Fast Reactors and Accelerator Driven Systems Knowledge Base

Conference Article: Preliminary safety analysis of a Swedish accelerator driven system employing nitride fuel and burnable absorbers

M. Eriksson, J. Wallenius, K. Tucek, W. Gudowski, J. Cahalan

Abstract

Safety features of a heavy-metal cooled accelerator driven waste burning system (ADS) subject to a series of accident events have been investigated. The fuel consists of plutonium and minor actinides contained in a zirconium-nitride matrix. The SAS4A [1] computer code is applied to the analysis of transients imposed by a step increase in neutron source and to loss of coolant flow events. Special attention is paid to the maximum permissible temperature in the nitride fuel with regards to thermal dissociation mechanisms. In general, it is found that the system copes with protected and unprotected loss of flow scenarios. Peak temperatures in fuel, cladding, and coolant are kept within postulated design criteria. The benign behavior is attributed to large pin pitches that allow for large coolant volume fractions, use of lead/bismuth as thermal bond between fuel and cladding, and a primary system designed to maintain large amounts of natural circulation flow. It is found that the system is most sensitive to source transients. An increase in source intensity introduce high fuel temperatures and this may jeopardize the stability of nitride fuel. Safety consequences of source transients depend strongly on the particular assumptions involved in the analysis. Above all, the rate and magnitude of the source disturbance and the effectiveness of the heat removal equipment may significantly alter the accident scenario. The importance for early detection and successful termination of source transients is acknowledged. Discussion is presented on the technique used in accelerators to fulfill emergency shut down of the proton beam. Key features are pointed out that distinguish accelerator beam shut off from the shut down mechanism used in critical reactors.

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key words: Fast Neutron Spectrum Systems, Nuclear Technology
Reference:
Proceedings of a Committee Meeting (TCM) on “Core Physics and Engineering Aspects of Emerging Nuclear Energy Systems for Energy Generation and Transmutation” held in Argonne, Illinois, U.S.A., 28 November - 1 December 2000
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--1356, pp:251-264