JP5085522B2 - Reactor core for long-term continuous operation - Google Patents
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Description
本発明は、高燃焼度で長期間連続運転する原子炉の炉心に関する。 The present invention relates to a reactor core that operates continuously at a high burnup for a long period of time.
特に、炉心の熱的余裕の確保をすると共に、炉内に滞在の全燃料集合体の燃焼度が制限値を超えるない原子炉の炉心に関する。 In particular, the present invention relates to a reactor core that ensures the thermal margin of the core and that the burnup of all fuel assemblies staying in the reactor does not exceed a limit value.
沸騰水型原子炉（ＢＷＲ）の燃料集合体および燃料棒の設計は、一般的に該原子炉の目標とする運転期間の長さによって決められる。 The design of a boiling water reactor (BWR) fuel assembly and fuel rod is generally determined by the length of the reactor's target operating period.
原子炉の運転期間の長さにより、燃料の核***性物質濃度（以下「濃縮度」と略称する）および可燃性毒物の濃度が適切に決められ、燃料集合体および燃料棒が設計される。 The fuel fissile material concentration (hereinafter abbreviated as “enrichment”) and the flammable poison concentration are appropriately determined according to the length of the operation period of the reactor, and the fuel assembly and the fuel rod are designed.
最近では、原子炉の運転期間は長期サイクル化が求められる傾向にあり、かつ、高出力化が求められる傾向にある。 Recently, there is a tendency that a long-term cycle is required for the operation period of the nuclear reactor, and a higher output is required.
原子炉が長期サイクルで運転を行った場合にも、燃料の経済性を損なわないように、燃料の濃縮度は高められる傾向にある。 Even when the nuclear reactor is operated in a long-term cycle, the fuel enrichment tends to be increased so as not to impair the fuel economy.
一方、燃料の高燃焼度も求められている。 On the other hand, high burnup of fuel is also required.
従来から燃料の濃縮度は順次高くなってきているが、濃縮度の高い燃料を使用する方が経済的にも有利であることから、従来は、移行期間を除き炉心内は１種類の濃縮度の燃料が装荷されていた。なお、先行技術文献として、特許第２５１０６１２号が知られている。 Conventionally, the enrichment of fuel has been increasing gradually. However, since it is economically advantageous to use fuel with a high enrichment, conventionally there is only one enrichment in the core except for the transition period. The fuel was loaded. Note that Japanese Patent No. 2510612 is known as a prior art document.
一般に、燃料の濃縮度を高くすると、出力が大きくなる一方、燃焼が速くなる。 In general, when the fuel concentration is increased, the output is increased while the combustion is accelerated.
原子炉の運転では、燃料棒の健全性を確保する観点から、燃料の熱的特性の制限値、たとえば燃料の最大線出力密度、限界出力などからの余裕（熱的余裕）を十分に確保することが必要である。 In the operation of nuclear reactors, from the viewpoint of ensuring the integrity of the fuel rods, sufficient limits (thermal margin) from the limit values of the thermal characteristics of the fuel, for example, the maximum linear power density of the fuel, the limit power, etc. are secured. It is necessary.
経験的にある値以下の線出力密度であれば燃料棒が破損しない閾値があり、原子炉の運転はこの限界出力を超えないようにしなければならない。前記限界出力は、燃料棒温度が上昇するいわゆる沸騰遷移現象によって把握することができる。 Empirically, there is a threshold at which the fuel rod will not break if the linear power density is below a certain value, and the operation of the reactor must not exceed this limit power. The limit output can be grasped by a so-called boiling transition phenomenon in which the fuel rod temperature rises.
運転中はこの限界出力に対する熱的余裕を十分に確保する必要があるため、原子炉の燃料の濃縮度の上限が定められている。 Since it is necessary to secure a sufficient thermal margin for this limit power during operation, an upper limit of the fuel enrichment of the nuclear reactor is set.
原子炉の運転期間が２４ヶ月程度の長期サイクル運転に長期化され、かつ、高い出力が要求されると、燃料の濃縮度を高めたとしても、燃料の濃縮度の上限が定められているため、燃料のバッチサイズは２サイクルと３サイクルの間になってしまうケースが多くなる。 If the operation period of the reactor is extended to a long-term cycle operation of about 24 months and a high output is required, even if the enrichment of the fuel is increased, the upper limit of the enrichment of the fuel is set. In many cases, the fuel batch size is between 2 and 3 cycles.
なお、燃料のバッチサイズとは、燃料の使用可能期間を原子炉の運転期間で割った値である。 The fuel batch size is a value obtained by dividing the fuel usable period by the reactor operation period.
この場合、燃料は炉心滞在の第三サイクルを全期間燃焼することができないため、ほとんどの燃料は炉心滞在第二サイクル後に取り出されてしまう。なお、炉心滞在第一サイクルとは、燃料が最初に使用される原子炉の運転期間である。以下、炉心滞在第二サイクル、炉心滞在第三サイクルとは、順次燃料が二回目、三回目に使用される原子炉の運転期間である。炉心滞在最終サイクルとは、燃料が使用される最後の原子炉の運転期間である。 In this case, since the fuel cannot be burned for the entire period of the third cycle of staying in the core, most of the fuel is taken out after the second cycle of staying in the core. The first cycle of staying in the core is the operating period of the reactor in which fuel is first used. Hereinafter, the core stay second cycle and the core stay third cycle are the operation periods of the reactor in which the fuel is used for the second time and the third time in sequence. The last cycle of staying in the core is the operation period of the last reactor in which fuel is used.
