JP2005009890A - Gaseous activity concentration measuring device - Google Patents
Gaseous activity concentration measuring device Download PDFInfo
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- JP2005009890A JP2005009890A JP2003171124A JP2003171124A JP2005009890A JP 2005009890 A JP2005009890 A JP 2005009890A JP 2003171124 A JP2003171124 A JP 2003171124A JP 2003171124 A JP2003171124 A JP 2003171124A JP 2005009890 A JP2005009890 A JP 2005009890A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
Description
【0001】
【発明の属する技術分野】
本発明は、原子力施設内等の放射線を監視するための気体放射能濃度測定装置に関する。
【0002】
【従来の技術】
原子力発電所の気体放射能濃度測定装置の一つであるプロセス放射線モニタは、プロセス配管内を流れる気体(希ガス)をプロセス配管に接続されたサンプリング配管により、低レンジ放射線モニタ用と高レンジ放射線モニタ用のそれぞれの測定容器に導引し、ここから発生する放射線を低レンジ放射線モニタ或いは高レンジ放射線モニタで連続測定している。
【0003】
これは、放射線モニタの計測レンジに限界があり、被測定気体の放射能濃度が低い場合と高い場合とを、一つの放射線モニタでカバーできない。そこで、上記プロセス放射線モニタとしては、低濃度時用と高濃度時用の2種類の検出器とそれぞれ個別の測定容器を設け、計測している。
【0004】
測定された気体放射能濃度は連続指示記録され、あらかじめ設定された放射能濃度以上が検出された場合は、警報が出力される。ここで、例えば原子力発電設備の気体放射能濃度は、プラントが正常状態にある場合は、きわめて微小な放射能濃度レベルであるが、万一プラントが異常状態になった場合には、正常時の測定レベルに対し、大幅に増加する。
【0005】
プラントの健全性、環境へ放射線の影響を評価すためには、微小な放射能濃度から高放射能濃度までの計測範囲を精度良く測定することが課題とされている。このような課題を解決した気体放射能濃度測定装置の公知例としては、特開2001−153956号公報(特許文献1)のように、計測範囲の異なる測定容器を設置して精度良く測定する例がある。
【0006】
【特許文献1】
特開2001−153956号公報
【0007】
【発明が解決しようとする課題】
ひとつの放射線モニタのみで低放射能濃度から高放射能濃度までの広範囲にわたって計測可能な連続計測可能な気体放射能濃度測定装置を提供することを目的とする。
【0008】
【課題を解決するための手段】
気体放射能濃度測定装置の計測値の増加を抑えるために、放射線の入射角度と計測値が比例することを利用し、検出器に入射する放射線量を制限させるものとする。
【0009】
本発明の気体放射能濃度測定装置では、被測定気体が流れるプロセス配管に接続されたサンプリング配管の途中に配置された気体放射能濃度の測定容器と、この測定容器の放射線量を計測する放射線検出器の間に自動位置調節機能付きコリメータを設ける。コリメータの位置を、放射線検出器に入射する放射線量が常に放射線検出器の計測可能レンジ内におさまるように放射線検出器の計測信号を用いて調節する。
【0010】
【発明の実施の形態】
以下図面を参照して本発明の実施例を説明する。
【0011】
図1に本発明請求項1の実施例を示す。プロセス配管1を流れる放射性気体は、プロセス配管1に接続されたサンプリング配管2を通り、サンプリング配管2の途中に設置された測定容器4を経て、測定容器4の下流に接続したサンプルポンプ5によりプロセス配管1に戻される。測定容器4に導かれた放射性気体は、その放射線量が放射線検出器7で連続的に計測され、その信号は信号処理部8で指示・記録される。
【0012】
本発明においては、測定容器4と放射線検出器7の間に自動コリメータ位置調節機構9を備えたコリメータ10が設けられている。コリメータ10は,放射線検出器7に入射する放射線量を調整する。放射線検出器7の出力信号は信号処理部8にて処理され、信号処理部8の出力、即ち放射線量計測レベルにより前記のコリメータの位置を作動させる。
ちなみに、被測定気体の放射能濃度は、放射線検出器の計測信号と、コリメータの位置や形状により求まる。
【0013】
図1は、被測定気体の放射能レベルが低い場合、即ち原子力発電プラントにおいては正常運転時における放射能測定の運転状態を示している。プロセス配管1の放射性気体はサンプル配管2、サンプル入口弁3より測定容器4に流入し放射線検出器7で計測される。
【0014】
一般に、原子力発電プラントの排気筒から排出される気体廃棄物の放射能濃度は極めて低く、従って、放射線検出器7としては、検出感度が極めて高く低放射線能濃度が計測可能な低レベル放射線検出器が用いられる。
被測定気体の放射能レベルが低い場合は、放射線検出器7の出力が飽和することなく継続して計測が可能である。
【0015】
ここで、万一、何らかの原因で、被測定気体の放射能濃度が上昇すると、放射線検出器7の出力が上昇し、いずれは計測上限値に接近する。計測上限値は、放射線検出器7の計測可能レンジにより定まるいわば計測飽和点である。放射線検出器7の計測レンジを超えて放射線量を計測することはできないので、この場合は、被測定気体が放射線計測レンジ外の高放射能濃度になったとしかわからない。
【0016】
低レベル放射線検出器の計測値が計測上限値に近接したことが、信号処理部8で検出された時には、自動コリメータ位置調節機構9からコリメータ10に対し移動信号を発し、図2に示すように放射線検出器7に入射する放射線の入射角度を小さくする。入射角度が小さくなったことにより放射線検出器に入射する放射線量が減少し、放射線検出器7で計測を継続することができる。
