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Title The use of reduced-moderation light water reactors for transuranic isotope burning in thorium fuel
Publication Date
Date Accessioned
University/Publisher University of Cambridge
Abstract Light water reactors (LWRs) are the world’s dominant nuclear reactor system. Uranium (U)-fuelled LWRs produce long-lived transuranic (TRU) isotopes. TRUs can be recycled in LWRs or fast reactors. The thermal neutron spectrum in LWRs is less suitable for burning TRUs as this causes a build-up of TRU isotopes with low fission probability. This increases the fissile feed requirements, which tends to result in a positive void coefficient (VC) and hence the reactor is unsafe to operate. Use of reduced-moderation LWRs can improve TRU transmutation performance, but the VC is still severely limiting for these designs. Reduced-moderation pressurized water reactors (RMPWRs) and boiling water reactors (RBWRs) are considered in this study. Using thorium (Th) instead of U as the fertile fuel component can greatly improve the VC. However, Th-based transmutation is a much less developed technology than U-based transmutation. In this thesis, the feasibility and fuel cycle performance of full TRU recycle in Th-fuelled RMPWRs and RBWRs are evaluated. Neutronic performance is greatly improved by spatial separation of TRU and 233-6U, primarily implemented here using heterogeneous RMPWR and RBWR assembly designs. In a RMPWR, the water to fuel ratio must be reduced to around 50% of the normal value to allow full actinide recycle. If implemented by retrofitting an existing PWR, steady-state thermal-hydraulic constraints can still be satisfied. However, in a large break loss-of-coolant accident, the emergency core cooling system may not be able to provide water to the core quickly enough to prevent fuel cladding failure. A discharge burn-up of ~40 GWd/t is possible in RMPWRs. Reactivity control is a challenge due to the reduced worth of neutron absorbers in the hard neutron spectrum, and their detrimental effect on the VC, especially when diluted, as for soluble boron. Control rods are instead used to control the core. It appears possible to achieve adequate power peaking, shutdown margin and rod-ejection accident response. In RBWRs, it appears neutronically feasible to achieve very high burn-ups (~120 GWd/t) but the maximum achievable incineration rate is less than in RMPWRs. The reprocessing and fuel fabrication requirements of RBWRs are less than RMPWRs but more than fast reactors. A two-stage TRU burning cycle, where the first stage is Th-Pu MOX in a conventional PWR feeding a second stage continuous burn in a RBWR, is technically reasonable. It is possible to limit the core area to that of an ABWR with acceptable thermal-hydraulic performance. In this case, it appears that RBWRs are of similar cost to inert matrix incineration in LWRs, and lower cost than RMPWRs and Th- and U-based fast reactor recycle schemes.
Subjects/Keywords Thorium; Light Water Reactor; Plutonium; Transuranic; Reduced-moderation; Nuclear fuel cycle; Reactor physics
Contributors Parks, Geoffrey T (advisor)
Language en
Country of Publication uk
Record ID oai:www.repository.cam.ac.uk:1810/247162
Repository cambridge
Date Retrieved
Date Indexed 2019-02-15
Issued Date 2015-02-03 00:00:00

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…also FH ) FLWR Flexible light water reactor FP Fission product FR Fast reactor FVR Fully voided reactivity – reactivity when core is filled with saturated steam GFR Gas-cooled fast reactor H/HM Hydrogen to heavy metal [ratio]…

…Loading pattern LWR Light water reactor MA Minor actinides (Pa, Np, Am, Cm, Cf – sometimes a relevant subset is specified) MCPR Minimum critical power ratio MDC Moderator density coefficient MDNBR Minimum departure from nuclear boiling…

…range of candidate fuel cycles and reactor platforms. In this thesis, conventional light water reactors (LWRs) are preferred as they are cheaper, lower risk and the technology already exists. TRU recycle in LWRs is limited by the moderator…

…capture 12 probability of most TRU isotopes in the hard spectrum, which allows a superior neutron economy to be achieved. Extensive studies have been conducted by the Japan Atomic Energy Agency (JAEA) to develop a flexible light water reactor

…successfully performed at the Shippingport Light  Water Breeder Reactor (Hecker, 1979). The neutronic properties of Th fuel allow it to maintain relatively flat reactivity with burn-up once sufficient 233U has been bred, in a relatively thermal…

…List of Abbreviations Elements are commonly abbreviated to their symbols (e.g. Th = thorium) ABWR Advanced boiling water reactor ADSR Accelerator-driven subcritical reactor AFF Axial form factor AGR Advanced gas-cooled reactor AHWR…

…Advanced heavy water reactor APA Advanced plutonium assembly BP Burnable poison BWR Boiling water reactor CHF Critical heat flux CR Conversion ratio CRP Control rod program CSDM Cold shutdown margin DC Doppler coefficient DDH Dalle Donne…

…HC High conversion HFP Hot full power HWR Heavy water reactor HZP Hot zero power JAEA Japanese Atomic Energy Agency LBLOCA Large-break loss-of-coolant accident LEU Low enriched uranium   3 LOCA Loss-of-coolant accident LP…