Annals of Nuclear Energy

Annals of Nuclear Energy, 2009

Prospective fuels for a new reactor type, the so called fixed bed nuclear reactor (FBNR) are investigated with respect to reactor criticality. These are ① low enriched uranium (LEU); ② weapon grade plutonium + ThO2; ③ reactor grade plutonium + ThO2; and ④ minor actinides in the spent fuel of light water reactors (LWRs) + ThO2. Reactor grade plutonium and minor actinides are considered as highly radio-active and radio-toxic nuclear waste products so that one can expect that they will have negative fuel costs.The criticality calculations are conducted with SCALE5.1 using S8–P3 approximation in 238 neutron energy groups with 90 groups in thermal energy region. The study has shown that the reactor criticality has lower values with uranium fuel and increases passing to minor actinides, reactor grade plutonium and weapon grade plutonium.Using LEU, an enrichment grade of 9% has resulted with keff = 1.2744. Mixed fuel with weapon grade plutonium made of 20% PuO2 + 80% ThO2 yields keff = 1.2864. Whereas a mixed fuel with reactor grade plutonium made of 35% PuO2 + 65% ThO2 brings it to keff = 1.267. Even the very hazardous nuclear waste of LWRs, namely minor actinides turn out to be high quality nuclear fuel due to the excellent neutron economy of FBNR. A relatively high reactor criticality of keff = 1.2673 is achieved by 50% MAO2 + 50% ThO2.The hazardous actinide nuclear waste products can be transmuted and utilized as fuel in situ. A further output of the study is the possibility of using thorium as breeding material in combination with these new alternative fuels.

Annals of Nuclear Energy, 2013

The present paper compares the reactor physics and transmutation performance of sodium-cooled Fast Reactors (FRs) for TRansUranic (TRU) burning with thorium (Th) or uranium (U) as fertile materials. The 1000 MWt Toshiba-Westinghouse Advanced Recycling Reactor (ARR) conceptual core has been used as benchmark for the comparison. Both burner and breakeven configurations sustained or started with a TRU supply, and assuming full actinide homogeneous recycle strategy, have been developed. State-ofthe-art core physics tools have been employed to establish fuel inventory and reactor physics performances for equilibrium and transition cycles. Results show that Th fosters large improvements in the reactivity coefficients associated with coolant expansion and voiding, which enhances safety margins and, for a burner design, can be traded for maximizing the TRU burning rate. A trade-off of Th compared to U is the significantly larger fuel inventory required to achieve a breakeven design, which entails additional blankets at the detriment of core compactness as well as fuel manufacturing and separation requirements. The gamma field generated by the progeny of U-232 in the U bred from Th challenges fuel handling and manufacturing, but in case of full recycle, the high contents of Am and Cm in the transmutation fuel impose remote fuel operations regardless of the presence of U-232.

Journal of Engineering Research, 2023

of advanced fuel systems formed ThO 2 75 wt.% and UO 2 25 wt.%, which worked with 19.5% enrichment of U 235. It analyzed the physical properties of mixed fuels using the composition of mixtures, such as the lattice parameters, thermal conductivity, specific heat, mechanical strength, and fission gas release. The codes FRAPCON-4.0 and FRAPTRAN-2.0 adapted can calculate the composite fuel response compared with uranium dioxide fuel used for light water reactors. In addition, the increased diffusion coefficient produced lower fuel swelling compared with UO 2. Thorium fuels had included an extensive range of applications, such as pressure-tube heavy water reactors (HWRs), light water reactors (LWRs), and thorium molten salt reactors. Advanced reactors, such as sodiumcooled fast reactors, can support the thorium mixed oxide fuel [1]. Early the Shippingport reactor, in Pennsylvania, USA, was a light water breeding reactor that operated with thorium as fuel during 1977-1982 [2]. Thorium is at least three times more abundant than uranium [3]. The natural isotopic distribution of thorium is 100% of Th 232 and is not fissile, but it is a fertile material, like U 238. Thorium requires fissile materials, such as U 235 and Pu 239 , to begin the reaction. Today, exist a few mixed fuel cycles based on thorium use (Th 232 +Pu 239), (Th 232 +U 233), (Th 232 +U 235), and other formulations, including dopant additions [4]. On the other hand, it researches innovative fuels, such as uranium nitride (UN) and uranium carbide (UC), which have several advantages over UO 2 , such as increased burnup capabilities and higher

Nuclear Engineering and Design, 2010

Large quantities of plutonium have been accumulated in the nuclear waste of civilian LWRs and CANDU reactors. Reactor grade plutonium and heavy water moderator can give a good combination with respect to neutron economy. On the other hand, TRISO type fuel can withstand very high fuel burn-up levels. The paper investigates the prospects of utilization of TRISO fuel made of reactor grade plutonium in CANDU reactors. TRISO fuels particles are imbedded body-centered cubic (BCC) in a graphite matrix with a volume fraction of 68%. The fuel compacts conform to the dimensions of CANDU fuel compacts are inserted in rods with zircolay cladding. In the first phase of investigations, five new mixed fuel have been selected for CANDU reactors composed of 4% RG-PuO 2 + 96% ThO 2 ; 6% RG-PuO 2 + 94% ThO 2 ; 10% RG-PuO 2 + 90% ThO 2 ; 20% RG-PuO 2 + 80% ThO 2 ; 30% RG-PuO 2 + 70% ThO 2. Initial reactor criticality (k ∞,0 values) for the modes , , , and are calculated as 1.

