JP6670133B2 - Fuel assemblies and reactor cores - Google Patents

Fuel assemblies and reactor cores Download PDF

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JP6670133B2
JP6670133B2 JP2016041736A JP2016041736A JP6670133B2 JP 6670133 B2 JP6670133 B2 JP 6670133B2 JP 2016041736 A JP2016041736 A JP 2016041736A JP 2016041736 A JP2016041736 A JP 2016041736A JP 6670133 B2 JP6670133 B2 JP 6670133B2
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fuel
end region
enrichment
effective portion
rod
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JP2017156291A (en
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道隆 小野
道隆 小野
岳 光安
岳 光安
肇男 青山
肇男 青山
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Hitachi GE Nuclear Energy Ltd
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
    • G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
    • G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/30—Assemblies of a number of fuel elements in the form of a rigid unit
    • G21C3/32—Bundles of parallel pin-, rod-, or tube-shaped fuel elements
    • G21C3/326—Bundles of parallel pin-, rod-, or tube-shaped fuel elements comprising fuel elements of different composition; comprising, in addition to the fuel elements, other pin-, rod-, or tube-shaped elements, e.g. control rods, grid support rods, fertile rods, poison rods or dummy rods
    • G21C3/328—Relative disposition of the elements in the bundle lattice
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

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  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Monitoring And Testing Of Nuclear Reactors (AREA)

Description

本発明は、燃料集合体及び原子炉の炉心に係り、特に、沸騰水型原子炉に適用するのに好適な燃料集合体及び原子炉の炉心に関する。 The present invention relates to a reactor core of fuel assemblies and reactor, more particularly, to the core of the preferred fuel assemblies and reactor for application to a boiling water reactor.

沸騰水型原子炉（Ｂｏｉｌｉｎｇ Ｗａｔｅｒ Ｒｅａｃｔｏｒ：ＢＷＲ）は、原子炉圧力容器内に設けられた炉心に複数の燃料集合体を装荷している。これらの燃料集合体は、ウランを含む核燃料物質で製造された複数の燃料ペレットを充填した複数の燃料棒、これらの燃料棒の下端を支持する下部タイプレート、燃料棒の上端部を保持する上部タイプレート、及び上部タイプレートに取り付けられて下部タイプレートに向かって延伸する横断面（水平断面）正方形の角筒であるチャンネルボックスを有している。複数の燃料棒は、相互の間隔を所定幅に保持する燃料スペーサによって束ねられてチャンネルボックス内に配される。
燃料の経済性を向上するため、単位重量当たりの核分裂性物質から発生するエネルギーを増大させる高燃焼度化炉心の開発が進んでいる。近年の原子炉用燃料集合体は、その上下端部に天然ウランブランケットを有している。天然ウランブランケットを設けることで、上下方向への中性子の漏れを抑え、中性子経済性の向上を図っている。 BACKGROUND ART A boiling water reactor (BWR) has a plurality of fuel assemblies loaded in a core provided in a reactor pressure vessel. These fuel assemblies include a plurality of fuel rods filled with a plurality of fuel pellets made of nuclear fuel material containing uranium, a lower tie plate supporting lower ends of these fuel rods, and an upper part holding upper ends of the fuel rods. It has a tie plate and a channel box which is a square tube with a horizontal cross section (horizontal cross section) attached to the upper tie plate and extending toward the lower tie plate. The plurality of fuel rods are bundled by a fuel spacer that keeps a mutual interval at a predetermined width, and are arranged in the channel box.
In order to improve fuel economy, the development of a high burnup core that increases the energy generated from fissile material per unit weight has been developed. Recent nuclear fuel assemblies have a natural uranium blanket at the upper and lower ends. By providing a natural uranium blanket, neutron leakage in the vertical direction is suppressed, and neutron economy is improved.

天然ウランブランケットを用いる場合の課題として、上下端部に天然ウラン燃料を設けるため、上下端部の出力が低下し軸方向出力ピーキングが増加すること、また、使用できる燃料の平均濃縮度に上限があるため、天然ウラン領域を設ける分、燃料集合体の平均濃縮度を上げることができないことが挙げられる。   As a problem when using a natural uranium blanket, since the natural uranium fuel is provided at the upper and lower ends, the output at the upper and lower ends is reduced and the axial output peaking is increased.In addition, there is an upper limit on the average enrichment of usable fuel. For this reason, the average enrichment of the fuel assembly cannot be increased by providing the natural uranium region.

この課題を解決するため、例えば、特許文献１に示す技術が提案されている。特許文献１では、燃料集合体において、可燃性毒物を含まない領域を、燃料有効部の上端及び下端側のなくとも一方に有し、上端から燃料有効長の１/２４の領域での平均濃縮度を２．１０ｗｔ％とする構成が記載されている。また、燃料有効長さに占めるガドリニアを含まない領域の長さの割合を２/２４とすること、及び部分長燃料棒を、最外周を除く外周部及びウォーターロッドに隣接するよう配する点が記載されている。これにより燃料経済性の向上を図るものである。
また、高燃焼度化に伴って燃料集合体の平均濃縮度は大きくなる。燃料集合体の平均濃縮度が大きくなると、ボイド係数の絶対値が増加する（大きくなる）。ボイド係数の絶対値を減少させるため、燃料集合体の水対ウラン体積比を大きくすることが考えられる。例えば、特許文献２では、１０行１０列の正方格子配列の燃料集合体内に、ウォーターロッドを４本以上１６本以下配し、燃料有効長の上部１/１２〜２/１２の領域に、他の領域よりも低濃縮度の燃料を配する。そして、このように４本以上１６本以下のウォータ―ロッド及び細径燃料棒を配することにより、水対ウラン比が体積比で３.０以上とし、高濃縮度化によるボイド係数の絶対値の増加を抑制可能とするものである。 To solve this problem, for example, a technique disclosed in Patent Document 1 has been proposed. In Patent Literature 1, in a fuel assembly, a region containing no burnable poison is provided on at least one of the upper and lower ends of the active fuel portion, and the average enrichment in a region of 1/24 of the active fuel length from the upper end is provided. A configuration in which the degree is 2.10 wt% is described. In addition, the ratio of the length of the region not including gadolinia to the active fuel length is set to 2/24, and the partial length fuel rods are arranged so as to be adjacent to the outer peripheral portion except the outermost periphery and the water rod. Has been described. This aims to improve fuel economy.
In addition, the average enrichment of the fuel assembly increases as the burnup increases. As the average enrichment of the fuel assembly increases, the absolute value of the void coefficient increases (increases). In order to reduce the absolute value of the void coefficient, it is conceivable to increase the water to uranium volume ratio of the fuel assembly. For example, in Patent Literature 2, four to sixteen water rods are arranged in a fuel assembly having a square lattice arrangement of 10 rows and 10 columns, and other water rods are disposed in the upper 1/12 to 2/12 regions of the active fuel length. Distribute fuel with lower enrichment than the area. By arranging four to sixteen water rods and small-diameter fuel rods in this way, the water to uranium ratio becomes 3.0 or more in volume ratio, and the absolute value of the void coefficient due to high enrichment is increased. Can be suppressed.

特許第３２６２０２２号公報Japanese Patent No. 3262022 特開昭６０−２０５２８１号公報JP-A-60-205281

特許文献１の構成では、可能な限り燃料集合体の平均濃縮度を高めることで、燃料集合体を高燃焼度化している。しかしながら、高濃縮度化に伴って絶対値が増加する炉心のボイド係数に関しては何ら考慮されていない。
また、特許文献２の構成では、水対ウラン体積比を３．０以上とするため燃料棒径を細くする必要があり、燃料装荷量の低減を招き燃料経済性が低下する。
本発明の目的は、所望の燃料装荷量を維持しつつ、ボイド係数の絶対値の増加を抑制できる燃料集合体及び原子炉の炉心を提供することにある。 In the configuration of Patent Document 1, the burnup of the fuel assembly is increased by increasing the average enrichment of the fuel assembly as much as possible. However, no consideration is given to the void coefficient of the core, whose absolute value increases with increasing enrichment.
Further, in the configuration of Patent Document 2, it is necessary to reduce the diameter of the fuel rod in order to make the water to uranium volume ratio 3.0 or more, which leads to a reduction in the amount of loaded fuel and a reduction in fuel economy.
An object of the present invention is to provide a core of desired while maintaining a fuel loading amount, fuel assemblies Ru can suppress an increase in the absolute value of the void coefficient and reactor.

上記課題を解決するため、本発明の燃料集合体は、核燃料物質及び可燃性毒物を含有する第１燃料棒と核燃料物質を含有して可燃性毒物を含有しない第２燃料棒をチャンネルボックス内に束ねて収容する燃料集合体であって、第１燃料棒及び第２燃料棒は、それぞれの燃料有効部の上端部に、核燃料物質を含有して可燃性毒物を含有しない燃料有効部上端領域を形成しており、第１燃料棒及び第２燃料棒のそれぞれにおいて、燃料有効部上端領域が燃料有効部の上端から下方に向かって形成され、燃料有効部の軸方向長さに対する燃料有効部上端領域の軸方向長さの割合が０．１６以上０．２１以下の範囲にあり、第１燃料棒及び第２燃料棒のそれぞれの燃料有効部上端領域の下端から上端に亘って存在する核燃料物質は濃縮された核燃料物質であり、それぞれの燃料有効部上端領域の平均濃縮度が２．０ｗｔ％以上２．５ｗｔ％以下の範囲にあることを特徴とする。
また、本発明の炉心は、複数体の燃料集合体が装荷される原子炉の炉心であって、その燃料集合体は、核燃料物質及び可燃性毒物を含有する第１燃料棒と核燃料物質を含有して可燃性毒物を含有しない第２燃料棒をチャンネルボックス内に束ねて収容し、第１燃料棒及び第２燃料棒は、それぞれの燃料有効部の上端部に、核燃料物質を含有して可燃性毒物を含有しない燃料有効部上端領域を形成しており、第１燃料棒及び第２燃料棒のそれぞれにおいて、燃料有効部上端領域が燃料有効部の上端から下方に向かって形成され、燃料有効部の軸方向長さに対する燃料有効部上端領域の軸方向長さの割合が０．１６以上０．２１以下の範囲にあり、第１燃料棒及び第２燃料棒のそれぞれの燃料有効部上端領域の下端から上端に亘って存在する核燃料物質は濃縮された核燃料物質であり、それぞれの燃料有効部上端領域の平均濃縮度が２．０ｗｔ％以上２．５ｗｔ％以下の範囲にあることを特徴とする。 In order to solve the above problems, a fuel assembly according to the present invention includes a first fuel rod containing a nuclear fuel substance and a burnable poison and a second fuel rod containing a nuclear fuel substance and not containing a burnable poison in a channel box. a fuel assembly for housing a bundle, first fuel rods and second fuel rods, the upper end portion of each of the fuel effective portion, the fuel effective portion upper area containing nuclear fuel material containing no flammable poison forms a, in each of the first fuel rods and second fuel rods, the fuel effective portion upper end region is formed from the upper end of the effective portion fuel downward, the fuel effective portion for the axial length of the fuel effective portion Nuclear fuel that has an axial length ratio of the upper end region in the range of 0.16 or more and 0.21 or less, and extends from the lower end to the upper end of the effective fuel portion upper end region of each of the first fuel rod and the second fuel rod. Material is enriched nuclear fuel And the average enrichment of the respective fuel effective portion upper end region, characterized in that in the range of 2.0 wt% or more 2.5 wt%.
Further, the core of the present invention is a core of a nuclear reactor in which a plurality of fuel assemblies are loaded, and the fuel assembly includes a first fuel rod containing a nuclear fuel substance and a burnable poison and a nuclear fuel substance. Then, the second fuel rods containing no burnable poisons are bundled and accommodated in the channel box, and the first fuel rods and the second fuel rods each contain a nuclear fuel substance at the upper end of the active fuel portion. The fuel effective portion upper end region not containing the burnable poison is formed. In each of the first fuel rod and the second fuel rod, the fuel effective portion upper end region is formed downward from the upper end of the fuel effective portion. The ratio of the axial length of the fuel effective portion upper end region to the axial length of the effective portion is in the range of 0.16 or more and 0.21 or less, and the upper end of the fuel effective portion of each of the first fuel rod and the second fuel rod. Nuclear fuel existing from the lower end to the upper end of the area Material is a nuclear fuel material enriched, the average enrichment of the respective fuel effective portion upper end region, characterized in that in the range of 2.0 wt% or more 2.5 wt%.

