ２２を組み込み、その測定信号を温度監視装置２３で監視すれば、燃焼量が増して主酸化反応領域２１が上方へと拡大すると、温度監視センサ２２の測定温度が上昇し、燃焼量が減少して主酸化反応領域２１が下方へと後退すると、温度監視センサ２２の測定温度が低下することとなる。したがって、温度監視センサ２２の測定信号を温度監視装置２３で監視し、上昇した温度が下降を始めて所定の温度まで下降した時点で、被処理物投入操作装置２５に制御信号を送り、被処理物収納容器３から新たに被処理物２０を投入する運転方法を採れば、被処理物２０の減容処理を、連続して、熱暴走を防ぎつつ効率的に行うことができる。図４は、このように温度監視センサ２２の測定信号をもとに被処理物２０を断続的に投入して処理した場合の温度監視センサ２２の測定信号の時間変化を示す特性図である。図
に見られるように、温度が上昇した後、下降に転じ、点線で示した所定の温度まで下降した時点で新規に投入する信号が発され、これに基づいて新たに被処理物２０を投入する操作が繰り返されている。もちろん、被処理物２０の性状がある程度均質なものであれば、断続的に投入するタイミングをあらかじめ求めた時間間隔に選定して定期的に行うこととしてもよい。
【００２６】
上記の運転方法では処理容器１の壁面温度を監視して被処理物２０の投入タイミングを決定する方法を用いたが、酸素投入量と排ガス中の酸素濃度、二酸化炭素濃度から、酸素消費量および二酸化炭素発生量を割り出し、二酸化炭素発生量の減少や、酸素消費量の減少信号で被処理物の投入タイミングを決定する運転方法を採ることもできる。図５は、排ガス中の二酸化炭素濃度を測定して、被処理物２０の投入操作を制御する運転方法を示すもので、燃焼量が増して主酸化反応領域２１が上方へと拡大すると、濃度センサ２６で測定される二酸化炭素濃度が上昇し、燃焼量が減少して主酸化反応領域２１が下方へと後退すると二酸化炭素濃度が下がることを利用したものである。図６に示した特性は、酸素供給量一定の場合の二酸化炭素濃度の測定値と被処理物２０の新規投入のタイミングを示したものである。二酸化炭素濃度が下降を始め、点線で示した所定濃度に達したとき、濃度監視装置２７から被処理物投入操作装置２５へと新規に被処理物２０を投入する信号が発せられている。
【００２７】
さらに、本構成では、燃焼反応が増大した場合など酸素濃度が低くなりすぎた時には、濃度監視装置２７から酸素流量制御装置２４へと制御信号を送り、酸素供給量を一時的に増やす処置が行われる。また、低カロリーの被処理物２０を投入して酸化反応が最高潮の時の二酸化炭素発生量が装置能力に比べて小さい場合は、投入量を増やすこともできる。
【００２８】
本構成の減容装置において、上記の様に被処理物を断続的に供給すると、被処理物は減容され重量も減少する。たとえば、可燃物の紙や綿などのセルロース系物質は 98 ％の重量が減少して投入量の 1/50 程度になる。難燃物のイオン交換樹脂ならば、投入量の約 1/2となる。
セルロース系の可燃物のみを処理する場合は、例えば、１日８時間運転後、酸化反応の終了を待って、図１には図示されていない搬出機構から残さが回収される。
【００２９】
難燃物を含む被処理物２０を処理する場合には、被処理物２０を断続的に投入し、例えば総量で 50 l 投入して酸化反応を終了させたのち、ヒータ温度をさらに700℃まで上昇させるとともに、燃焼酸素供給ノズル４からの酸素供給量を増大させて酸化反応を促進させ、一定時間経過後、ヒータ温度を下げ、酸素の供給を遮断し、窒素ガスを注入して処理容器１の内部を大気圧に復帰させて反応を強制終了させる方法が採られる。本構成の減容装置は、この様に反応時間によって被処理物の減容率を制御することが可能であり、イオン交換樹脂においては、初期投入量の 1/5から 1/20 までの範囲に減容すると、後工程でセメント固化する場合に好適な残さ性状となる。もちろん、反応を時間で制御する方法のほかに、二酸化炭素濃度を積分した総二酸化炭素発生量と重量減少量がほぼ比例する関係に着目して、総二酸化炭素発生量によって反応を終了させるタイミングを決定しても良い。
【００３０】
【発明の効果】
上述のごとく、本発明によれば、放射性廃棄物の減容装置を請求項１のごとく構成することとしたので、排ガス量が極小化され、処理容器の内部圧力が 0.01 MPa 以上と従来の約 10 倍の高い圧力においても充分安定してプラズマを立てられることとなった。したがって、従来装置に用いられていた排気系の真空ポンプを用いても処理能力が約 10 倍に増大し、多量の放射性廃棄物の減容処理が可能な放射性廃棄物の減容装置が得られることとなった。
【００３１】
また、本構成の減容装置では、放射性核種が固形残さに内包化して処理されるので、核種の大気や一般環境への散逸が抑制される装置が得られ、また、単純構造が採用でき、補修・メンテナンスが極めて容易で且つ２次廃棄物も少ない装置が得られる。さらに、請求項２〜８のごとく構成することとしたので、放射性廃棄物がより効果的に減容処理される減容装置が構成され、さらには、請求項９〜１４のごとき運転方法によって減容処理を行うこととしたので、断続的に放射性廃棄物を投入しながら連続的に減容処理できることとなり、効率的に減容処理できることとなった。
【図面の簡単な説明】
【図１】本発明の放射性廃棄物の減容装置の実施例を示す構成図
【図２】図１の減容装置の酸素プラズマ加熱手段の構成を示す横断面図
【図３】処理容器の壁面温度を監視して図１の減容装置を運転制御する方法を示す構成図
【図４】図３の構成における処理容器壁温の時間変化と被処理物投入時期との関係を示す特性図
【図５】排ガス中の二酸化炭素濃度を監視して図１の減容装置を運転制御する方法を示す構成図
【図６】図５の構成における排ガス中の二酸化炭素濃度の時間変化と被処理物投入時期との関係を示す特性図
【符号の説明】
１処理容器
２ヒーター
３被処理物収納用器
４燃焼酸素供給ノズル
５プラズマ発生手段
６旋回流形成ノズル
７排気口
８サイクロン
９ドライポンプ
１０コンダクタンスバルブ
１１２次燃焼室（高周波誘導結合型プラズマ式）
２０被処理物
２１主酸化反応領域
２２温度監視センサ
２３温度監視装置
２４酸素流量制御装置
２５被処理物投入操作装置
２６濃度センサ
２７濃度監視装置
３１ロードロック式投入口
３２排気装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a volume reducing device for flammable or flame retardant radioactive waste generated in a nuclear facility, and more particularly, a device for thermally decomposing radioactive waste and heating oxygen to promote oxidation reaction to reduce the volume. , And its driving method.
[0002]
[Prior art]
Conventionally, the incineration method using a burner, the thermal decomposition method that decomposes by heating to a high temperature in an incombustible gas, the oxidative decomposition method using hydrogen peroxide, etc. are used for volume reduction treatment of this kind of radioactive waste. Or application is being considered.
Among these volume reduction treatment methods, the incineration method is a method in which air is heated to a high temperature with a fuel combustion flame and the resin is burned to reduce ashing. In the thermal decomposition method, the gas component is separated into a gas component and a solid component, and the gas component containing no radionuclide is incinerated to reduce the volume. In the oxidative decomposition method, the resin component is decomposed and separated into water and carbon dioxide using hydrogen peroxide and a catalyst to reduce the volume. In addition, as a method different from these methods, a method of oxidizing and decomposing a resin with oxygen plasma at a low pressure to reduce ashing has also been studied. Further, a plasma combustion processing method as described in Japanese Patent Application No. 2000-127020 has also been proposed.
[0003]
[Problems to be solved by the invention]