【0017】
また、その後、気体の放射能レベルが低レベルに戻った時は、放射線検出器7による計測信号が計測下限値に近接したことを信号処理部8で判定し、自動コリメータ位置調節機構9から前述のコリメータ10の移動信号を発して図1の状態に戻す。
【0018】
これらにより、放射線検出器に入射される放射線量が、放射線検出器の計測可能レンジ内に保たれ、低放射能濃度から高放射線濃度までの広範囲で、放射線検出器の計測値が飽和することがない。
【0019】
さて、被測定気体の放射能濃度は、放射線検出器による検出信号にコリメータの位置を勘案して求めることができる。
【0020】
低レベル測定位置における、放射能濃度換算係数をα1、高レベル測定位置における放射能濃度換算係数をα2、放射線検出器の検出値をrとすると、被測定気体の放射能濃度Rは
(数式1)R=α1 × r
(但し、コリメータ位置が低レベル測定位置の場合)
及び
(数式2)R=α2 × r
(但し、コリメータ位置が高レベル測定位置の場合)
となる。
【0021】
ここで、放射能濃度換算係数α1、放射能濃度換算係数α2は、主としてコリメータの形状とコリメータの位置で決まるが、本実施例では、コリメータの位置があらかじめ決められているため、放射線濃度換算係数α1、α2もあらかじめ求めておくことができる。従って、被測定気体の放射能濃度は、放射線検出器の検出値を定数(α1、α2)倍することにより、容易に求めることが出来る。
【0022】
ちなみに、計測当初など、被測定気体の放射能濃度が不明の場合は、コリメータを高レベル測定位置に設定して計測を開始する。コリメータ位置が高レベル測定位置で放射線検出器の計測信号が計測可能範囲に入っている場合は、このままその位置で計測を継続してよい。放射線検出器に入射する放射線量が放射線検出器の検出可能レンジ以下にある場合は、計測信号が得られないので、この場合は、コリメータ位置を低レベル測定位置に変更する。これにより、放射線検出器に入射する放射線量が増加し、放射線検出器の計測可能レンジに入る。
【0023】
なお、被測定気体の放射能濃度が、ちょうど、低レベル測定位置で測定すべきレベルと高レベル測定位置で測定すべきレベル付近で変動することも考えられる。従って、コリメータの低レベル測定位置と高レベル測定位置間での移動に際しては、適切な幅のヒステリシス特性を位置の切り替えロジックにもたせる。
【0024】
なお上記実施例では、コリメータの位置として、低レベル位置と高レベル位置の2箇所としたが、3箇所以上にしても良い。
【0025】
例えば、コリメータ位置が低レベル測定位置と高レベル測定位置の2箇所では放射線検出器の計測レンジとの関係において計測すべき被測定気体の放射能濃度の変化幅全域をカバーできない場合には、コリメータ位置を追加して3箇所、或いはそれ以上とする。
【0026】
また、被測定気体の放射能濃度がヒステリシス特性幅を超えたレンジで変化する場合には、コリメータの位置を低レベル測定位置と高レベル測定位置に頻繁に切り替えなくてはならないケースも発生する。これを防ぐために、ヒステリシス特性の幅を広げようとすると、必要な計測レンジ全域を確保できなくなる可能性もある。この場合は、中間レベル測定位置を設けることにより対策できる。なお、中間レベル測定位置を必ずしもひとつに限定する必要はなく、複数の中間レベル測定位置を設けても良い。
【0027】
なお、上記は、放射線検出器の検出信号から放射能濃度への換算を容易にするためにコリメータ位置をいずれも予め定められた複数の測定位置に設定する方式としているが、放射線検出器の検出信号に応じて、コリメータ位置を連続的に自動調整し、コリメータ位置から放射能濃度換算係数αを求める方法もある。
【0028】
放射能濃度換算係数αは、上記したように、コリメータの特性(形状)とコリメータの位置により定まるが、本方式では、コリメータの位置が変化するので、放射能濃度換算係数αを求めるのにやや複雑な演算が必要となる。しかし本方式では、例えば、常に、放射線検出器の検出感度が最も優れているレンジ或いは、放射線検出器の検出レンジのほぼ中央に常に検出信号が来るようコリメータの位置を自動制御することにより、計測対象レンジのほぼ全域に亘って適切な計測が可能となる。
【0029】
また、上記実施例ではいずれもコリメータを移動するシステムとしたが、測定容器と検出器の間に放射線の吸収率が既知の遮へい材を挿入するシステムとすることも可能である。例えば、遮蔽材を1枚挿入した場合は、コリメータ位置を高レンジ測定位置にセットした場合と同等の効果が得られる。
【0030】
また、遮蔽材を0枚、1枚、2枚挿入可能とした場合には、測定レベル位置を3箇所にした場合に相当する。
【0031】
また、本例では、コリメータを移動するシステムとしたが、コリメータの代わりに検出器を移動するシステムとしても良い。
同様に、コリメータの代わりに、測定容器を移動するシステムとしても良い。
【0032】
【発明の効果】
コリメータ位置自動調整機構により,それぞれ検出感度の異なるポジションを設定することにより放射線検出器の測定可能レンジが等価的に拡大し、気体放射能濃度測定装置の濃度測定範囲を拡大することができる。
【図面の簡単な説明】
【図1】本特許における気体放射能濃度測定装置の系統構成の実施例を示す図である。なお、コリメータ位置としては、低レベル放射能計測時の位置を示している。
【図2】図1の実施例において、高レベル放射能計測時のコリメータ位置を説明するための図である。
【符号の説明】
1…プロセス配管、
2…サンプリング配管、
3…サンプル入口弁、
4…測定容器、
5…サンプルポンプ、
6…遮へい材、
7…放射線検出器、
8…信号処理部、
9…自動コリメータ位置調節装置、
10…コリメータ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas radioactivity concentration measuring apparatus for monitoring radiation in a nuclear facility or the like.