燃料の濃縮度を高め、燃料のバッチサイズが２サイクルと３サイクルの間になってしまってほとんどの燃料が炉心滞在第二サイクル後に取り出されてしまうような場合、炉内に滞在する燃料は炉心滞在第一サイクルの燃料、および、まだ出力が高い炉心滞在第二サイクルの燃料になってしまい、出力が高く、燃料の熱的特性の制限値に対して厳しい部分が炉心の中心部に発生する可能性がある。 If the fuel enrichment is increased and the fuel batch size is between 2 and 3 cycles and most of the fuel is taken out after the second cycle, the fuel staying in the reactor is the core. It becomes the fuel for the first cycle of stay and the fuel for the second cycle of stay in the core where the output is still high, and the output is high and a severe part occurs in the center of the core against the limit value of the thermal characteristics of the fuel. there is a possibility.
これを抑えるため、少量の燃料を炉心滞在第三サイクルまで使用するようにし、これらの炉心滞在第三サイクルの燃料を炉心の中心部に装荷すると、これらの炉心滞在第三サイクルの燃料は燃焼度が制限値を超えてしまう可能性がある。 In order to suppress this, if a small amount of fuel is used until the third cycle in which the core stays, and the fuel in the third cycle in which the core stays is loaded in the center of the core, the fuel in the third cycle in which the core stays is burned. May exceed the limit.
なお、燃焼度は、核燃料の消費の度合いを示す数値であり、単位重量あたりの熱出力（ＭＷｄ／ｔ）で表され、上限が定められている。バッチサイズが２サイクルと３サイクルの間の燃料を炉心中心部において炉心滞在第三サイクルまで使用すると、燃料の消費の度合いすなわち燃焼度が制限値を超えることが生じる。 The burnup is a numerical value indicating the degree of consumption of nuclear fuel, and is represented by a heat output (MWd / t) per unit weight, and has an upper limit. When fuel with a batch size between 2 and 3 cycles is used up to the third cycle of staying in the core in the core, the degree of fuel consumption, that is, the burnup, may exceed the limit value.
このように、従来の原子炉炉心によれば、単一の核***性物質濃縮度の燃料を使用し、長期間連続運転される場合、炉心滞在第一サイクルおよび炉心滞在第二サイクルの燃料のみを使用するため、炉心中心部で熱的余裕が少なくなり、これを解消しようとして炉心滞在第三サイクルの燃料を炉心中心部に装荷すると、燃焼度の制限値を超える可能性があった。 As described above, according to the conventional nuclear reactor core, when a single fissile material enrichment fuel is used and it is operated continuously for a long period of time, only the fuel for the first cycle staying in the core and the second cycle staying in the core is used. Therefore, there is a possibility that the limit value of the burnup may be exceeded when the fuel of the third cycle staying in the core is loaded to the core center in order to solve this problem.
そこで、本発明の目的は、上記従来技術の課題を解決し、高燃焼度、長期連続運転の原子炉の炉心において、炉心の熱的余裕の確保をすると共に、炉内滞在中の全燃料集合体の燃焼度が制限値を超えることのない原子炉の炉心を提供することにある。 Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, ensure the thermal margin of the core in the core of a high burnup, long-term continuous operation reactor, and collect all fuel assemblies during the stay in the reactor The object is to provide a nuclear reactor core in which the burnup of the body does not exceed the limit value.
本発明による炉心は、
平均核***性物質濃度の異なる２種類の燃料集合体を有し、
平均核***性物質濃度が高い高濃縮度燃料集合体の平均炉心滞在サイクル数より大きい平均炉心滞在サイクル数を有する平均核***性物質濃度が低い低濃縮度燃料集合体を有し、
炉心の最外周部に装荷された、炉心滞在最終サイクル前の低濃縮度燃料集合体と、
前記炉心最外周部の内側に装荷された、炉心滞在最終サイクル前の高濃縮度燃料集合体および炉心滞在最終サイクルの低濃縮度燃料集合体と、
を備えることを特徴とする。
The core according to the present invention comprises:
It has two types of fuel assemblies with different average fissile material concentrations,
A low enriched fuel assembly having a low average fissile material concentration having an average core stay cycle number greater than an average core stay cycle number of a high enrichment fuel assembly having a high average fission material concentration;
A low enrichment fuel assembly loaded on the outermost periphery of the core before the last cycle of staying in the core;
A high enrichment fuel assembly before the last cycle of staying in the core and a low enrichment fuel assembly of the last cycle of staying in the core loaded inside the outermost periphery of the core;
It is characterized by providing .