本発明によれば、所望の燃料装荷量を維持しつつ、ボイド係数の絶対値の増加を抑制できる燃料集合体及び原子炉の炉心を提供することが可能となる。
上記した以外の課題、構成及び効果は、以下の実施形態の説明により明らかにされる。 According to the present invention, it is possible to provide a core of desired while maintaining a fuel loading amount, fuel assemblies Ru can suppress an increase in the absolute value of the void coefficient and reactor.
Problems, configurations, and effects other than those described above will be apparent from the following description of the embodiments.

本発明の一実施例に係る実施例１の燃料集合体の全体概略構成図である。FIG. 1 is an overall schematic configuration diagram of a fuel assembly according to a first embodiment of the present invention. 図１に示す燃料集合体のＡ−Ａ断面図矢視図（水平断面図）及び各燃料棒の濃縮度を示す図である。FIG. 2 is a sectional view taken along line AA of the fuel assembly shown in FIG. 1 (a horizontal sectional view) and a diagram showing enrichment of each fuel rod. 図２に示す燃料集合体を装荷する炉心を備えた改良型沸騰水型原子炉の概略構成図である。FIG. 3 is a schematic configuration diagram of an improved boiling water reactor provided with a core for loading the fuel assembly shown in FIG. 2. 燃料領域上端部領域の４ノードに、天然ウラン燃料、可燃性毒物を含まない低濃縮度燃料、及び高濃縮度燃料をそれぞれ設けた燃料を用いた炉心のボイド係数を示す図である。It is a figure which shows the void coefficient of the core which used the fuel which provided the natural uranium fuel, the low-enrichment fuel which does not contain a burnable poison, and the high-enrichment fuel in four nodes of the fuel area upper end area | region respectively. 燃料領域上端部領域の４ノードに、天然ウラン燃料、可燃性毒物を含まない低濃縮度燃料、高濃縮度燃料をそれぞれ設けた燃料を用いた炉心の軸方向出力分布を示す図である。It is a figure which shows the axial power distribution of the core which used the fuel which provided the natural uranium fuel, the low-enrichment fuel which does not contain a burnable poison, and the high-enrichment fuel in each of 4 nodes of the fuel area upper end area | region. 可燃性毒物を含まない低濃縮度燃料領域のノード数とボイド係数の関係を示す図である。It is a figure which shows the relationship between the number of nodes of a low enrichment fuel area | region which does not contain a burnable poison, and a void coefficient. 燃料領域上端部領域の４ノードに可燃性毒物を含まない低濃縮度燃料を設けた場合における、低濃縮度燃料領域の平均濃縮度とボイド係数の関係を示す図である。It is a figure which shows the relationship between the average enrichment of a low-enrichment fuel area | region, and a void coefficient, when the low-enrichment fuel which does not contain a burnable poison is provided in 4 nodes of a fuel area upper end area. 燃料領域上端部領域の４ノードに可燃性毒物を含まない低濃縮度燃料を設けた場合における、燃料集合体水平断面の濃縮度と減速材ボイド係数との関係を示す図である。It is a figure which shows the relationship between the enrichment of a fuel assembly horizontal cross section, and a moderator void coefficient at the time of providing the low enrichment fuel which does not contain a burnable poison in four nodes of the fuel area upper end area | region. 本発明の他の実施例に係る実施例２の燃料集合体の水平断面図及び各燃料棒の濃縮度を示す図である。It is a horizontal sectional view of a fuel assembly of Example 2 concerning other examples of the present invention, and a figure showing the enrichment of each fuel rod. 本発明の他の実施例に係る実施例３の燃料集合体の水平断面図及び各燃料棒の濃縮度を示す図である。It is a horizontal sectional view of a fuel assembly of Example 3 concerning other examples of the present invention, and a figure showing enrichment of each fuel rod.

本発明者等は鋭意努力の結果、沸騰水型原子炉の燃料集合体のボイド係数の絶対値を減少させるための新たな知見を得た。
沸騰水型原子炉では、炉心に装荷される燃料集合体の上端若しくは下端には天然ウラン燃料領域を設けている。これは、燃料有効部の端部に反応度の低い天然ウラン燃料を設けることで、炉心より漏洩する中性子の量を抑制し中性子経済性を向上させているためである。一般に、濃縮度が大きくなるほどボイド係数の絶対値は増加する傾向を示すことから、濃縮度の低い天然ウラン燃料領域を燃料集合体の上端若しくは下端に設けることで、燃料集合体のボイド係数の絶対値が減少することを期待している。 The present inventors have earnestly obtained new findings for reducing the absolute value of the void coefficient of a fuel assembly of a boiling water reactor.
In a boiling water reactor, a natural uranium fuel region is provided at an upper end or a lower end of a fuel assembly loaded in a reactor core. This is because the provision of low-reactivity natural uranium fuel at the end of the fuel effective portion suppresses the amount of neutrons leaking from the reactor core and improves neutron economics. In general, the absolute value of the void coefficient tends to increase as the enrichment increases.Therefore, by providing a natural uranium fuel region with a low enrichment at the upper end or the lower end of the fuel assembly, the absolute value of the void coefficient of the fuel assembly is increased. We expect the value to decrease.

図４に、燃料領域上端部領域の４ノードに、天然ウラン燃料、可燃性毒物を含まない低濃縮度燃料、及び高濃縮度燃料をそれぞれ設けた燃料を用いた炉心のボイド係数を示す。図４では、横軸に上端部（燃料領域上端部領域の４ノード）に設けた燃料料領域の平均濃縮度（ｗｔ％）、縦軸に炉心のボイド係数×１０−３（％ｄｋ／ｋ／％ｖｏｉｄ）をとり、可燃性毒物を含まない低濃縮度燃料についてはその濃縮度を２．５ｗｔ％とし、可燃性毒物を含む高濃縮度燃料についてはその濃縮度を４.６ｗｔ％としたときの、平衡炉心のサイクル末期におけるボイド係数の解析値を示している。なお、本明細書において、高濃縮度燃料とは、平均濃縮度が３.０ｗｔ％以上の燃料集合体を指すものとする。また、可燃性毒物を含まない低濃縮度燃料については、軸方向ノード、２４ノードのうち、燃料領域上端部領域の４ノードを除く他の２０ノードについては高濃縮度燃料とした。 FIG. 4 shows a void coefficient of a core using a fuel in which natural uranium fuel, a low-enrichment fuel containing no burnable poison, and a high-enrichment fuel are provided at four nodes in the upper end region of the fuel region. In FIG. 4, the horizontal axis represents the average enrichment (wt%) of the fuel charge region provided at the upper end (four nodes in the upper end region of the fuel region), and the vertical axis represents the void coefficient of the core × 10 −3 (% dk / k). /% Void), the enrichment of the low-enrichment fuel containing no burnable poison is 2.5 wt%, and the enrichment of the high-enrichment fuel containing burnable poison is 4.6 wt%. The figure shows the analysis value of the void coefficient at the end of the cycle of the equilibrium core. In this specification, the term "high enrichment fuel" refers to a fuel assembly having an average enrichment of 3.0 wt% or more. For the low enrichment fuel containing no burnable poison, the high enrichment fuel was used for the other 20 nodes except the 4 nodes in the upper end region of the fuel region among the axial nodes and the 24 nodes.

図４に示すように、燃料領域上端部領域の４ノードに天然ウラン燃料を設けた燃料では、炉心のボイド係数の絶対値の低減は認められない。すなわち、天然ウラン燃料を燃料領域上端部領域の４ノードに設けてもボイド係数の改善効果（炉心のボイド係数の絶対値の低減効果）は達成できないことが分かる。また、同様に、図４に示すように、燃料領域上端部領域の４ノードに高濃縮度燃料を設けた燃料では、炉心のボイド係数の絶対値の低減は認められない。すなわち、高濃縮度燃料を燃料領域上端部領域の４ノードに設けてもボイド係数の改善効果（炉心のボイド係数の低減効果）は達成できないことが分かる。これに対し、燃料領域上端部領域の４ノードに低濃縮度燃料を設けた燃料では、炉心のボイド係数の絶対値の低減に効果的であることが分かる。   As shown in FIG. 4, in the fuel in which the natural uranium fuel is provided at the four nodes in the upper end region of the fuel region, the absolute value of the core void coefficient is not reduced. In other words, it can be seen that the effect of improving the void coefficient (the effect of reducing the absolute value of the void coefficient of the core) cannot be achieved even when the natural uranium fuel is provided at the four nodes in the upper end region of the fuel region. Similarly, as shown in FIG. 4, in the fuel in which the high enrichment fuel is provided at the four nodes in the upper end region of the fuel region, the absolute value of the void coefficient of the core is not reduced. In other words, it can be seen that the effect of improving the void coefficient (the effect of reducing the void coefficient of the core) cannot be achieved even when the highly enriched fuel is provided at the four nodes in the upper end region of the fuel region. On the other hand, it can be seen that the fuel in which the low enrichment fuel is provided at the four nodes in the upper end region of the fuel region is effective in reducing the absolute value of the core void coefficient.

