JPH0827366B2 - Nuclear fuel assembly - Google Patents
Nuclear fuel assemblyInfo
- Publication number
- JPH0827366B2 JPH0827366B2 JP61120001A JP12000186A JPH0827366B2 JP H0827366 B2 JPH0827366 B2 JP H0827366B2 JP 61120001 A JP61120001 A JP 61120001A JP 12000186 A JP12000186 A JP 12000186A JP H0827366 B2 JPH0827366 B2 JP H0827366B2
- Authority
- JP
- Japan
- Prior art keywords
- fuel
- assembly
- rod
- rods
- short
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- 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
Description
【発明の詳細な説明】 〔産業上の利用分野〕 本発明は、核燃料集合体、特に、沸騰水型原子炉に装
荷される核燃料集合体に関するものである。TECHNICAL FIELD The present invention relates to a nuclear fuel assembly, and more particularly to a nuclear fuel assembly loaded in a boiling water reactor.
沸騰水型原子炉には、核燃料集合体が数多く装荷さ
れ、例えば電気出力1100MW級の沸騰水型原子炉には約76
0体の核燃料集合体が装荷されている。A large number of nuclear fuel assemblies are loaded into a boiling water reactor, and for example, a boiling water reactor with an electric output of 1100 MW has about 76
Zero nuclear fuel assemblies are loaded.
全発電量の中で、原子力発電が占める割合が増えてい
る今日、原子力発電コストを下げることは重要な課題と
なつている。そのための方法の一つとして核燃料集合体
構造を変えることによつて、中性子を充分に減速してそ
の利用率を高め、燃料ウランなどを有効に利用して燃料
費を削減する方法がある。勿論、燃料費削減と同時に十
分な熱的余裕と安定性を確保し、原子炉を安全に運転す
ることも重要である。Reducing the cost of nuclear power generation has become an important issue today, as nuclear power generation accounts for an increasing proportion of the total power generation. As one of the methods for this purpose, there is a method of sufficiently reducing the speed of neutrons to increase the utilization rate by changing the structure of the nuclear fuel assembly, and effectively using fuel uranium or the like to reduce the fuel cost. Of course, it is also important to operate the reactor safely while ensuring sufficient thermal margin and stability while reducing fuel costs.
第２図には核燃料集合体の縦断面が示してあり、第３
図には第２図のＩ−Ｉ′横断面が示してある。核燃料集
合体１は、格子状に規則正しく配置された燃料棒２、水
ロツド３、スペーサー４、下部タイプレート５、上部タ
イプレート６とそれらを取り囲む集合体壁７とから成つ
ている。第３図の11は制御棒を示している。FIG. 2 shows a vertical cross section of the nuclear fuel assembly.
The drawing shows a cross section I--I 'of FIG. The nuclear fuel assembly 1 is composed of fuel rods 2, water rods 3, spacers 4, a lower tie plate 5, an upper tie plate 6 and an assembly wall 7 surrounding them, which are regularly arranged in a grid pattern. Reference numeral 11 in FIG. 3 indicates a control rod.
冷却材であるとともに中性子を減速する軽水８は、単
相流状態で入口オリフイス９から流入し、燃料棒２から
熱を奪いながら上方に流れ、沸騰を起し蒸気と水の混じ
つた二相流状態で流出する。また集合体壁７の外側も軽
水10が流れている。The light water 8 that is a coolant and slows down neutrons flows from the inlet orifice 9 in a single-phase flow state, flows upward while removing heat from the fuel rods 2, and causes boiling to cause a two-phase flow of steam and water. Spill in the state. Also, light water 10 is flowing outside the aggregate wall 7.
水ロツドは、特開昭59−13981,59−65792,59−16689
3,59−178387号公報等にみられるように、中性子を充分
に減速して利用率を高め、燃料経済性を向上させるのに
用いられており、また、最近は通常の燃料棒の上部を切
り取つたいわゆる短尺燃料棒も使われている。Water rods are disclosed in JP-A-59-13981, 59-65792, 59-16689.
As seen in Japanese Patent No. 3,59-178387, etc., it is used to sufficiently slow down neutrons to increase the utilization rate and improve fuel economy. So-called short fuel rods are also used.
前述の短尺燃料棒ではその上部を切り取つてあるの
で、短尺燃料棒の先では燃料を欠いており発熱はなく、
しかも冷却材流路も広がつている。また前述の水ロツド
の発熱割合は燃料棒の数パーセント以下である。そのた
めに、たとえば短尺燃料棒や水ロツドの位置が適切に分
散せず一カ所にかたまつたりすると、核燃料集合体内の
冷却材流量や蒸気体積率の分布が均一でなく歪んだもの
となつて、熱的余裕が小さくなつたり、圧力損失が大き
くなつて炉心安定性が悪くなつたりする。Since the upper part of the short fuel rod is cut off, the tip of the short fuel rod lacks fuel and does not generate heat.
