JP5329748B2 - Method and apparatus for measuring subcriticality of spent fuel - Google Patents

Method and apparatus for measuring subcriticality of spent fuel Download PDF

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JP5329748B2
JP5329748B2 JP2006241717A JP2006241717A JP5329748B2 JP 5329748 B2 JP5329748 B2 JP 5329748B2 JP 2006241717 A JP2006241717 A JP 2006241717A JP 2006241717 A JP2006241717 A JP 2006241717A JP 5329748 B2 JP5329748 B2 JP 5329748B2
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spent fuel
subcriticality
neutrons
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研一 吉岡
偉司 三橋
哲郎 竹下
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Toshiba Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To measure the subcriticality of a spent nuclear fuel without arranging a neutron source and a neutron detector in a storage vessel when the spent nuclear fuel is transported. <P>SOLUTION: A target 1 made of a substance undergoing a photonuclear reaction to produce a neutron is arranged within the storage vessel 4 storing the spent nuclear fuel 7, and an X-ray generator 2 and at least one neutron detector 3a, 3b are arranged outside of the storage vessel 4. The neutrons produced when the X-ray generated by the X-ray generator 2 collides against the target 1 are counted by the neutron detector 3a, 3b for estimating the subcriticality. Further, the target 1 may be arranged within an FP gas reservoir space 11 in the storage vessel 4, and an abnormality of the spent fuel 7 can be detected by the count value derived by the neutron detector 3a, 3b. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

この発明は、使用済み原子燃料の未臨界度を測定する未臨界度測定方法および装置に関する。
This invention also relates to the subcriticality measurement method and equipment for measuring the subcriticality of the spent nuclear fuel.

原子炉内で使用され燃焼された使用済み燃料は、一時的に燃料貯蔵プールに保管され、また使用済み燃料貯蔵容器（以下、単に「貯蔵容器」ともいう）に収納され再処理施設などに輸送される。   Spent fuel used and burned in the reactor is temporarily stored in a fuel storage pool, and stored in a spent fuel storage container (hereinafter also simply referred to as “storage container”) to be transported to a reprocessing facility. Is done.

一方、使用済み燃料の未臨界度測定方法として、最も容易なものに中性子増倍法がある。これは、強度が既知の中性子源から発生した中性子を使用済み燃料に入射させ、使用済み燃料から発生する中性子を測定するものである。しかし、この手法を、中性子を外部に漏洩させないように構成した使用済み燃料貯蔵装置に用いることは、一般的には難しい。   On the other hand, the neutron multiplication method is the easiest method for measuring the subcriticality of spent fuel. In this method, a neutron generated from a neutron source having a known intensity is incident on a spent fuel, and the neutron generated from the spent fuel is measured. However, it is generally difficult to use this method for a spent fuel storage device configured to prevent neutrons from leaking outside.

例えば、使用済み燃料貯蔵容器内に収納された使用済み燃料の未臨界度測定システムとして、特許文献１に示すように使用済み燃料の輸送容器（貯蔵容器）等に予め中性子検出器を設置しておく未臨界度測定システムが知られている。
特開平１１−１１８９８１号公報 共立出版実験物理学講座２９ 伏見康治編集「原子炉」第８章 For example, as a system for measuring the subcriticality of spent fuel stored in a spent fuel storage container, a neutron detector is previously installed in a spent fuel transport container (storage container) as shown in Patent Document 1. Subcriticality measurement systems are known.
Japanese Patent Laid-Open No. 11-118981 Kyoritsu Publishing Experimental Physics Course 29 "Reactor" Chapter 8 edited by Koji Fushimi

しかしながら、特許文献１に示すようなシステムの場合、貯蔵容器が長期間密封されることになり、貯蔵容器内部に中性子検出器を配置することは現実的ではない。   However, in the case of the system shown in Patent Document 1, the storage container is sealed for a long period of time, and it is not realistic to arrange the neutron detector inside the storage container.

また、貯蔵容器の外部に中性子検出器を配置して測定することも考えられるが、貯蔵容器は中性子を十分遮蔽するように設計されているため、使用済み燃料自体から発生する中性子を利用することは困難である。さらに中性子を検出するために、予め中性子源を貯蔵容器内に内蔵し、中性子を増倍させ、貯蔵容器外部から中性子を検出できるようにすることも、輸送時の中性子線量を増大させることになるため、採用しにくい。   It is also possible to place a neutron detector outside the storage vessel for measurement, but since the storage vessel is designed to sufficiently shield neutrons, use neutrons generated from the spent fuel itself. It is difficult. In addition, in order to detect neutrons, a neutron source is built in the storage container in advance, and neutron multiplication can be performed so that neutrons can be detected from the outside of the storage container. Therefore, it is difficult to adopt.

