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Feasible ways to achieve high conversion in thorium-fueled CANDU and PWR reactors

Abstract : This study focuses on Th-fueled CANDU and PWR reactors as the third and last component of a reactor fleet. Plutonium extracted from spent fuel of a standard CANDU or PWR is converted in the second component (FR or CANDU) to Uranium (mainly 233U) which feeds a Th/U multirecycling third component. Breeding and multirecycling of 233U in CANDU is optimized by modifying the core. It has been shown that slight Moderation Ratio (MR) variations have no sensible impact on conversion. We demonstrate that heterogeneous bundles with fertile and fissile zones allow savings of about 7% of 233U initial inventory for the same burnup. However, for all the examined geometric modifications in Th/U fueled CANDU, the fissile inventory ratio at end of cycle is observed to be only dependent on the final burnup. Breeding is achieved for short burnups of 6-7GWd/t. Multirecycling in CANDU is also simulated. In the multirecycling regime, higher burnup (~15-20GWd/t at slightly lower conversion) can be sustained by the addition of a small quantity of Uranium from the second component of the reactor fleet at each recycle. A simple Th/U cycle neutronic analysis explains why the irradiation time is identical at each recycle if the 233U initial mass introduced is kept constant. For the PWR case, studies show that variations in either the MR or the use of heterogeneous seed/blanket assemblies do little to improve conversion. In fact, it is found that at equivalent burnup the Th/U conversion progress margin by standard modifications is smaller in PWR than in CANDU. The faster neutron spectra, achievable by extreme sub-moderation, are required to expect breeding in existing PWR vessel and core. Obviously lower values of MR provoke difficulties in proper heat extraction and thermal-hydraulics. To get rid of these difficulties, we propose to use the so-called Spectrum Shift Control technique with a standard MR, a heavy water coolant and reactivity managed by progressive addition of H2O in the coolant. But managing reactivity this way has a cost in terms of conversion. Finally we evaluate another reactivity management technique based on fertile material withdrawal.
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Conference papers
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http://hal.in2p3.fr/in2p3-00422474
Contributor : Emmanuelle Vernay <>
Submitted on : Wednesday, October 7, 2009 - 11:02:44 AM
Last modification on : Wednesday, September 16, 2020 - 4:07:54 PM

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  • HAL Id : in2p3-00422474, version 1

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P. Guillemin, A. Nuttin, A. Bidaud, J. Brizi, N. Capellan, et al.. Feasible ways to achieve high conversion in thorium-fueled CANDU and PWR reactors. International Conference GLOBAL 2009 "The Nuclear Fuel Cycle: Sustainable Options & Industrial Perspectives", Sep 2009, Paris, France. pp.62-72. ⟨in2p3-00422474⟩

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