Core and Fuel Design of ABWR and ABWR-II

Transcription

1 GENES4/ANP2003, Sep , 2003, Kyoto, JAPAN Paper 1108 Core and Fuel Design of ABWR and ABWR-II Takaaki Mochida 1*, Motoo Aoyama 1, Kouichi Sakurada 2 and Kouji Hiraiwa 2 1 Hitachi Ltd., Nuclear Systems Division, Hitachi, Ibaraki, , Japan 2 Toshiba Cooperation, Power Systems & Services Company, Isogo, Yokohama, Kanagawa, , Japan Core and fuel design features and engineering summary of Advanced BWR-II (ABWR-II) are presented in comparison to ABWR. The core and fuel of ABWR is designed with emphasis on the proven technology and the compatibility with other commercial BWR fuels in order to provide high reliability. So the fuel bundle configuration of ABWR is no different from other BWRs, On the contrary, in the core design of ABWR-II, more emphasis was put on the improvement of fuel economy and the flexibility to the variety of fuel cycles. A new K-lattice concept and large fuel bundle was introduced in order to cope with improvement of shutdown margin which is confronted with high burnup fuel (more than 60 GWd/t) or MOX fuels. Also, 1.5 times larger fuel bundle helps to reduce number of fuel bundles, CRs and CRDs as well as the improvement of thermal margin. For the 1700 MWe/4960MWt plant, 424 fuel bundles and 197 CR/CRDs are used and preliminary core design analysis shows the feasibility of high burnup core of 60 GWd/t. Moreover, an innovative design of the Spectral Shift Rod fuel bundle core design is studied for the purpose of fuel economy improvement, though it is optional. KEYWORDS: ABWR, ABWR-II, core design, fuel design, thermal margin, shutdown margin, N-lattice, K-lattice, fuel assembly, power density I. Introduction BWR plant development and core and fuel design change is described historically at first. Core design of BWRs has been modified in accordance with the design progress in fuel assembly type especially, average core power density and LHGR (linear heat generation rate) has been improved as the plant capacity becomes large. Fig.1 illustrates the outline of BWR development and fuel design changes. First commercial BWR in Japan is 356 MWe class BWR-2 and succeeding two BWRs are 460 MWe class BWR-3s. The power density of these BWRs is about 41kW/l and they used 7x7 fuel originally, which maximum LHGR is limited as 17.5kW/ft (57.5kW/m). For the development of BWR-4, design power density is significantly improved by the thermal design criteria changes based on the operation experience and the new experimental results. That is, Hench-Levy correlation based on the multi-channel experiment was introduced for the critical heat flux and fuel mechanical design criteria was changed into 1% solid deformation of cladding, instead of the fuel center melting criteria at excess power. The MLHGR was increase from 17.5kW/ft to 18.5 kw/ft (60.7 kw/m) and the power density is also increased into 51kW/l. Typical BWR-4 has a plant capacity of 784 MWe. Above design changes focused on the increase of power density, however, high LHGR brought large PCIOMR loss in order to keep the fuel integrity. Thus, LHGR reduction * Corresponding author, Tel , Fax , takaaki_mochida@pis.hitachi.co.jp with high power density was the another challenge. The solution was the development of 8x8 fuels, with more thin fuel rod than that of 7x7 fuels. Moreover, 8x8 fuel for BWR-5 has extended its active fuel length into 3710 mm (146 inch) from 3660 mm (144 inch). Typical power density of BWR-5 is about 50 kw/l and the plant capacity is 1100 MWe. The Advanced BWR (ABWR) is a succeeding BWR next to BWR-5 and the design work started in early 1980s among GE, Toshiba, Hitachi and TEPCO. First Establish Permit was certified in 1991 in Japan and the construction was started in 1991 and it was commercially operated in II. Design Objectives of ABWR The core and fuel of ABWR is designed with emphasis on the proven technology and the compatibility with other commercial BWR fuels in order to provide high reliability. Following core design conditions are required as well as BWR-5 design. - Capability of thermal power to meet 1300 MWe - Improvement of fuel economy with currently available technology - Operate with sufficient thermal margins to allow changes in reactor operations and transient accident without damage to core - MLHGR < 13.4 kw/ft (44 kw/m) - Less than 0.1% of the core experience boiling transition during worst expected transients - More than 1% cold shutdown margin - Meet stand-by liquid control injection system requirement

