JP2004325437A - METHOD OF MANUFACTURING PELLET OF URANIUM OXIDE ADDED WITH Gd2O3 USING SPHEROIDIZING AFTER CONTINUOUS ATTRITION CO-MILLING (SACAM) PROCESS - Google Patents
METHOD OF MANUFACTURING PELLET OF URANIUM OXIDE ADDED WITH Gd2O3 USING SPHEROIDIZING AFTER CONTINUOUS ATTRITION CO-MILLING (SACAM) PROCESS Download PDFInfo
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本発明はGd2O3添加UO2ペレットの製造方法に関する。より詳しくはUO2ペレットの焼結密度と結晶粒サイズを効果的に制御できる共粉砕後球状化(SACAM)工程を利用したペレットの製造方法に関する。 The present invention relates to a method for producing Gd 2 O 3 added UO 2 pellets. More particularly, the present invention relates to a method for producing pellets using a co-milling and spheroidizing (SACAM) process capable of effectively controlling the sintering density and crystal grain size of UO 2 pellets.
酸化ガドリニウム(Gd2O3)を添加してUO2ペレットを製造する従来の一般的な製造工程を図１．１に示してある。図１．１のように、従来にはUO2粉末とGd2O3粉末とを機械的に混合した後、予備成形、 造粒、成形、及び焼結する工程を経てUO2ペレットを製造し、この際、UO2粉末とGd2O3粉末とを機械的に混合する方法としては図２．１と図２．２に夫々示したV型混合方式や円錐型混合方式などを用いるのが一般であった。 A conventional general manufacturing process for manufacturing UO 2 pellets by adding gadolinium oxide (Gd 2 O 3 ) is shown in FIG. 1.1. Conventionally, as shown in Figure 1.1, after mechanically mixing UO 2 powder and Gd 2 O 3 powder, UO 2 pellets are manufactured through the steps of preforming, granulating, forming, and sintering. At this time, as a method of mechanically mixing the UO 2 powder and the Gd 2 O 3 powder, a V-type mixing method or a conical mixing method shown in FIGS. 2.1 and 2.2, respectively, may be used. It was common.
Gd2O3粉末が添加されたUO2ペレットの焼結密度と結晶粒サイズを制御する因子としては成形圧力、焼結温度、及び焼結雰囲気が挙げられる。しかし、成形圧力と焼結温度の因子のみでは粉末特性や混合状態自体に因る焼結特性を変化させるのがほぼ不可能であり微細組織が良好な焼結ペレットの製造も困難である。したがって、これを解決すべく一部では焼結雰囲気を、乾燥した水素雰囲気から水分の含まれた雰囲気に変えて焼結を行っている。 Factors controlling the sintering density and crystal grain size of the UO 2 pellet to which the Gd 2 O 3 powder is added include a molding pressure, a sintering temperature, and a sintering atmosphere. However, it is almost impossible to change the powder characteristics and the sintering characteristics due to the mixed state itself only by the factors of the molding pressure and the sintering temperature, and it is also difficult to produce sintered pellets having a good microstructure. Therefore, in order to solve this, sintering is performed in part by changing the sintering atmosphere from a dry hydrogen atmosphere to an atmosphere containing moisture.
このように成形圧力と焼結因子(温度及び雰囲気)を制御して焼結密度及び結晶粒サイズを制御するのには一定の制約が伴われ、同時に利用する機器の使用上の限界点が問題となりかねない。したがって、Gd2O3が添加されたUO2ペレットの製造にあたって制限された範囲の成形圧力及び焼結条件しか利用できず、品質上の制限も受けるようになる。 Controlling the sintering density and grain size by controlling the molding pressure and sintering factors (temperature and atmosphere) in this way involves certain restrictions, and at the same time there is a problem in the use of equipment to be used. It could be. Therefore, only limited ranges of molding pressure and sintering conditions can be used in the production of UO 2 pellets to which Gd 2 O 3 is added, and quality is limited.