Moreover, the coolant channel is wide. The heat generation rate of the water rod is less than a few percent of the fuel rod. For this reason, for example, if the positions of short fuel rods and water rods are not properly dispersed and are gathered in one place, the distribution of the coolant flow rate and vapor volume fraction in the nuclear fuel assembly may become uneven and distorted. , The thermal margin becomes small, and the core loss becomes poor due to the large pressure loss.
このような事情に鑑み、本発明は中性子利用率向上に
よる燃料経済性向上、核燃料集合体内での圧力低減によ
る炉心安定性向上、沸騰遷移に対する熱的余裕向上を可
能にすることのできる沸騰水型原子炉用の核燃料集合体
を提供することを目的とするものである。In view of such circumstances, the present invention is a boiling water type that can improve fuel economy by improving neutron utilization rate, improve core stability by reducing pressure in a nuclear fuel assembly, and improve thermal margin for boiling transition. The purpose of the present invention is to provide a nuclear fuel assembly for a nuclear reactor.
前記問題点を解決するために為された本発明の構成
は、長さの異なる２種類以上の燃料棒と水ロッドを、格
子状に配置した核燃料集合体において、前記核燃料集合
体の横断面を中央部と周辺部に分けたとき、前記水ロッ
ドが前記中央部に配置され、該水ロッドの総断面積は前
記燃料棒の４本分以上の断面積を有し、前記燃料棒のう
ち短尺の燃料棒は、前記周辺部で前記水ロッドと隣り合
わない位置に配置されたことを特徴とするものである。The structure of the present invention made to solve the above-mentioned problems is a nuclear fuel assembly in which two or more types of fuel rods and water rods having different lengths are arranged in a grid pattern. When divided into a central portion and a peripheral portion, the water rod is arranged in the central portion, and the total cross-sectional area of the water rod has a cross-sectional area of four or more of the fuel rods. The fuel rod is disposed at a position that is not adjacent to the water rod in the peripheral portion.
ここで、核燃料集合体（以下集合体と称する）断面の
周辺部とは、集合体の外側から２層目までの燃料棒の含
まれる領域をさし、チヤンネルボツクスの外側の水の影
響で中性子が充分に減速されている領域をさし、それよ
り内側の領域を中央部とみなしている。Here, the peripheral portion of the cross section of a nuclear fuel assembly (hereinafter referred to as an assembly) refers to a region containing fuel rods from the outer side of the assembly to the second layer, and neutrons are influenced by water outside the channel box. Indicates an area where the speed is sufficiently decelerated, and the area inside the area is regarded as the central portion.
そして、短尺燃料棒として通常の長さを有する通常燃
料棒の15/24〜21/24の長さの燃料棒を用いる場合に効果
的である。And, it is effective when using the fuel rod having the length of 15/24 to 21/24 of the normal fuel rod having the normal length as the short length fuel rod.
このように構成される本発明の集合体の作用を、その
構成理由によつて説明する。The operation of the assembly of the present invention having such a configuration will be described based on the reason for the configuration.
まず、集合体内に燃料棒を正方格子状に規則正しく配
置した場合、集合体断面の中央部では減速材が足りない
状態であつて中性子が充分に減速されないので中性子利
用率は悪くなつている。そこで、本発明の集合体では、
集合体断面の中央部に水ロッドを設け、中央部において
は４本分以上の大きい断面積を確保できるので、中性子
を十分に減速して利用率を高め、燃料経済性を向上させ
ることができる。これに対して、集合体断面の周辺部で
は、中性子がチヤンネルボツクス外の水で充分に減速さ
れており、水ロツドなどを設けても燃料経済性を向上さ
せる効果は小さい。First, when the fuel rods are regularly arranged in a square lattice shape in the assembly, the neutron utilization rate is poor because the moderator is insufficient in the central portion of the assembly cross section and the neutrons are not sufficiently decelerated. Therefore, in the aggregate of the present invention,
A water rod is provided at the center of the cross section of the assembly, and a large cross-sectional area of four or more can be secured at the center, so neutrons can be sufficiently decelerated to increase the utilization rate and improve fuel economy. . On the other hand, in the periphery of the cross section of the assembly, the neutrons are sufficiently decelerated by the water outside the channel box, and even if a water rod or the like is provided, the effect of improving fuel economy is small.