また、貯蔵容器外部から中性子源を入射させ、同様に貯蔵容器外部に配置した中性子検出器により中性子を測定しようとすると、容器の中性子遮蔽を透過できるだけの強力な中性子発生装置が必要となり、非常に高価となるとともに、貯蔵容器が中性子により放射化し、環境線量を上昇させることになる。   In addition, if a neutron source is incident from the outside of the storage container and neutrons are similarly measured by a neutron detector arranged outside the storage container, a powerful neutron generator that can penetrate the neutron shield of the container is required, which is very In addition to being expensive, the storage vessel is activated by neutrons, increasing the environmental dose.

そこで本発明は、貯蔵中または輸送中の使用済み燃料の未臨界度を安価で安全に測定する方法および装置を提供することを目的とする。
The present invention aims to provide a method and equipment for inexpensive and safe measurement of subcriticality of the spent fuel or during transport storage.

本発明は、上記目的を達成するものであって、本発明の一つの態様は、使用済み燃料を貯蔵した貯蔵プール内に光核反応により中性子を発生する物質からなるターゲットを配置し、前記貯蔵プール内であって使用済み燃料の側面に少なくとも１つの中性子検出器を配置し、前記貯蔵プール外にＸ線発生装置を配置し、前記Ｘ線発生装置により発せられプール水を透過したＸ線が前記ターゲットと衝突する際に発生する中性子を前記中性子検出器で計数し、前記中性子検出器による計数値に基づいて未臨界度を推定すること、を特徴とする使用済み燃料の未臨界度測定方法である。 The present invention has been made to achieve the above object, one aspect of the present invention is to place a target made of a substance in a storage pool that was stored spent fuel for generating neutrons by Hikarikaku reaction, said reservoir An at least one neutron detector is disposed inside the pool and on the side of the spent fuel, an X-ray generator is disposed outside the storage pool, and X-rays emitted by the X-ray generator and transmitted through the pool water are generated. A method for measuring the subcriticality of spent fuel, characterized in that neutrons generated when colliding with the target are counted by the neutron detector, and the subcriticality is estimated based on the count value by the neutron detector. It is.

本発明の他の一つの態様は、使用済み燃料を貯蔵した貯蔵プール内に設けた光核反応により中性子を発生する物質からなるターゲットと、前記貯蔵プール内の使用済み燃料側面に設けた少なくとも１つの中性子検出器と、前記貯蔵プール外に設けたＸ線発生装置と、前記Ｘ線発生装置により発せられプール水を透過したＸ線が前記ターゲットと衝突する際に発生する中性子を計数する中性子検出器と、前記中性子検出器の係数値に基づいて未臨界度を推定する手段と、を備えたことを特徴とする使用済み燃料の未臨界度測定装置である。 According to another aspect of the present invention , there is provided a target made of a substance that generates neutrons by a photonuclear reaction provided in a storage pool storing spent fuel, and at least one provided on a side of the spent fuel in the storage pool. Two neutron detectors, an X-ray generator provided outside the storage pool, and a neutron detector that counts neutrons generated when X-rays emitted from the X-ray generator and transmitted through pool water collide with the target And a means for estimating the subcriticality based on a coefficient value of the neutron detector.

本発明によれば、貯蔵容器等内に中性子源を配置しなくても、貯蔵中または輸送中の使用済み燃料の未臨界度を測定することができる。
According to the present invention, the subcriticality of spent fuel during storage or transportation can be measured without arranging a neutron source in a storage container or the like .

以下、本発明の実施の形態を、図面を参照して詳細に説明する。ここで、互いに同一または類似の部分には共通の符号を付して、重複説明は省略する。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

［第１の実施形態］
図１は本発明に係る使用済み燃料の未臨界度測定装置の第１の実施形態の基本的構成を示した概略図である。 [First Embodiment]
FIG. 1 is a schematic view showing a basic configuration of a first embodiment of a spent fuel subcriticality measuring apparatus according to the present invention.