Among the volume reduction methods described above, the incineration method has a basic problem that its application is limited to resins with a relatively low dose. Even when applied to resins with relatively low doses, in addition to the gas generated by the combustion of the resin, combustion exhaust gas from the fuel combustion burner to obtain high-temperature air is generated, further preventing incomplete combustion Therefore, the amount of exhaust gas generated from the entire processing apparatus becomes enormous. Therefore, this incineration method has a problem that it is necessary to install a large-scale exhaust gas treatment device. In addition, since the resin to be processed is high in calorie, the furnace wall material of the incinerator is easily damaged by high temperatures and needs to be repaired frequently, so the amount of secondary radioactive waste increases, There is a problem that maintenance costs also increase.
[0004]
In the pyrolysis method, mist of a large amount of taraceous components containing radionuclides is generated along with pyrolysis, so it is necessary to provide a large-capacity filter at the subsequent stage of the processing equipment, and the system is increased in size. There is a problem of doing. Further, since the above-mentioned filter is easily clogged and needs to be replaced frequently, there is a problem that a large amount of secondary radioactive waste is generated and a large maintenance cost is required.
[0005]
In addition, in the conventional plasma incineration method, it is necessary to maintain the reaction processing pressure at a relatively low pressure of around 0.001 MPa, so in order to increase the processing capacity, it is necessary to use a vacuum pump with a large exhaust capacity, There is a problem that the processing capacity is practically limited by the exhaust capacity of the vacuum pump.
In particular, flammable radioactive waste has a low bulk specific gravity, so even if batch-type incinerators supply a large amount of waste at a time, the treatment weight is small and it is difficult to improve the treatment capacity.
[0006]
The present invention has been made in consideration of the problems of the prior art as described above, and the object of the present invention is that the required exhaust capacity of the vacuum pump of the exhaust system is significantly higher than that of the vacuum pump of the conventional plasma processing apparatus. The amount of radioactive waste can be reduced, or the processing speed can be dramatically increased even at the same capacity, and continuous processing can be performed. In addition, the generation of secondary radioactive waste is reduced and maintenance costs are reduced. It is in providing a container apparatus and its operating method.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention,
A device for reducing the volume of flammable or incombustible radioactive waste generated in a nuclear facility. It is a cylindrical processing container that is arranged almost vertically, and a processing container that is arranged at the lower end of the processing container and is coaxial with the processing container. A combined heater, at least one oxygen introduction means, at least one plasma generation means, and an exhaust means. Oxygen is introduced, oxygen is heated to a high temperature by the plasma generation means, exhausted by the exhaust means to form a low-pressure oxygen atmosphere, and the radioactive waste charged on the heater by the radioactive waste input means is heated by the heater and heated. In a volume reduction device for radioactive waste that decomposes,
(1) The above plasma generating means includes a quartz tube and an induction coil wound coaxially around the quartz tube. Oxygen is supplied to the quartz tube and high frequency power is supplied to the induction coil to generate oxygen plasma. And at least one of the oxygen introduction means is a swirl flow forming nozzle configured so that the introduced oxygen forms a swirl flow inside the processing container, and is disposed inside the processing container during the volume reduction process. The pressure is adjusted to 0.005 to 0.05 MPa, preferably 0.01 to 0.02 MPa .
[0008]
(2) In the above (1), radioactive waste was approximately equal to the outer diameter side in contact with the heater of the inner diameter and the processing vessel of the heater for heating, and radioactive waste of the linked object to be processed The structure will not spill.