2 - Enough hot excess reactivity for full power operation through cycle (13 EFPM) - Meet energy utilization plan - Meet current fuel bundle design limit - Capability of MOX fuel loading up to 1/3 of core - Capability of daily load follow operation - Capability of high burnup fuel up to 45 GWd/t in average discharge exposure III. Design features of ABWR 1. Standard Design The outline of ABWR reactor and reactor core is illustrated in Fig. 2. Since the proven technology and the compatibility with other commercial BWR fuels were important in design objectives, the 8x8 fuel with Zr liner (Step I fuel), which was the latest BWR bundle at that moment, was selected as the reference fuel bundles. The power density is also kept as 50 kw/l, which is almost same as BWR/5 and the number of fuel bundle in the core becomes 872 for 1356 Mwe /3926 MWt plant. Also the improvement of economy was the major objectives of ABWR core design, improved core designs such as control cell core concept (CCC), axially enrichment and gadolinia zoning, multi enrichment initial core and Zr liner fuel claddings are applied for the ABWR as well as other BWRs. The only difference with the former BWRs is the fuel bundle pitch of 155 mm (6.1 inch), while the standard BWR has fuel bundle pitch of 152 mm (6.0 inch). The outline is illustrated in Fig. 3. This design change increases H/U and reduces the void reactivity coefficient eventually. The new lattice is called N lattice (N stands for Niigata) and it is ideal for high burn up fuels or larger loading of MOX fuels. Moreover, with the combination of the design optimization of the FMCRD and the Reactor Internal Pump capacity, flow window of 10 % at the rated power is also introduced in order to extend the operational flexibility of the power control by the core flow and to enhance the BWR spectral shift effect by the flow control consequently. 2. Core and fuel design renewal for K-6 and 7. During the plant construction of Kashiwazaki-Kariwa Unit 6/7 (K-6/7), which are the first ABWRs, the high burnup 8x8 fuel (Step II fuel) has commercialized in Japan and the license renewal for core and fuel design was made before the initial fuel loading. The fuel configuration of the original Step I fuel and the renewed Step II fuel is compared in Fig. 4. Max. fuel burnup becomes 50 GWd/t and the core average discharge burnup for the reload fuel is increased to 39.5 GWd/t for K-6/7. It is also important to note that fuel configuration design as shown in Fig.4. is free from the BWR generation. In other words, recent development of BWR fuel has been independent of the reactor development. Therefore, latest fuel configuration of 9x9 fuel (Step III fuel) is also applicable to ABWR and latest ABWRs in Japan are licensed with 9x9 fuels. IV. Design objectives of ABWR-II Although ABWR already stand for the Advanced BWR, the conceptual design for the more advanced BWR was started in early 1990s in order to improve plant economy of BWR plants in the 21 st century. The reactor is now called ABWR-II. Japanese utilities and major BWR vendors in Japan and USA has participated in the development programs of ABWR-II. Major working reports for ABWR-II core development are found in several International meetings such as ICONEs 2)-8) and ICAPPs 9)-10) The design objectives of ABWR-II are summarized as follows. - Capability of thermal power to meet 1500 MWe or 1700 MWe. - Improvement of fuel economy with advanced technology, including the under-developing technology, whichi can be feasible before Operate with thermal margins equivalent to the current ABWR - More than 1% cold shutdown margin - Meet stand-by liquid control injection system requirement - Enough hot excess reactivity for full power operation of 18 months without refueling. - Meet current fuel bundle design limit - Capability of full MOX fuel loading. - Capability of high burnup fuel up to 60 GWd/t in average discharge exposure - Capability to provide flexibility in fuel cycle strategy. V. Design features of ABWR-II Most innovative and remarkable design change for the ABWR-II core design is the large K-lattice concept. Among the above-mentioned design objectives, fulfillment of large thermal power may require large number of fuel bundles if conventional core and fuel configuration is used. Since the large number of fuel bundle is disadvantageous in the plant capital cost and the maintenance cost, initial study of core design was focused in the reduction of the bundle number. Also, high burnup lead to the improvement of fuel economy, however, it eventually requires the another improvement of the core design of BWR. During the preliminary studies of fuel bundle selection, it was found that the conventional lattice (N-lattice) only offers limited opportunity for increasing the fuel bundle size due to the limitations to satisfy the cold shutdown margin (CSDM). However, K-lattice configuration shown in Fig. 5 with the bundle pitch of 1.5 times larger than N-lattice gives satisfactory results in CSDM and in the reduction of fuel number. Typical relation between the bundle pitch and CSDM is shown in Fig. 6. Also, the uprate of the power density was reviewed in