図１において、中性子遮蔽体６とγ線遮蔽体５により遮蔽された貯蔵容器４に使用済み燃料７が内蔵されている。この使用済み燃料７は、複数の使用済み燃料集合体からなっており、その中央部に光核反応により中性子を発生する中性子発生物質からなるターゲット１が配置されている。また、貯蔵容器４の外周部に、中性子を検出する中性子検出器３ａ、３ｂが配置されている。これらの中性子検出器は１つでも測定は可能であるが、誤信号や誤動作を防ぐため、対称位置に２つ配置するのが望ましい。   In FIG. 1, spent fuel 7 is built in a storage container 4 shielded by a neutron shield 6 and a γ-ray shield 5. The spent fuel 7 is composed of a plurality of spent fuel assemblies, and a target 1 made of a neutron generating material that generates neutrons by a photonuclear reaction is disposed at the center thereof. Further, neutron detectors 3 a and 3 b for detecting neutrons are arranged on the outer periphery of the storage container 4. Although it is possible to measure even one of these neutron detectors, it is desirable to arrange two neutron detectors at symmetrical positions in order to prevent erroneous signals and malfunctions.

ここで、上記ターゲット１を構成する中性子発生物質としては、光核反応の閾値が低く、構造材中に含まれないベリリウムや水中にわずかしか存在しない重水が適している。これらのベリリウムや重水素などは、数ＭｅＶ程度の高エネルギーのＸ線に反応し、中性子を放出する光核反応を起こすことが知られている。   Here, as the neutron generating material constituting the target 1, beryllium which has a low threshold for the photonuclear reaction and is not contained in the structural material or heavy water which is present in a small amount in water is suitable. It is known that these beryllium and deuterium react with high-energy X-rays of about several MeV and cause a photonuclear reaction that emits neutrons.

また、光核反応により中性子発生物質であるターゲット１と衝突させ、中性子を発生させるＸ線を発するＸ線発生装置２を貯蔵容器４の外部に配置する。このＸ線発生装置２のような、高エネルギーのＸ線を発生する装置は、最近、医療分野等で開発が進められており、１０ＭｅＶ程度のＸ線発生装置も容易に製造可能で、コストも低減されている。   Further, an X-ray generator 2 that emits X-rays that collide with a target 1 that is a neutron generating substance by a photonuclear reaction to generate neutrons is disposed outside the storage container 4. An apparatus that generates high-energy X-rays, such as the X-ray generator 2, has recently been developed in the medical field and the like, and an X-ray generator of about 10 MeV can be easily manufactured at a low cost. Has been reduced.

ここで、光核反応によりターゲット１から中性子を発生させるためには、Ｘ線のエネルギーは２ＭｅＶ程度が必要である。γ線遮蔽体を効率よく通過するためにはなるべく高い方が望ましいが、５〜６ＭｅＶを超えるとウランが光核反応により中性子を発生する確率が高くなり、１０ＭｅＶ近くになると構造材の鉄も中性子を発生する確率が高くなる。したがって、Ｘ線エネルギー強度は貯蔵容器４の外部に設置された中性子検出器３ａ、３ｂの検出レベルを超える程度であれば十分で、２〜５ＭｅＶ程度が適当であり、このような条件の下では、貯蔵容器４の放射化も問題ない。また、Ｘ線発生強度を調節することにより検出できる中性子強度も調整可能である。   Here, in order to generate neutrons from the target 1 by photonuclear reaction, the energy of X-rays needs to be about 2 MeV. Although it is desirable that it is as high as possible in order to pass through the γ-ray shield efficiently, if it exceeds 5 to 6 MeV, the probability that uranium will generate neutrons by photonuclear reaction increases, and if it is close to 10 MeV, the iron of the structural material is also neutron Is likely to occur. Therefore, it is sufficient that the X-ray energy intensity exceeds the detection level of the neutron detectors 3a and 3b installed outside the storage container 4, and about 2 to 5 MeV is appropriate. Under such conditions, The activation of the storage container 4 is no problem. Also, the neutron intensity that can be detected by adjusting the X-ray generation intensity can be adjusted.