( 3 ) Further, in the above (1) or (2), at least one of the oxygen introduction means is a combustion oxygen supply nozzle that forms a flow toward the heater in which the introduced oxygen is connected to the lower end of the processing vessel. And
[0009]
( 4 ) Further, in the above (1), an exhaust port connected to an exhaust means for exhausting the inside of the processing vessel is provided above the central axis of the swirling gas flow formed by the swirling flow forming nozzle.
[0010]
( 5 ) Further, in the above (1) to ( 4 ), a high frequency inductively coupled plasma type secondary combustion chamber is provided between the processing vessel and an exhaust means for exhausting the inside of the processing vessel. Volume reduction device to do.
( 6 ) In the above (1) to ( 5 ), at least one temperature monitoring sensor for detecting the temperature inside the processing container is provided on the side wall of the processing container.
[0011]
( 7 ) Alternatively, in the above (1) to ( 5 ), at least one oxygen concentration measuring means for measuring the oxygen concentration in the exhaust gas is provided in the exhaust means of the apparatus.
( 8 ) Alternatively, in the above (1) to ( 5 ), at least one carbon dioxide concentration measuring means for measuring the carbon dioxide concentration in the exhaust gas is provided in the exhaust means of the apparatus.
[0012]
( 9 ) In addition, the volume reduction device of the above (1) to ( 5 ) is continuously operated for volume reduction while intermittently introducing radioactive waste.
( 10 ) The volume reducing device according to ( 6 ) above, using a method in which radioactive waste is introduced when the temperature detected by the temperature monitoring sensor rises and then falls and falls to a predetermined temperature level. Will be continuously reduced in volume.
[0013]
( 11 ) Further, the volume reducing device of the above ( 7 ) is continuously volume-reduced while adjusting the amount of oxygen supplied by the oxygen introducing means based on the oxygen concentration detected by the oxygen concentration measuring means.
( 12 ) Further, when the carbon dioxide gas concentration detected by the carbon dioxide concentration measuring means rises, then the carbon dioxide gas concentration starts to fall and when the radioactive waste is dropped to a predetermined concentration level, the above-mentioned ( 8 ) Volume reduction equipment is continuously operated for volume reduction.
[0014]
( 13 ) The radioactive waste volume reducing device of ( 5 ) above is operated with the pressure of the high frequency inductively coupled plasma type secondary combustion chamber set to 600 Pa or more.
( 14 ) In the operations of ( 9 ) to ( 13 ), the volume reduction operation is performed by adjusting the pressure inside the processing vessel to 0.005 to 0.05 MPa, preferably 0.01 to 0.02 MPa.
[0015]
As described above, in the processing apparatus using the conventional plasma incineration method, the limit of stable plasma generation is 0.003 MPa or less, and the reaction processing pressure is limited to around 0.001 MPa.
On the other hand, as a result of the experiment by the present inventor, as described in (1) above, oxygen is introduced into the quartz tube, and high frequency power is supplied to the induction coil wound coaxially around the quartz tube to generate oxygen plasma. The oxygen plasma swirl flow introduced from the oxygen plasma heating means is additionally accelerated by introducing a swirl flow of oxygen plasma into the inside of the processing vessel using a plasma generating means, that is, a torch type plasma source , It became clear that the plasma can be generated sufficiently stably even when the internal pressure of the processing vessel is as high as 0.03 MPa or higher. Therefore, it is possible to supply high-temperature oxygen stably at a pressure about 10 times higher than the conventional one, and when the amount of oxygen supply gas is the same, the required exhaust capacity of the vacuum pump of the exhaust system is about 1/10. It was over. Contrary to this, it became possible to deal with large-scale processing in which about 10 times the supply gas flowed with a vacuum pump with the same exhaust capacity. In addition, since the amount of supplied gas can be increased by about 10 times, the processing speed is increased by about 10 times for the same processing amount, and the processing time is greatly shortened.