また、本発明による他の炉心は、
平均核***性物質濃度の異なる２種類の燃料集合体を有し、
平均核***性物質濃度が高い高濃縮度燃料集合体の平均炉心滞在サイクル数より大きい平均炉心滞在サイクル数を有する平均核***性物質濃度が低い低濃縮度燃料集合体を有し、
炉心の最外周部に装荷された、炉心滞在最終サイクルの平均核***性物質濃度が高い高濃縮度燃料集合体および炉心滞在最終サイクルの平均核***性物質濃度が低い低濃縮度燃料集合体と、
前記炉心最外周部の内側に装荷された、炉心滞在最終サイクル前の高濃縮度燃料集合体および炉心滞在第一サイクルの低濃縮度燃料集合体と、
を備えることを特徴とする。
Further, another core according to the present invention is
It has two types of fuel assemblies with different average fissile material concentrations,
A low enriched fuel assembly having a low average fissile material concentration having an average core stay cycle number greater than an average core stay cycle number of a high enrichment fuel assembly having a high average fission material concentration;
A high enrichment fuel assembly having a high average fissile material concentration in the last cycle of staying in the core and a low enrichment fuel assembly having a low average fissile material concentration in the last cycle of staying in the core, loaded on the outermost periphery of the core;
A high enrichment fuel assembly before the last cycle of staying in the core and a low enrichment fuel assembly of the first cycle staying in the core, loaded inside the outermost periphery of the core;
It is characterized by providing .
前記高濃縮度燃料集合体と前記低濃縮度燃料集合体の間の平均核***性物質濃度を有する１種類以上の中間濃度燃料集合体を有し、前記中間濃度燃料集合体は、炉心滞在サイクルが低いときは炉心中心部に装荷され、炉心滞在サイクルが高くなるにつれて炉心外周部に装荷されるようにすることができる。 One or more intermediate concentration fuel assemblies having an average fissile material concentration between the high enrichment fuel assembly and the low enrichment fuel assembly, the intermediate concentration fuel assembly having a core stay cycle When the temperature is low, the core is loaded at the center of the core, and as the core stay cycle becomes high, the core can be loaded at the outer periphery of the core.
前記炉心中心部に装荷される炉心滞在最終サイクルの低濃縮度燃料集合体は、コントロールセルに装荷されているようにすることができる。 The low enrichment fuel assembly in the final core stay cycle loaded in the core center may be loaded in the control cell.
前記高濃縮度燃料集合体と前記低濃縮度燃料集合体の核***性物質濃度差は、０．２ｗｔ％以上あるようにすることができる。 The difference in fissile material concentration between the high enrichment fuel assembly and the low enrichment fuel assembly may be 0.2 wt% or more.
燃料集合体のチャンネルボックスの内面と対向する外周部に配置された燃料棒の核***性物質濃度の、その燃料集合体の集合体平均核***性物質濃度に対する比を、燃料集合体の核***性物質濃度差比とすると、
前記低濃縮度燃料集合体の核***性物質濃度差比は、前記高濃縮度燃料集合体の核***性物質濃度差比より大きいようにすることができる。
Of fissile material concentration of the fuel rods disposed in the outer peripheral portion of the inner surface facing the channel box of a fuel assembly, fissile material concentration of the ratio aggregate average fissile material concentration of the fuel assembly, the fuel assembly As a difference ratio,
The fissionable material concentration difference ratio of the low enrichment fuel assembly may be greater than the fissionable material concentration difference ratio of the high enrichment fuel assembly.
前記低濃縮度燃料集合体の制御棒側に最も近い（１，１）、（１，２）、（２，１）位置の燃料棒の核***性物質濃度が、前記高濃縮度燃料集合体の同一位置の燃料棒の核***性物質濃度より低いようにすることができる。 The fissile material concentration of the fuel rods at positions (1, 1), (1, 2), (2, 1) closest to the control rod side of the low enrichment fuel assembly is It can be made lower than the fissile material concentration of the fuel rod in the same position.
核***性物質はウランおよびプルトニウム、トリウムを含むようにすることができる。 The fissile material can include uranium, plutonium and thorium.
本発明の炉心によれば、炉心滞在最終サイクル前の低濃縮度燃料集合体（Ｌ１，Ｌ２）を炉心最外周部に装荷し、炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）を炉心中心部に装荷するようにしている。 According to the core of the present invention, the low enrichment fuel assemblies (L1, L2) before the final cycle of staying in the core are loaded on the outermost periphery of the core, and the low enrichment fuel assemblies (L3) of the final cycle of staying in the core are loaded into the core. It is loaded in the center.
一般に、燃料の濃縮度を高くすると、出力が大きくなる一方、燃焼が速くなる。反対に、燃料の濃縮度を低くすると、出力が小さくなる一方、燃焼が遅くなり燃焼度の進行が遅くなる。 In general, when the fuel concentration is increased, the output is increased while the combustion is accelerated. On the other hand, when the fuel enrichment is lowered, the output is reduced, while the combustion is slowed down and the progress of the burnup is slowed down.
本発明においては、低濃縮度燃料集合体の炉心滞在最終サイクルを炉心中心部に装荷するため、炉心中心部の出力の過度の上昇を抑え、これによって炉心中心部の熱的余裕を大きくし、かつ、低濃縮度燃料集合体の燃焼度の進行が遅いため、炉心滞在最終サイクルまで炉心に滞在させても、燃焼度が制限値５５ＧＷｄ／ｔを超えることがない。 In the present invention, in order to load the core staying final cycle of the low enrichment fuel assembly to the core center, an excessive increase in the power of the core center is suppressed, thereby increasing the thermal margin of the core center, Moreover, since the progress of the burnup of the low enrichment fuel assembly is slow, the burnup does not exceed the limit value of 55 GWd / t even if the fuel stays in the core until the final cycle of staying in the core.
すなわち、本発明によれば、高濃度燃料集合体と低濃度燃料集合体とを用いることにより、炉心の熱的余裕を十分確保することができるとともに、燃料の燃焼度が制限値５５ＧＷｄ／ｔを超えることを防止することができるのである。 That is, according to the present invention, by using the high-concentration fuel assembly and the low-concentration fuel assembly, a sufficient thermal margin of the core can be secured, and the burnup of the fuel has a limit value of 55 GWd / t. It can be prevented from exceeding.
