High-Temperature XAFS Measurement of Molten Salt Systems
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GENES4/ANP2003, Sep. 15-19, 2003, Kyoto, JAPAN Paper 1017 Study on High Performance MOX Fuel and Core Design in Full MOX ABWR(1) by GNF-J Sadayuki Izutsu1*, Daisuke Goto1, Jun Saeki1, Takehiro Kokubun1 and Jun Yokoya2 1Global Nuclear Fuel-Japan Co.,Ltd., Yokosuka, Kanagawa, 239-0836, Japan 2Electric Power Development Co.,Ltd., Tokyo, 104-8165, Japan The concepts of high-performance MOX fuel using 10x10 lattices suitable for full-MOX ABWR are shown in this paper, in which average discharge exposure is extended up to 45GWd/t with heavy-metal inventory increased over current MOX, reducing the number of refueling bundles, resulting in fuel cycle cost reduction and core performance satisfaction. Also, the increase of Pu inventory is taken into account from the viewpoint to extend the flexibility of MOX fuel utilization. KEYWORDS: High Performance MOX Fuel, Full MOX ABWR, 10x10 lattice, Discharge exposure I. Introduction for thermal margin, the power-exposure envelope can be set Discharge exposure is progressively extended for uranium lower than that of 9×9 uranium fuel by increase of the fuel used for BWR currently in operation, and thus fuel number of fuel rods, and therefore the active fuel length of cycle economy is being improved. In contrast, discharge MOX rods could be extended to 3.71m from 3.55m of exposure (33GWd/t) of current MOX fuel to be loaded in current MOX and Pu inventory can be increased. BWRs including ABWR as Pu-thermal utilization program Reprocessed material composition is assumed to be is less than that (45GWd/t) of uranium fuel by 25%. mixture of the reprocessed Pu isotope and U isotope. Besides, current MOX fuel bundle has slightly reduced heavy-metal inventory owing to the shortened active fuel Table 1 Basic specification of core and fuel design length compared to uranium fuel as the countermeasure to fuel rod internal pressure increase. Items Specification The concepts of high-performance MOX fuel suitable for Core full-MOX ABWR are shown in this paper, in which Type Advanced Boiling discharge exposure is extended up to that of current Water Reactor (ABWR) high-burnup uranium fuel with heavy-metal inventory Thermal power (MW) 3,926 increased over current MOX, reducing the number of Core flow (t/h) 52.2x103 refueling bundles, resulting in fuel cycle cost reduction and Core pressure (MPa) 7.17 core performance satisfaction. Also, the increase of Pu Number of fuel bundles 872 inventory is taken into account from the viewpoint to extend Number of control rods 205 the flexibility of MOX fuel utilization. Fuel Assembly Two types of lattice concepts are approached aiming at Lattice configuration 10x10 average discharge exposure of 45GWd/t on the basis of the Average discharge exposure 45 10x10 lattice configuration, that is, the high moderation (GWd/t) concept and the low moderation concept are possible. Peak pellet exposure (GWd/t) about 75 The channel, core, and regional stabilities are analyzed, Pellet material UO2-PuO2 (MOX rods) and satisfy design target. The SLMCPR is shown to be UO2-Gd2O3 (UO2 rods) almost equal to full MOX-fueled core loaded with current MOX matrix material Depleted U (0.22wt%) 8×8 MOX fuel. The ∆MCPR is estimated to be higher for Cladding outside diameter (mm) 10.3 the first type concept and lower for the second type concept Cladding wall thickness (mm) 0.66 compared to current MOX within the plant design margin. Cladding material Zirc-2 (with Zr liner) Operating Condition II. Design Conditions Cycle length (month) 13 (Equilibrium) High burnup MOX fuel designs of average discharge Reprocessed material exposure 45GWd/t have been studied for full-MOX ABWR composition 239 241 under the conditions shown in Table 1. Based on the Pu isotope composition Pu =61%,Pu =7% 235 10x10 lattices selected to improve performance, especially U isotope composition U =0.9% * Corresponding author, Tel. +81-468-33-9053, Fax. +81-468-33- 9248, E-mail: [email protected] III. Fuel and Core Design Concepts The current MOX design concept of discharge exposure High Burnup MOX 33GWd/t as the reference is shown in Fig.1, the (fuel economy enhancement) configuration of which is selected to be the same design as STEP-2 bundle (39.5GWd/t discharge exposure) with a large water rod at the center of 8x8 fuel rod configuration and Void Coefficient Gd Rod Fraction Fuel Rod Internal Increase Increase Pressure Increase with 12 Gd-contained UO2 rods. The MOX fuel rod is designed to make the fuel stack length shorter and the plenum volume larger than those of the UO fuel rod so as to 2 