燃料棒の先端を切り取つたいわゆる短尺燃料棒を用い
ると集合体圧力損失を有効に低減できる。一般に冷却材
の流路面積を増加させると摩擦圧力損失を低減できる
が、特に短尺燃料棒の先端のような集合体の上部では蒸
気体積率が大きいために二相流圧力損失係数が大きくな
つているのでそこで流路面積が増加すると、蒸気体積率
が小さい集合体下部などに較べて、圧力損失低減効果は
大きい。If a so-called short fuel rod in which the tip of the fuel rod is cut off is used, the assembly pressure loss can be effectively reduced. Generally, increasing the flow area of the coolant can reduce the friction pressure loss, but especially at the upper part of the assembly such as the tip of a short fuel rod, the two-phase flow pressure loss coefficient becomes large because the vapor volume ratio is large. Therefore, if the flow path area increases there, the pressure loss reducing effect is greater than that in the lower part of the assembly where the vapor volume ratio is small.
燃料経済性の観点からウラン燃料装荷量（インベント
リ）一定という条件で評価すると、後述するように、短
尺燃料棒が通常燃料棒の15/24〜21/24の長さのとき、圧
力損失低減効果が大きい。When evaluated under the condition that the uranium fuel loading (inventory) is constant from the viewpoint of fuel economy, as will be described later, when the short fuel rod is 15/24 to 21/24 the length of the normal fuel rod, the pressure loss reduction effect Is big.
次に、短尺燃料棒が水ロッドと相隣りあつた場合に
は、短尺燃料棒の上部では冷却材流路面積が広がり、ま
た水ロツドなどの発熱量が小さいことなどのために、蒸
気体積率が減つて冷却水が多く流れるようになる。この
とき集合体の他の部分では、冷却材流量が減り、蒸気体
積率が増して、沸騰遷移が起こりやすくなつている。ま
た集合体内で、このように蒸気体積率や冷却材流量の分
布が歪むと圧力損失が大きくなつて、炉心に装荷された
ときの安定性が悪くなる。そこで、本発明の集合体で
は、短尺燃料棒は集合体周辺部に配置して、水ロツドと
相隣りあわないようにして集合体内での蒸気体積率や冷
却材流量などの分布を歪ませないようにして圧力損失を
できるだけ小さくし、かつ熱的余裕を大きくたもって炉
心安定性を良好に保つようにする。Next, when the short fuel rod and the water rod are adjacent to each other, the area of the coolant passage is widened in the upper part of the short fuel rod, and the calorific value of the water rod is small. Is reduced and more cooling water flows. At this time, in other parts of the assembly, the coolant flow rate decreases, the vapor volume ratio increases, and the boiling transition is likely to occur. In addition, when the distribution of the vapor volume ratio or the coolant flow rate is distorted in the assembly, the pressure loss becomes large, and the stability when loaded in the core deteriorates. Therefore, in the assembly of the present invention, the short fuel rods are arranged in the peripheral portion of the assembly so as not to be adjacent to the water rods so as not to distort the distribution such as the vapor volume ratio and the coolant flow rate in the assembly. In this way, the pressure loss is minimized and the thermal margin is increased to maintain good core stability.
すなわち、本発明では集合体断面の中央部に配置した
水ロツドで中性子を有効に減速して燃料経済性を高め、
集合体断面の周辺部の短尺燃料棒によつて沸騰遷移がお
こりやすい燃料発熱部をのぞいて熱的余裕を向上させ、
さらに短尺燃料棒を水ロツドとは相隣りあわないように
配置して燃料集合体内の冷却材流量や蒸気体積率の分布
をできるだけ平坦にして圧力損失を低減し炉心安定性を
向上させるのである。That is, in the present invention, the water rod arranged in the center of the cross section of the assembly effectively slows down neutrons to enhance fuel economy,
The thermal margin is improved except for the fuel heat generating part where boiling transition is likely to occur due to the short fuel rods in the peripheral part of the assembly cross section,
Further, the short fuel rods are arranged so as not to be adjacent to the water rods to make the distribution of the coolant flow rate and the vapor volume ratio in the fuel assembly as flat as possible to reduce the pressure loss and improve the core stability.
以下、本発明を実施例により、詳細に説明する。 Hereinafter, the present invention will be described in detail with reference to Examples.
第１図は、本発明の第一の実施例の集合体の横断面を
示し、第２図及び第３図と同一部分には同一符号が付し
てあり、12及び13はそれぞれ断面中央部及び断面周辺部
を示し、14は短尺燃料棒を示している。FIG. 1 shows a cross section of the assembly of the first embodiment of the present invention, the same parts as those in FIGS. And a peripheral portion of the cross section, and 14 indicates a short fuel rod.
本実施例では、集合体壁７の内側に長さ370.8cm（146
inch）の燃料棒２を正方９×９格子状に規則正しく配置
し、その断面中央部12に水ロツド３を９本、断面周辺部
13に長さ278.1cm（109.5inch）の短尺燃料棒14を８本設
け、しかも、水ロツド３と短尺燃料棒14とが相隣りあわ
ないように離して配置してある。短尺の燃料棒14は第４
図の説明図に示すように、燃料装荷部すなわち発熱部の
長さが、そのほかの通常燃料棒２の18/24の長さになつ
ている。In this embodiment, a length of 370.8 cm (146
inch) fuel rods 2 are regularly arranged in a square 9 × 9 lattice, and 9 water rods 3 are provided in the central portion 12 of the cross section and the peripheral portion of the cross section.