[0016]
Moreover, if it carries out like said (2), the leakage of a to-be-processed object will be prevented.
If the combustion oxygen supply nozzle is incorporated as described in (3) above, oxygen is effectively supplied to the object to be processed put on the heater and the object to be processed is combusted.
[0017]
Further, if an exhaust port connected to the exhaust means for exhausting the inside of the processing container as described in ( 4 ) above is disposed, the rolled up fine particles accompanying the swirling flow are separated and separated by the cyclone action and fall. If a high-frequency inductively coupled plasma type secondary combustion chamber is provided between the processing vessel and the exhaust means for exhausting the inside of the processing vessel as described in (5) above, a small amount of unburned gas contained in the exhaust gas can be removed. Can be burned.
[0018]
Further, if a temperature monitoring sensor is provided as described in ( 6 ) above, knowledge of the combustion state inside the processing container can be obtained. Therefore, efficient volume reduction operation as described in ( 10 ) above becomes possible. Moreover, knowledge of the combustion state inside the processing vessel can be obtained by providing oxygen concentration measuring means for measuring the oxygen concentration in the exhaust gas as described in (7) above. Therefore, efficient volume reduction operation as described in ( 11 ) above is possible.
[0019]
Moreover, if the carbon dioxide concentration measuring means for measuring the carbon dioxide concentration in the exhaust gas is provided as in ( 8 ) above, knowledge of the combustion state inside the processing container can be obtained. Therefore, efficient volume reduction operation as described in ( 12 ) above is possible.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described using examples.
FIG. 1 is a block diagram showing an embodiment of the radioactive waste volume reducing device of the present invention. In the figure, 1 is a metal cylindrical processing container, and 2 is a heater for heating an object to be processed, hermetically connected to the lower end of the processing container 1. 3 is a processing object storage device for storing the radioactive waste for processing. The load lock type inlet 31 for inputting the processing object into the processing container 1 and the inside of the processing object storage device are provided. An exhaust device 32 for vacuum disposal is attached. Reference numeral 4 denotes a combustion oxygen supply nozzle for introducing oxygen in the direction of the heater 2 connected to the lower end of the processing container 1, and reference numeral 5 denotes plasma generating means for supplying high-temperature oxygen plasma into the processing container 1. , 6 are swirl flow forming nozzles for introducing oxygen so as to form a swirl flow inside the processing vessel 1.
[0021]
Among these, the plasma generating means 5 is cooled by flowing cooling water between the double quartz tubes 5a as shown in the cross-sectional view shown in FIG. 2, and 30 l / min inside the quartz tube 5a. Oxygen is introduced from a flange provided at one end of the quartz tube 5a so as to form an axial gas and a swirling gas of 20 l / min. Outside the quartz tube 5a, a water-cooled induction coil 5b is wound five turns coaxially with the quartz tube 5a. By supplying high frequency power of 13.56 MHz to the induction coil 5b, oxygen inside the quartz tube 5a is provided. Is turned into plasma and approximately 2 kW of power is supplied. Since the high-frequency power directly heats the oxygen gas, there is little other energy loss and high-temperature oxygen can be efficiently generated. As shown in FIG. 2, the plasma generating means 5 is connected so that the central axis of the quartz tube 5a is in the vicinity of the outer periphery deviating from the central axis of the processing vessel 1, and is about 2000 ° C. generated by the plasma generating means 5. The high-temperature oxygen plasma is introduced into the processing vessel 1 as a swirling flow, contributing to the promotion of the oxidation reaction of the object to be processed.