Nuclear Engineering and Design, 2019

The reactor performance and safety characteristics of mixed thorium mononitride (ThN) and uranium mononitride (UN) fuels in a pressurized water reactor (PWR) are investigated to discern the potential nonproliferation, waste, and accident tolerance benefits provided by this fuel form. This paper presents results from an initial screening of mixed ThN-UN fuels in normal PWR operating conditions and compares their reactor performance to UO 2 in terms of fuel cycle length, reactivity coefficients, and thermal safety margin. ThN has been shown to have a significantly greater thermal conductivity than UO 2 and UN. Admixture with a UN phase is required because thorium initially contains no fissile isotopes. Results from this study show that ThN-UN mixtures exist that can match the cycle length of a UO 2-fueled reactor by using 235 U enrichments greater than 5% but less than 20% in the UN phase. Reactivity coefficients were calculated for UO 2 , UN, and ThN-UN mixtures, and it was found that the fuel temperature and moderator temperature coefficients of the nitride-based fuels fall within the acceptable limits specified by the AP1000 Design Control Document. Reduced soluble boron and control rod worth for these fuel forms indicates that the shutdown margin may not be sufficient, and design changes to the control systems may need to be considered. The neutronic impact of 15 N enrichment on reactivity coefficients is also included. Due to the greatly enhanced thermal conductivity of the nitride-based fuels, the UN and ThN-UN fuels provide additional margin to fuel melting temperature relative to UO 2 .

International Journal of Energy Research, 2016

Spent nuclear fuel out of conventional light water reactors contains significant amount of even plutonium isotopes, so called reactor grade plutonium. Excellent neutron economy of Canada deuterium uranium (CANDU) reactors can further burn reactor grade plutonium, which has been used as a booster fissile fuel material in form of mixed ThO 2 /PuO 2 fuel in a CANDU fuel bundle in order to assure reactor criticality. The paper investigates incineration of nuclear waste and the prospects of exploitation of rich world thorium reserves in CANDU reactors. In the present work, the criticality calculations have been performed with 3-D geometrical modeling of a CANDU reactor, where the structure of all fuel rods and bundles is represented individually. In the course of time calculations, nuclear transformation and radioactive decay of all actinide elements as well as fission products are considered. Four different fuel compositions have been selected for investigations: ① 95% thoria (ThO 2) + 5% PuO 2 , ② 90% ThO 2 + 10% PuO 2 , ③ 85% ThO 2 + 15% PuO 2 and ④ 80% ThO 2 + 20% PuO 2. The latter is used for the purpose of denaturing the new 233 U fuel with 238 U. The behavior of the criticality k ∞ and the burnup values of the reactor have been pursued by full power operation for~10 years. Among the investigated four modes, 90% ThO 2 + 10% PuO 2 seems a reasonable choice. This mixed fuel would continue make possible extensive exploitation of thorium resources with respect to reactor criticality. Reactor will run with the same fuel charge for~7 years and allow a fuel burnup~55 GWd/t.

This work investigates the possibility of using thorium-based fuels as an alternative fuel for advanced power reactor APR-1400. MCNPX code version 2.7 with crosssection library ENDF.VII has been used to design an APR-1400 fuel assembly. This code has been used to study the neutronic performance of the proposed thoriumbased Fuel types (0.944 Th, U)O 2 , (0.955 Th, 233 U)O 2 , (0.934 Th, rgPu)O 2. The fuel burn-up parameters such as infinity multiplication factor (k inf), initial heavy metals concentrations, Minor actinides concentration and fission products concentration have been analyzed during 1500 effective full power days (FPDSs) for thoriumbased Fuel types and compared with the common fuel. The analysis of the horizontal thermal power and neutron flux distribution provides valuable insights into the behavior and performance of the suggested Fuel types in the APR-1400 assembly. The analysis of the neutronic results ensures the viability of using the proposed thorium-based fuel types as an alternative fuel to UO 2 because they achieved acceptable safety parameter values and provided a good power distribution through the fuel assembly compared to UO 2 .

2011

The growing inventory of spent nuclear fuel generated in the current “open cycle” adopted in the US can hamper the long term growth of nuclear energy. A proper strategy for closing the fuel cycle and generating “acceptable waste” should hence be a priority of the nuclear industry. While satisfactory technological solutions exist addressing portions of the overall problem, a fully integrated effective solution satisfying all public concerns has yet to be developed. Westinghouse is proposing a new approach, which involves redefining the specifics of the main components involved (fuel form, reactor type and reprocessing technique) so that the nuclear system overall generates wastes which are not perceived as a hazard by the public and with reduced requirements on their disposal. In a closed fuel cycle, the actinides in the spent fuel are typically recovered by reprocessing and recycled in a combination of reactors. Although the transmutation rate of actinides depends on the specific pr...

Journal of Nuclear Science and Technology, 1995

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The PUMA project, a Specific Targeted Research Project (STREP) of the European Union EURATOM 6th Framework Program, is mainly aimed at providing additional key elements for the utilisation and transmutation of plutonium and minor actinides in contemporary and future (high temperature) gas-cooled reactor design, which are promising tools for improving the sustainability of the nuclear fuel cycle, hereby also contributing to the reduction of Pu and MA stockpiles, and to the development of safe and sustainable reactors for CO2-free energy generation. The project runs from