[0002]
[Prior art]
The process radiation monitor, which is one of the gas radioactivity concentration measurement equipment at nuclear power plants, is used for low-range radiation monitoring and high-range radiation by sampling piping connected to the process piping. Each measurement container for monitoring is led, and the radiation generated therefrom is continuously measured by a low range radiation monitor or a high range radiation monitor.
[0003]
This is because the measurement range of the radiation monitor is limited, and the case where the radioactivity concentration of the gas to be measured is low and high cannot be covered by one radiation monitor. Therefore, as the process radiation monitor, two types of detectors for low concentration and for high concentration are provided and measured separately.
[0004]
The measured gas radioactivity concentration is continuously indicated and recorded, and an alarm is output when a predetermined radioactivity concentration or more is detected. Here, for example, when the plant is in a normal state, the gas radioactivity concentration of the nuclear power generation facility is an extremely minute level of radioactivity concentration, but in the unlikely event that the plant is in an abnormal state, Significant increase over the measurement level.
[0005]
In order to evaluate the health of the plant and the influence of radiation on the environment, it has been an issue to accurately measure the measurement range from a minute radioactivity concentration to a high radioactivity concentration. As a known example of a gas radioactivity concentration measuring apparatus that solves such a problem, an example in which measuring containers with different measuring ranges are installed and measured with high accuracy as disclosed in Japanese Patent Application Laid-Open No. 2001-153958 (Patent Document 1). There is.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-153958
[Problems to be solved by the invention]
It is an object of the present invention to provide a gas radioactivity concentration measuring apparatus capable of continuous measurement that can be measured over a wide range from a low radioactivity concentration to a high radioactivity concentration with only one radiation monitor.
[0008]
[Means for Solving the Problems]
In order to suppress an increase in the measurement value of the gas radioactivity concentration measurement apparatus, the radiation dose incident on the detector is limited by utilizing the proportionality between the incident angle of the radiation and the measurement value.
