Large Bundle Design and its Development for ABWR-II

The next generation ABWR, the ABWR-II, has been under development for more than a decade in Japan. Among various features newly adopted for the ABWR-II, a 1.5 times lager fuel bundle is notable. This bundle design makes it possible to increase the total number of fuel rods in the core while minimizing the reactor pressure vessel size increase. Also, the number of fuel bundles in the core will be reduced to almost half that of the ABWR. Due to larger cruciform control rods and the K-lattice configuration, in which a bundle faces two control rods along all four faces, the ABWR-II core has better shut-down performance while using fewer control rods than the ABWR. These features provide more core and fuel design flexibility. By using this flexibility, an innovative reactor core concept applying spectral shift rods (SSRs) is proposed to improve the plant economy and the operability of the 1700 MWe ABWR-II reactor. The SSR is a new type of water rod, in which a water level is naturally developed during operation and changed according to the coolant flow rate through the fuel channel. By taking advantage of the largeness of the ABWR-II bundle, enhanced spectral shift operation by SSRsmore » allows operation of the ABWR-II with all control rods withdrawn. In addition, the ABWR-II core with SSRs can be expected to provide a maximum uranium saving factor of 8% against the reference ABWR-II core with conventional water rods. The feasibility of manufacturing large fuel bundles has been studied. (authors)« less