[0022]
The processing container 1 is evacuated by an exhaust system connected to the upper exhaust port 7 and is maintained at a predetermined pressure. In the volume reduction apparatus of the present embodiment, a dry pump 9 with an exhaust speed of 80 m ³ / h is incorporated, and is controlled using a conductance valve 10 so that the internal pressure of the processing container 1 becomes 0.02 MPa.
In addition, when the oxidation reaction is performed in the processing container 1, the substance containing the small piece of the to-be-processed object and granular radionuclide by a gas flow rises in the processing container 1. FIG. For this reason, an oxygen supply port for flowing swirl gas from the periphery is arranged in the ceiling portion of the processing container 1 shown in FIG. 1 so that particulate matter is not taken in the vicinity of the exhaust port 7 by the cyclone effect. However, since it is impossible to eliminate the flow of unburned gas components from the exhaust port 7, as shown in FIG. 1, a high-frequency inductively coupled plasma type secondary combustion chamber 11 is provided between the exhaust port 7 and the exhaust system. Is provided. In the secondary combustion chamber 11, unburned gas or oxygen gas collides with electrons in the plasma and is activated to cause an oxidation reaction. Since the lifetime of molecules ionized by collision with electrons is about 1 μs, if the exhaust gas velocity in the secondary combustion chamber 11 is 1 m / s and the ionization rate is 0.01%, the plasma length is about 10 mm. Thus, all molecules are turned into plasma once on average. Therefore, 99% or more of molecules can be easily ionized by generating plasma with a plasma length of several tens of millimeters in the secondary combustion chamber 11. Since the ionized unburned gas and oxygen easily undergo an oxidation reaction, the exhaust gas can be almost completely burned by passing through the secondary combustion chamber 11.
[0023]
In the configuration of the embodiment shown in FIG. 1, a system is adopted in which fine particles that could not be separated by the cyclone at the upper end of the processing vessel 1 are collected by the cyclone 8 installed in the subsequent stage. As described above, the dry pump 9 is arranged downstream of the cyclone 8 to exhaust the processing container 1. Since the exhaust gas discharged from the dry pump 9 contains a radioactive substance with a low concentration of about 10 ⁻⁶ as a radionuclide migration rate, in order to completely filter these particulate nuclides at the subsequent stage of the dry pump 9 A flammable pre-filter and a HEPA filter (not shown) are incorporated. Further, when sulfur or nitrogen atoms are contained in the object 20 to be processed, SO _X and NO _X are generated by an oxidation reaction, and therefore, a system that releases it to the atmosphere as a detoxification device for exhaust gas through a small scrubber. Is adopted.
[0024]
In the radioactive waste volume reducing device of this configuration, the heater 2 connected to the lower end of the processing container 1 is heated to about 500 ° C., and the load lock type inlet 31 is opened and stored in the processing object storage container 3. The flammable / flammable material 20 to be treated is put on the heater 2 in the processing container for about 1 liter. The charged workpiece 20 emits combustible gas on the heater 2, is mixed with oxygen gas, and complete combustion proceeds with the help of high-temperature oxygen plasma supplied from the plasma generating means 5 described above. . The amount of combustible gas released gradually increases with time, and the main oxidation reaction region 21 as shown by a dotted line in FIG. 1 expands upward. As time further elapses and the combustion proceeds and the combustion amount decreases, the amount of combustible gas released also decreases, and the main oxidation reaction region 21 moves backward.
[0025]