そしてGd2O3とUO2との混合酸化物はUO2に比して焼結性が低く、同一焼結条件下においては焼結ペレットの密度、結晶粒サイズ全てがUO2焼結ペレットに比して小さいことが分かっている。また、水素気流中で焼結した場合には、焼結ペレットに多数の微細亀裂が発生したり、微細組織が不均一であるとの問題が生じる。したがって、かかる問題を解決すべくGd2O3を添加したUO2においては通常水分の含まれた水素雰囲気や二酸化炭素と一酸化炭素との混合ガス雰囲気下で焼結を行う。 And the mixed oxide of Gd 2 O 3 and UO 2 has low sinterability compared to UO 2, and under the same sintering conditions, the density and crystal grain size of the sintered pellet are all UO 2 sintered pellets It turns out to be small. In the case of sintering in a hydrogen stream, there are problems that a large number of fine cracks are generated in the sintered pellet and that the microstructure is not uniform. Therefore, in order to solve this problem, sintering is usually performed in UO 2 to which Gd 2 O 3 is added in a hydrogen atmosphere containing moisture or a mixed gas atmosphere of carbon dioxide and carbon monoxide.
したがって、本発明は上述した従来技術の問題を解決すべく案出されたものとして、Gd2O3を添加してUO2ペレットを製造する工程において、その焼結密度と結晶粒サイズを制御する因子として成形圧力、焼結温度、及び雰囲気の他にその混合方法を最適化することにより均一な焼結密度と結晶粒サイズを有するUO2ペレットの製造方法を提供することに目的がある。 Accordingly, the present invention as being devised to solve the problems in the conventional technology, in the step of producing UO 2 pellets with the addition of Gd 2 O 3, to control the crystal grain size and its sintered density It is an object of the present invention to provide a method for producing UO 2 pellets having uniform sintering density and grain size by optimizing the mixing method in addition to the molding pressure, sintering temperature, and atmosphere as factors.
上記目的を成し遂げるための本発明は、Gd2O3を添加したUO2ペレットの製造工程において、UO2粉末に1〜10重量%のGd2O3粉末を混合機内でその粉末自体の流動性を利用して予備的に混合する段階；上記混合粉末を連続型アトリッションミル方式混合粉砕機に装入して混合粉砕する段階；上記粉砕された粉末を混合機に装入して該粉末粒子を球状化させる段階；及び、上記球状化された粉末を用いて成形体を製造した後焼結する段階；を含む共粉砕後球状化(SACAM)工程を利用したGd2O3添加UO2ペレットの製造方法に関する。 The present invention for accomplishing the above object, Gd in 2 O 3 UO 2 pellets of the manufacturing process with the addition of 1 to 10 wt% of Gd 2 O 3 powder in the mixer flowability of the powder itself UO 2 powder Preliminarily mixing using: mixing the above mixed powder into a continuous attrition mill type mixing and crushing machine; mixing and crushing; mixing the above crushed powder into a mixing machine to obtain the powder Gd 2 O 3 -added UO 2 using a co-milling and spheroidizing (SACAM) process including spheroidizing the particles; and sintering after manufacturing a compact using the spheroidized powder. The present invention relates to a method for producing pellets.