本発明者等は、種々の検討を重ね、炉心のボイド係数の絶対値を低減するための軸方向の燃料構成について明らかにした。図５は、燃料領域上端部領域の４ノードに、天然ウラン燃料、可燃性毒物を含まない低濃縮度燃料、高濃縮度燃料をそれぞれ設けた燃料を用いた炉心の軸方向出力分布を示す図である。図５では横軸に軸方向出力分布を、縦軸に軸方向ノード位置をとり、可燃性毒物を含まない低濃縮度燃料についてはその濃縮度を２．５ｗｔ％とし、可燃性毒物を含む高濃縮度燃料についてはその濃縮度を４.６ｗｔ％としたときの、平衡炉心のサイクル末期における軸方向出力分布を示している。
図５に示すように、燃料領域上端部領域の４ノードに天然ウラン燃料を設けた燃料では、燃焼を通して反応度が小さいため、平衡炉心サイクル末期では天然ウラン領域の下に設けられている高濃縮度燃料領域の出力が大きくなる特徴を持つ。ボイド率が大きくなるほどボイド係数の絶対値は大きくなる傾向を持つ。天然ウラン燃料を燃料領域上端部領域の４ノードに設けた場合、炉心のボイド係数が改善されないのは、点線Ａにて示す領域おいて軸方向出力分布が大きくなる。すなわち、ノード１６〜ノード２０の位置である上部に設けられた高濃縮度燃料のボイド係数の寄与を大きくしてしまうためである。 The present inventors have conducted various studies and clarified an axial fuel composition for reducing the absolute value of the core void coefficient. FIG. 5 is a diagram showing an axial power distribution of a core using a fuel in which natural uranium fuel, a low-enrichment fuel containing no burnable poison, and a high-enrichment fuel are provided at four nodes in the upper end region of the fuel region. It is. In FIG. 5, the horizontal axis represents the axial output distribution, and the vertical axis represents the axial node position. The low enrichment fuel containing no burnable poison has a concentration of 2.5 wt%, and the high enrichment contains burnable poison. For the enriched fuel, the axial power distribution at the end of the cycle of the equilibrium core is shown when the enrichment is 4.6 wt%.
As shown in FIG. 5, in the fuel in which natural uranium fuel is provided at the four nodes in the upper end region of the fuel region, the reactivity is small through combustion, and therefore, at the end of the equilibrium core cycle, the high enrichment provided below the natural uranium region It has the feature that the output in the fuel region increases. As the void ratio increases, the absolute value of the void coefficient tends to increase. When natural uranium fuel is provided at four nodes in the upper end region of the fuel region, the reason why the void coefficient of the core is not improved is that the axial power distribution increases in the region indicated by the dotted line A. In other words, this is because the contribution of the void coefficient of the highly enriched fuel provided at the upper part which is the position of the nodes 16 to 20 is increased.

燃料領域上端部領域の４ノードに低濃縮度燃料を設けた燃料では、燃焼初期は反応度が大きいため、図５に示すように、平衡炉心のサイクル末期における軸方向出力分布において、上部（ノード１６〜ノード２０）に設けられた高濃縮度燃料領域の出力の上昇が抑制される。そのため、上述の図４に示す通り、燃料領域上端部領域（以下では、燃料有効部上端領域と称する場合もある）に可燃性毒物を含まない低濃縮度燃料を設けることにより、高濃縮度燃料或いは天然ウラン燃料を燃料有効部上端領域に設ける場合と比較して、炉心のボイド係数の絶対値を低減するという、ボイド係数改善効果が得られる。
一方、燃料有効部下端領域に低濃縮度燃料を設けることは、平衡炉心のサイクル末期における軸方向出力分布において、上部（ノード１６〜ノード２０）に設けられた高濃縮度燃料領域の出力上昇の抑制に寄与しないため、ボイド係数改善の効果（炉心のボイド係数の絶対値の低減効果）をもたらさない。
以上の通り、可燃性毒物を含まない低濃縮度燃料を燃料有効部上端領域に設けることにより、ボイド係数改善の効果（炉心のボイド係数の絶対値の低減効果）を得ることができることがわかった。 In the fuel in which the low-enrichment fuel is provided at the four nodes in the upper end region of the fuel region, the reactivity is large in the early stage of the combustion. Therefore, as shown in FIG. 16 to the node 20), an increase in the output of the high enrichment fuel region is suppressed. Therefore, as shown in FIG. 4 described above, by providing a low-enrichment fuel containing no burnable poison in the upper end region of the fuel region (hereinafter, also referred to as an effective fuel upper end region), the high-enrichment fuel is provided. Alternatively, as compared with the case where natural uranium fuel is provided in the upper end region of the fuel effective portion, the void coefficient improvement effect of reducing the absolute value of the void coefficient of the core can be obtained.
On the other hand, the provision of the low enrichment fuel in the lower end region of the active fuel portion increases the power increase of the high enrichment fuel region provided in the upper portion (nodes 16 to 20) in the axial power distribution at the end of the cycle of the equilibrium core. Since it does not contribute to the suppression, it does not bring about the effect of improving the void coefficient (the effect of reducing the absolute value of the void coefficient of the core).
As described above, it was found that the effect of improving the void coefficient (the effect of reducing the absolute value of the void coefficient of the reactor core) can be obtained by providing the low-enrichment fuel containing no burnable poison in the upper end region of the fuel effective portion. .

図６は、可燃性毒物を含まない低濃縮度燃料領域のノード数とボイド係数の関係を示す図である。図６では、横軸に可燃性毒物を含まない燃料領域（燃料有効部）の軸方向ノード数を、縦軸に炉心のボイド係数×１０−３（％ｄｋ／ｋ／％ｖｏｉｄ）をとり、可燃性毒物を含まない燃料領域（燃料有効部）を軸方向に２４ノードに分割した場合を想定している。図６に示すように、ボイド係数改善の効果を最大化し得るノード数は、可燃性毒物を含まない低濃縮度燃料の燃料有効部２４ノードの内、４ノード若しくは５ノードであることが分かる。換言すれば、燃料有効部の軸方向長さ（２４ノード）に占める可燃性毒物を含有しない領域の長さの割合が０．１６以上０．２１以下とすることにより、ボイド係数改善の効果を最大化することが可能となる。なお、本明細書では、燃料領域（燃料有効部）を軸方向に２４ノードに分割した場合を一例として説明するが、分割するノード数はこれに限られるものではなく、燃料領域（燃料有効部）を軸方向に２５ノードに分割しても良い。この場合においても、燃料有効部の軸方向長さに占める可燃性毒物を含有しない領域の長さの割合が０．１６以上０．２１以下とすることにより、ボイド係数改善の効果を最大化が図られる。 FIG. 6 is a diagram illustrating a relationship between the number of nodes and a void coefficient in a low-enrichment fuel region that does not include a burnable poison. In FIG. 6, the horizontal axis represents the number of nodes in the axial direction of the fuel region (fuel effective portion) containing no burnable poison, and the vertical axis represents the void coefficient of the core × 10 −3 (% dk / k /% void). It is assumed that the fuel region (effective fuel portion) containing no burnable poison is divided into 24 nodes in the axial direction. As shown in FIG. 6, it can be seen that the number of nodes that can maximize the effect of improving the void coefficient is 4 or 5 nodes out of the 24 fuel effective portions of low-enrichment fuel containing no burnable poison. In other words, by setting the ratio of the length of the region containing no burnable poison to the axial length (24 nodes) of the active fuel portion to be 0.16 or more and 0.21 or less, the effect of improving the void coefficient can be improved. It is possible to maximize. In this specification, a case where the fuel region (fuel effective portion) is divided into 24 nodes in the axial direction will be described as an example. However, the number of nodes to be divided is not limited to this, and the fuel region (fuel effective portion) is not limited to this. ) May be divided into 25 nodes in the axial direction. Also in this case, the effect of improving the void coefficient can be maximized by setting the ratio of the length of the region containing no burnable poison to the axial length of the active fuel portion to be 0.16 or more and 0.21 or less. It is planned.

図７は、燃料領域上端部領域の４ノードに可燃性毒物を含まない低濃縮度燃料を設けた場合における、低濃縮度燃料領域の平均濃縮度とボイド係数の関係を示す図である。図７では、横軸に低濃縮度燃料領域の平均濃縮度（ｗｔ％）をとり、縦軸に炉心のボイド係数×１０−３（％ｄｋ／ｋ／％ｖｏｉｄ）をとり、これらの相関関係を示している。なお、図７では、燃料領域（燃料有効部）を軸方向に２４ノードに分割し、燃料領域上端部領域（燃料有効部上端領域）の４ノードに可燃性毒物を含まない低濃縮度燃料を設け、それ以外の領域、すなわち２０ノードを高濃縮度燃料とした。図７に示すように、低濃縮度燃料領域の平均濃度が２.０ｗｔ％未満になると、ボイド系係数の改善効果（炉心のボイド係数の絶対値の低減効果）が急激に（顕著に）低下している。このことから、燃料領域上端部領域の４ノードに設ける可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２.０％以上とする必要がある。換言すれば、燃料領域上端部領域の４ノードに設ける可燃性毒物を含まない低濃縮度燃料の平均濃縮度の下限値は、２.０ｗｔ％である。 FIG. 7 is a diagram showing the relationship between the average enrichment in the low-enrichment fuel region and the void coefficient when low-enrichment fuel containing no burnable poison is provided at four nodes in the upper end region of the fuel region. In FIG. 7, the horizontal axis represents the average enrichment (wt%) of the low enrichment fuel region, and the vertical axis represents the void coefficient of the core × 10 −3 (% dk / k /% void). Is shown. In FIG. 7, the fuel region (effective fuel portion) is divided into 24 nodes in the axial direction, and low-enrichment fuel containing no burnable poison is contained in four nodes at the upper end region of the fuel region (effective fuel upper end region). And the other area, that is, 20 nodes, was used as high-enrichment fuel. As shown in FIG. 7, when the average concentration in the low enrichment fuel region is less than 2.0 wt%, the effect of improving the void coefficient (the effect of reducing the absolute value of the void coefficient of the core) decreases rapidly (notably). are doing. For this reason, it is necessary to set the average enrichment of the low enrichment fuel containing no burnable poison provided at the four nodes in the upper end region of the fuel region to 2.0% or more. In other words, the lower limit value of the average enrichment of the low enrichment fuel containing no burnable poison provided at the four nodes in the upper end region of the fuel region is 2.0 wt%.