3 ABWR-II study. As the recent BWR-6 plants, which power density is about 55 kw/l, in USA and Europe, give acceptable operation experience without the any changes in fuel thermal margin criteria, the reference power density for ABWR-II was set as 58 kw/l. Enlarged bundle size also helps to increase the power density, because the large bundle is able to increase the area inside the channel box under the same water gap between adjacent two channel box, and it give more fuel rods by 10% in case of bundle size of 1.5 times larger. At the present, the number of fuel bundles for the reference 1700Mwe plant is 424 and the number of the control rod drives (CRDs) is 197, which is less than the ABWR and it lead to the reduction in the capital cost of the reactor equipments. Typical core configuration of ABWR-II is shown in Fig. 7. Reference core design with the bundle configuration shown in Fig. 8 showed satisfactory results in MLHGR and MCPR performance as well as CSDM performance for UO 2 core of 60 GWD/t and MOX core of 45GWD/t with 18 month cycle operation. 5)-7) The thermal mechanical design of the large K-lattice fuel bundle for ABWR-II is under way and it is expected that the present thermal design criteria can be satisfied. The major core design parameters for ABWR-II is described in Table 1 in comparison of the ABWR design. Moreover, the optional core design of the spectral shift rod has been performed recently and the results are presented in ICCAP 9),10) and this GENES4/ANP2003 meeting. VI. Conclusion Core and fuel design features and engineering summary of ABWR-II are presented in comparison to ABWR. Although the design objectives of both reactors are similar, there are some differences in design approach. So far, the preliminary design of ABWR-II has been studied for about 10 years and based on the steady progress of development results, we understand that the basic core design of ABWR-II is quite feasible and it is expected to be realized until References 1) S. Hucik, GE Advanced Boiling Water Reactors and Plant systems design, 8 th Pacific Basin Nuclear Conference, Taipei, Taiwan (1992). 2) A. Omoto, The Japanese Utilities Requirements of Next Century BWR, Third International Conference on Nuclear Engineering (ICONE-3), Kyoto Japan (1995). 3) L. E. Fennern et al., Core and Transient Design for a BWR of the Next Century, Third Internal Conference on Nuclear Engineering (ICONE-3), S208-2, Kyoto Japan (1995). 4) R. Yoshioka et al., Core and Transient Design of a BWR for the Next Century, Forth Internal Conference on Nuclear Engineering (ICONE-4), Vol.2, p109, New Orleans LA. (1996). 5) M. Aoyama et al., Optimization of Core Design for the Next Generation BWR, Fifth Internal Conference on Nuclear Engineering (ICONE-5), No-2636, Nice France (1997). 6) M. Aoyama et al., Toward Enhanced Flexibility in the Fuel Cycle For ABWR-II Core Design, Fifth Internal Conference on Nuclear Engineering (ICONE-6), No-6562, San Diego CA. (1998). 7) K. Yamada, et al, Core and Dynamic Characteristic Design for ABWR-II, Proc. 7th International Conference on Nuclear Engineering (ICONE7), No.-7426, Tokyo Japan (1999). 8) T. Anegawa, et al, The Status of Development Activities of ABWR-II, Proc. 9th International Conference on Nuclear Engineering (ICONE9), No.-377, Nice France (2001). 9) M. Moriwaki, et al, ABWR-II Core Design with Spectral Shift Rods for Operation with All Control Rods Withdrawn, Proc. International Congress on Advanced Nuclear Power Plant (ICAPP), Session 6.02, Hollywood, Florida, USA (2002).

4 Table 1 Major Design Features for ABWR and ABWR-II Item Unit ABWR-II ABWR Electric power MWe Reactor thermal power MWt Maximum core flow rate t/hr 62.1x x10 3 Active core height m Core diameter m Fuel bundle pitch cm Number of control rods Number of fuel bundles

5 P l a BWR-3 BWR-2 BWR-4 Scale Effect BWR-5 ABWR 8x8 lattice 7x7 lattice Year 9x9 lattice 2000 ABWR- 1700MWe Large K lattice 2010 Fig. 1 BWR development and fuel design changes Fig. 2 ABWR reactor internals

6 12.0 inch Fuel Bundle Control Blade Conventional Lattice Design (C -lattice) 12.2 inch Wide Pitch Lattice Design (N -lattice) Fig. 3 Wide pitch fuel lattice for ABWR STEP-I Fuel STEP-II Fuel STEP-III Fuel Upper Tie Plate Upper Tie Plate Upper Tie Plate Water Rod Water Rod Water Rod Part length Rod Spacer Spacer Spacer Lower Tie Plate Lower Tie Plate Lower Tie Plate Fig. 4 Recent Fuel Design Changes

7 Fuel Bundle Control Blade Conventional N-Lattice Design 1.5 Times Large K-Lattice Design Fig. 5 Lattice Configuration for ABWR and ABWR-II Cold shutdown margin (% k) K-lattice with inventory 20%up Base(Conventional N-lattice) Bundle size Fig. 6 Relation between Bundle size and CSDM

8 Fuel bundle 424 Control rod 197 Fig. 6 ABWR-II core configuration Fig. 7 ABWR-II Core configuration Water rod Water box Partition Water rod or SSR Fuel Reference bundle configuration Partition SSR bundle configuration Fig. 8 Typical ABWR-II Fuel Bundle Configuration

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