なお、使用済み燃料７からもγ線が発生するが、そのエネルギーは高々１ＭｅＶ程度であり、光核反応は、２ＭｅＶ程度以上のγ線またはＸ線を必要とするため、使用済み燃料７からのγ線でターゲット１が中性子を発生する確率は非常に小さい。   Gamma rays are also generated from the spent fuel 7, but the energy is about 1 MeV at most, and the photonuclear reaction requires gamma rays or X-rays of about 2 MeV or more. The probability that the target 1 generates neutrons with gamma rays is very small.

また、貯蔵容器４の中性子遮蔽はＸ線に対する効果は小さく、γ線遮蔽は使用済み燃料７から発生する高々１ＭｅＶ程度のγ線を想定しているため、高エネルギーのＸ線であれば、貯蔵容器４内部には十分到達できる。また、Ｘ線を貯蔵容器４に照射しても中性子のように材質が放射化することはなく、環境線量を上昇させることもない。   Further, the neutron shielding of the storage container 4 has little effect on X-rays, and the γ-ray shielding assumes γ-rays of about 1 MeV generated from the spent fuel 7 at most. The inside of the container 4 can be sufficiently reached. Moreover, even if the storage container 4 is irradiated with X-rays, the material is not activated like neutrons, and the environmental dose is not increased.

以上のような構成の使用済み燃料の未臨界度測定装置において、未臨界度を測定するためには、貯蔵容器４の外部に配置したＸ線発生装置２から、中性子発生物質であるターゲット１に２〜５ＭｅＶ程度のＸ線を入射させる。ターゲット１では光核反応により中性子が発生し、発生した中性子は使用済み燃料７内で増倍し、中性子検出器３ａ、３ｂに到達し、検出される。中性子検出器３ａ、３ｂにより検出された計数率に基づいて、未臨界度測定手段２０により、予め計算により求めておいた相関を用いて、未臨界度を算出することができる。   In the spent fuel subcriticality measuring apparatus configured as described above, in order to measure the subcriticality, the X-ray generator 2 arranged outside the storage container 4 is moved to the target 1 which is a neutron generating substance. An X-ray of about 2 to 5 MeV is incident. At the target 1, neutrons are generated by the photonuclear reaction, and the generated neutrons are multiplied in the spent fuel 7 and reach the neutron detectors 3a and 3b to be detected. Based on the count rates detected by the neutron detectors 3a and 3b, the subcriticality can be calculated by the subcriticality measuring means 20 using the correlation previously obtained by calculation.

また、装置は複雑になるが、Ｘ線発生装置２からパルス上にＸ線を発生させれば、パルス中性子法（非特許文献１など参照）を用いて未臨界度を推定することも可能である。すなわち、Ｘ線をパルス状に発生させることにより、ターゲットからパルス状に中性子を発生させ、中性子検出器に現れる時間応答から、中性子数の時間減衰定数を評価し、時間減衰定数から未臨界度を算出することができる。   Although the apparatus is complicated, if the X-ray generator 2 generates X-rays on the pulse, it is possible to estimate the subcriticality using a pulse neutron method (see Non-Patent Document 1, etc.). is there. That is, by generating X-rays in pulses, neutrons are generated in pulses from the target, the time decay constant of the number of neutrons is evaluated from the time response appearing in the neutron detector, and the subcriticality is calculated from the time decay constant. Can be calculated.

以上により、光核反応を起こす物質を予め貯蔵容器に内蔵しておくことで、輸送時に中性子源を存在させることなく、未臨界度を評価することができる。すなわち、貯蔵時等において定期的に未臨界度を測定する場合にのみ、Ｘ線を発生させ、ターゲットに衝突させることで、中性子を使用済み燃料に照射し増倍させ、貯蔵容器外に設置された中性子検出器により、貯蔵容器を放射化させることなく、未臨界度を評価することができる。   As described above, by incorporating a substance that causes a photonuclear reaction in a storage container in advance, the subcriticality can be evaluated without the presence of a neutron source during transportation. That is, only when subcriticality is measured periodically during storage, etc., X-rays are generated and collided with the target to irradiate the spent fuel and multiply it, and it is installed outside the storage container. By using the neutron detector, the subcriticality can be evaluated without activating the storage container.

［第２の実施形態］
本発明に係る使用済み燃料の未臨界度測定装置およびその測定方法の第２の実施形態を、図１および図２により説明する。図１は第１の実施形態と共通である。図２は、第２の実施形態の使用済み燃料の未臨界度測定装置の縦方向の概略構成を示すものである。 [Second Embodiment]
A second embodiment of the spent fuel subcriticality measuring apparatus and measuring method according to the present invention will be described with reference to FIGS. FIG. 1 is common to the first embodiment. FIG. 2 shows a schematic configuration in the vertical direction of the subcriticality measuring apparatus for spent fuel according to the second embodiment.