上述したように、本発明はGd2O3を添加してUO2ペレットを製造する工程において、粉末を連続型アトリッションミル方式の粉砕混合機を用いて粉砕混合することによりミーリング回数の調整及び後続する球状化処理により粉末の均質混合と流動性が向上され、予備成形及び 造粒工程無しで潤滑剤を添加して直接Gd2O3添加UO2ペレットを焼結成形することができる。また、小さい成形圧力及び乾いた還元性焼結雰囲気においても微細亀裂が無く均質で結晶粒の大きい焼結体を得られ、所望の焼結密度を得たければ、気孔形成剤などを添加すると焼結体製造に対する余裕度を高めることができる。したがって、かかる余裕度によりGd2O3添加UO2ペレットの品質が改善され生産性も向上された。さらに、本発明法により製造された混合粉末は、成形時潤滑剤を添加せずダイ壁潤滑により直接成形する場合にも欠陥の無い焼結体を製造させることができる。 As described above, in the present invention, in the step of producing UO 2 pellets by adding Gd 2 O 3 , the number of milling times is adjusted by grinding and mixing the powder using a continuous attrition mill type grinding mixer. In addition, the homogenization and fluidity of the powder are improved by the subsequent sphering treatment, and the Gd 2 O 3 -added UO 2 pellets can be directly formed by adding a lubricant without a preforming and granulating step. In addition, even under a low molding pressure and a dry reducing sintering atmosphere, a homogeneous sintered body having large crystal grains without fine cracks can be obtained. It is possible to increase the margin for the production of the consolidated body. Accordingly, the quality of the Gd 2 O 3 -added UO 2 pellet was improved and the productivity was also improved by such a margin. Further, the mixed powder produced by the method of the present invention can produce a defect-free sintered body even when directly molded by die wall lubrication without adding a lubricant during molding.
以下、添付の図を参照しながら本発明を説明する。図１．２は本発明の共粉砕後球状化(SACAM：Spheroidizing After Continuous Attrition Co-Milling)工程のGd2O3添加UO2ペレットの製造工程図である。Gd2O3の添加されたUO2ペレットは固溶体を形成し、Gd2O3のUO2に対する固溶状態の変化に応じてその焼結密度と結晶粒サイズが変化する。固溶状態を変化させる要素としては成形圧力、即ち成形密度、焼結温度、及び雰囲気、粉末(UO2とGd2O3)粒子サイズ、UO2粉末とGd2O3粉末との混合状態などが挙げられる。 Hereinafter, the present invention will be described with reference to the accompanying drawings. FIG. 1.2 is a production process diagram of Gd 2 O 3 -added UO 2 pellets in the Spheroidizing After Continuous Attrition Co-Milling (SACAM) process of the present invention. The UO 2 pellet to which Gd 2 O 3 is added forms a solid solution, and the sintered density and the crystal grain size change according to the change of the solid solution state of Gd 2 O 3 to UO 2 . Factors that change the solid solution state include molding pressure, i.e. molding density, sintering temperature, atmosphere, powder (UO 2 and Gd 2 O 3 ) particle size, mixed state of UO 2 powder and Gd 2 O 3 powder, etc. Is mentioned.
本発明者らは、Gd2O3の添加されたUO2ペレットの焼結密度を制御するために、従来用いられてきた成形圧力、焼結温度、及び雰囲気条件の他に粉末(UO2とGd2O3)特性、そしてUO2粉末とGd2O3粉末との粉砕混合状態を制御因子に用いられることに着目した。とりわけ、UO2粉末とGd2O3粉末とを混合する方法として、従来用いられていたV型混合方式や円錐型混合方式などの機械的混合方式の代わりに、単に粉末の流動性を利用して混合した後連続型アトリッションミル方式を利用すると焼結密度及び結晶粒サイズの制御がより向上されることを発見し、本発明を提示するまでに至ったのである。
先ず、本発明においてはUO2粉末とGd2O3粉末とを粉末の流動性を利用して予備的に混合する。この際、添加されるGd2O3粉末を1〜10重量%範囲に制限することが好ましい。その添加量が1重量%未満であるとその添加による効果が微々しく、10重量%を超過するとUO2固溶限界を外れかねないからである。より好ましくは、2〜8重量%の範囲で添加する。
The present inventors have found that in order to control the sintered density of the added UO 2 pellets Gd 2 O 3, a molding pressure which has been conventionally used, and in addition to the powder (UO 2 sintering temperature, and atmospheric conditions Gd 2 O 3 ) characteristics, and the fact that the pulverized mixed state of UO 2 powder and Gd 2 O 3 powder can be used as control factors. In particular, as a method of mixing the UO 2 powder and the Gd 2 O 3 powder, instead of using a mechanical mixing method such as a V-type mixing method or a conical mixing method which has been conventionally used, simply use the fluidity of the powder. It has been found that the use of a continuous attrition mill system after the mixing has further improved the control of the sintering density and the crystal grain size, leading to the present invention.