Therefore, as shown in FIG. 3, if the temperature monitoring sensor 22 is incorporated in the wall surface of the processing vessel 1 and the measurement signal is monitored by the temperature monitoring device 23, the combustion amount increases and the main oxidation reaction region 21 moves upward. When enlarged, the measured temperature of the temperature monitoring sensor 22 rises, and when the combustion amount decreases and the main oxidation reaction region 21 recedes downward, the measured temperature of the temperature monitoring sensor 22 falls. Therefore, the measurement signal of the temperature monitoring sensor 22 is monitored by the temperature monitoring device 23, and when the increased temperature starts to decrease and falls to a predetermined temperature, a control signal is sent to the workpiece input operation device 25, and the workpiece is processed. If an operation method in which the workpiece 20 is newly introduced from the storage container 3 is adopted, the volume reduction processing of the workpiece 20 can be performed efficiently while continuously preventing thermal runaway. FIG. 4 is a characteristic diagram showing the time change of the measurement signal of the temperature monitoring sensor 22 when the workpiece 20 is intermittently charged and processed based on the measurement signal of the temperature monitoring sensor 22 in this way. As shown in the figure, after the temperature rises, the temperature starts to drop, and when the temperature falls to the predetermined temperature indicated by the dotted line, a new input signal is issued. Based on this, a new workpiece 20 is input. The operation is repeated. Of course, as long as the properties of the workpiece 20 are homogeneous to some extent, the timing of intermittent input may be selected at a predetermined time interval and periodically performed.
[0026]
In the above operation method, the method of monitoring the wall surface temperature of the processing container 1 and determining the timing of charging the workpiece 20 is used. From the oxygen input amount, the oxygen concentration in the exhaust gas, and the carbon dioxide concentration, the oxygen consumption amount and It is also possible to adopt an operation method in which the carbon dioxide generation amount is determined, and the input timing of the object to be processed is determined by a decrease signal of the carbon dioxide generation amount or a decrease signal of the oxygen consumption amount. FIG. 5 shows an operation method in which the carbon dioxide concentration in the exhaust gas is measured to control the operation of charging the object 20 to be processed. When the combustion amount increases and the main oxidation reaction region 21 expands upward, This utilizes the fact that the carbon dioxide concentration decreases as the carbon dioxide concentration measured by the sensor 26 increases, the combustion amount decreases, and the main oxidation reaction region 21 recedes downward. The characteristics shown in FIG. 6 show the measured value of the carbon dioxide concentration when the oxygen supply amount is constant and the timing of new input of the workpiece 20. When the carbon dioxide concentration starts to decrease and reaches a predetermined concentration indicated by a dotted line, a signal for newly feeding the workpiece 20 from the concentration monitoring device 27 to the workpiece loading operation device 25 is issued.
[0027]
Furthermore, in this configuration, when the oxygen concentration becomes too low, such as when the combustion reaction increases, a control signal is sent from the concentration monitoring device 27 to the oxygen flow rate control device 24 to perform a procedure for temporarily increasing the oxygen supply amount. Is called. Further, when the low-calorie workpiece 20 is input and the amount of carbon dioxide generated when the oxidation reaction is at its peak, the input amount can be increased.
[0028]
In the volume reducing device of this configuration, when the workpiece is intermittently supplied as described above, the workpiece is reduced in volume and the weight is also reduced. For example, combustible materials such as paper and cotton are reduced by 98% to about 1/50 of the input. If it is a flame-retardant ion exchange resin, it will be about half of the input.
In the case of processing only the cellulose-based combustible material, for example, after the operation for 8 hours a day, after completion of the oxidation reaction, the residue is recovered from the unloading mechanism not shown in FIG.
[0029]