Eight short fuel rods 14 each having a length of 278.1 cm (109.5 inch) are provided at 13, and the water rod 3 and the short fuel rods 14 are arranged so as not to be adjacent to each other. Short fuel rod 14 is fourth
As shown in the explanatory view of the drawing, the length of the fuel loading portion, that is, the heat generating portion is 18/24 of the other normal fuel rods 2.
この第一の実施例では、集合体中央部の９本の水ロツ
ド３により、例えば第３図に示すような従来の核燃料集
合体に較べて、８％の天然ウランの節約、すなわち燃料
経済性の向上を達成している。In this first embodiment, the nine water rods 3 in the central part of the assembly save 8% of natural uranium, that is, fuel economy, as compared with the conventional nuclear fuel assembly as shown in FIG. 3, for example. Has improved.
次に、第１表は短尺燃料棒の位置による集合体圧力損
失の変化を示している。この表は、第５図の横断面図に
示した９×９正方格子の中央部に水ロツドを９本設けた
ものを基準として、その他に燃料棒の位置を（Ix,Iy）
で示したとき、それぞれケースA:（1,1），ケースB:
（2,2），ケースC:（3,3），ケースD:4,5）の燃料棒と
それと90゜回転対称の位置にある合計４本の燃料棒を長
さ15/24の短尺燃料としたときの、集合体圧力損失の増
加をプラスで、減少をマイナスで示している。第５図中
のA,B,C,Dは第１表に示した各ケースA,B,C,Dでの短尺燃
料棒の位置を示している。Next, Table 1 shows changes in the assembly pressure loss depending on the positions of the short fuel rods. This table is based on the 9 × 9 square lattice shown in FIG. 5 with nine water rods at the center, and the other fuel rod positions (Ix, Iy).
, Case A: (1,1), case B:
(2,2), Case C: (3,3), Case D: 4,5) Fuel rods and a total of four fuel rods at 90 ° rotational symmetry with a total of 15/24 short fuel rods. , The increase in the aggregate pressure loss is shown as a positive value and the decrease is shown as a negative value. A, B, C and D in FIG. 5 indicate the positions of the short fuel rods in each case A, B, C and D shown in Table 1.
ケースA,Bのように、短尺燃料棒が集合体周辺部にあ
るとき、圧力損失低減効果が大きいのに対し、ケースＤ
のように集合体中央部で水ロツドに囲まれているとき
は、実質的に流路は広くなつているにもかかわらず、圧
力損失はむしろ増加する。As in Cases A and B, when the short fuel rods are in the periphery of the assembly, the pressure loss reduction effect is great, while in Case D
When surrounded by a water rod at the central portion of the assembly, the pressure loss is rather increased although the flow path is substantially wide.
この圧力損失の増加は第５図を参照して説明できる。
すなわち水ロツドに囲まれた中央部では発熱燃料棒が少
ないので蒸気体積率が小さく、しかも短尺燃料棒の先端
では流路が広がつているので 摩擦圧力損失係数は小さく冷却材は多く流れる。これに
対し集合体周辺部では発熱量が大きいにもかかわらず、
冷却材が比較的少ししか流れず蒸気体積率が大きくな
る。このように中央部に水ロツドと短尺燃料棒が集まる
と蒸気体積率や冷却材流量の分布が歪んで圧力損失が大
きくなるのである。又、このとき集合体周辺部では流量
が少なく蒸気体積率が大きいので沸騰遷移が起りやすく
熱的余裕が小さくなつている。This increase in pressure loss can be explained with reference to FIG.
That is, since there are few exothermic fuel rods in the central part surrounded by the water rod, the vapor volume ratio is small, and the flow path is wide at the tip of the short fuel rod. The coefficient of friction pressure loss is small and a large amount of coolant flows. On the other hand, despite the large amount of heat generated in the periphery of the assembly,
The coolant flows relatively little and the vapor volume ratio increases. When water rods and short fuel rods gather in the central portion in this way, the distribution of the vapor volume ratio and the coolant flow rate is distorted and the pressure loss increases. Further, at this time, since the flow rate is small and the vapor volume ratio is large in the peripheral portion of the assembly, boiling transition is likely to occur and the thermal margin is reduced.
このような圧力損失や熱的余裕などの伝熱流動特性に
もとづいて短尺燃料棒は集合体周辺部にしかも水ロツド
とは離して配置する。Based on such heat transfer and flow characteristics as pressure loss and thermal margin, the short fuel rods are arranged in the periphery of the assembly and apart from the water rod.