First, in the present invention, the UO 2 powder and the Gd 2 O 3 powder are preliminarily mixed using the fluidity of the powder. In this case, it is preferable to limit the Gd 2 O 3 powder is added to 10 wt% range. If the amount is less than 1% by weight, the effect of the addition is insignificant, and if it exceeds 10% by weight, it may deviate from the UO 2 solid solution limit. More preferably, it is added in the range of 2 to 8% by weight.
本発明においては、かかる2種の粉末を該粉末の流動性のみ利用して混合機で予備混合する。言い換えると、如何なる媒介物質も用いずに2種の粉末の流れを利用して粉末同士を混合させるもので、通常円筒形の容器に2種の粉末を装入した後、一定時間該容器を混合機で回転させ混合することによって容易に成し遂げることができる。 In the present invention, the two kinds of powders are premixed by a mixer using only the fluidity of the powders. In other words, two kinds of powders are mixed using the flow of two kinds of powders without using any mediator.After charging the two kinds of powders into a usually cylindrical container, the containers are mixed for a certain period of time. It can be easily achieved by spinning and mixing on a machine.
UO2とGd2O3粉末の初期粒度範囲は夫々0.5〜103μmと1.16〜93.6μmの範囲にあり、その平均粒子サイズも夫々4.75μmと9.8μmほどと大変不均一である。したがって、かかる粒度分布を有するUO2 とGd2O3粉末を上述した混合比で混合し従来の機械的方式により混合すると、粒子サイズの不均一及び混合比率差により均一性の良くない粉末ができ、かかる混合粉末から製造されたペレットでは結晶粒が均一な微細組織が得難い。図2は従来の機械的方式の混合機として、図２．１はV型混合機、図２．２は円錐型混合機を示す。 The initial particle size ranges of the UO 2 and Gd 2 O 3 powders are in the range of 0.5 to 103 μm and 1.16 to 93.6 μm, respectively, and their average particle sizes are very non-uniform, at 4.75 μm and 9.8 μm, respectively. Therefore, if UO 2 and Gd 2 O 3 powders having such a particle size distribution are mixed at the above-mentioned mixing ratio and mixed by a conventional mechanical method, a powder having poor uniformity due to non-uniform particle size and a difference in mixing ratio can be obtained. However, it is difficult to obtain a fine structure having uniform crystal grains in the pellets manufactured from the mixed powder. 2 shows a conventional mechanical mixer, FIG. 2.1 shows a V-type mixer, and FIG. 2.2 shows a conical mixer.
したがって、本発明においては、上記問題に鑑みて、上記のように混合されたUO2とGd2O3粉末を図3のような連続型アトリッションミル方式の混合粉砕機を用いて混合粉砕することを特徴とする。かかる連続型アトリッションミル方式の混合粉砕機を用いると、図３．１の設備でミーリング回数を変化させたり、または図３．２の多段一回設備を用いることで、粉末の粒子サイズ及び混合状態を微細制御でき、また焼結密度及び結晶粒サイズを幅広く所望の範囲内に制御することができる。なお、所望のサイズの結晶粒を有する状態で気孔形成剤などを添加し焼結密度を制御するのも可能である。 Therefore, in the present invention, in view of the above problems, the UO 2 and Gd 2 O 3 powders mixed as described above are mixed and pulverized using a continuous attrition mill type mixing and pulverizer as shown in FIG. It is characterized by doing. When such a continuous attrition mill type mixing and crushing machine is used, the particle size and the powder size of the powder can be changed by changing the number of times of milling in the equipment of FIG. 3.1 or by using the multi-stage single equipment of FIG. 3.2. The mixing state can be finely controlled, and the sintering density and the crystal grain size can be controlled widely within a desired range. In addition, it is also possible to control the sintering density by adding a pore-forming agent or the like in a state having crystal grains of a desired size.