次に、本発明を実施するための最良の形態について以下に説明する。 Next, the best mode for carrying out the present invention will be described below.
図１に、本発明の第1の実施形態による原子炉の炉心の構成を示す。 FIG. 1 shows the configuration of the reactor core according to the first embodiment of the present invention.
図１は、本実施形態による沸騰水型原子力発電所（ＢＷＲ）のＢＷＲ／５型取替炉心を1／４サイズで示している。 FIG. 1 shows a BWR / 5 type replacement core of a boiling water nuclear power plant (BWR) according to this embodiment in a quarter size.
本実施形態では、運転サイクル長さとして２４ヶ月（１サイクル）を想定している。本実施形態の取替燃料集合体の多数は、燃料集合体の集合体平均核***性物質濃度が3.9重量％程度に設計されている。一方、相対的に少数の燃料集合体は、燃料集合体の集合体平均核***性物質濃度が3.9重量％よりも0.2重量％以上低く設計している。 In this embodiment, it is assumed that the operation cycle length is 24 months (one cycle). Many of the replacement fuel assemblies of the present embodiment are designed such that the fuel assembly average fissile material concentration is about 3.9% by weight. On the other hand, a relatively small number of fuel assemblies are designed such that the fuel assembly average fissile material concentration is 0.2 wt% or less lower than 3.9 wt%.
ここでは、前者の平均核***性物質濃度が高い燃料集合体を「高濃縮度燃料集合体」と呼び、後者の平均核***性物質濃度が低い燃料集合体を「低濃縮度燃料集合体」と呼ぶ。 Here, the former fuel assembly having a high average fissile material concentration is referred to as a “high enrichment fuel assembly”, and the latter fuel assembly having a low average fissile material concentration is referred to as a “low enrichment fuel assembly”. .
この高濃縮度燃料集合体を使用したとき、ＢＷＲ／５炉心（総燃料体数７６４体）の場合、取替燃料体数は３００体強となり、燃料の平均炉心滞在サイクル数は約２．５サイクルとなる。ほとんどの高濃縮度燃料集合体は２サイクル炉心に滞在した後に取り出される（図１の右側の表参照）。 When this highly enriched fuel assembly is used, in the case of a BWR / 5 core (total number of fuel bodies: 764), the number of replacement fuel bodies is over 300, and the average number of fuel core stay cycles is about 2.5. It becomes a cycle. Most highly enriched fuel assemblies are removed after staying in the two-cycle core (see the table on the right side of FIG. 1).
なお、「平均炉心滞在サイクル数」とは、燃料集合体の炉心滞在サイクル数の総和を燃料集合体の総数で割ったものである。 The “average core stay cycle number” is obtained by dividing the total number of core stay cycles of the fuel assembly by the total number of fuel assemblies.
これに対して、低濃縮度燃料集合体の多数は３サイクルまで炉心に滞在した後に取り出される（同じく図１の右側の表参照）。すなわち、低濃縮度燃料集合体の平均炉心滞在サイクル数は高濃縮度燃料集合体のそれより大きくなっている。 In contrast, many of the low enrichment fuel assemblies are removed after staying in the core for up to three cycles (also see the table on the right side of FIG. 1). That is, the average core stay cycle number of the low enrichment fuel assembly is larger than that of the high enrichment fuel assembly.
炉内に装荷される燃料集合体（高濃縮度燃料集合体と低濃縮度燃料集合体の双方の燃料集合体）の燃料には、核***性物質であるウラン２３５と共に可燃性毒物であるガドリニアが含まれており、このガドリニアによって中性子が吸収され、中性子の増倍率を制御している。 The fuel assemblies loaded in the furnace (both high and low enrichment fuel assemblies) include uranium 235, a fissile material, and gadolinia, a combustible poison. This gadolinia absorbs neutrons and controls the multiplication factor of neutrons.
核***性物質にはウランの他、プルトニウム、トリウムが含まれる。 Fissile materials include plutonium and thorium in addition to uranium.
図１に示すように、本実施形態による炉心は、炉心の最外周部に、炉心滞在最終サイクルの低濃縮度燃料集合体が混在して装荷されている。 As shown in FIG. 1, the core according to the present embodiment is loaded with a low enrichment fuel assembly in the final cycle of staying in the core at the outermost periphery of the core.
すなわち、図１に示すように、炉心の最外周部には、特に炉心最外周には、炉心滞在第三サイクルの低濃縮度燃料集合体（Ｌ３）が、混在比率が高い状態で装荷されている。炉心の最外周部には、この他に、炉心滞在第三サイクルの高濃縮度燃料集合体（３）と、炉心滞在第一サイクルの低濃縮度燃料集合体（Ｌ１）と、炉心滞在第二サイクルの低濃縮度燃料集合体（Ｌ２）が装荷されている。炉心滞在第三サイクルの高濃縮度燃料集合体（３）と、炉心滞在第一サイクルの低濃縮度燃料集合体（Ｌ１）と、炉心滞在第二サイクルの低濃縮度燃料集合体（Ｌ２）の装荷数は、原子炉の要求により適宜調整することができる。 That is, as shown in FIG. 1, the low-concentration fuel assembly (L3) of the third cycle of staying in the core is loaded in a state where the mixing ratio is high, particularly on the outermost periphery of the core. Yes. In addition to the outermost peripheral portion of the core, a high enrichment fuel assembly (3) for the third cycle staying in the core, a low enrichment fuel assembly (L1) for the first cycle staying in the core, and a second staying core The cycle low enrichment fuel assembly (L2) is loaded. A high enrichment fuel assembly (3) for the third cycle staying in the core, a low enrichment fuel assembly (L1) for the first cycle staying in the core, and a low enrichment fuel assembly (L2) for the second cycle staying in the core The number of loads can be appropriately adjusted according to the requirements of the reactor.