[0009]
In the gas radioactivity concentration measuring apparatus of the present invention, a gas radioactivity concentration measurement container disposed in the middle of a sampling pipe connected to a process pipe through which a gas to be measured flows, and radiation detection for measuring the radiation dose of the measurement container A collimator with an automatic position adjustment function is provided between the devices. The position of the collimator is adjusted using the measurement signal of the radiation detector so that the radiation dose incident on the radiation detector is always within the measurable range of the radiation detector.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0011]
FIG. 1 shows an embodiment of claim 1 of the present invention. The radioactive gas flowing through the process pipe 1 passes through the
[0012]
In the present invention, a
Incidentally, the radioactivity concentration of the gas to be measured is obtained from the measurement signal of the radiation detector and the position and shape of the collimator.
[0013]
FIG. 1 shows an operating state of radioactivity measurement when the radioactivity level of the gas to be measured is low, that is, in a nuclear power plant during normal operation. The radioactive gas in the process pipe 1 flows into the measurement container 4 from the
[0014]
Generally, the radioactive concentration of the gaseous waste discharged from the exhaust pipe of the nuclear power plant is extremely low. Therefore, the radiation detector 7 is a low-level radiation detector that has a very high detection sensitivity and can measure a low radiation concentration. Is used.
When the radioactivity level of the gas to be measured is low, measurement can be continued without saturating the output of the radiation detector 7.
[0015]
Here, if the radioactivity concentration of the gas to be measured increases for some reason, the output of the radiation detector 7 increases and eventually approaches the measurement upper limit value. The measurement upper limit is a so-called measurement saturation point determined by the measurable range of the radiation detector 7. Since the radiation dose cannot be measured beyond the measurement range of the radiation detector 7, in this case, it is only known that the gas to be measured has a high radioactivity concentration outside the radiation measurement range.
[0016]
When the signal processing unit 8 detects that the measurement value of the low-level radiation detector is close to the measurement upper limit value, a movement signal is issued from the automatic collimator position adjustment mechanism 9 to the
[0017]
After that, when the radioactivity level of the gas returns to a low level, the signal processing unit 8 determines that the measurement signal from the radiation detector 7 is close to the measurement lower limit value, and the automatic collimator position adjustment mechanism 9 determines that The movement signal of the
[0018]
As a result, the amount of radiation incident on the radiation detector is kept within the measurable range of the radiation detector, and the measurement value of the radiation detector is saturated over a wide range from a low radioactivity concentration to a high radiation concentration. Absent.
[0019]
The radioactivity concentration of the gas to be measured can be obtained by taking the position of the collimator into consideration with the detection signal from the radiation detector.
[0020]
The radioactivity concentration conversion coefficient at the low level measurement position is α1, the radioactivity concentration conversion coefficient at the high level measurement position is α2, and the detection value of the radiation detector is r. ) R = α1 × r
(However, when the collimator position is the low level measurement position)
And (Formula 2) R = α2 × r
(However, when the collimator position is the high level measurement position)
It becomes.
[0021]
Here, the radioactivity concentration conversion coefficient α1 and the radioactivity concentration conversion coefficient α2 are mainly determined by the shape of the collimator and the position of the collimator. However, in this embodiment, the position of the collimator is determined in advance. α1 and α2 can also be obtained in advance. Therefore, the radioactivity concentration of the gas to be measured can be easily obtained by multiplying the detection value of the radiation detector by a constant (α1, α2).
[0022]
Incidentally, when the radioactivity concentration of the gas to be measured is unknown, such as at the beginning of measurement, the collimator is set to the high level measurement position and measurement is started. If the collimator position is at the high level measurement position and the measurement signal of the radiation detector is within the measurable range, the measurement may be continued at that position. When the radiation dose incident on the radiation detector is below the detectable range of the radiation detector, a measurement signal cannot be obtained. In this case, the collimator position is changed to a low level measurement position. As a result, the amount of radiation incident on the radiation detector increases and enters the measurable range of the radiation detector.
[0023]
It is also conceivable that the radioactivity concentration of the gas to be measured fluctuates between the level to be measured at the low level measurement position and the level to be measured at the high level measurement position. Therefore, when the collimator is moved between the low level measurement position and the high level measurement position, a hysteresis characteristic having an appropriate width is provided to the position switching logic.
[0024]
In the above-described embodiment, the collimator positions are two positions, the low level position and the high level position, but may be three positions or more.
[0025]
For example, if the collimator position cannot cover the entire change range of the radioactivity concentration of the gas to be measured in relation to the measurement range of the radiation detector at the two positions of the low level measurement position and the high level measurement position, the collimator Add three locations or more.