図２において、使用済み燃料７内に配置されるターゲット１の軸方向長さは、少なくとも使用済み燃料の燃料有効部と同じ長さ以上としている。また、Ｘ線発生装置２はＸ線発生装置軸方向駆動装置８により、軸方向位置を変化させることができる構成となっている。   In FIG. 2, the length in the axial direction of the target 1 disposed in the spent fuel 7 is at least as long as the effective fuel portion of the spent fuel. Further, the X-ray generator 2 is configured such that the axial position can be changed by the X-ray generator axial drive device 8.

この構成により、Ｘ線とターゲット１の衝突位置を変化させ、中性子発生位置を軸方向の任意の位置に移動することができる。これにより、軸方向に長い使用済み燃料の未臨界度を複数の高さで測定することができ、未臨界測定の信頼性を高めることができる。   With this configuration, the collision position between the X-ray and the target 1 can be changed, and the neutron generation position can be moved to an arbitrary position in the axial direction. Thereby, the subcriticality of the spent fuel that is long in the axial direction can be measured at a plurality of heights, and the reliability of the subcritical measurement can be improved.

［第３の実施形態］
図３は本発明に係る使用済み燃料の未臨界度測定装置の第３の実施形態の構成を示した概略図である。 [Third Embodiment]
FIG. 3 is a schematic view showing the configuration of a third embodiment of the spent fuel subcriticality measuring apparatus according to the present invention.

図３において、使用済み燃料貯蔵プール９に保管された使用済み燃料７の中央部に光核反応により中性子を発生する中性子発生物質からなるターゲット１を配置し、使用済み燃料７の側面外側に中性子を検出する中性子検出器３ａ、３ｂを配置する。また、使用済み燃料貯蔵プール９の外側にＸ線発生装置２を配置する。   In FIG. 3, a target 1 made of a neutron generating material that generates neutrons by a photonuclear reaction is disposed in the center of the spent fuel 7 stored in the spent fuel storage pool 9, and the neutrons are disposed outside the side surface of the spent fuel 7. The neutron detectors 3a and 3b are arranged for detecting. In addition, the X-ray generator 2 is disposed outside the spent fuel storage pool 9.

この第３の実施形態は、第１の実施形態における使用済み燃料の貯蔵容器４を貯蔵プールに置き換えたものであり、それ以外の基本的な構成およびそれぞれの構成要素は、第１の実施形態と同様である。   In the third embodiment, the spent fuel storage container 4 in the first embodiment is replaced with a storage pool. Other basic configurations and respective components are the same as those in the first embodiment. It is the same.

したがって、本実施の形態の使用済み燃料貯蔵プールにおいても、第１の実施形態と同様に使用済み燃料の未臨界度を測定することができるという作用効果を奏するものである。   Therefore, also in the spent fuel storage pool of the present embodiment, the subcriticality of the spent fuel can be measured as in the first embodiment.

［第４の実施形態］
本発明に係る使用済み燃料の未臨界度測定装置およびその方法の第４の実施形態を、図３および図４により説明する。図３は第３の実施形態と共通である。図４において、使用済み燃料貯蔵プール９の上部に、使用済み燃料貯蔵プール９内でターゲット１を移動する駆動装置１０が設けられている。 [Fourth Embodiment]
A spent fuel subcriticality measuring apparatus and method according to a fourth embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is common to the third embodiment. In FIG. 4, a drive device 10 that moves the target 1 in the spent fuel storage pool 9 is provided above the spent fuel storage pool 9.

この構成によれば、駆動装置１０によりターゲット１を移動させることにより、使用済み燃料貯蔵プール９内の任意の位置に中性子発生源を移動させることができ、より詳細な未臨界度の測定が可能となるという効果を奏する。   According to this configuration, the neutron source can be moved to an arbitrary position in the spent fuel storage pool 9 by moving the target 1 by the driving device 10, and more detailed subcriticality measurement is possible. It has the effect of becoming.

［第５の実施形態］
図５は本発明に係る使用済み燃料の健全性評価装置の第５の実施形態としての基本的構成例を示した概略図である。 [Fifth Embodiment]
FIG. 5 is a schematic view showing a basic configuration example as a fifth embodiment of the spent fuel integrity evaluation apparatus according to the present invention.