なお、「炉心の最外周部」は、炉心の最外周とその内側の数列の燃料集合体をいい、炉心の最外周からどの程度内側までを炉心の最外周部というかは、原子炉の要求により適宜決定される。 The “outermost part of the core” refers to the fuel assembly in the outermost part of the core and several rows inside it, and how far the innermost part from the outermost part of the core to the innermost part is the outermost part of the core. As appropriate.
炉心滞在第三サイクルの低濃縮度燃料集合体（Ｌ３）は、後述する炉心中心部とこの炉心最外周部にのみ装荷される。この意味で、炉心滞在第三サイクルの低濃縮度燃料集合体（Ｌ３）の炉心における混在比率は、炉心中心部と炉心最外周部において高い。 The low enrichment fuel assembly (L3) in the third cycle of staying in the core is loaded only in the core center described later and the outermost periphery of the core. In this sense, the mixing ratio in the core of the low enrichment fuel assembly (L3) in the third core stay third cycle is high in the core center and the outermost periphery of the core.
前記炉心最外周部の内側の炉心外周部について見れば、この炉心外周部には、炉心滞在サイクル数の異なる高濃縮度燃料集合体が混在して装荷されている。 Looking at the core outer peripheral portion inside the outermost peripheral portion of the core, high-concentration fuel assemblies having different numbers of core stay cycles are mixedly loaded in the core outer peripheral portion.
すなわち、図１の例では、炉心外周部には、ガドリニアが含まれる炉心滞在第一サイクルの高濃縮度燃料集合体（１）と、既にガドリニアが燃え尽きて燃焼しやすい状態になっている炉心滞在第二サイクルの高濃縮度燃料集合体（２）が、交互にチェッカーボード状に配置され、炉内の出力のバランスを保っている。 That is, in the example of FIG. 1, the core enrichment fuel assembly (1) of the first stay in the core containing gadolinia and the core stay in the state where the gadolinia has already burned out and is easily combusted. The highly enriched fuel assemblies (2) of the second cycle are alternately arranged in a checkerboard shape to maintain the balance of power in the furnace.
最後に、前記炉心外周部の内側の炉心中心部について見れば、炉心中心部には、炉心滞在最終サイクル前の高濃縮度燃料集合体（１，２）と炉心滞在最終サイクル前の低濃縮度燃料集合体（Ｌ２）と炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）が混在して装荷されている。 Finally, in the core center inside the outer periphery of the core, the high concentration fuel assembly (1, 2) before the final cycle of staying in the core and the low enrichment before the final cycle of staying in the core The fuel assembly (L2) and the low enrichment fuel assembly (L3) in the final stay in the core are mixed and loaded.
本発明の第一実施形態は、図１に示された具体的な燃料集合体の配置に限られず、要するに炉心滞在最終サイクル前の低濃縮度燃料集合体（Ｌ１，Ｌ２）を炉心最外周部に装荷し、炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）を炉心中心部に装荷するようにすればよい。炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）は、必要に応じて炉心最外周部にも装荷してよい。 The first embodiment of the present invention is not limited to the specific arrangement of the fuel assemblies shown in FIG. 1. In short, the low enrichment fuel assemblies (L1, L2) before the final cycle of staying in the core are disposed at the outermost peripheral portion of the core. And the low enrichment fuel assembly (L3) in the final cycle of staying in the core may be loaded in the center of the core. The low enrichment fuel assembly (L3) in the final cycle of staying in the core may be loaded on the outermost peripheral portion of the core as necessary.
つまり、低濃縮度燃料集合体は、平均核***性物質濃度が低い分燃焼度の上昇が遅くなるため、最初は炉心最外周部に装荷することにより、炉心中心部や炉心外周部では高濃縮度燃料集合体によって高出力を実現し、一方、炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）を炉心中心部に装荷することにより、炉心中心部での高濃縮度燃料集合体による過度の出力上昇を抑えて熱的余裕を確保するとともに、該低濃縮度燃料集合体（Ｌ３）は燃焼が遅いため、燃焼度を制限値以内に抑えられるのである。 In other words, low enrichment fuel assemblies slow down the increase in burnup as the average fissile material concentration is low, so by loading them at the outermost periphery of the core at first, high enrichment at the core center and core periphery High power is achieved by the fuel assembly, while the low enrichment fuel assembly (L3) in the final cycle of staying in the core is loaded into the core center, so that excessive enrichment by the high enrichment fuel assembly at the core center While suppressing an increase in output to secure a thermal margin, the low enrichment fuel assembly (L3) burns slowly, so that the burnup can be suppressed within a limit value.
なお、図１において、太線で囲われた部分は制御棒が主に挿入される位置で、コントロールセルと呼ばれる。 In FIG. 1, a portion surrounded by a thick line is a position where a control rod is mainly inserted, and is called a control cell.