この際、混合粉砕のために上記アトリッションミル方式の混合粉砕機に装入される粉末装入量は混合容器内容積の１０〜３０％、そして装入されたボール装入量を50〜70%に夫々制限することが好ましい。粉末装入量をこのように設定する理由は混合粉砕効果を最大化させるためである。詳述すると、ボール装入量が多くなると混合粉砕効果は増大するが投入される粉末量は少なくなり、逆にボール装入量が少なくなると投入される粉末量は多くなるが混合粉砕効果は低下する為である。より好ましくは上記ボールのサイズを直径3mm〜10mm範囲に制限することである。 At this time, the amount of the powder charged into the attrition mill type mixing and crushing machine for mixing and crushing is 10 to 30% of the volume of the mixing vessel, and the amount of the charged ball is 50 to 50%. It is preferable to limit each to 70%. The reason for setting the powder charging amount in this way is to maximize the mixing and pulverizing effect. More specifically, as the ball charge increases, the mixing and crushing effect increases, but the amount of powder input decreases.On the contrary, when the ball charge decreases, the amount of powder input increases, but the mixing and crushing effect decreases. To do it. More preferably, the size of the ball is limited to a range of 3 mm to 10 mm in diameter.
かかる効果は回転羽の回転数とも相関関係があるので、ボール及び粉末装入量そして回転羽の回転数などの組合により粉砕効果を極大化することができる。本発明においては上記混合粉砕機の回転羽の回転数を30〜200rpmに制限することが好ましい。 Since such an effect is correlated with the number of revolutions of the rotating blade, the pulverizing effect can be maximized by a combination of the amount of the ball and the powder charged and the number of revolutions of the rotating blade. In the present invention, it is preferable to limit the number of rotations of the rotating blades of the mixing and crushing machine to 30 to 200 rpm.
また、アトリッションミルは連続型なので通過時間が即ち混合粉砕時間であり、一般に投入量がほぼ100%排出されるまでには2〜5分かかる。 In addition, since the attrition mill is a continuous type, the passing time is the mixing and pulverizing time, and it generally takes 2 to 5 minutes until almost 100% of the input amount is discharged.
一方、通常の機械的方式のミル工程を経た粉末は、粉末が微粉砕されながら粉末の流動性が良くなくなり、これにより粉末の流動性を向上させるべく次のような粉末処理作業を行った。即ち、先ず流動性の良くない粉末を装入させた後約50〜200MPaの成形圧力で予備成形体(slug)を製造した(この際、成形密度(green density)は理論密度の約30〜50%)。そして、かかる予備成形体を造粒機(granulator)においてローター(rotar)と直径約1mmの打孔篩(sieve)との間に挟ませ衝撃と摩擦により造粒した。こうして出来上がった顆粒は該粉末流動性に優れ後続する成形工程においてプレス成形すると、長さが一定な成形体(green pellet)(直径10mm、長さ10mm)を素早く製造することができた。 On the other hand, the powder that has been subjected to the ordinary mechanical milling process has a poor powder flowability while the powder is finely pulverized, and thus the following powder processing operation was performed to improve the powder flowability. That is, first, a powder having poor fluidity was charged, and then a preform (slug) was produced at a molding pressure of about 50 to 200 MPa (where the green density was about 30 to 50% of the theoretical density). %). The preform was sandwiched between a rotor and a sieve having a diameter of about 1 mm in a granulator and granulated by impact and friction. The granules thus obtained were excellent in the fluidity of the powder, and were press-molded in a subsequent molding step, whereby a green pellet having a constant length (diameter: 10 mm, length: 10 mm) could be rapidly produced.
しかし、混合されたUO2とGd2O3粉末を図3のような連続型アトリッションミル方式混合粉砕機を用いて粉砕する本発明においては、上述した予備成形や造粒工程が不要になる。 However, in the present invention in which the mixed UO 2 and Gd 2 O 3 powders are pulverized using a continuous attrition mill type mixing and pulverizing machine as shown in FIG. 3, the above-described preforming and granulating steps are not required. Become.