When processing the processing object 20 including the flame retardant, the processing object 20 is intermittently charged, for example, 50 l in total is added to terminate the oxidation reaction, and then the heater temperature is further increased to 700 ° C. In addition to increasing the oxygen supply amount from the combustion oxygen supply nozzle 4, the oxidation reaction is promoted. After a certain period of time, the heater temperature is lowered, the supply of oxygen is shut off, nitrogen gas is injected, and the processing vessel 1 is injected. The reaction is forcibly terminated by returning the inside of the chamber to atmospheric pressure. In this way, the volume reduction device of this configuration can control the volume reduction rate of the object to be processed according to the reaction time. For ion exchange resins, the range is from 1/5 to 1/20 of the initial charge. When the volume is reduced to 1, the residual properties suitable for cement solidification in a subsequent process are obtained. Of course, in addition to the method of controlling the reaction by time, paying attention to the relationship that the total carbon dioxide generation amount integrated with the carbon dioxide concentration is approximately proportional to the weight loss amount, the timing for terminating the reaction by the total carbon dioxide generation amount is determined. You may decide.
[0030]
【The invention's effect】
As described above, according to the present invention, since the radioactive waste volume reducing device is configured as described in claim 1, the amount of exhaust gas is minimized, and the internal pressure of the processing vessel is 0.01 MPa or more, which is about the conventional level. It was possible to generate a plasma with sufficient stability even at a pressure 10 times higher. Therefore, even if the exhaust system vacuum pump used in the conventional equipment is used, the treatment capacity is increased about 10 times, and a radioactive waste volume reduction device capable of volume reduction of a large amount of radioactive waste is obtained. It became a thing.
[0031]
In addition, in the volume reduction device of this configuration, since the radionuclide is encapsulated in the solid residue and processed, a device that suppresses the dissipation of the nuclide to the atmosphere and the general environment can be obtained, and a simple structure can be adopted. Equipment that is extremely easy to repair and maintain and that has little secondary waste can be obtained. Further, since it is configured as claimed in claims 2 to 8 , a volume reduction device for reducing the volume of radioactive waste more effectively is constructed, and further reduced by the operation method as in claims 9 to 14. Since the volume treatment was performed, it was possible to continuously reduce the volume while intermittently adding radioactive waste, and to reduce the volume efficiently.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a radioactive waste volume reducing apparatus according to the present invention. FIG. 2 is a cross-sectional view showing a configuration of oxygen plasma heating means of the volume reducing apparatus shown in FIG. 1 is a block diagram showing a method for controlling the operation of the volume reduction device of FIG. 1 by monitoring the wall surface temperature. FIG. 4 is a characteristic diagram showing the relationship between the time variation of the processing vessel wall temperature and the workpiece input timing in the configuration of FIG. FIG. 5 is a block diagram showing a method for controlling the operation of the volume reduction device of FIG. 1 by monitoring the carbon dioxide concentration in the exhaust gas. FIG. 6 is a time variation of the carbon dioxide concentration in the exhaust gas in the configuration of FIG. Characteristic diagram showing the relationship with the material input time [Explanation of symbols]
1 Processing container
2 Heater
3 Containers for storing objects
4 Combustion oxygen supply nozzle
5 Plasma generation means
6 Swirling flow forming nozzle
7 Exhaust port
8 Cyclone
9 Dry pump 10 Conductance valve 11 Secondary combustion chamber (high frequency inductively coupled plasma type)
DESCRIPTION OF SYMBOLS 20 To-be-processed object 21 Main oxidation reaction area | region 22 Temperature monitoring sensor 23 Temperature monitoring apparatus 24 Oxygen flow control apparatus 25 To-be-processed object throwing-in operation apparatus 26 Concentration sensor 27 Concentration monitoring apparatus 31 Load-lock type inlet 32 Exhaust apparatus

