Fast Reactors and Accelerator Driven Systems Knowledge Base

Conference Article: Neutronic analysis of a U-Th fuel cycle, lead cooled accelerator-driven system

Landeyro, P.A.; Guidotti, M. (ENEA, Rome (Italy))

Abstract

This report analyses several events that involve the introduction of reactivity in an accelerator driven system, having a fast neutron spectrum, using Th solid fuel and cooled by Pb. The analysis comprises two phases: the first studies the burning of 232Th in order to determine the equilibrium condition of this type of system. The second, starting from this condition (taken as reference) simulates various possible deviations, some leading to accidents. It can be shown easily that the burning capability of an accelerator-driven system can be evaluated by means of the same calculation tools and cross section sets used for a traditional reactor. The same applies also to the safety conditions. Two irradiation cycles of 1 ton of 232Th have been analyzed. At the end of the first cycle the fuel was reprocessed recovering the isotopes of Th, Pa and U and subsequently recharged after adding 232Th. The Kinf values calculated by ORIGEN2 remain substantially constant during the second irradiation cycle. From these data the average Kinf has been evaluated and with this factor the irradiation time necessary to obtain the closest Kinf to the average has been determined, the Th, Pa and U isotope concentrations corresponding to this time are considered those pertaining to the state of equilibrium, therefore these compositions are regarded as reference configuration. From the calculations of the reactivity values introduced during the transients from the reference to the studied configurations result that one of the most interesting characteristics of this system is the strong void negative coefficient which is surely due to the great quantity of Pb in the reflector.

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key words: Fast Neutron Spectrum Systems, Nuclear Technology
Reference:
Advanced fuels with reduced actinide generation.Technical committee meeting, Vienna (Austria). 21-23 Nov 1995
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--916, pp:179-184