図８は、燃料領域上端部領域の４ノードに可燃性毒物を含まない低濃縮度燃料を設けた場合における、燃料集合体水平断面の濃縮度と減速材ボイド係数との関係を示す図である。図８では、横軸に燃料集合体水平断面の濃縮度（平均濃縮度）（ｗｔ％）をとり、縦軸に燃料集合体水平断面の減速材ボイド係数×１０−３（％ｄｋ／ｋ／％ｖｏｉｄ）をとり、これらの相関関係を示している。なお、図８では、燃料領域（燃料有効部）を軸方向に２４ノードに分割し、燃料領域上端部領域（燃料有効部上端領域）の４ノードに可燃性毒物を含まない低濃縮度燃料を設け、それ以外の領域、すなわち２０ノードを高濃縮度燃料とした。図８に示すように、燃料集合体水平断面の濃縮度（平均濃縮度）の低下に従い、燃料集合体水平断面の減速材ボイド係数の値は小さくなり、減速材ボイド係数の変化量も大きくなる傾向を示す。燃料集合体水平断面の濃縮度を２.５ｗｔ％以下とすることで、減速材ボイド係数を高濃縮度燃料の半分以下とすることができる。このことから、燃料領域上端部領域の４ノードに設ける可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２.５％以下とする必要がある。換言すれば、燃料領域上端部領域の４ノードに設ける可燃性毒物を含まない低濃縮度燃料の平均濃縮度の上限値は、２.５ｗｔ％である。 FIG. 8 is a diagram showing a relationship between enrichment of a fuel assembly horizontal section and moderator void coefficient when low-enrichment fuel containing no burnable poison is provided at four nodes in the upper end region of the fuel region. . In FIG. 8, the enrichment (average enrichment) (wt%) of the horizontal cross section of the fuel assembly is plotted on the horizontal axis, and the moderator void coefficient of the horizontal cross section of the fuel assembly × 10 −3 (% dk / k / % Void), showing these correlations. In FIG. 8, the fuel region (effective fuel portion) is divided into 24 nodes in the axial direction, and low-enrichment fuel containing no burnable poison is contained in four nodes at the upper end region of the fuel region (effective fuel upper end region). And the other area, that is, 20 nodes, was used as high-enrichment fuel. As shown in FIG. 8, as the enrichment (average enrichment) of the horizontal section of the fuel assembly decreases, the value of the moderator void coefficient of the horizontal section of the fuel assembly decreases, and the amount of change in the moderator void coefficient also increases. Show the trend. By setting the enrichment of the fuel assembly horizontal section to 2.5 wt% or less, the moderator void coefficient can be made half or less of the high enrichment fuel. For this reason, it is necessary to set the average enrichment of the low enrichment fuel containing no burnable poison provided at the four nodes in the upper end region of the fuel region to 2.5% or less. In other words, the upper limit value of the average enrichment of the low enrichment fuel containing no burnable poison provided at the four nodes in the upper end region of the fuel region is 2.5 wt%.

以上より、燃料有効部の軸方向長さに占める可燃性毒物を含有しない領域（燃料有効部上端領域）の長さの割合を０．１６以上０．２１以下とし、且つ、燃料領域上端部領域（燃料有効部上端領域）に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２．０ｗｔ％以上２．５ｗｔ％以下とすることで、所望の燃料装荷量を維持しつつ、炉心のボイド係数の絶対値の増加を抑制することが可能となる。   As described above, the ratio of the length of the area not containing the burnable poison (the upper end area of the active fuel section) to the axial length of the active fuel section is set to 0.16 to 0.21 and the upper end area of the fuel area. By setting the average enrichment of the low enrichment fuel containing no burnable poison provided in the (fuel effective portion upper end region) to be 2.0 wt% or more and 2.5 wt% or less, while maintaining a desired fuel loading amount, It is possible to suppress an increase in the absolute value of the void coefficient of the core.

以下、図面を用いて本発明の実施例について説明する。なお、以下では、インターナルポンプを備え、冷却材を原子炉圧力容器内で循環させる改良型沸騰水型原子炉（Ａｄｖａｎｃｅｄ Ｂｏｉｌｉｎｇ Ｗａｔｅｒ Ｒｅａｃｔｏｒ：ＡＢＷＲ）を一例として説明するが、これに限られるものではない。再循環ポンプを備え、冷却材（中性子の減速材としても機能）を原子炉圧力容器外へ通流し再び原子炉圧力容器内のダウンカマへ流入させることで冷却材を循環させる通常の沸騰水型原子炉（ＢＷＲ）へも同様に適用できる。また、可燃性毒物として、例えば、ガドリニア（Ｇｄ）が用いられる。   Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following, an improved boiling water reactor (ABWR) having an internal pump and circulating a coolant in a reactor pressure vessel will be described as an example, but is not limited thereto. Absent. A normal boiling water atom that has a recirculation pump and circulates coolant by flowing coolant (also functioning as a neutron moderator) out of the reactor pressure vessel and back into the downcomer in the reactor pressure vessel The same can be applied to a furnace (BWR). Further, for example, gadolinia (Gd) is used as the burnable poison.

図１に、本発明の一実施例に係る実施例１の燃料集合体の全体概略構成図を示し、図２に図１に示す燃料集合体のＡ−Ａ断面図矢視図（水平断面図）及び各燃料棒の濃縮度示す図を、図３に図２に示す燃料集合体を装荷する炉心を備えた改良型沸騰水型原子炉の概略構成図を示す。   FIG. 1 is an overall schematic configuration diagram of a fuel assembly according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the fuel assembly shown in FIG. FIG. 3 is a diagram showing the enrichment of each fuel rod, and FIG. 3 is a schematic configuration diagram of an improved boiling water reactor provided with a core for loading the fuel assembly shown in FIG.

（改良型沸騰水型原子炉（ＡＢＷＲ）の構成）
図３に示すように、本実施例の燃料集合体（詳細後述する）が装荷される炉心を備える改良型沸騰水型原子炉１０は、原子炉圧力容器１１内に円筒状の炉心シュラウド１６が設けられ、炉心シュラウド１６内に、複数体の燃料集合体（図示せず）が装荷された初装荷炉心である炉心１２が設置されている。また、原子炉圧力容器１１内には、炉心１２を覆うシュラウドヘッド２０、シュラウド２０に取り付けられ上方へと延伸する気水分離器１８、及び気水分離器１８の上方に配される蒸気乾燥器１９が設けられている。
上部格子板１４が、シュラウドヘッド２０の下方で炉心シュラウド１６内に配され、炉心シュラウド１６に取り付けられて炉心１２の上端部に位置している。炉心支持板１３が、炉心１２の下端部に位置して炉心シュラウド１６内に配され、炉心シュラウド１６に設置されている。また、複数の燃料支持金具１５が炉心支持板１３に設置されている。
また、原子炉圧力容器１１内には、燃料集合体の核反応を制御するため炉心１２へ複数の横断面十字状の制御棒（図示せず）を挿入可能とする制御棒案内管２２が設けられている。原子炉圧力容器１１の底部より下方に設置された制御棒駆動機構ハウジング（図示せず）内に制御棒駆動機構２３を備え、制御棒は制御棒駆動機構２３に連結されている。 (Configuration of improved boiling water reactor (ABWR))
As shown in FIG. 3, an improved boiling water reactor 10 including a core in which a fuel assembly (described later in detail) of the present embodiment is loaded has a cylindrical core shroud 16 in a reactor pressure vessel 11. A core 12, which is an initially loaded core loaded with a plurality of fuel assemblies (not shown), is provided in a core shroud 16. In the reactor pressure vessel 11, a shroud head 20 covering the reactor core 12, a steam-water separator 18 attached to the shroud 20 and extending upward, and a steam dryer disposed above the steam-water separator 18 are provided. 19 are provided.
An upper grid plate 14 is disposed within the core shroud 16 below the shroud head 20 and is attached to the core shroud 16 and located at the upper end of the core 12. A core support plate 13 is disposed in the core shroud 16 at the lower end of the core 12, and is installed on the core shroud 16. Further, a plurality of fuel support members 15 are provided on the core support plate 13.
A control rod guide tube 22 is provided in the reactor pressure vessel 11 so that a plurality of control rods (not shown) having a cross-shaped cross section can be inserted into the core 12 to control the nuclear reaction of the fuel assembly. Have been. A control rod drive mechanism 23 is provided in a control rod drive mechanism housing (not shown) installed below the bottom of the reactor pressure vessel 11, and the control rods are connected to the control rod drive mechanism 23.

原子炉圧力容器１１の底部である下鏡２４に、その下方より原子炉圧力容器１１の内部へ貫通するよう複数のインターナルポンプ２１が設置されている。複数のインターナルポンプ２１は、複数の制御棒案内管２２の最外周部より外側であって、環状に相互に所定の間隔にて離間し、複数台配されている。これにより、インターナルポンプ２１は、制御棒案内管２２等と干渉することはない。そして、各インターナルポンプ２１のインペラが、円筒状の炉心シュラウド１６と原子炉圧力容器１１の内面との間に形成される環状のダウンカマ１７内に位置付けられている。原子炉圧力容器１１内の冷却水は、各インターナルポンプ２１のインペラにより、ダウンカマ１７を介して、下鏡２４側から炉心１２へ供給される。炉心１２内に流入する冷却水は、燃料集合体（図示せず）の核反応により加熱され気液二相流となり、気水分離器１８へ流入する。気水分離器１８を通流する気液二相流は、湿分を含む蒸気（気相）と水（液相）に分離され、液相は再び冷却水としてダウンカマ１７へ降下する。一方、蒸気（気相）は、蒸気乾燥器１９へと導入され湿分が除去された後、主蒸気配管２５を介してタービン（図示せず）へ供給される。復水器等を介して給水配管２６より原子炉圧力容器１１内に流入する冷却水は、ダウンカマ１７内を下方へと通流する（降下する）。このように、インターナルポンプ２１は、炉心１２で発生する熱を効率良く冷却するため、冷却水を炉心１２へ強制循環させる。   A plurality of internal pumps 21 are installed in the lower mirror 24 at the bottom of the reactor pressure vessel 11 so as to penetrate the reactor pressure vessel 11 from below. The plurality of internal pumps 21 are arranged outside the outermost peripheral portions of the plurality of control rod guide tubes 22 and are annularly spaced apart from each other at a predetermined interval. Thus, the internal pump 21 does not interfere with the control rod guide tube 22 and the like. The impeller of each internal pump 21 is positioned in an annular downcomer 17 formed between the cylindrical core shroud 16 and the inner surface of the reactor pressure vessel 11. The cooling water in the reactor pressure vessel 11 is supplied to the reactor core 12 from the lower mirror 24 side via the downcomer 17 by the impeller of each internal pump 21. The cooling water flowing into the reactor core 12 is heated by a nuclear reaction of a fuel assembly (not shown), becomes a gas-liquid two-phase flow, and flows into the steam separator 18. The gas-liquid two-phase flow flowing through the steam separator 18 is separated into steam (gas phase) containing moisture and water (liquid phase), and the liquid phase falls again to the downcomer 17 as cooling water. On the other hand, the steam (gas phase) is supplied to a turbine (not shown) via the main steam pipe 25 after being introduced into the steam dryer 19 and removing moisture. The cooling water flowing into the reactor pressure vessel 11 from the water supply pipe 26 via the condenser or the like flows downward (falls) in the downcomer 17. Thus, the internal pump 21 forcibly circulates the cooling water to the core 12 in order to efficiently cool the heat generated in the core 12.