第６図は、短尺燃料棒の長さによる集合体圧力損失の
変化を示している。（2.2）及び90゜回転対称の位置に
ある合計４本の燃料棒の長さが変わつたときの集合体圧
力損失を、短尺燃料棒のない集合体と較べたもので、横
軸には短尺燃料棒の長さ（通常燃料棒との比）、縦軸に
は集合体圧力損失の変化（％）が、ΔP1,ΔP0を、それ
ぞれ、当該集合体の圧力損失，短尺燃料棒などの基準集
合体の圧力損失としたとき、 で示してある。FIG. 6 shows changes in the assembly pressure loss depending on the length of the short fuel rod. (2.2) and the pressure loss of the assembly when the total length of the four fuel rods at 90 ° rotational symmetry was changed, compared with the assembly without the short fuel rods. The length of the fuel rod (ratio to the normal fuel rod), the change in the assembly pressure loss (%) on the vertical axis, ΔP 1 and ΔP 0 , are the pressure loss of the assembly, short fuel rod, etc. Given the pressure loss of the reference assembly, Indicated by
第６図は、燃料経済性を悪くしないためにウラン燃料
装荷量（インベントリ）一定という条件のもとで比較し
ている。このため、短尺燃料棒が短くなつて燃料の切り
取り部分が大きくなると残りの燃料棒は太くなる。そし
て、この図に示すように、短尺燃料棒が通常燃料棒の15
/24〜21/24の長さのとき、一定の燃料切り取り長さに対
する圧力損失低減効果は大きく、燃料棒が短くなるにつ
れて次第に小さくなる傾向をもち、さらに短くなると燃
料棒が太くなつて流路面積が減少して摩擦圧損増加が顕
著となりむしろ圧力損失は増加する。Figure 6 compares under the condition that the uranium fuel loading (inventory) is constant in order not to deteriorate fuel economy. Therefore, as the short fuel rod becomes shorter and the fuel cut-out portion becomes larger, the remaining fuel rods become thicker. And as shown in this figure, the short fuel rod is
When the length is / 24 to 21/24, the effect of reducing the pressure loss for a fixed fuel cut length is large, and it tends to become smaller as the fuel rod becomes shorter. The area decreases and the friction pressure loss increases remarkably, but rather the pressure loss increases.
以上のような圧力損失低減効果にもとづいて、短尺燃
料棒は通常燃料棒の長さの15/24〜21/24の長さとする。
これは蒸気体積率の高い集合体上部の二相流圧損係数が
大きいところで流路面積を広げて圧力損失を低減するの
である。Based on the pressure loss reduction effect as described above, the length of the short fuel rod is set to 15/24 to 21/24 of the length of the normal fuel rod.
This is to expand the flow passage area and reduce the pressure loss where the two-phase flow pressure loss coefficient at the upper part of the assembly having a high vapor volume ratio is large.
第７図は、短尺燃料棒の長さによる集合体限界出力比
の変化を示しており、第６図と同じく（2,2）及びそれ
と90゜回転対称の位置にある合計４本の燃料棒の長さが
変つたときの集合体限界出力比を短尺燃料棒のない燃料
集合体と較べている。ここで、限界出力比（CPR）と
は、燃料棒表面で沸騰遷移が起るときの集合体出力Pcr
に対する当該集合体出力Ｐの比、つまり で表わされる。したがつて、限界出力比が1.0を越えて
大きくなるほど、沸騰遷移に対する熱的余裕が増し、逆
に1.0に近づくほど沸騰遷移を起す確立が増す。Fig. 7 shows changes in the assembly critical power ratio depending on the length of the short fuel rods. As with Fig. 6, (2, 2) and a total of four fuel rods at 90 ° rotational symmetry with it. The limit power ratio of the assembly when the length of the fuel cell is changed is compared with the fuel assembly without the short fuel rod. Here, the critical power ratio (CPR) is the aggregate power Pcr when boiling transition occurs on the fuel rod surface.
The ratio of the aggregate output P to Is represented by Therefore, the thermal margin for the boiling transition increases as the limiting power ratio exceeds 1.0, and conversely, the probability of causing the boiling transition increases as it approaches 1.0.