図５において、貯蔵容器４内の使用済み燃料７の上方にＦＰガスたまり空間１１が設けられ、このＦＰガスたまり空間１１に中性子発生物質であるターゲット１が配置されている。また、貯蔵容器４の外部には、Ｘ線発生装置２およびＦＰ漏洩検出用中性子検出装置１２が配置されている。   In FIG. 5, an FP gas pool space 11 is provided above the spent fuel 7 in the storage container 4, and the target 1 that is a neutron generating substance is disposed in the FP gas pool space 11. In addition, the X-ray generator 2 and the FP leakage detection neutron detector 12 are disposed outside the storage container 4.

このような構成において、使用済み燃料７が破損した場合、核分裂性物質（以下、ＦＰという）であるＸｅが漏洩し、貯蔵容器４の上部に設けたＦＰガスたまり空間１１内にＦＰガスであるＸｅが滞留する。Ｘｅは中性子吸収断面が大きいため、Ｘ線発生装置２からのＸ線照射による光核反応で発生した中性子はＸｅに吸収され、ＦＰ漏洩検出用中性子検出器１２の指示値が下がる。この指示値をモニタすることにより、燃料破損の有無を判定できる。使用済み燃料７の破損の有無を判定することにより、使用済み燃料の健全性を評価できる。   In such a configuration, when the spent fuel 7 is damaged, Xe which is a fissile material (hereinafter referred to as FP) leaks and is FP gas in the FP gas pool space 11 provided in the upper part of the storage container 4. Xe stays. Since Xe has a large neutron absorption cross section, neutrons generated by the photonuclear reaction caused by X-ray irradiation from the X-ray generator 2 are absorbed by Xe, and the indicated value of the neutron detector 12 for FP leakage detection decreases. By monitoring this indicated value, it is possible to determine the presence or absence of fuel damage. By determining whether or not the spent fuel 7 is damaged, the soundness of the spent fuel can be evaluated.

なお、ここで用いられるＸ線発生装置は容器材の非破壊検査にも使用できる。また、内部からの中性子を検出することにより、未臨界度を判定できるだけでなく、中性子吸収物質である中性子遮蔽材の健全性や燃料破損時に漏洩する核分裂生成物（ＦＰ）ガスであり中性子吸収断面積の大きなＸｅ、特にＸｅ−１３１を検知することにより燃料健全性の評価にも有効である。   In addition, the X-ray generator used here can be used also for the nondestructive inspection of a container material. In addition to detecting neutrons from the inside, not only can the subcriticality be determined, but also the integrity of the neutron-absorbing material, neutron shielding material, and fission product (FP) gas that leaks when fuel is damaged. By detecting Xe having a large area, particularly Xe-131, it is also effective for evaluating fuel integrity.

［第６の実施形態］
図６は、本発明の使用済み燃料の健全性評価装置の第６の実施形態としての基本的構成例を示した概略図である。中性子発生物質であるターゲット１を使用済み燃料７内に配置し、使用済み燃料７の上方にＦＰガスをためる遮蔽容器付ＦＰガス捕集部１３を設けている。このＦＰガス捕集部１３とほぼ同じ高さの貯蔵容器４外部の位置にＦＰ漏洩検出用γ線検出器１４を設けている。また、貯蔵容器４外部には、縦方向に駆動可能になるようにＸ線発生装置２と駆動機構８を設けている。 [Sixth Embodiment]
FIG. 6 is a schematic diagram showing a basic configuration example as a sixth embodiment of the spent fuel health evaluation apparatus of the present invention. A target 1 that is a neutron-generating substance is disposed in the spent fuel 7, and a FP gas collection unit 13 with a shielding container that accumulates FP gas is provided above the spent fuel 7. An FP leakage detection γ-ray detector 14 is provided at a position outside the storage container 4 that is substantially the same height as the FP gas collection unit 13. Moreover, the X-ray generator 2 and the drive mechanism 8 are provided outside the storage container 4 so as to be driven in the vertical direction.