コントロールセルは制御棒が挿入されるため、他の位置の燃料に比べ比較的燃焼は進みにくい。このため、コントロールセルに炉心滞在最終サイクルの低濃縮度燃料集合体（Ｌ３）を装荷することにより、燃焼度を制限値以内に抑えることを、確実に実現することができる。 Since the control rod is inserted into the control cell, combustion is relatively difficult to proceed as compared with the fuel at other positions. For this reason, it is possible to surely realize the suppression of the burnup within the limit value by loading the control cell with the low enrichment fuel assembly (L3) in the final core stay cycle.
なお、低濃縮度燃料集合体は燃焼度の上昇が遅くても、炉心滞在最終サイクルである第三サイクル目まで炉内に滞在し、かつ、第三サイクル目において炉心中心部に装荷されるため、最初から低濃縮度燃料集合体を炉心中心部に装荷すると、燃焼度が制限値を超えることがある。このため、低濃縮度燃料集合体の多くは炉心滞在第一サイクルと炉心滞在第二サイクルは燃焼が進みにくい炉心最外周部に装荷する。 In addition, even if the increase in burnup is slow, the low enrichment fuel assembly stays in the reactor until the third cycle, which is the last cycle of staying in the core, and is loaded in the core center in the third cycle When the low enrichment fuel assembly is loaded from the beginning to the core center, the burnup may exceed the limit value. For this reason, most of the low enrichment fuel assemblies are loaded on the outermost peripheral portion of the core where combustion does not proceed easily in the first cycle of staying in the core and the second cycle of staying in the core.
上記構造によれば、各燃料集合体のうち、もっとも燃焼度が進む炉心滞在第三サイクルの低濃縮度燃料集合体の燃焼度において、燃焼度の制限値である５５ＧＷｄ／ｔを超えることがない。 According to the above structure, among the fuel assemblies, the burnup of the low enrichment fuel assembly of the third staying core cycle in which the burnup is most advanced does not exceed 55 GWd / t which is the limit value of the burnup. .
図２は本実施形態の炉心に用いる燃料集合体の構造図である。 FIG. 2 is a structural diagram of a fuel assembly used in the core of the present embodiment.
本燃料集合体は９×９の正方格子状に配列された核***性物質であるウラン２３５を含む多数の燃料棒から構成され、その一部は標準燃料棒より燃料有効長の短い短尺燃料棒または部分長燃料棒と呼ばれる燃料棒である。また一部の燃料棒には可燃性毒物であるガドリニアが含まれている。燃料中心部には水ロッドが２本配置され、燃料中心部の減速材面積を大きくしている。 This fuel assembly is made up of a number of fuel rods containing uranium 235, a fissile material arranged in a 9 × 9 square lattice, some of which are short fuel rods having a shorter effective fuel length than standard fuel rods. It is a fuel rod called a partial-length fuel rod. Some fuel rods contain gadolinia, a flammable poison. Two water rods are arranged in the center of the fuel to increase the moderator area in the center of the fuel.
一般的にコーナー部や濃度燃料集合体の外周部の燃料棒は、燃料棒出力が高くなりやすいため、濃縮度は他の燃料棒に比べ低く設計してある。 In general, the fuel rods at the corners and the outer periphery of the concentrated fuel assembly tend to have high fuel rod output, so the enrichment is designed to be lower than that of other fuel rods.
図２の例では、低濃縮度の燃料棒は燃料集合体のコーナー部にのみ装荷され、高濃縮度燃料集合体の低濃縮度燃料棒は、低濃縮度燃料集合体の低濃縮度燃料棒に比して、核***性物質濃度が高くなっている。 In the example of FIG. 2, the low enrichment fuel rods are loaded only at the corners of the fuel assembly, and the low enrichment fuel rods of the high enrichment fuel assembly are the low enrichment fuel rods of the low enrichment fuel assembly. The fissile material concentration is higher than that.
上記核***性物質濃度の関係をさらに一般化すると以下の通りである。 The relationship of the fissile material concentration is further generalized as follows.
燃料集合体の外周部の燃料棒の核***性物質濃度の該燃料集合体の集合体平均核***性物質濃度に対する比を、燃料集合体の核***性物質濃度差比とすると、低濃縮度燃料集合体の核***性物質濃度差比は、高濃縮度燃料集合体の核***性物質濃度差比より大きいというものである。 When the ratio of the fissile material concentration of the fuel rods on the outer periphery of the fuel assembly to the assembly average fissile material concentration of the fuel assembly is defined as the fissile material concentration difference ratio of the fuel assembly, the low enrichment fuel assembly The fissionable material concentration difference ratio is greater than the fissionable material concentration difference ratio of the highly enriched fuel assembly.
低濃縮度燃料集合体の多くは、炉心滞在第三サイクル目において、コントロールセルに装荷される。前述したようにコントロールセルには制御棒を挿入するため、コントロールセルの制御棒を引き抜いた際に燃料集合体の制御棒側にある（１，１）、（１，２）、（２，１）の燃料棒の線出力が高くなる傾向がある。 Most of the low enrichment fuel assemblies are loaded into the control cell in the third cycle of staying in the core. As described above, since the control rod is inserted into the control cell, (1, 1), (1, 2), (2, 1) on the control rod side of the fuel assembly when the control rod of the control cell is pulled out. ) Fuel rod line output tends to increase.