第７図の横軸には短尺燃料棒の長さ（通常燃料棒との
比）、縦軸には集合体限界出力比の変化（％）が、CPR1
及びCPR0をそれぞれ当該集合体の限界出力比及び短尺燃
料棒なしの基準集合体の限界出力比としたとき、 で示してある。The length of the short fuel rods in the horizontal axis of FIG. 7 (a ratio between the normal fuel rod), the change in aggregate critical power ratio on the vertical axis (%) is, CPR 1
And CPR 0 are the limit power ratio of the assembly and the limit power ratio of the reference assembly without short fuel rods, respectively, Indicated by
第７図は、燃料集合体出力を一定として比較してい
る。このため、短尺燃料棒が短くなつて燃料の切り取り
部分が大きくなると残りの燃料棒の単位体積あたりの発
熱量は増加する。したがつて一般に短尺燃料棒が短くな
るにつれ、熱的余裕は小さくなる。ところが沸騰遷移は
比較的発熱量の大きい水平方向には（2,2）などの位置
にある燃料棒で、しかも軸方向には集合体出口に近い発
熱部分全長の〜20/24にあるスペーサの直下で起つてい
るので、この燃料棒を通常燃料棒の長さの〜19/24程度
の短尺にしてやれば沸騰遷移は起らなくなり、熱的余裕
は増大する。短尺燃料棒をこの長さにしたとき、熱的に
最も厳しいのは他の燃料棒となるので、この燃料棒を更
に短くしても熱的余裕は大きくならない。また、（2,
2）などの位置にある短尺燃料棒を通常燃料棒の長さの
〜22/24の長さとしても、沸騰遷移は依然として発熱部
分全長の〜20/24にあるスペーサの直下で起こることは
かわらないので熱的余裕は大きくならない。FIG. 7 compares the fuel assembly output with a constant value. Therefore, when the short fuel rod becomes short and the cut-out portion of the fuel becomes large, the calorific value per unit volume of the remaining fuel rods increases. Therefore, in general, the shorter the short fuel rod, the smaller the thermal margin. However, the boiling transition is the fuel rod at a position such as (2,2) in the horizontal direction where the calorific value is relatively large, and the spacer in the axial direction is about 20/24 of the total length of the heat generating portion near the assembly outlet. Since it occurs immediately below, if this fuel rod is made as short as about 19/24 of the length of a normal fuel rod, boiling transition does not occur and the thermal margin increases. When the length of the short fuel rod is set to this length, other fuel rods are most severely thermally demanded. Therefore, even if the fuel rod is further shortened, the thermal margin does not increase. Also, (2,
Even if the short fuel rods in positions such as 2) have a length of ~ 22/24 of the length of a normal fuel rod, it is clear that the boiling transition still occurs just below the spacer at ~ 20/24 of the total length of the heat generating part. The thermal margin does not increase because it is not present.
このような、熱的余裕の観点から短尺燃料棒は通常燃
料棒の長さの〜19/24の長さとする。From the standpoint of thermal margin, the length of the short fuel rods is normally set to 19/24 of the length of the fuel rods.
以上述べたような圧力損失や熱的余裕などの伝熱流動
特性にもとづき本発明の第一の実施例では短尺燃料棒は
通常燃料棒の長さの18/24の長さとする。第一の実施例
では、短尺燃料棒を全く用いなかつた場合に比べ、圧力
損失の低減4.5％により炉心安定性は約５％向上する。
熱的余裕は５％向上する。Based on the heat transfer and flow characteristics such as pressure loss and thermal margin as described above, in the first embodiment of the present invention, the short fuel rod has a length of 18/24 of the length of the normal fuel rod. In the first embodiment, the core stability is improved by about 5% due to the pressure loss reduction of 4.5%, as compared with the case where no short fuel rod is used at all.
Thermal margin is improved by 5%.
また、本発明の第一の実施例では短尺燃料棒を通常燃
料棒の長さの18/24の長さとしたが、たとえば炉心安定
性の改善に重きをおくならば、15/24の長さとしても良
い。このときには18/24の長さとしたときに較べ、集合
体圧力損失は1.8％減少し、炉心安定性は1.8％向上す
る。なお、通常燃料棒の長さの15/24と18/24の短尺燃料
棒を混在させても良く、この場合には、外側に15/24、
内側に15/24の短尺燃料棒を配置する。この場合の集合
体圧力損失は0.9％減少し、炉心安定性は0.9％向上す
る。Further, in the first embodiment of the present invention, the length of the short fuel rod is set to 18/24 of the length of the normal fuel rod, but if the emphasis is on improving the core stability, the length of 15/24 is set. Also good. At this time, the pressure loss of the assembly is reduced by 1.8% and the core stability is improved by 1.8% compared with the case of the length of 18/24. It is also possible to mix short fuel rods of the length of normal fuel rods of 15/24 and 18/24, and in this case, 15/24 on the outside,
Place a 15/24 short fuel rod inside. In this case, the assembly pressure loss is reduced by 0.9% and the core stability is improved by 0.9%.