（燃料集合体の構成）
図１に、炉心１２に装荷される燃料集合体１の全体概略構成図を示す。
図１に示すように、燃料集合体１は、上部タイプレート５、下部タイプレート７、これらのタイプレートに両端が保持されている複数の燃料棒３、ウォーターロッド２（ウォーターチャネルとも称される）、これらの燃料棒３を束ねる燃料スペーサ９、及び、燃料スペーサ９により束ねられている燃料棒束を取り囲み上部タイプレート５に取り付けられたチャンネルボックス４を備えている。上部タイプレート５にはハンドル６が締結されており、ハンドル６を吊り上げると、燃料集合体１全体を引き上げることができる。燃料棒３は、その一部に高さが上部タイプレート５まで達しない部分長燃料棒を有する。すなわち、部分長燃料棒は、上部タイプレート５へ達する全長燃料棒よりも内部に充填される燃料有効長が短い燃料棒である。また、複数の燃料棒３内には、核分裂性物質（ウラン２３５）を含む核燃料物質を用いて製造した円筒形状の多数の燃料ペレットが充填されている。各燃料棒３の下端部が下部タイプレート７によって支持され、各燃料棒３の上端部が上部タイプレート５によって保持される。複数の燃料スペーサ９は、燃料集合体１の軸方向に所定の間隔にて配され、燃料棒相互間に所定の間隔を有するよう複数の燃料棒３を保持する。 (Composition of fuel assembly)
FIG. 1 shows an overall schematic configuration diagram of a fuel assembly 1 loaded in a core 12.
As shown in FIG. 1, the fuel assembly 1 includes an upper tie plate 5, a lower tie plate 7, a plurality of fuel rods 3 whose both ends are held by these tie plates, and a water rod 2 (also referred to as a water channel). ), A fuel spacer 9 for bundling the fuel rods 3, and a channel box 4 attached to the upper tie plate 5 surrounding the fuel rod bundle bundled by the fuel spacer 9. A handle 6 is fastened to the upper tie plate 5, and when the handle 6 is lifted, the entire fuel assembly 1 can be pulled up. The fuel rod 3 has a part-length fuel rod whose height does not reach the upper tie plate 5. That is, the partial length fuel rod is a fuel rod having a shorter active fuel length filled therein than the full length fuel rod reaching the upper tie plate 5. The plurality of fuel rods 3 are filled with a large number of cylindrical fuel pellets manufactured using a nuclear fuel material containing a fissile material (uranium 235). The lower end of each fuel rod 3 is supported by a lower tie plate 7, and the upper end of each fuel rod 3 is held by an upper tie plate 5. The plurality of fuel spacers 9 are arranged at predetermined intervals in the axial direction of the fuel assembly 1, and hold the plurality of fuel rods 3 so as to have a predetermined interval between the fuel rods.

図２は、図１に示す燃料集合体１のＡ−Ａ断面図矢視図（水平断面図）及び各燃料棒の濃縮度を示す図である。
図２の上図に示すように、本実施例の燃料集合体１では、燃料集合体１の水平断面において、チャンネルボックス４内に形成される１０行１０列の正方格子に、全長燃料棒３１ａ〜３１ｃ、部分長燃料棒４１、水ロッド（ＷＲ）２、及び可燃性毒物入り全長燃料棒５１が配されている。燃料集合体１の水平断面（横断面）の中央部には、燃料棒を４本配置可能な領域を占有する横断面積を有する水ロッド（ＷＲ）２が２本配されている。水ロッド（ＷＲ）２は、少なくとも２本の燃料棒が配置可能な領域を占有する横断面積を有する太径水ロッドである。 FIG. 2 is an AA cross-sectional view (horizontal cross-sectional view) of the fuel assembly 1 shown in FIG. 1 and a diagram showing enrichment of each fuel rod.
As shown in the upper diagram of FIG. 2, in the fuel assembly 1 of the present embodiment, in a horizontal cross section of the fuel assembly 1, a 10 × 10 square grid formed in the channel box 4 has full length fuel rods 31 a. 31c, a partial length fuel rod 41, a water rod (WR) 2, and a full length fuel rod 51 containing burnable poison. Two water rods (WR) 2 having a cross-sectional area occupying a region where four fuel rods can be arranged are arranged at the center of the horizontal section (cross section) of the fuel assembly 1. The water rod (WR) 2 is a large-diameter water rod having a cross-sectional area occupying a region where at least two fuel rods can be arranged.

図２の上図及び下図に示すように、全長燃料棒３１ａは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が２.８０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有する。４本の全長燃料棒３１ａが、燃料集合体１の水平断面内において、最外周の四隅（４つのコーナー部）の格子位置にそれぞれ配されている。   As shown in the upper and lower diagrams of FIG. 2, the full length fuel rod 31a has four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24 have an average enrichment of 2.50 wt%. And the nodes 1 to 20 have a low-enrichment fuel containing no burnable poison with an average enrichment of 2.80 wt%. The four full-length fuel rods 31a are arranged at the lattice positions of the outermost four corners (four corners) in the horizontal cross section of the fuel assembly 1 respectively.

全長燃料棒３１ｂは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が３.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。８本の全長燃料棒３１ｂが、燃料集合体１の水平断面内において、最外周の四隅（４つのコーナー部）の格子位置に配される全長燃料棒３１ａに隣接するよう最外周の格子位置に配されている。   The full-length fuel rod 31b has four nodes at the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24 are provided with low-enrichment fuel not containing a burnable poison having an average enrichment of 2.50 wt%. Nodes 1 to 20 have a high enrichment fuel having an average enrichment of 3.90 wt% and containing no burnable poisons. The eight full-length fuel rods 31b are positioned at the outermost circumferential grid positions in the horizontal cross section of the fuel assembly 1 so as to be adjacent to the full-length fuel rods 31a arranged at the grid positions of the four outermost corners (four corner portions). Are arranged.

全長燃料棒３１ｃは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。５２本の全長燃料棒３１ｃが、燃料集合体１の水平断面内において、最外周、最外周より１層内側、最外周より２層内側、最外周より３層内側、及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full-length fuel rod 31c has a low-enriched fuel containing no burnable poison having an average enrichment of 2.50 wt% in four nodes at the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, nodes 21 to 24. Nodes 1 to 20 have a high enrichment fuel having an average enrichment of 4.90 wt% and containing no burnable poisons. In the horizontal cross section of the fuel assembly 1, 52 full-length fuel rods 31 c are arranged at the outermost periphery, one layer inside the outermost periphery, two layers inside the outermost periphery, three layers inside the outermost periphery, and the water rod (WR) 2. Are arranged at lattice positions so as to be adjacent to.

部分長燃料棒４１は、ノード１〜ノード１４に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。１４本の部分長燃料棒４１が、燃料集合体１の水平断面内において、最外周より１層内側及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The partial length fuel rod 41 has a high enrichment fuel that does not include a burnable poison with an average enrichment of 4.90 wt% at nodes 1 to 14. Fourteen part-length fuel rods 41 are arranged at lattice positions in the horizontal cross section of the fuel assembly 1 so as to be one layer inside from the outermost periphery and adjacent to the water rod (WR) 2.

可燃性毒物入り全長燃料棒５１は、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の高濃縮度燃料を有する。ノード１〜ノード２０の高濃縮度燃料に含まれる可燃性毒物であるガドリニア（Ｇｄ）の濃度は９.０ｗｔ％である。１４本の可燃性毒物入り全長燃料棒５１が、燃料集合体１の水平断面内において、最外周より１層内側及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full length fuel rod 51 containing the burnable poison has four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24 do not contain the burnable poison having an average enrichment of 2.50 wt%. Node 1 to node 20 have high enrichment fuel with an average enrichment of 4.90 wt%. The concentration of gadolinia (Gd), which is a burnable poison contained in the highly enriched fuel of the nodes 1 to 20, is 9.0 wt%. Fourteen full-length burnable poison-containing fuel rods 51 are arranged at lattice positions in the horizontal cross section of the fuel assembly 1 so as to be one layer inside from the outermost periphery and adjacent to the water rod (WR) 2.

本実施例では、全長燃料棒３１ａ〜全長燃料棒３１ｃ、及び可燃性毒物入り全長燃料棒５１の何れにおいても、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、燃料有効部の軸方向長さ（２４ノード）に占める可燃性毒物を含有しない領域の長さの割合が０．１６である。そして、燃料領域上端部領域（燃料有効部上端領域）の可燃性毒物を含まない低濃縮度燃料の平均濃縮度は２.５０ｗｔ％である。   In this embodiment, in each of the full length fuel rods 31a to 31c and the full length fuel rod 51 containing a burnable poison, four nodes of the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the fuel effective portion The ratio of the length of the region containing no burnable poison to the axial length (24 nodes) is 0.16. The average enrichment of the low enrichment fuel containing no burnable poison in the upper end region of the fuel region (the upper end region of the fuel effective portion) is 2.50 wt%.

また、上述の通り、全長燃料棒３１ｂ、３１ｃ、及び可燃性毒物入り全長燃料棒５１の燃料領域上端部領域（燃料有効部上端領域）を除く燃料有効部は、高濃縮度燃料であることから、燃料の経済性を向上することができる。   Further, as described above, the active fuel portion of the full-length fuel rods 31b and 31c and the upper end region of the fuel region (the upper effective region of the active fuel portion) of the full-length fuel rod 51 containing a burnable poison is a highly enriched fuel. The fuel economy can be improved.