その代わりに、上記連続型アトリッションミル方式混合粉砕機において粉砕された粉末を所定の混合機に装入して回転させることにより、効果的にその粉末粒子を顆粒形態に球状化させることを特徴とする。かかる球状化工程は、上述した粉末の流動性のみ利用して粉末同士を混合させる工程と同様に、通常円筒形の容器に混合粉砕された粉末を装入した後一定時間該容器を回転させることにより容易に成し遂げられる。 Instead, by charging the powder pulverized in the continuous attrition mill type mixing pulverizer into a predetermined mixer and rotating it, the powder particles can be effectively spheroidized into a granular form. Features. The spheroidizing step is similar to the above-described step of mixing powders only by using the fluidity of the powder, and is usually performed by charging the mixed and ground powder in a cylindrical container and then rotating the container for a predetermined time. Can be more easily achieved.
一般に回転時間が短いと球状化が良からず、回転時間が長すぎると粒子が大きくなり過ぎて後続する成形工程において装入が困難となり長さが均一な成形体を製造し難くなる。したがって、本発明においては上記容器内容積の30〜50%粉末を容器に装入した後、30〜90分間該容器を回転させることが好ましい。 In general, if the rotation time is short, the spheroidization is not good, and if the rotation time is too long, the particles become too large, making it difficult to charge in a subsequent molding step and making it difficult to produce a molded body having a uniform length. Therefore, in the present invention, it is preferable to rotate the container for 30 to 90 minutes after charging 30 to 50% of the powder in the container to the container.
このように本発明において従来法と異なって予備成形工程や別途の造粒工程を必要とせず、上述した球状化工程を通して微粉末を顆粒化できるのは、粉末がボールの衝撃と摩擦により微粉砕されながら、あられのように硬くなり表面が活性化される為である。したがって、かかる粉末を通常使用する円筒形の容器に装入して予備混合において使用する混合機に装填した後一定時間回転させると所望のサイズの顆粒を得られるのである。 Thus, unlike the conventional method, the present invention does not require a preforming step or a separate granulation step and can granulate the fine powder through the spheroidizing step described above because the powder is finely ground by the impact and friction of the ball. This is because the surface becomes activated while the surface is activated. Therefore, a granule having a desired size can be obtained by charging the powder into a commonly used cylindrical container, loading the powder into a mixer used for premixing, and rotating the powder for a certain period of time.
上記のように球状化処理されたUO2とGd2O3混合粉末は流動性が大変優れている。したがって、本発明においてはかかる流動性が優れた顆粒を用いることにより、後続する成形体製造時、従前の潤滑剤を添加する方法の代わりに潤滑剤を添加せずダイ壁への潤滑剤塗布のみで良好な成形体を製造可能な直接成形工程(direct compacting)を実現することができる。 The mixed powder of UO 2 and Gd 2 O 3 spheroidized as described above has excellent fluidity. Therefore, in the present invention, by using such granules having excellent fluidity, at the time of subsequent molded article production, instead of the method of adding the conventional lubricant, only the lubricant is applied to the die wall without adding the lubricant. Thus, it is possible to realize a direct compacting process capable of producing a good molded article.
そして、このように製造された成形体に通常の焼結工程を施すと物性の優れたUO2ペレットを製造することができる。この際、本発明は具体的な焼結条件に制限されるわけではないが、好ましくは上記成形体を1650〜1750℃の還元雰囲気(一般的に水素雰囲気)下で2〜6時間焼結する。 Then, by subjecting the compact thus produced to a normal sintering step, UO 2 pellets having excellent physical properties can be produced. At this time, the present invention is not limited to specific sintering conditions, but preferably, the compact is sintered for 2 to 6 hours under a reducing atmosphere (generally, a hydrogen atmosphere) of 1650 to 1750 ° C. .