ガス捕集部１３は、図７に示すように、γ線を遮蔽する遮蔽材１３ａで覆い、使用済み燃料７側にＦＰガスを捕集する開口部１３ｃが設けられている。また、検出器に向く側１３ｂのみを遮蔽を薄くすることにより、燃料からの強いγ線を遮蔽し、バックグランドγ線を除去できる構成となっている。   As shown in FIG. 7, the gas collection unit 13 is covered with a shielding material 13 a that shields γ rays, and an opening 13 c that collects FP gas is provided on the spent fuel 7 side. Further, only the side 13b facing the detector is thinned so that strong γ rays from the fuel can be shielded and background γ rays can be removed.

このような構成によれば、Ｘ線発生装置２によりＸ線を中性子発生物質からなるターゲット１と衝突させると中性子が発生し、この中性子が使用済み燃料７に短期間低出力照射させることになる。この照射は、原子炉内に比べはるかに低い量であるため、熱発生や長半減期核種による恒常的な線量増加は伴わないが、使用済み燃料７は低レベルの核分裂を起こし、短半減期のＦＰを発生させることができる。   According to such a configuration, when X-rays are caused to collide with the target 1 made of a neutron generating material by the X-ray generator 2, neutrons are generated, and the neutrons irradiate the spent fuel 7 with low power for a short period of time. . This irradiation is much lower than in the reactor, so there is no constant heat increase due to heat generation or long half-life nuclides, but the spent fuel 7 undergoes a low level of fission and a short half-life. FP can be generated.

このとき使用済み燃料７が破損していれば、短半減期のＦＰでガス状のもの、例えば、Ｘｅ−１３５（半減期９．１ｈ）に代表される希ガスが、使用済み燃料７から漏れ出し、強いγ線源となる。このように短半減期の放射性物質は量が少なくても強い放射能を持つため、これらから発生するγ線を計数することにより、燃料破損の有無を判定できる。   If the spent fuel 7 is damaged at this time, a gas with a short half-life FP, for example, a rare gas represented by Xe-135 (half-life 9.1 h) leaks from the spent fuel 7. It becomes a strong gamma ray source. As described above, since the radioactive substance having a short half-life has a strong radioactivity even if the amount is small, the presence or absence of fuel breakage can be determined by counting the γ-rays generated therefrom.

以上の構成により、使用済み燃料の破損の有無を判定でき、健全性を評価できるという効果を奏するものである。   With the above configuration, it is possible to determine whether the spent fuel is damaged or not and to evaluate the soundness.

本発明による燃料貯蔵容器の未臨界度測定装置に係る第１または第２の実施形態の構成を示す模式的平断面図。The typical plane sectional view showing the composition of the 1st or 2nd embodiment concerning the subcriticality measuring device of the fuel storage container by the present invention. 本発明による燃料貯蔵容器の未臨界度測定装置に係る第２の実施形態の構成を示す図であって、図１のII−II線矢視模式的立断面図。It is a figure which shows the structure of 2nd Embodiment which concerns on the subcriticality measuring apparatus of the fuel storage container by this invention, Comprising: The II-II typical arrow sectional view of FIG. 本発明による使用済み燃料貯蔵プールの未臨界度測定装置に係る第３または第４の実施形態の構成を示す模式的平断面図。The typical plane sectional view showing the composition of the 3rd or 4th embodiment concerning the subcriticality measuring device of the spent fuel storage pool by the present invention. 本発明による使用済み燃料貯蔵プールの未臨界度測定装置に係る第４の実施形態の構成を示す図であって、図３のIV−IV矢視模式的立断面図。It is a figure which shows the structure of 4th Embodiment which concerns on the subcriticality measuring apparatus of the spent fuel storage pool by this invention, Comprising: The IV-IV arrow typical sectional drawing of FIG. 本発明による使用済み燃料の健全性評価装置に係る第５の実施形態の構成を示す模式的立断面図。The typical elevation sectional view showing the composition of the 5th embodiment concerning the soundness evaluation apparatus of the used fuel by the present invention. 本発明による使用済み燃料の健全性評価装置に係る第６の実施形態の構成を示す模式的立断面図。The typical elevation sectional view showing the composition of the 6th embodiment concerning the soundness evaluation device of the spent fuel by the present invention. 図６のＦＰガス捕集容器拡大立断面図。The FP gas collection container expansion sectional view of FIG.