以上の通り、本実施例によれば、所望の燃料装荷量を維持しつつ、ボイド係数の絶対値の増加を抑制することが可能となる。
また、本実施例によれば、燃料の経済性を向上することが可能となる。 As described above, according to the present embodiment, it is possible to suppress an increase in the absolute value of the void coefficient while maintaining a desired fuel loading amount.
Further, according to the present embodiment, it is possible to improve fuel economy.

図９は、本発明の他の実施例に係る実施例２の燃料集合体の水平断面図及び各燃料棒の濃縮度示す図である。本実施例では、部分長燃料棒を燃料集合体の水平断面内において最外周部と水ロッド（ＷＲ）２に隣接して配する点が実施例１と異なる。本実施例における燃料集合体の全体概略構成は、実施例１にて説明した図２に示す構成と同様であり、また、本実施例の燃料集合体は、図３に示した改良型沸騰水型原子炉（ＡＢＷＲ）の炉心に装荷される。   FIG. 9 is a horizontal sectional view of a fuel assembly according to a second embodiment of the present invention and a diagram showing enrichment of each fuel rod. This embodiment is different from the first embodiment in that the partial length fuel rods are arranged adjacent to the outermost peripheral portion and the water rod (WR) 2 in the horizontal cross section of the fuel assembly. The overall schematic configuration of the fuel assembly according to the present embodiment is the same as the configuration illustrated in FIG. 2 described in the first embodiment, and the fuel assembly according to the present embodiment includes the improved boiling water illustrated in FIG. To the core of an advanced reactor (ABWR).

図９の上図に示すように、本実施例の燃料集合体１ａでは、燃料集合体１ａの水平断面において、チャンネルボックス４内に形成される１０行１０列の正方格子に、全長燃料棒３２ａ〜３２ｃ、部分長燃料棒４２、水ロッド（ＷＲ）２、及び可燃性毒物入り全長燃料棒５２が配されている。燃料集合体１ａの水平断面（横断面）の中央部には、燃料棒を４本配置可能な領域を占有する横断面積を有する水ロッド（ＷＲ）２が２本配されている。水ロッド（ＷＲ）２は、少なくとも２本の燃料棒が配置可能な領域を占有する横断面積を有する太径水ロッドである。   As shown in the upper diagram of FIG. 9, in the fuel assembly 1a of the present embodiment, in the horizontal cross section of the fuel assembly 1a, the full length fuel rods 32a are arranged in a square grid of 10 rows and 10 columns formed in the channel box 4. 32c, a partial length fuel rod 42, a water rod (WR) 2, and a full length fuel rod 52 containing burnable poison. Two water rods (WR) 2 having a cross-sectional area occupying a region where four fuel rods can be arranged are arranged at the center of the horizontal section (cross section) of the fuel assembly 1a. The water rod (WR) 2 is a large-diameter water rod having a cross-sectional area occupying a region where at least two fuel rods can be arranged.

図９の上図及び下図に示すように、全長燃料棒３２ａは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が２.８０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有する。４本の全長燃料棒３２ａが、燃料集合体１ａの水平断面内において、最外周の四隅（４つのコーナー部）の格子位置にそれぞれ配されている。   As shown in the upper and lower views of FIG. 9, the full length fuel rod 32a has four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24 have an average enrichment of 2.50 wt%. And the nodes 1 to 20 have a low-enrichment fuel containing no burnable poison with an average enrichment of 2.80 wt%. Four full-length fuel rods 32a are arranged at lattice positions of four outermost corners (four corner portions) in a horizontal cross section of the fuel assembly 1a.

全長燃料棒３２ｂは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が３.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。８本の全長燃料棒３２ｂが、燃料集合体１ａの水平断面内において、最外周の四隅（４つのコーナー部）の格子位置に配される全長燃料棒３２ａに隣接するよう最外周の格子位置に配されている。   The full-length fuel rod 32b is a low-enriched fuel that does not contain a burnable poison having an average enrichment of 2.50 wt% in four nodes at the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24. Nodes 1 to 20 have a high enrichment fuel having an average enrichment of 3.90 wt% and containing no burnable poisons. Eight full-length fuel rods 32b are positioned at the outermost circumferential grid position in the horizontal cross section of the fuel assembly 1a so as to be adjacent to the full-length fuel rods 32a arranged at the four outermost circumferential corners (four corner portions). Are arranged.

全長燃料棒３２ｃは、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。５２本の全長燃料棒３２ｃが、燃料集合体１ａの水平断面内において、最外周、最外周より１層内側、最外周より２層内側、最外周より３層内側、及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full-length fuel rod 32c has a low-enriched fuel that does not contain a burnable poison having an average enrichment of 2.50 wt% in four nodes at the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24. Nodes 1 to 20 have a high enrichment fuel having an average enrichment of 4.90 wt% and containing no burnable poisons. In the horizontal cross section of the fuel assembly 1a, 52 full-length fuel rods 32c are arranged at the outermost periphery, one layer inside the outermost periphery, two layers inside the outermost periphery, three layers inside the outermost periphery, and the water rod (WR) 2 Are arranged at lattice positions so as to be adjacent to.

部分長燃料棒４２は、ノード１〜ノード１４に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。１４本の部分長燃料棒４２が、燃料集合体１ａの水平断面内において、最外周及び水ロッド（ＷＲ）２に隣接するよう格子位置に配され、最外周の格子位置に配される部分長燃料棒４２は、８本であり、水ロッド（ＷＲ）２に隣接して配される部分長燃料棒４２は６本である。   The partial length fuel rod 42 has a high enrichment fuel containing no burnable poison with an average enrichment of 4.90 wt% at nodes 1 to 14. Fourteen partial length fuel rods 42 are arranged at lattice positions in the horizontal cross section of the fuel assembly 1a so as to be adjacent to the outermost periphery and the water rod (WR) 2, and are arranged at the outermost lattice positions. The number of the fuel rods 42 is eight, and the number of the partial length fuel rods 42 arranged adjacent to the water rod (WR) 2 is six.

可燃性毒物入り全長燃料棒５２は、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、ノード２１〜ノード２４に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の高濃縮度燃料を有する。ノード１〜ノード２０の高濃縮度燃料に含まれる可燃性毒物であるガドリニア（Ｇｄ）の濃度は９.０ｗｔ％である。１４本の可燃性毒物入り全長燃料棒５２が、燃料集合体１ａの水平断面内において、最外周より１層内側及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full length fuel rod 52 containing the burnable poison has four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the nodes 21 to 24 do not contain the burnable poison having an average enrichment of 2.50 wt%. Node 1 to node 20 have high enrichment fuel with an average enrichment of 4.90 wt%. The concentration of gadolinia (Gd), which is a burnable poison contained in the highly enriched fuel of the nodes 1 to 20, is 9.0 wt%. Fourteen full-length burnable poison-containing fuel rods 52 are arranged at a lattice position in the horizontal cross section of the fuel assembly 1a so as to be one layer inside from the outermost periphery and adjacent to the water rod (WR) 2.

本実施例では、全長燃料棒３２ａ〜全長燃料棒３２ｃ、及び可燃性毒物入り全長燃料棒５２の何れにおいても、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、燃料有効部の軸方向長さ（２４ノード）に占める可燃性毒物を含有しない領域の長さの割合が０．１６である。そして、燃料領域上端部領域（燃料有効部上端領域）の可燃性毒物を含まない低濃縮度燃料の平均濃縮度は２.５０ｗｔ％である。
また、上述の通り、全長燃料棒３２ｂ、３２ｃ、及び可燃性毒物入り全長燃料棒５２の燃料領域上端部領域（燃料有効部上端領域）を除く燃料有効部は、高濃縮度燃料であることから、燃料の経済性を向上することができる。 In this embodiment, in each of the full length fuel rods 32a to 32c and the burnable poison-containing full length fuel rod 52, the four nodes of the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the fuel effective portion The ratio of the length of the region containing no burnable poison to the axial length (24 nodes) is 0.16. The average enrichment of the low enrichment fuel containing no burnable poison in the upper end region of the fuel region (the upper end region of the fuel effective portion) is 2.50 wt%.
In addition, as described above, the active fuel portion of the full length fuel rods 32b and 32c and the upper end region of the fuel region (the upper end region of the active fuel portion) of the full length fuel rod 52 containing burnable poison is a highly enriched fuel. The fuel economy can be improved.

また、本実施例では、高濃縮度燃料のみを有する部分長燃料棒４２が、燃料集合体１ａの水平断面内において最外周の格子位置に配されている。燃料集合体１ａのチャンネルボックス４の外側及び水ロッド（ＷＲ）２の内側は非沸騰領域（ボイド率が０％）である。そのため、最外周に配される燃料棒及び水ロッド（ＷＲ）２に隣接して配される燃料棒は、最外周より内側へ配される燃料棒に比べて、ボイド反応度が高くなる（負に大きくなる）傾向を持つ。従って、チャンネルボックス４の外側の影響が最も多い最外周及び水ロッド（ＷＲ）２の隣接位置に部分長燃料棒４２を配することで、燃料集合体１ａのボイド係数改善（正側にシフトする）効果を増大することができる。   Further, in this embodiment, the partial length fuel rods 42 having only the highly enriched fuel are arranged at the outermost lattice positions in the horizontal cross section of the fuel assembly 1a. The outside of the channel box 4 of the fuel assembly 1a and the inside of the water rod (WR) 2 are non-boiling regions (void ratio is 0%). Therefore, the fuel reactivity of the fuel rods disposed adjacent to the outermost periphery and the water rods (WR) 2 is higher than that of the fuel rods disposed inside the outermost periphery (negative). Tend to be larger). Therefore, by disposing the partial length fuel rod 42 at the outermost periphery and the position adjacent to the water rod (WR) 2 where the influence outside the channel box 4 is the largest, the void coefficient of the fuel assembly 1a is improved (shifted to the positive side). ) The effect can be increased.

以上の通り、本実施例によれば、実施例１の効果に加え、更に、ボイド係数改善（正側にシフトする）効果を増大することができる。   As described above, according to this embodiment, the effect of improving the void coefficient (shifting to the positive side) can be further increased in addition to the effect of the first embodiment.