このため、制御棒側である（１，１）、（１，２）、（２，１）の位置にある燃料棒は、低濃縮度の燃料集合体のコーナー部よりも更に濃縮度を低く設計している。 For this reason, the fuel rods at the positions (1, 1), (1, 2), (2, 1) on the control rod side have lower enrichment than the corners of the low enrichment fuel assembly. Designing.
ここで、制御棒の中心に最も近い燃料棒を（１，１）とし、水平方向の燃料棒の配列を行とし垂直方向の燃料棒の配列を列とすると、ｎ行ｍ列の位置の燃料棒を（ｎ，ｍ）の燃料棒とする。 Here, assuming that the fuel rod closest to the center of the control rod is (1, 1), the horizontal fuel rod arrangement is a row, and the vertical fuel rod arrangement is a column, the fuel at the position of n rows and m columns. Let the rods be (n, m) fuel rods.
表１に、炉心滞在第三サイクル終了後において、コントロールセルに装荷する低濃縮度燃料集合体の平均燃焼度の変化を示す。この表から低濃縮度燃料集合体の燃焼度が制限値である５５ＧＷｄ／ｔを超えていないことがわかる。
次に、図３にこの低濃縮度燃料集合体の核***性物質の濃縮度を変化させた場合において、炉心滞在第三サイクル終了後のコントロールセルに装荷されていた低濃縮度燃料集合体の平均燃焼度変化のグラフを示す。 Next, in FIG. 3, when the enrichment of the fissile material in the low enrichment fuel assembly is changed, the average of the low enrichment fuel assembly loaded in the control cell after the third cycle staying in the core is completed. The graph of burnup change is shown.
図３から、高濃縮度燃料集合体と低濃縮度燃料集合体の核***性物質の濃縮度差がないときは、炉内の最高バンドル燃焼度燃料集合体の燃焼度が９ｘ９燃料集合体の燃焼度の制限値である５５ＧＷｄ／ｔを超えているのに対し、濃縮度差を０．２重量％付けた場合は炉内の最高バンドル燃焼度燃料集合体の燃焼度が９ｘ９燃料集合体の燃焼度の制限値を超えないことがわかる。また、更に核***性物質の濃縮度差を付けていった場合、炉内の最高バンドル燃焼度燃料集合体の燃焼度は更に低くなる傾向にあることがわかる。 From FIG. 3, when there is no enrichment difference between the fissile material of the high enrichment fuel assembly and the low enrichment fuel assembly, the burnup of the highest bundle burnup fuel assembly in the furnace is the combustion of the 9x9 fuel assembly. However, when the enrichment difference is 0.2% by weight, the burnup of the highest bundle burnup fuel assembly in the furnace is 9x9 fuel assembly combustion It can be seen that the degree limit is not exceeded. It can also be seen that the burn-up of the highest bundle burn-up fuel assembly in the furnace tends to be even lower when the difference in enrichment of the fissile material is added.
すなわち、高濃縮度燃料集合体の核***性物質の濃縮度に対して、低濃縮度燃料集合体の核***性物質の濃縮度が小さいほど、低濃縮度燃料集合体の最終の燃焼度が小さくなるということである。 That is, the lower the enrichment of the fissile material in the low enrichment fuel assembly relative to the enrichment of the fissile material in the high enrichment fuel assembly, the smaller the final burnup of the low enrichment fuel assembly. That's what it means.
次に、本発明の第二の実施形態について説明する。 Next, a second embodiment of the present invention will be described.
図４は本発明の第二の実施形態による炉心を示している。 FIG. 4 shows a core according to the second embodiment of the present invention.
第一の実施形態と同じく沸騰水型原子力発電所（ＢＷＲ）のＢＷＲ／５型取替炉心を1／４サイズで示している。 The BWR / 5 type replacement core of the boiling water nuclear power plant (BWR) is shown in 1/4 size as in the first embodiment.
本実施形態においても、原子炉の運転サイクル長さとして２４ヶ月を想定しており、燃料としては第一実施形態と同様の低濃縮度燃料集合体、高濃縮度燃料集合体を用いる。 Also in this embodiment, the operation cycle length of the reactor is assumed to be 24 months, and the same low enrichment fuel assembly and high enrichment fuel assembly as in the first embodiment are used as the fuel.
炉心の最外周部には、炉心滞在最終サイクルの平均核***性物質濃度が高い高濃縮度燃料集合体（３）と炉心滞在最終サイクルの平均核***性物質濃度が低い低濃縮度燃料集合体（３）が混在して装荷され、前記炉心最外周部の内側の炉心外周部には、炉心滞在最終サイクル前の高濃縮度燃料集合体（１，２）が交互にチェッカーボード状に混在して装荷され、前記炉心外周部の内側の炉心中心部には、炉心滞在最終サイクル前の高濃縮度燃料集合体（１，２）と炉心滞在第一サイクルの低濃縮度燃料集合体（Ｌ１）が混在して装荷されている。 At the outermost periphery of the core, a highly enriched fuel assembly (3) having a high average fissile material concentration in the last cycle of staying in the core and a low enriched fuel assembly (3) having a low average fissile material concentration in the last cycle of staying in the core. ), And the highly concentrated fuel assemblies (1, 2) before the final cycle of staying in the core are alternately mixed and loaded in a checkerboard shape on the outer periphery of the core inside the outermost periphery of the core. In the center of the core inside the outer periphery of the core, the high enrichment fuel assembly (1, 2) before the last cycle of staying in the core and the low enrichment fuel assembly (L1) of the first cycle staying in the core are mixed. Is loaded.