符号の説明Explanation of symbols

１：ターゲット
２：Ｘ線発生装置
３ａ，３ｂ：中性子検出器
４：貯蔵容器
５：γ線遮蔽体
６：中性子遮蔽体
７：使用済み燃料
８：Ｘ線発生装置軸方向駆動装置
９：使用済み燃料貯蔵プール
１０：駆動装置
１１：ＦＰガスたまり空間
１２：ＦＰ漏洩検出用中性子検出器
１３：ＦＰガス捕集部
１４：ＦＰ漏洩検出用γ線検出器
２０：未臨界度測定手段 1: Target 2: X-ray generator 3a, 3b: Neutron detector 4: Storage container 5: γ-ray shield 6: Neutron shield 7: Spent fuel 8: X-ray generator axial drive 9: Spent Fuel storage pool 10: Drive device 11: FP gas pool space 12: FP leak detection neutron detector 13: FP gas collector 14: FP leak detection γ-ray detector 20: Subcriticality measuring means

Claims (5)

使用済み燃料を貯蔵した貯蔵プール内に光核反応により中性子を発生する物質からなるターゲットを配置し、
前記貯蔵プール内であって使用済み燃料の側面に少なくとも１つの中性子検出器を配置し、
前記貯蔵プール外にＸ線発生装置を配置し、
前記Ｘ線発生装置により発せられプール水を透過したＸ線が前記ターゲットと衝突する際に発生する中性子を前記中性子検出器で計数し、
前記中性子検出器による計数値に基づいて未臨界度を推定すること、
を特徴とする使用済み燃料の未臨界度測定方法。 A target made of a substance that generates neutrons by photonuclear reaction is placed in a storage pool that stores spent fuel.
Placing at least one neutron detector in a side of the spent fuel in the storage pool ;
Arranging an X-ray generator outside the storage pool;
The neutron detector counts neutrons generated when the X-rays emitted by the X-ray generator and transmitted through pool water collide with the target,
Estimating the subcriticality based on the count value by the neutron detector;
A method for measuring the subcriticality of spent fuel, characterized by: 光核反応により中性子を発生する物質からなるターゲットを貯蔵プール内の任意の位置に移動させることを特徴とする請求項１に記載の使用済み燃料の未臨界度測定方法。 The method for measuring the subcriticality of spent fuel according to claim 1, wherein a target made of a substance that generates neutrons by photonuclear reaction is moved to an arbitrary position in the storage pool . 前記Ｘ線発生装置からのＸ線をパルス状に発生させることにより、ターゲットからパルス状に中性子を発生させ、中性子検出器に現れる時間応答から中性子数の時間減衰定数を評価し、時間減衰定数から未臨界度を算出することを特徴とする請求項１または請求項２に記載の使用済み燃料の未臨界度測定方法。 By generating X-rays from the X-ray generator in pulses, neutrons are generated in pulses from the target, and the time decay constant of the number of neutrons is evaluated from the time response appearing in the neutron detector. The method for measuring the subcriticality of spent fuel according to claim 1 or 2, wherein the subcriticality is calculated. 光核反応により中性子を発生する物質にベリリウムまたは重水の少なくとも一方を含有する物質を使用することを特徴とする請求項１ないし請求項３のいずれか一項に記載の使用済み燃料の未臨界度測定方法。 Subcriticality of the spent fuel according to any one of claims 1 to claim 3, characterized by using a material containing at least one of beryllium or heavy water to a substance which generates neutrons by light nuclear reaction Measuring method. 使用済み燃料を貯蔵した貯蔵プール内に設けた光核反応により中性子を発生する物質からなるターゲットと、
前記貯蔵プール内の使用済み燃料側面に設けた少なくとも１つの中性子検出器と、
前記貯蔵プール外に設けたＸ線発生装置と、
前記Ｘ線発生装置により発せられプール水を透過したＸ線が前記ターゲットと衝突する際に発生する中性子を計数する中性子検出器と、
前記中性子検出器の係数値に基づいて未臨界度を推定する手段と、
を備えたことを特徴とする使用済み燃料の未臨界度測定装置。 A target made of a substance that generates neutrons by photonuclear reaction provided in a storage pool for storing spent fuel;
At least one neutron detector provided on the spent fuel side in the storage pool;
An X-ray generator provided outside the storage pool;
A neutron detector for counting neutrons generated when the X-rays emitted by the X-ray generator and transmitted through pool water collide with the target;
Means for estimating subcriticality based on a coefficient value of the neutron detector;
An apparatus for measuring subcriticality of spent fuel, comprising:
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