Claims

A device for reducing the volume of flammable or incombustible radioactive waste generated in a nuclear facility. It is a cylindrical processing container that is arranged almost vertically, and a processing container that is arranged at the lower end of the processing container and is coaxial with the processing container. A heater to be combined, a radioactive waste input means for processing, at least one oxygen introducing means, at least one plasma generating means, and an exhaust means, and oxygen is introduced into the processing container by the oxygen introducing means. The oxygen introduced by the plasma generating means is heated to a high temperature, exhausted by the exhaust means to form a low-pressure oxygen atmosphere, and the radioactive waste thrown onto the heater by the radioactive waste throwing means is heated by the heater. In the volume reduction device for radioactive waste that is thermally decomposed,
The plasma generating means comprises a quartz tube and an induction coil wound coaxially around the quartz tube, supplies oxygen to the quartz tube, and supplies high frequency power to the induction coil to generate oxygen plasma. And at least one of the oxygen introduction means is a swirl flow forming nozzle configured so that the introduced oxygen forms a swirl flow inside the processing container, and the pressure inside the processing container during the volume reduction treatment is volume reduction device for radioactive waste, characterized by comprising adjusted to 0.005 to 0.05MP a.

The radioactive waste volume reducing device according to claim 1, wherein the inner diameter of the heater for heating the radioactive waste is substantially equal to the outer diameter of the side surface in contact with the heater of the processing container, and these are connected. Feature volume reduction device.

3. The radioactive waste volume reducing device according to claim 1, wherein at least one of the oxygen introduction means forms a flow toward the heater in which the introduced oxygen is arranged at the lower end of the processing vessel. Volume reducing device characterized by being a combustion oxygen nozzle.

2. The radioactive waste volume reducing device according to claim 1, wherein the exhaust port connected to the exhaust means for exhausting the inside of the processing container is on the central axis of the swirling gas flow formed in the processing container by the swirling flow forming nozzle. A volume reducing device, which is provided on the upper side.

In volume reduction device for radioactive waste according to any one of claims 1 to 4, a secondary combustion chamber of a high-frequency inductively coupled plasma type is provided between the exhaust means for exhausting the processing vessel inside the processing container A volume reduction device characterized by comprising:

In volume reduction device for radioactive waste according to any one of claims 1 to 5, volume reduction device, wherein a temperature monitoring sensor for detecting the temperature inside the processing vessel sidewall of the processing vessel, at least one provided .

In volume reduction device for radioactive waste according to any one of claims 1 to 5, volume reduction, characterized in that provided at least one oxygen concentration measuring means for measuring the oxygen concentration in the exhaust gas to the exhaust means of the apparatus apparatus.

In volume reduction device for radioactive waste according to any one of claims 1 to 5, characterized by providing at least one carbon dioxide concentration measuring means for measuring the carbon dioxide concentration in the exhaust gas to the exhaust means of the apparatus Volume reduction device.

A method for operating a volume reducing device, wherein the volume reduction device for radioactive waste according to any one of claims 1 to 8 is continuously volume-reduced while intermittently charging the radioactive waste.

7. The radioactive waste volume reducing device according to claim 6 , wherein when the temperature detected by the temperature monitoring sensor rises and then falls, the radioactive waste is injected when the temperature is lowered to a predetermined temperature level. The volume reduction device is operated continuously by volume reduction.

8. A method for operating a volume reducing apparatus according to claim 7 , wherein the volume reducing apparatus for operating radioactive waste according to claim 7 is operated while adjusting the amount of oxygen supplied from the oxygen introducing means based on the oxygen concentration detected by the oxygen concentration measuring means. .

The radioactive waste according to claim 8 , wherein the concentration of carbon dioxide gas detected by the carbon dioxide concentration measuring means rises and then falls, and the radioactive waste is introduced when the concentration drops to a predetermined concentration level. An operation method of a volume reduction device, wherein the volume reduction device is continuously operated for volume reduction.

6. A method for operating a volume reducing device according to claim 5 , wherein the pressure of the high frequency inductively coupled plasma type secondary combustion chamber is set to 600 Pa or more to operate the radioactive waste volume reducing device according to claim 5 .

Method of operating a volume reduction device according to claim 9 or 13, in the volume reduction step, which characterized in that the operating volume reduction by adjusting the pressure inside the process vessel to 0.005 to 0.05MP a driving Method.