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Upgraded core design of a small-sized High Temperature Gas-cooled Reactor suitable for application in emerging countries presented at the international conference in Kazakhstan

Jun. 26, 2012

JAEA has conducted conceptual study of a small-sized High Temperature Gas-cooled Reactor (HTGR) with thermal power of 50 MW since 2010 with support of Japanese vendors: Toshiba Corporation, Fuji Electric Co., Ltd., Kawasaki Heavy Industries, Ltd., Nuclear Fuel Industries, Ltd., Shimizu Corporation, and Marubeni Utility Services, Ltd. for distributed power and heat supply in regional cities in emerging countries without developed power grid. Employing heat resistant coated fuel particles with ceramic coatings, graphite core components with high heat capacity compared with low power density of the core, the HTGR has superior inherent safety feature that it does not have a harmful effect on environment and human beings even in the worst accident that external power supply and primary coolant is lost.

In June 2012, upgraded core design of the small-sized HTGR was presented by the six Japanese vendors and JAEA in the first International Conference of young scientists and specialists "Current issues on the peaceful use of atomic energy" in Kazakhstan. The presentation included basic specifications, system configuration, and the nuclear reactor core thermal-hydraulic design of the small-sized HTGR. The result of the upgraded core design that allows cost reduction was highly praised, and the prize for the best report was awarded to the presentation. Three best reports were selected among approximately 20 presentations by foreign participants.

Since temperature difference between core inlet and outlet of the High Temperature Engineering Test Reactor (HTTR) at JAEA Oarai is large, about 550 °C, it was necessary to use twelve kinds of uranium enrichment from 3% to 10% and optimize power distribution in order to keep the maximum fuel temperature below a limit value. The presented core design achieved the optimization of power distribution and maintenance of its state for the period of operation with only three kinds of uranium enrichment. More specifically, the attempt to optimize power distribution by adjusting fuel enrichment as well as the density and diameter of burnable poison has succeeded, which enables to lower the fuel temperature at the bottom of the core and flatten the fuel temperature distribution in the vertical direction. As a result, the small-sized HTGR can realize the core power density approximately 1.4 times as large as that of HTTR (Fig. 1). This is the result that leads to reduction in construction cost and fuel cost per unit output.

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