以下、実施例を通して本発明を詳しく説明する。 Hereinafter, the present invention will be described in detail through examples.
UO2粉末にGd2O3粉末8重量%を粉末の流動性を利用して予備的に混合した。そしてかかる混合粉末を連続型アトリッションミル方式による混合粉砕機で混合粉砕し、この際、ミーリング回数を0、3、5、7及び10回の5段階に変化させた。ここで、ミーリング回数は連続型アトリッションミルを通過した回数を示し、ミーリング回数5回の意味は同一試料が連続型アトリッションミルで5回繰り返しミーリングされたことを意味する。そして、この際の連続型アトリッションミルの回転羽の回転数は150rpm、装入されるボールは直径8mmのジルコニアボールであり、ボール装入量は70vol.%、粉末試料の量は20vol.%にした。 8% by weight of Gd 2 O 3 powder was preliminarily mixed with UO 2 powder using the fluidity of the powder. Then, the mixed powder was mixed and pulverized by a mixing and pulverizer using a continuous attrition mill method, and the number of times of milling was changed to five stages of 0, 3, 5, 7, and 10 times. Here, the number of times of milling indicates the number of times of passing through the continuous attrition mill, and the meaning of five times of milling means that the same sample was repeatedly milled five times by the continuous attrition mill. In this case, the rotation speed of the rotary blades of the continuous attrition mill was 150 rpm, the balls to be charged were zirconia balls having a diameter of 8 mm, the ball loading amount was 70 vol.%, And the amount of the powder sample was 20 vol. %.
このように微粉砕された粉末を混合機を使って一定時間粉末同士の自体流動性を利用して回転させ粒子を粗大化させながら球形化させ、この際球状化処理時間は60分にした。 The finely pulverized powder was rotated using a mixer for a certain period of time using the fluidity of the powders by a mixer to make the particles coarse while spheroidizing, and the spheroidizing treatment time was 60 minutes.
これら試料に対して、即ちミーリング回数及び球状化処理による見かけ密度、成形圧力による成形密度及び焼結密度、そして焼結体微細組織を調べた。その結果を焼結特性試験結果として図4〜6に示した。 For these samples, the number of times of milling, the apparent density by the spheroidizing treatment, the molding density and the sintering density by the molding pressure, and the microstructure of the sintered body were examined. The results are shown in FIGS.
図4はアトリッションミーリング回数及びミーリング後の球状化処理による粉末の見かけ密度を示したグラフである。図4に示したように、UO2粉末にGd2O3粉末を8重量%添加して予備混合する際、粉末粒子の平均寸法は4.7μmであるが連続型アトリッションミルにおいて5回混合粉砕した後の混合粉末の粒子寸法は3.7μmとして、混合粉砕性が向上することがわかる。即ち、本発明法によると、連続型アトリッションミルのミーリング回数及び球状化処理により粉末の見かけ密度は増加することがわかり、これにより粉末の流動性が増大して予備成形及び造粒工程を省略して直に成形体を製造できることがわかる。 FIG. 4 is a graph showing the number of attrition milling and the apparent density of the powder by the spheroidizing treatment after the milling. As shown in FIG. 4, when adding 8% by weight of Gd 2 O 3 powder to UO 2 powder and pre-mixing, the average size of the powder particles is 4.7 μm, but mixed 5 times in a continuous attrition mill. When the particle size of the mixed powder after pulverization is 3.7 μm, it can be seen that the mixed pulverizability is improved. That is, according to the method of the present invention, it can be seen that the apparent density of the powder is increased by the number of milling and spheroidizing treatment of the continuous attrition mill, whereby the fluidity of the powder is increased and the preforming and granulating steps are performed. It can be seen that the compact can be manufactured directly by omitting it.
