Fast Reactors and Accelerator Driven Systems Knowledge Base

Conference Article: The design of a backup reactor shutdown system of DFBR

Okada, K. (Mitsubishi Heavy Industries, Ltd., Yokohama (Japan)); Tarutani, K. (Toshiba Corp., Tokyo (Japan)); Shibata, Y. (Hitachi Ltd., Tokyo (Japan)); Ueta, M.; Inagaki, T. (Japan Atomic Power Co., Tokyo (Japan))

Abstract

This paper outlines the status of the development of passive safety measures to achieve subcriticality in DFBR. Two independent reactor shutdown systems (RSSs), a primary RSS and a backup RSS, are provided each of which can rapidly bring the reactor to a safe shutdown condition. The backup RSS is provided with a Self-Actuated Shutdown System (SASS), which is passively released due to the Curie point effect by abnormal rising of coolant temperature. Two independent RSSs reduce the occurrence probability of core damage due to the ATWS (ULOF, UTOP & ULOHS) events to less than 10 –7/ry1. Installation of the SASS reduces the occurrence probability of ULOF & ULOHS further by two orders of magnitude. Overall frequency of core damage due to ATWS events is reduced to the order of less than10 -9/ry owing to the SASS installation. A screening study was conducted to search for promising core safety enhancement technologies based on a consideration of reactivity requirements for passive success scenarios in ATWS events. As a result of this study, an installation of Gas Expansion Modules (GEMS) in DFBR was recently proposed to enhance the core safety further. The reactivity worth of 66 GEMS arranged outside of the core was approximately -1.5$, and it is possible to prevent the sodium boiling on ULOF by GEMS alone. In ‘Addition to SASS and GEM, the feasibility study of the Enhanced Thermal Elongation Mechanisms (ETEM) has been conducted. As the results of some experiments and design studies, it was confirmed that ETEM could be one of the promising mechanisms to enhance core safety, and gives less impact on the performance of a future large scale reactor core.

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key words: equipment; failures; fast reactors; feasibility studies; reactivity worths; reactor cores; reactor shutdown; safety; temperature dependence
Reference:
Technical committee meeting on absorber materials, control rods and designs of backup reactivity shutdown systems for breakeven cores and burner cores for reducing plutonium stockpiles. Obninsk (Russian Federation). 3-7 Jul 1995
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--884, pp:111-123