[0026]
Further, when the radioactivity concentration of the gas to be measured changes in a range exceeding the hysteresis characteristic width, there may be a case where the collimator position must be frequently switched between the low level measurement position and the high level measurement position. In order to prevent this, if the hysteresis characteristic is widened, there is a possibility that the entire necessary measurement range cannot be secured. In this case, measures can be taken by providing an intermediate level measurement position. The intermediate level measurement position is not necessarily limited to one, and a plurality of intermediate level measurement positions may be provided.
[0027]
In the above, the collimator position is set to a plurality of predetermined measurement positions in order to facilitate the conversion from the detection signal of the radiation detector to the radioactivity concentration. There is also a method in which the collimator position is continuously and automatically adjusted according to the signal, and the radioactivity concentration conversion coefficient α is obtained from the collimator position.
[0028]
As described above, the radioactivity concentration conversion coefficient α is determined by the characteristics (shape) of the collimator and the position of the collimator. However, in this method, the position of the collimator changes, so it is somewhat difficult to obtain the radioactivity concentration conversion coefficient α. Complex operations are required. However, in this method, for example, measurement is performed by automatically controlling the position of the collimator so that the detection signal is always at the center of the detection range of the radiation detector or the center of the detection range of the radiation detector. Appropriate measurement is possible over almost the entire target range.
[0029]
In each of the above embodiments, the collimator is moved. However, a system in which a shielding material having a known radiation absorption rate is inserted between the measurement container and the detector may be used. For example, when one sheet of shielding material is inserted, the same effect as when the collimator position is set to the high range measurement position can be obtained.
[0030]
Further, when it is possible to insert zero, one, or two shielding materials, this corresponds to the case where the measurement level positions are three.
[0031]
Further, in this example, the collimator is moved, but the detector may be moved instead of the collimator.
Similarly, a system for moving the measurement container may be used instead of the collimator.
[0032]
【The invention's effect】
By setting the positions with different detection sensitivities by means of the collimator position automatic adjustment mechanism, the measurable range of the radiation detector is equivalently expanded, and the concentration measurement range of the gas radioactivity concentration measuring device can be expanded.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a system configuration of a gas radioactivity concentration measuring apparatus according to this patent. In addition, as a collimator position, the position at the time of a low level radioactivity measurement is shown.
FIG. 2 is a diagram for explaining a collimator position at the time of high level radioactivity measurement in the embodiment of FIG. 1;
[Explanation of symbols]
1 ... Process piping,
2 ... Sampling piping,
3 ... Sample inlet valve,
4 ... Measuring container,
5 ... Sample pump,
6 ... Shielding material,
7 ... Radiation detector,
8: Signal processing unit,
9 ... Automatic collimator position adjustment device,
10 ... Collimator.
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Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2011180061A (en) * | 2010-03-03 | 2011-09-15 | Mitsubishi Electric Corp | Radioactive gas monitor |
US8901500B2 (en) | 2013-04-02 | 2014-12-02 | Mitsubishi Electric Corporation | Radiation measurement system |
JP2015141158A (en) * | 2014-01-30 | 2015-08-03 | 日立Geニュークリア・エナジー株式会社 | Radiation measuring apparatus, apparatus for identifying whether fuel debris is present and measuring position of fuel debris using the same, and method of determining whether fuel debris is present and measuring position of fuel debris |
US9476864B2 (en) | 2014-03-28 | 2016-10-25 | Mitsubishi Electric Corporation | Radioactive gas monitor |
US9519067B1 (en) | 2010-09-21 | 2016-12-13 | Hitachi, Ltd. | Radioactive gas measurement apparatus and failed fuel inspection apparatus |
-
2003
- 2003-06-16 JP JP2003171124A patent/JP3999166B2/en not_active Expired - Fee Related
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2011180061A (en) * | 2010-03-03 | 2011-09-15 | Mitsubishi Electric Corp | Radioactive gas monitor |
US9519067B1 (en) | 2010-09-21 | 2016-12-13 | Hitachi, Ltd. | Radioactive gas measurement apparatus and failed fuel inspection apparatus |
US8901500B2 (en) | 2013-04-02 | 2014-12-02 | Mitsubishi Electric Corporation | Radiation measurement system |
JP2015141158A (en) * | 2014-01-30 | 2015-08-03 | 日立Geニュークリア・エナジー株式会社 | Radiation measuring apparatus, apparatus for identifying whether fuel debris is present and measuring position of fuel debris using the same, and method of determining whether fuel debris is present and measuring position of fuel debris |
US9476864B2 (en) | 2014-03-28 | 2016-10-25 | Mitsubishi Electric Corporation | Radioactive gas monitor |
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