次に、本発明の第二の実施例になる集合体を第８図の
横断面図を用いて詳細に説明する。この図で第１図、第
３図及び第５図と同一の部分には同一の符号が付してあ
る。この第二の実施例では、正方８×８格子状に規則正
しく配置して長さ370.8cm（146inch）の燃料棒２の中央
部には燃料４本分の面積を占める大径の水ロッド15を設
け、断面周辺部に長さ231.8cm（91.3inch）の短尺燃料
棒16を８本設け、しかも水ロッド15と短尺燃料棒16が相
隣りあわないように配置している。Next, the assembly according to the second embodiment of the present invention will be described in detail with reference to the cross sectional view of FIG. In this figure, the same parts as those in FIGS. 1, 3, and 5 are designated by the same reference numerals. In the second embodiment, a large diameter water rod 15 occupying an area of four fuels is arranged in the center of a fuel rod 2 having a length of 370.8 cm (146 inch) arranged regularly in a square 8 × 8 lattice. Eight short fuel rods 16 having a length of 231.8 cm (91.3 inch) are provided around the cross section, and the water rods 15 and the short fuel rods 16 are arranged so as not to be adjacent to each other.
第二の実施例が第一の実施例と異なるところは、燃料
棒が正方８×８格子状に配列されていること、断面中央
部の水ロッド15が太径であること、短尺燃料棒16の長さ
が通常燃料棒の15/24の長さである点である。第二の実
施例では、断面中央部の太径の水ロッド15のために第３
図で示した従来の燃料集合体に比べ、４％の天然ウラン
が節約できる。また周辺部の短尺燃料棒によって４％の
熱的余裕の増大と３％の炉心安定性向上が実現できる。The second embodiment differs from the first embodiment in that the fuel rods are arranged in a square 8 × 8 lattice, the water rod 15 at the center of the cross section has a large diameter, and the short fuel rod 16 is used. The point is that the length is usually 15/24 of a fuel rod. In the second embodiment, because of the large diameter water rod 15 in the center of the cross section, the third
Compared with the conventional fuel assembly shown in the figure, 4% of natural uranium can be saved. Further, the short fuel rods in the peripheral portion can realize a 4% increase in thermal margin and a 3% improvement in core stability.
以上、説明したように本発明によれば、中性子を充分
に減速して利用率を高め、燃料経済性を向上することが
できる。また集合体内の冷却材流量や蒸気体積率の分布
を平坦にして沸騰遷移に対する熱的余裕を大きくした
り、集合体圧力損失を小さくして安定性を向上させるこ
とができる。As described above, according to the present invention, neutrons can be sufficiently decelerated to increase the utilization rate and improve fuel economy. Further, it is possible to improve the stability by flattening the distribution of the coolant flow rate and the vapor volume ratio in the assembly to increase the thermal margin for the boiling transition and reducing the assembly pressure loss.
そのほかに、たとえば熱的余裕が大きい本発明の集合
体を用いた原子炉では、熱的制限値を容易に満足できる
ことにより、原子炉の利用率を高めることができる。さ
らに熱的余裕を従来並みとした場合、出力密度の大きい
小型の原子炉が実現できる。In addition, for example, in a reactor using the assembly of the present invention having a large thermal margin, the utilization factor of the reactor can be increased by easily satisfying the thermal limit value. Furthermore, if the thermal margin is made the same as the conventional one, it is possible to realize a compact nuclear reactor with high power density.
特に、各実施例に示すように、最外層のコーナに短尺
燃料棒を配置してある場合は、制御棒価値が増大する。
これは短尺燃料棒より上方で短尺燃料棒の延長線上の領
域で冷却材量が増大するため、その領域での減速効果が
増し、制御棒に吸収されやすい熱中性子が増大すること
によるものである。In particular, as shown in each of the examples, when the short fuel rods are arranged in the outermost corners, the control rod value increases.
This is because the amount of coolant increases in the region above the short fuel rods and on the extension line of the short fuel rods, so the deceleration effect in that region increases and the thermal neutrons that are easily absorbed by the control rods increase. .
本発明は、中性子利用率向上による燃料経済性向上、
核燃料集合体内での圧力損失低減による炉心安定性向
上、沸騰遷移に対する熱的余裕向上を図るのに好適な沸
騰水型原子炉用の核燃料集合体を提供可能とするもの
で、産業上の効果の大なるものである。The present invention improves fuel economy by improving neutron utilization,
It is possible to provide a nuclear fuel assembly for a boiling water reactor suitable for improving core stability by reducing pressure loss in the nuclear fuel assembly and improving the thermal margin for boiling transition. It is great.