この第二実施形態の肝要な部分は、炉心中心部に炉心滞在第一サイクルの低濃縮度燃料集合体（Ｌ１）を装荷することにある。 The essential part of this second embodiment is to load the low enrichment fuel assembly (L1) of the first cycle staying in the core at the core center.
第二実施形態は炉心中心部に炉心滞在第一サイクルの低濃縮度燃料集合体（Ｌ１）を装荷し、炉心滞在サイクル数が上がるにつれて、炉心最外周部に向かって移動配置させてもよい。 In the second embodiment, the low enrichment fuel assembly (L1) in the first cycle of staying in the core may be loaded at the center of the core, and may be moved toward the outermost periphery of the core as the number of core staying cycles increases.
この第二実施形態によれば、低濃縮度燃料集合体は反応度が低いため、炉心中心部に装荷することにより、炉内の熱的に厳しい部分の反応度を下げ、炉心の熱的余裕の確保することができるのである。 According to this second embodiment, since the low enrichment fuel assembly has low reactivity, by loading it in the center of the core, the reactivity of the thermally severe part in the reactor is lowered and the thermal margin of the core is reduced. Can be secured.
１ 炉心滞在第一サイクルの高濃度燃料集合体
２ 炉心滞在第二サイクルの高濃度燃料集合体
３ 炉心滞在第三サイクルの高濃度燃料集合体
Ｌ１ 炉心滞在第一サイクルの低濃度燃料集合体
Ｌ２ 炉心滞在第二サイクルの低濃度燃料集合体
Ｌ３ 炉心滞在第三サイクルの低濃度燃料集合体
DESCRIPTION OF
Claims (8)
平均核***性物質濃度が高い高濃縮度燃料集合体の平均炉心滞在サイクル数より大きい平均炉心滞在サイクル数を有する平均核***性物質濃度が低い低濃縮度燃料集合体を有し、
炉心の最外周部に装荷された、炉心滞在最終サイクル前の低濃縮度燃料集合体と、
前記炉心最外周部の内側に装荷された、炉心滞在最終サイクル前の高濃縮度燃料集合体および炉心滞在最終サイクルの低濃縮度燃料集合体と、
を備えることを特徴とする炉心。 It has two types of fuel assemblies with different average fissile material concentrations,
A low enriched fuel assembly having a low average fissile material concentration having an average core stay cycle number greater than an average core stay cycle number of a high enrichment fuel assembly having a high average fission material concentration;
A low enrichment fuel assembly loaded on the outermost periphery of the core before the last cycle of staying in the core;
A high enrichment fuel assembly before the last cycle of staying in the core and a low enrichment fuel assembly of the last cycle of staying in the core loaded inside the outermost periphery of the core;
A reactor core comprising:
平均核***性物質濃度が高い高濃縮度燃料集合体の平均炉心滞在サイクル数より大きい平均炉心滞在サイクル数を有する平均核***性物質濃度が低い低濃縮度燃料集合体を有し、
炉心の最外周部に装荷された、炉心滞在最終サイクルの平均核***性物質濃度が高い高濃縮度燃料集合体および炉心滞在最終サイクルの平均核***性物質濃度が低い低濃縮度燃料集合体と、
前記炉心最外周部の内側に装荷された、炉心滞在最終サイクル前の高濃縮度燃料集合体および炉心滞在第一サイクルの低濃縮度燃料集合体と、
を備えることを特徴とする炉心。 It has two types of fuel assemblies with different average fissile material concentrations,
A low enriched fuel assembly having a low average fissile material concentration having an average core stay cycle number greater than an average core stay cycle number of a high enrichment fuel assembly having a high average fission material concentration;
A high enrichment fuel assembly having a high average fissile material concentration in the last cycle of staying in the core and a low enrichment fuel assembly having a low average fissile material concentration in the last cycle of staying in the core, loaded on the outermost periphery of the core;
A high enrichment fuel assembly before the last cycle of staying in the core and a low enrichment fuel assembly of the first cycle staying in the core, loaded inside the outermost periphery of the core;
A reactor core comprising:
前記中間濃度燃料集合体は、炉心滞在サイクルが低いときは炉心中心部に装荷され、炉心滞在サイクルが高くなるにつれて炉心外周部に装荷される、ことを特徴とする請求項１記載の炉心。 Having one or more intermediate concentration fuel assemblies having an average fissile material concentration between the high enrichment fuel assembly and the low enrichment fuel assembly;
2. The core according to claim 1, wherein the intermediate concentration fuel assembly is loaded at the core center when the core stay cycle is low, and is loaded at the outer periphery of the core as the core stay cycle becomes high.
前記低濃縮度燃料集合体の核***性物質濃度差比は、前記高濃縮度燃料集合体の核***性物質濃度差比より大きい、ことを特徴とする請求項１〜５のいずれか一項に記載の炉心。 Of fissile material concentration of the fuel rods disposed in the outer peripheral portion of the inner surface facing the channel box of a fuel assembly, fissile material concentration of the ratio aggregate average fissile material concentration of the fuel assembly, the fuel assembly As a difference ratio,
The fissile material concentration difference ratio of the low enrichment fuel assembly is larger than the fissionable material concentration difference ratio of the high enrichment fuel assembly. Core.
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