Peripheral Gd 10x10 suppress the rod internal pressure. W/R W/R addition minimization Rod Disposition Configuration The high burnup to increase the generation of energy per (Concept(I)) (Concept(II)) heavy metal weight is effective to enhance fuel economy due to the reduction of fabricated fuel bundles and spent fuel Fig. 2 High-burnup MOX design concept bundles. On the other hand, the high burnup to increase the Pu content has the tendency toward the absolute value increase of void coefficient and Gd worth reduction, causing Table 2 Main features of 10x10 MOX concepts severer transient result and Gd-contained UO rod fraction 2 Current Concept (I) Concept (II) increase. Also, it may make bundle heavy metal weight MOX (10x10 MOX) (10x10 MOX) reduce through the rod plenum volume increase against rod (8x8) internal pressure. Therefore, on the basis of the 10x10 bundle configuration Number of 1 (4) 2 (4) 1 (1) selected to reduce linear heat generation rate mitigating the water rod types 2 (1) rod internal pressure, two types of lattice concepts are (*) approached: the concept (I) where the water rods are added Number of 48 / 12 78 / 12 99 / 6 (High moderation concept) and the concept (II) where the MOX rods / water rods are minimized (Low moderation concept), in Gd rods Number of Pu 4 2 3 addition to the optimization of Gd-contained UO2 rod locations. Fig.2 shows the relation on the influence of high content rod burnup and the selected concepts. The main features of the types concepts are shown in Table 2. Fuel active 3.55 3.71 3.71 length (m) (same as UO2 ) (same as UO2 ) Heavy metal base + 5% + 16% inventory MOX Bundle Pu weight base x 1.6 x 2.2 24 * : Number of fuel rods corresponding to each W/R area 18 1.Concept (I) The configuration of concept (I) is shown in Fig.3. In order to avoid the absolute value increase of void coefficient, two large water rods with each area corresponding to four 12 fuel rods and two water rods with the same diameter as fuel rod are disposed in the central region of 10x10 bundle Axial Hight configuration, resulting in the moderator to heavy metal volume ratio of 3.02 similar to 3.07 of STEP-3(9x9) UO2 6 UO -Gd O fuel rod 2 2 3 fuel. Water rod The fundamental idea of nuclear design is that most MOX fuel rod Gd-contained UO2 rods are placed in the bundle peripheral region and the water rod neighboring region so as to reduce the Gd-contained rods and to increase Pu inventory. Fig.4 shows the relation between Gd rod worth and Gd-contained Fig. 1 Current MOX design concept rod location. The Gd rod worth placed in the bundle (33GWd/t discharge exposure ) peripheral region is 35% improved than that in the bundle internal region. It is possible to extend burnup exposure of MOX fuel without the decrease of MOX fuel rod fraction with Gd rod worth increase effect and power flattening effect by the Gd-contained rods placed in the bundle showing that the absolute value of void coefficient is smaller peripheral region. Two rod types of Pu content, the in the case of larger H/HM fuel. To the contrary, the fabrication cost reduction per unit Pu weight due to Pu moderator density coefficient for MOX fuel has a maximum inventory increase and uranium enrichment decrease are point and decreasing tendency in the both sides of H/HM, realized. Twelve partial fuel rods (PLR) are utilized to showing that the absolute value of void coefficient is smaller keep the same pressure loss as 8x8 or 9x9 bundles. The in the case of larger Pu content. This concept (II) utilizes average Puf content of the bundle is 4.2wt% and the the decreasing feature of moderator density coefficient in the maximum PuO2 content of the MOX rod is 10wt%, resulting low H/HM region, and the increasing feature of Pu and in the increase of 5% in heavy metal weight and x1.6 in Pu heavy metal inventory. weight compared to the current 8x8 MOX design. The fundamental idea of nuclear design is that Gd-contained UO2 rods are placed in the bundle corner G G G region so as to reduce the Gd-contained rods and to increase Low Puf content Pu inventory. Because the UO2 rods disposed in the bundle corner region contain depleted uranium without Pu, the part High Puf content G G of which contains Gd, the low enrichment of high neutron G PLR(Low Puf content) importance region contributes the reduction of void G coefficient and hot operation to cold reactivity swing. G G G Nat-U+Gd conc. Three types of Puf content, the fabrication cost reduction per unit Pu weight due to Pu inventory increase and uranium Water rod enrichment decrease are realized. Twelve partial fuel rods G G G (PLR) are utilized to keep the same pressure loss as 8x8 or 9x9 bundle.