図１０は、本発明の他の実施例に係る実施例３の燃料集合体の水平断面図及び各燃料棒の濃縮度を示す図である。本実施例では、燃料領域上端部領域（燃料有効部上端領域）内において上端部に向かうほど濃縮度を低い点が実施例１と異なる。本実施例における燃料集合体の全体概略構成は、実施例１にて説明した図２に示す構成と同様であり、また、本実施例の燃料集合体は、図３に示した改良型沸騰水型原子炉（ＡＢＷＲ）の炉心に装荷される。   FIG. 10 is a horizontal sectional view of a fuel assembly according to a third embodiment of the present invention and a diagram showing enrichment of each fuel rod. This embodiment is different from the first embodiment in that the enrichment becomes lower toward the upper end in the upper end region of the fuel region (the upper end region of the fuel effective portion). The overall schematic configuration of the fuel assembly according to the present embodiment is the same as the configuration illustrated in FIG. 2 described in the first embodiment, and the fuel assembly according to the present embodiment includes the improved boiling water illustrated in FIG. To the core of an advanced reactor (ABWR).

図１０の上図に示すように、本実施例の燃料集合体１ｂでは、燃料集合体１ｂの水平断面において、チャンネルボックス４内に形成される１０行１０列の正方格子に、全長燃料棒３３ａ〜３３ｃ、部分長燃料棒４３、水ロッド（ＷＲ）２、及び可燃性毒物入り全長燃料棒５３が配されている。燃料集合体１ｂの水平断面（横断面）の中央部には、燃料棒を４本配置可能な領域を占有する横断面積を有する水ロッド（ＷＲ）２が２本配されている。水ロッド（ＷＲ）２は、少なくとも２本の燃料棒が配置可能な領域を占有する横断面積を有する太径水ロッドである。   As shown in the upper diagram of FIG. 10, in the fuel assembly 1b of the present embodiment, in the horizontal section of the fuel assembly 1b, the full length fuel rods 33a are arranged in a square grid of 10 rows and 10 columns formed in the channel box 4. 33c, a partial length fuel rod 43, a water rod (WR) 2, and a full length fuel rod 53 containing burnable poison. Two water rods (WR) 2 having a cross-sectional area occupying a region where four fuel rods can be arranged are arranged at the center of the horizontal section (cross section) of the fuel assembly 1b. The water rod (WR) 2 is a large-diameter water rod having a cross-sectional area occupying a region where at least two fuel rods can be arranged.

図１０の上図及び下図に示すように、全長燃料棒３３ａは、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２３に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有すると共に、上端部（最上部）のノード２４に平均濃縮度が２.００ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が２.８０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有する。４本の全長燃料棒３３ａが、燃料集合体１ｂの水平断面内において、最外周の四隅（４つのコーナー部）の格子位置にそれぞれ配されている。   As shown in the upper and lower diagrams of FIG. 10, the full-length fuel rod 33a has an average enrichment of 2.50 wt% at the nodes 21 to 23 among the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion). And a low-enriched fuel containing no burnable poison and having an average enrichment of 2.00 wt% in the upper end (top) node 24. Node 20 has a low enriched fuel with an average enrichment of 2.80 wt% and no burnable poisons. The four full length fuel rods 33a are arranged at the lattice positions of the outermost four corners (four corners) in the horizontal cross section of the fuel assembly 1b.

全長燃料棒３３ｂは、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２３に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有すると共に、上端部（最上部）のノード２４に平均濃縮度が２.００ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が３.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。８本の全長燃料棒３３ｂが、燃料集合体１ｂの水平断面内において、最外周の四隅（４つのコーナー部）の格子位置に配される全長燃料棒３３ａに隣接するよう最外周の格子位置に配されている。   The full-length fuel rod 33b is a low-enriched fuel that does not contain a burnable poison having an average enrichment of 2.50 wt% in the nodes 21 to 23 among the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion). And a low-enriched fuel containing no burnable poison having an average enrichment of 2.00 wt% at the upper end (uppermost) node 24, and an average enrichment of 3.90 wt% at nodes 1 to 20. It has a high enrichment fuel that does not contain any burnable poisons. Eight full-length fuel rods 33b are positioned at the outermost peripheral grid position in the horizontal cross section of the fuel assembly 1b so as to be adjacent to the full-length fuel rods 33a arranged at the four outermost peripheral corners (four corners). Are arranged.

全長燃料棒３３ｃは、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２３に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有すると共に、上端部（最上部）のノード２４に平均濃縮度が２.００ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。５２本の全長燃料棒３３ｃが、燃料集合体１ｂの水平断面内において、最外周、最外周より１層内側、最外周より２層内側、最外周より３層内側、及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full-length fuel rod 33c is a low-enriched fuel that does not contain a burnable poison having an average enrichment of 2.50 wt% in the nodes 21 to 23 among the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion). Node 24 at the upper end (top) has a low enrichment fuel containing no burnable poison having an average enrichment of 2.00 wt%, and nodes 1 to 20 have an average enrichment of 4.90 wt% It has a high enrichment fuel that does not contain any burnable poisons. In the horizontal cross section of the fuel assembly 1b, 52 full-length fuel rods 33c are arranged at the outermost periphery, one layer inside the outermost periphery, two layers inside the outermost periphery, three layers inside the outermost periphery, and the water rod (WR) 2 Are arranged at lattice positions so as to be adjacent to.

部分長燃料棒４３は、ノード１〜ノード１４に平均濃縮度が４.９０ｗｔ％の可燃性毒物を含まない高濃縮度燃料を有する。１４本の部分長燃料棒４３が、燃料集合体１ｂの水平断面内において、最外周より１層内側及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The partial length fuel rod 43 has a high enrichment fuel that does not include burnable poisons with an average enrichment of 4.90 wt% at nodes 1 to 14. Fourteen part-length fuel rods 43 are arranged in the horizontal section of the fuel assembly 1b at a lattice position one layer inside from the outermost periphery and adjacent to the water rod (WR) 2.

可燃性毒物入り全長燃料棒５３は、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２３に平均濃縮度が２.５０ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有すると共に、上端部（最上部）のノード２４に平均濃縮度が２.００ｗｔ％の可燃性毒物を含まない低濃縮度燃料を有し、ノード１〜ノード２０に平均濃縮度が４.９０ｗｔ％の高濃縮度燃料を有する。ノード１〜ノード２０の高濃縮度燃料に含まれる可燃性毒物であるガドリニア（Ｇｄ）の濃度は９.０ｗｔ％である。１４本の可燃性毒物入り全長燃料棒５３が、燃料集合体１ｂの水平断面内において、最外周より１層内側及び水ロッド（ＷＲ）２に隣接するよう格子位置に配されている。   The full-length fuel rod 53 containing the burnable poison has a low concentration in which the nodes 21 to 23 out of the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion) do not contain the burnable poison having an average enrichment of 2.50 wt%. In addition to having the enriched fuel, the uppermost (uppermost) node 24 has a low-enriched fuel having an average enrichment of 2.00 wt% and containing no burnable poison, and the nodes 1 to 20 have the average enrichment. It has 4.90 wt% high enrichment fuel. The concentration of gadolinia (Gd), which is a burnable poison contained in the highly enriched fuel of the nodes 1 to 20, is 9.0 wt%. Fourteen full-length burnable poison-containing fuel rods 53 are arranged at a lattice position in the horizontal cross section of the fuel assembly 1b so as to be one layer inside from the outermost periphery and adjacent to the water rod (WR) 2.

本実施例では、全長燃料棒３３ａ〜全長燃料棒３３ｃ、及び可燃性毒物入り全長燃料棒５３の何れにおいても、燃料領域上端部領域（燃料有効部上端領域）の４ノード、すなわち、燃料有効部の軸方向長さ（２４ノード）に占める可燃性毒物を含有しない領域の長さの割合が０．１６である。そして、燃料領域上端部領域（燃料有効部上端領域）の上端部（最上部）を除く領域に設けられ可燃性毒物を含まない低濃縮度燃料の平均濃縮度は２.５０ｗｔ％であり、燃料領域上端部領域（燃料有効部上端領域）の上端部（最上部）に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度は２.００ｗｔ％である。燃料領域上端部領域（燃料有効部上端領域）の上端部（最上部）は、炉心特性に対する寄与が他の燃料領域上端部領域（燃料有効部上端領域）に比べて小さい。よって、このように燃料領域上端部領域（燃料有効部上端領域）の上端部（最上部）に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を、他の燃料領域上端部領域（燃料有効部上端領域）に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度より低くできることから、更なる燃料の経済性向上を図ることができる。
また、上述の通り、全長燃料棒３３ｂ、３３ｃ、及び可燃性毒物入り全長燃料棒５３の燃料領域上端部領域（燃料有効部上端領域）を除く燃料有効部は、高濃縮度燃料であることから、燃料の経済性を向上することができる。 In the present embodiment, in each of the full length fuel rods 33a to 33c and the full length fuel rod 53 containing a burnable poison, four nodes of the upper end region of the fuel region (the upper end region of the fuel effective portion), that is, the fuel effective portion The ratio of the length of the region containing no burnable poison to the axial length (24 nodes) is 0.16. The average enrichment of the low-enrichment fuel, which is provided in an area other than the upper end (uppermost area) of the upper end area of the fuel area (upper area of the active fuel section) and does not contain burnable poisons, is 2.50 wt%. The average enrichment of the low enrichment fuel containing no burnable poison provided at the upper end (uppermost portion) of the upper end region (effective fuel upper end region) is 2.00 wt%. The upper end portion (uppermost portion) of the upper end portion of the fuel region (the upper end portion of the active fuel portion) has a smaller contribution to the core characteristics than the upper end portion region of the other fuel region (the upper end region of the active fuel portion). Therefore, the average enrichment of the low enrichment fuel not containing the burnable poison provided at the upper end (uppermost portion) of the upper end region of the fuel region (the upper end region of the fuel effective portion) is calculated by comparing the average enrichment of the other enrichment region of the fuel region. Since the average enrichment of the low enrichment fuel containing no burnable poison provided in the (fuel effective portion upper end region) can be made lower, the fuel economy can be further improved.
Further, as described above, the effective fuel portion of the full length fuel rods 33b and 33c and the upper end region of the fuel region of the full length fuel rod 53 containing the burnable poison (effective upper end region of the fuel effective portion) is a highly enriched fuel. The fuel economy can be improved.