図5は夫々の連続型アトリッションミーリング回数(milling cycles)及び球状化処理を施した粉末に潤滑剤を0.3重量%添加混合した後、成形圧力(150MPa、300MPa)による成形密度(green density)、そしてかかる条件下で製造された成形体を乾気流の水素雰囲気下において1750℃で4時間焼結したペレットの焼結密度(sintered density)を示したものである。図5から分かるように、ミーリング回数が増加し成形圧力が増加すると成形密度は増加する一般的な傾向があらわれる。それに比して、焼結密度は成形密度が増加しても3回以上のミーリング回数においては飽和になる傾向をあらわす。即ち、低い成形圧力でも高い焼結密度を得られることがわかる。 Fig. 5 shows the number of continuous attrition milling cycles (milling cycles) and the addition of 0.3% by weight of lubricant to the spheroidized powder, followed by the molding density (green density) by molding pressure (150MPa, 300MPa). 1 shows the sintered density of pellets obtained by sintering a compact produced under the above conditions at 1750 ° C. for 4 hours under a hydrogen atmosphere in a dry air flow. As can be seen from FIG. 5, there is a general tendency that the molding density increases as the number of milling increases and the molding pressure increases. On the other hand, the sintered density tends to be saturated when the number of times of milling is three or more even if the molding density is increased. That is, it is understood that a high sintering density can be obtained even with a low molding pressure.
一方、図6は本発明の製造法により製造された(ミーリング回数：5)UO2-8wt%Gd2O3焼結体の微細組織写真として、図６．１は混合酸化物核燃料の均質度を、図６．２は結晶粒サイズを示す。図６．１から分かるように、一部に遊離UO2(白部分)があらわれるが、全体的に遊離UO2や遊離Gd2O3がほぼ無い均質な固溶体を形成することが分かり、微細亀裂もまた存在しないことが分かる。また、図６．２において、結晶粒サイズは約15μmと測定され、その寸法がほぼ均質なことが分かる。 On the other hand, FIG. 6 is a microstructure photograph of a UO 2 -8 wt% Gd 2 O 3 sintered body manufactured by the manufacturing method of the present invention (number of milling: 5), and FIG. 6.1 is a homogeneity of the mixed oxide nuclear fuel. Figure 6.2 shows the grain size. As can be seen from FIG. 6.1, free UO 2 (white portion) appears in part, but a homogeneous solid solution almost free of free UO 2 and free Gd 2 O 3 is formed. Also does not exist. Also, in FIG. 6.2, the crystal grain size was measured to be about 15 μm, and it can be seen that the dimensions were almost uniform.
Claims (5)
UO2粉末に1〜10重量%のGd2O3粉末を混合機内で該粉末自体の流動性のみ利用して予備的に混合する段階；
上記混合粉末を連続型アトリッションミル方式の混合粉砕機に装入して混合粉砕する段階；
上記粉砕された粉末を混合機に装入してその粉末粒子を球状化させる段階；及び、
上記球状化された粉末を用いて成形体を製造した後焼結する段階；
を含む共粉砕後球状化(SACAM)工程を利用したGd2O3添加UO2ペレットの製造方法。 In the production process of UO 2 pellets added with Gd 2 O 3 ,
Step of mixing preliminarily using UO 2 powder from 1 to 10 wt% of Gd 2 O 3 powder mixer on the flowability of the powder itself only;
Charging the mixed powder into a continuous attrition mill type mixing and crushing machine and mixing and crushing;
Charging the ground powder into a mixer to make the powder particles spherical; and
Sintering after manufacturing a compact using the spheroidized powder;
A method for producing Gd 2 O 3 -added UO 2 pellets using a co-milling and spheroidization (SACAM) process comprising:
Gd 2 O 3 added UO 2 method for producing pellets according to claim 1, characterized in that sintering in a reducing atmosphere of the shaped body 1,650-1,750 ° C..
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| CN100364016C (en) * | 2004-12-02 | 2008-01-23 | 中国核动力研究设计院 | Material mixing process and device for preparing (U, Gd) 02 combustible poisonous core block |
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| CN107837761A (en) * | 2016-09-20 | 2018-03-27 | 中核四〇四有限公司 | A kind of MOX powder rolls spheronization process |
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