第１図は本発明の核燃料集合体の第一の実施例の横断面
図、第２図は従来の核燃料集合体の縦断面図、第３図は
第２図のＩ−Ｉ′線断面図、第４図は本発明の核燃料集
合体の通常燃料棒及び短尺燃料棒の縦断面図、第５図は
同じく水ロツドと短尺燃料棒の位置関係を示す横断面
図、第６図は同じく短尺燃料棒の長さによる集合体圧力
損失の変化を示す線図、第７図は同じく短尺燃料棒の長
さによる集合体限界出力比の変化を示す線図、第８図は
本発明の核燃料集合体の第二の実施例の横断面図であ
る。 １……核燃料集合体、２……燃料棒、３……水ロツド、
７……集合体壁、8,10……軽水、11……制御棒、12……
断面中央部、13……断面周辺部、14……短尺燃料棒、15
……（大径の）水ロッド、16……短尺燃料棒。FIG. 1 is a cross-sectional view of a first embodiment of a nuclear fuel assembly of the present invention, FIG. 2 is a vertical cross-sectional view of a conventional nuclear fuel assembly, and FIG. 3 is a cross-sectional view taken along the line II 'of FIG. FIG. 4 is a vertical sectional view of a normal fuel rod and a short fuel rod of the nuclear fuel assembly of the present invention, FIG. 5 is a transverse sectional view showing the positional relationship between the water rod and the short fuel rod, and FIG. FIG. 7 is a diagram showing a change in the assembly pressure loss with the length of the fuel rod, FIG. 7 is a diagram showing a change in the assembly limit output ratio with the length of the short fuel rod, and FIG. 8 is a nuclear fuel assembly of the present invention. FIG. 6 is a cross-sectional view of the second embodiment of the body. 1 ... Nuclear fuel assembly, 2 ... Fuel rod, 3 ... Water rod,
7 …… Assembly wall, 8,10 …… Light water, 11 …… Control rod, 12 ……
Cross-section central part, 13 …… cross-section peripheral part, 14 …… short fuel rod, 15
... (large diameter) water rod, 16 ... short fuel rod.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 内川 貞夫 茨城県日立市森山町1168番地 株式会社日 立製作所エネルギー研究所内 (72)発明者 森本 裕一 茨城県日立市森山町1168番地 株式会社日 立製作所エネルギー研究所内 (56)参考文献 特開 昭60−224092（ＪＰ，Ａ) 特開 昭61−281993（ＪＰ，Ａ) ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadao Uchikawa 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture, Hitachi Energy Research Institute Co., Ltd. Energy Research Institute (56) Reference JP 60-224092 (JP, A) JP 61-281993 (JP, A)
Claims (2)
ドを、格子状に配置した核燃料集合体において、前記核
燃料集合体の横断面を中央部と周辺部に分けたとき、前
記水ロッドが前記中央部に配置され、該水ロッドの総断
面積は前記燃料棒の４本分以上の断面積を有し、前記燃
料棒のうち短尺の燃料棒は、前記周辺部で前記水ロッド
と隣り合わない位置に配置されたことを特徴とする核燃
料集合体。1. A nuclear fuel assembly in which two or more types of fuel rods and water rods having different lengths are arranged in a grid pattern, and when the cross section of the nuclear fuel assembly is divided into a central portion and a peripheral portion, the water A rod is disposed in the central portion, and the total cross-sectional area of the water rod has a cross-sectional area of four or more of the fuel rods, and a short fuel rod among the fuel rods has the water rod in the peripheral portion. A nuclear fuel assembly characterized by being arranged in a position not adjacent to.
の15/24〜21/24の長さを有する特許請求の範囲第１項記
載の核燃料集合体。2. The nuclear fuel assembly according to claim 1, wherein the short fuel rod has a length of 15/24 to 21/24 of a fuel rod having a normal length.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61120001A JPH0827366B2 (en) | 1986-05-24 | 1986-05-24 | Nuclear fuel assembly |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP61120001A JPH0827366B2 (en) | 1986-05-24 | 1986-05-24 | Nuclear fuel assembly |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP9066120A Division JP2804752B2 (en) | 1997-03-19 | 1997-03-19 | Nuclear fuel assembly |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS62276493A JPS62276493A (en) | 1987-12-01 |
| JPH0827366B2 true JPH0827366B2 (en) | 1996-03-21 |
Family
ID=14775436
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP61120001A Expired - Lifetime JPH0827366B2 (en) | 1986-05-24 | 1986-05-24 | Nuclear fuel assembly |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0827366B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2768673B2 (en) * | 1987-09-30 | 1998-06-25 | 株式会社東芝 | Fuel assembly |
| JP2597589B2 (en) * | 1987-07-20 | 1997-04-09 | 株式会社東芝 | Fuel assembly |
| US5112570A (en) * | 1988-04-04 | 1992-05-12 | Hewlett-Packard Company | Two-phase pressure drop reduction bwr assembly design |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58129385A (en) * | 1982-01-29 | 1983-08-02 | 株式会社東芝 | Fuel assembly for bwr type reactor |
| JPS60224092A (en) * | 1984-04-20 | 1985-11-08 | 株式会社東芝 | Fuel aggregate |
| US4675154A (en) * | 1985-12-20 | 1987-06-23 | General Electric Company | Nuclear fuel assembly with large coolant conducting tube |
-
1986
- 1986-05-24 JP JP61120001A patent/JPH0827366B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62276493A (en) | 1987-12-01 |
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| Date | Code | Title | Description |
|---|---|---|---|
| EXPY | Cancellation because of completion of term |