なお、本実施例では、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２３に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度よりも、上端部（最上部）のノード２４に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を低くする構成としたが、これに限られるものではない。例えば、燃料領域上端部領域（燃料有効部上端領域）の４ノードのうち、ノード２１〜ノード２２に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２.５０ｗｔとし、ノード２３に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２.２５ｗｔ、ノード２４に設けられる可燃性毒物を含まない低濃縮度燃料の平均濃縮度を２.００ｗｔとする構成としても良い。すなわち、燃料領域上端部領域（燃料有効部上端領域）内において、上端部（最上部）へ向かうほど可燃性毒物を含まない低濃縮度燃料の平均濃縮度が低くなるような構成としても良い。   In the present embodiment, of the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), the average enrichment of the low enrichment fuel containing no burnable poison provided at the nodes 21 to 23 is higher than the average enrichment of the fuel. Although the average enrichment of the low enrichment fuel containing no burnable poison provided at the upper end (uppermost) node 24 is set to be low, the present invention is not limited to this. For example, among the four nodes in the upper end region of the fuel region (the upper end region of the fuel effective portion), the average enrichment of the low enrichment fuel containing no burnable poison provided at the nodes 21 to 22 is set to 2.50 wt, and the node 23 The average enrichment of the low-enrichment fuel containing no burnable poison provided at the node 24 is 2.25 wt, and the average enrichment of the low-enrichment fuel containing no burnable poison provided at the node 24 is 2.00 wt. good. That is, in the upper end region of the fuel region (the upper end region of the fuel effective portion), the average enrichment of the low enrichment fuel containing no burnable poison may be reduced toward the upper end (uppermost portion).

以上の通り、本実施例によれば、実施例１の効果に加え、燃料領域上端部領域（燃料有効部上端領域）内における可燃性毒物を含まない低濃縮度燃料の平均濃縮度を段階的に低くできることから、更なる燃料の経済性向上が可能となる。   As described above, according to the present embodiment, in addition to the effect of the first embodiment, the average enrichment of the low enrichment fuel containing no burnable poison in the upper end region of the fuel region (the upper end region of the effective fuel portion) is gradually increased. , The fuel economy can be further improved.

なお、上述の実施例１乃至実施例３では、燃料領域（燃料有効部）を軸方向に２４ノードに分割した場合を一例として説明したが、上述のように、例えば、燃料領域（燃料有効部）を軸方向に２５ノードに分割しても良い。   In the above-described first to third embodiments, the case where the fuel region (the fuel effective portion) is divided into 24 nodes in the axial direction has been described as an example. ) May be divided into 25 nodes in the axial direction.

なお、本発明は上記した実施例に限定されるものではなく、様々な変形例が含まれる。例えば、上記した実施例は本発明を分かりやすく説明するために詳細に説明したものであり、必ずしも説明した全ての構成を備えるものに限定されるものではない。   Note that the present invention is not limited to the above-described embodiment, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described above.

１，１ａ，１ｂ・・・燃料集合体
２・・・ウォーターロッド
３・・・燃料棒
４・・・チャンネルボックス
５・・・上部タイプレート
６・・・ハンドル
７・・・下部タイプレート
８・・・エントランスノズル
９・・・燃料スペーサ
１０・・・改良型沸騰水型原子炉
１１・・・原子炉圧力容器
１２・・・炉心
１３・・・炉心支持板
１４・・・上部格子板
１５・・・燃料支持金具
１６・・・炉心シュラウド
１７・・・ダウンカマ
１８・・・気水分離器
１９・・・蒸気乾燥器
２０・・・シュラウドヘッド
２１・・・インターナルポンプ
２２・・・制御棒案内管
２３・・・制御棒駆動機構
２４・・・下鏡
２５・・・主蒸気配管
２６・・・給水配管
３１ａ〜３１ｃ，３２ａ〜３２ｃ，３３ａ〜３３ｃ・・・全長燃料棒
４１，４２，４３・・・部分長燃料棒
５１，５２，５３・・・可燃性毒物入り全長燃料棒 1, 1a, 1b Fuel assembly 2 Water rod 3 Fuel rod 4 Channel box 5 Upper tie plate 6 Handle 7 Lower tie plate 8 Entrance nozzle 9 Fuel spacer 10 Improved boiling water reactor 11 Reactor pressure vessel 12 Core 13 Core support plate 14 Upper grid plate 15 ..Fuel support bracket 16 Core shroud 17 Downcomer 18 Steam separator 19 Steam dryer 20 Shroud head 21 Internal pump 22 Control rod Guide pipe 23: control rod drive mechanism 24: lower mirror 25: main steam pipe 26: water supply pipes 31a to 31c, 32a to 32c, 33a to 33c: full length fuel rods 41, 42, 43 ・ ・ ・ Part length fuel rod 1,52,53 ... burnable poison containing the full-length fuel rods

Claims (9)

核燃料物質及び可燃性毒物を含有する第１燃料棒と前記核燃料物質を含有して前記可燃性毒物を含有しない第２燃料棒をチャンネルボックス内に束ねて収容する燃料集合体であって、
前記第１燃料棒及び前記第２燃料棒は、それぞれの燃料有効部の上端部に、前記核燃料物質を含有して前記可燃性毒物を含有しない燃料有効部上端領域を形成しており、
前記第１燃料棒及び前記第２燃料棒のそれぞれにおいて、前記燃料有効部上端領域が前記燃料有効部の上端から下方に向かって形成され、
前記燃料有効部の軸方向長さに対する前記燃料有効部上端領域の軸方向長さの割合が０．１６以上０．２１以下の範囲にあり、
前記第１燃料棒及び前記第２燃料棒のそれぞれの前記燃料有効部上端領域の下端から上端に亘って存在する前記核燃料物質は濃縮された核燃料物質であり、前記それぞれの燃料有効部上端領域の平均濃縮度が２．０ｗｔ％以上２．５ｗｔ％以下の範囲にあることを特徴とする燃料集合体。 A fuel assembly containing a first fuel rod containing a nuclear fuel substance and a burnable poison and a second fuel rod containing the nuclear fuel substance and not containing the burnable poison in a channel box in a bundle.
Wherein the first fuel rods and the second fuel rods, the upper end portion of each of the fuel effective portion, forms a fuel effective portion upper end region not containing the burnable poison contains the nuclear fuel material,
In each of the first fuel rod and the second fuel rod, the fuel effective portion upper end region is formed downward from an upper end of the fuel effective portion,
The ratio of the axial length of the fuel active portion upper end region to the axial length of the fuel active portion is in the range of 0.16 or more and 0.21 or less,
The nuclear fuel material present from the lower end to the upper end of the fuel effective portion upper end region of each of the first fuel rod and the second fuel rod is a concentrated nuclear fuel material, and average enrichment fuel assemblies, characterized in range near Rukoto below 2.0 wt% or more 2.5 wt%. 前記第１燃料棒の前記燃料有効部上端領域の軸方向の長さは、前記第２燃料棒の前記燃料有効部上端領域の軸方向の長さに等しい請求項１に記載の燃料集合体。 Before Symbol of the axial length of the fuel effective portion upper end region of the first fuel rods, the fuel assembly according to claim 1 is equal to the axial length of the fuel effective portion upper end region of the second fuel rods . 前記燃料有効部の軸方向全長を２４ノードに分割としたとき、前記第１燃料棒の前記燃料有効部上端領域及び前記第２燃料棒の前記燃料有効部上端領域のそれぞれの軸方向長さは、４ノード以上５ノード以下である請求項２に記載の燃料集合体。 When the divided axial length of the fuel effective portion 24 nodes, each of the axial length of the fuel effective portion upper end region of the fuel effective portion upper end region and the second fuel rods of the first fuel rod 3. The fuel assembly according to claim 2, wherein the number of nodes is 4 or more and 5 or less. ウォーターロッドを備え、
前記第２燃料棒の一部は、前記燃料有効部の軸方向長さが短い部分長燃料棒であり、
前記部分長燃料棒は、前記燃料集合体の水平断面内において最外周及び／又はウォーターロッドに隣接して配される請求項３に記載の燃料集合体。 Equipped with a window Otaroddo,
A part of the second fuel rod is a partial length fuel rod in which the axial length of the fuel effective portion is short,
4. The fuel assembly according to claim 3, wherein the partial length fuel rod is disposed adjacent to an outermost circumference and / or a water rod in a horizontal cross section of the fuel assembly . 5. 前記第１燃料棒の前記燃料有効部上端領域及び前記第２燃料棒の前記燃料有効部上端領域を除いた、前記第１燃料棒及び前記第２燃料棒の前記燃料有効部には、高濃縮度燃料が存在する請求項３または４に記載の燃料集合体。 The fuel effective portion upper area and the fuel effective portion upper end region of the second fuel rods before Symbol first fuel rods were divided, the fuel effective portion of the first fuel rods and the second fuel rods, high the fuel assembly according to claim 3 or 4 that exists is enrichment fuel. 前記高濃縮度燃料の平均濃縮度が、３.９０ｗｔ％及び４.９０ｗｔ％のいずれかである請求項５に記載の燃料集合体。 Before SL average enrichment of high enrichment fuel, 3. 9 0 wt% and fuel assembly according to claim 5 is any one of 4.90wt%. 前記第１燃料棒の前記燃料有効部上端領域及び前記第２燃料棒の前記燃料有効部上端領域は、前記燃料有効部の上端に向かうほど平均濃縮度が低い請求項３に記載の燃料集合体。 Fuel assembly according to prior Symbol the fuel effective portion upper end region of the fuel effective portion upper end region and the second fuel rods of the first fuel rods, the average enrichment is lower claim 3 increases toward the upper end of the fuel effective portion body. 前記第１燃料棒の前記燃料有効部上端領域及び前記第２燃料棒の前記燃料有効部上端領域のそれぞれの平均濃縮度は、前記第１燃料棒の前記燃料有効部上端領域及び前記第２燃料棒の前記燃料有効部上端領域を除いた、前記第１燃料棒及び前記第２燃料棒のそれぞれの前記燃料有効部の平均濃縮度よりも低い請求項３または４に記載の燃料集合体。The average enrichment of each of the fuel effective portion upper end region of the first fuel rod and the fuel effective portion upper end region of the second fuel rod is equal to the fuel effective portion upper end region of the first fuel rod and the second fuel rod. 5. The fuel assembly according to claim 3, wherein the average enrichment of each of the first fuel rods and the second fuel rods is lower than an average enrichment of the first fuel rods and the second fuel rods, excluding an upper end region of the rods. 複数体の燃料集合体が装荷される原子炉の炉心であって、
前記燃料集合体は、請求項１ないし８のいずれか１項に記載の燃料集合体であることを特徴とする原子炉の炉心。 A reactor core loaded with a plurality of fuel assemblies,
The reactor core according to claim 1, wherein the fuel assembly is the fuel assembly according to claim 1 .
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