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‣ "Separação e recuperação de Chumbo-208 dos resíduos de Tório e Terras Raras gerados na Unidade Piloto de purificação de Nitrato de Tório" ; RECOVERY OF RADIOGENIC LEAD- 208 FROM A RESIDUE OF THORIUM AND RARE EARTHS OBTAINED DURING THE OPERATION OF A THORIUM PURIFICATION PILOT PLANT

Seneda, José Antonio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/05/2006 Português
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O Brasil tem uma longa tradição na tecnologia do tório, desde a abertura do principal mineral, a monazita, até compostos de pureza grau nuclear, com reservas minerais estimados em 1.200.000 ton – ThO2. Como conseqüência desta produção, foi acumulado um resíduo produzido na unidade piloto de purificação de nitrato de tório, do Instituto de Pesquisas Energéticas e Nucleares- CNEN/SP, mais de 25 toneladas ao longo das últimas três décadas, proveniente dos rafinados e soluções de lavagem do processo de extração por solventes, conhecido como RETOTER. Sua composição, um hidróxido, contendo tório, terras raras e impurezas menores, incluindo o chumbo-208 do decaimento do 232 Th, com abundância isotópica em 88,34 %, enriquecido naturalmente ao longo das eras geológicas. Neste trabalho são discutidos os estudos dos principais parâmetros do processo de recuperação deste chumbo, 0,42 % em massa no RETOTER seco, utilizando-se a técnica de troca iônica com resinas aniônicas em meio clorídrico. A abundância isotópica do chumbo foi analisada por espectrometria de massa termoiônica (TIMS) e de alta resolução (ICPMS), e com os dados calculou-se a secção de choque de captura para nêutrons térmicos. O valor resultante foi de s? o = 14...

‣ Recuperação de Tório e terras raras via peróxido do resíduo  originado na unidade de purificação de  Tório; RECOVERY OF THORIUM AND RARE EARTHS BY THEIR PEROXIDES PRECIPITATION FROM A RESIDUE PRODUCED IN THE THORIUM PURIFICATION FACILITY

Freitas, Antonio Alves de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/05/2008 Português
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Como conseqüência da operação de uma unidade de purificação de tório para a produção de nitrato de tório puro, o Instituto de Pesquisas Energéticas e Nucleares (IPEN) armazenou um resíduo rico em terras raras contendo tório e pequeno teor de urânio. Este resíduo é registrado como RETOTER (Resíduo de Tório e Terras Raras). O resíduo contém os radioisótopos naturais das séries do urânio e do tório. Contribuição radioativa significativa é dada pelos descendentes do tório, especialmente o rádio-228 (T1/2 = 5,7 anos) comumente conhecido como mesotório e o tório-228 (T1/2 = 1,90 anos). Um descendente do tório de muito interesse e presente com teor razoável é o chumbo-208, um isótopo estável. A partir do encerramento das atividades da planta de purificação de tório, os técnicos do IPEN vêm trabalhando no estabelecimento de tecnologia de aproveitamento do tório, das terras raras e do chumbo-208 contidos no RETOTER. O presente trabalho consiste em dissolver o RETOTER com ácido nítrico separando e confinando os contribuintes radioativos, especialmente o rádio-228, por coprecipitação com sulfato de bário. Em seguida o tório foi separado por precipitação como peróxido. As terras raras presentes no filtrado...

‣ Usos das cromatografias  de extração e de troca iônica na separação de Tório e Terras Raras de um resíduo gerado na unidade de purificação de Tório. Aplicação das terras raras como catalisadores na geração  de hidrogênio; Uses of extraction and ion exchange chromatography in the thorium and rare earths separation from industrial residue generated in thorium purification unity at IPEN. Application of rare earths as catalysts for generation of hydrogen

Zini, Josiane
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/03/2010 Português
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Na década de 70 operou-se no IPEN/CNEN-SP uma instalação piloto para estudos do processamento de diferentes concentrados de tório obtidos do tratamento químico da monazita com intuito da obtenção de compostos de tório de pureza nuclear. Esta instalação passou a operar em escala industrial em 1985, gerando em torno de 25 toneladas de resíduo até meados de 2002, quando encerrou suas atividades. Este resíduo contendo tório e terras raras foi denominado Retoter (Resíduo de Tório e Terras Raras) e armazenado no galpão de Salvaguardas do IPEN. O presente trabalho estuda o tratamento deste resíduo, visando questões ambientais, radiológicas e tecnológicas. Estudaram-se dois processos cromatográficos para a separação do tório das terras raras. Um deles, a cromatografia de extração, onde o agente extrator fosfato de tri-n-butila foi suportado em resinas poliméricas Amberlite XAD16. O outro processo, estudado para fins comparativos, já que o material utilizado na cromatografia de extração é inédito no que diz respeito à separação do tório, foi a cromatografia de troca iônica utilizando resinas catiônicas fortes DOWEX 1-X8. Estudou-se, também, o processo cromatográfico de extração com o agente extrator DEHPA suportado em Amberlite XAD16 para o fracionamento...

‣ Determinação de isótopos de Urânio e Tório e Polônio em perfis de sedimento da Baixada Santista, SP; Determination of uranium and thorium isotopes and polonium in sediment profiles from Baixada Santista, SP

Ramos, Guilherme da Franca
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 24/11/2010 Português
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O objetivo do presente trabalho é determinar a concentração de atividade de isótopos de ocorrência natural de urânio e tório e o polônio em perfis de sedimento marinho da Baixada Santista. A Baixada Santista é uma região populosa e abrange os municípios de Bertioga, Guarujá, Santos, São Vicente, Cubatão, Praia Grande, Mongaguá, Itanhaém e Peruíbe. Esta é uma das mais importantes regiões industriais do Brasil, dado ao grande número de indústrias, como as de fertilizantes, petroquímicas e do aço. A grande atividade industrial, juntamente com a grande população da região, exerce forte pressão sobre a biota marinha. O presente trabalho analisou 10 perfis de sedimentos marinhos extraídos da região. Foram coletados perfis com tamanhos variando de 41 a 98 cm, na região de Santos, Cubatão, São Vicente e Bertioga. Os perfis foram fatiados a cada 2 cm e passaram por um pré-tratamento físico e químico. Para a dissolução total e digestão foram utilizados ataques com ácidos fortes. As técnicas radioquímicas utilizadas para a separação dos radionuclídeos e preparação das fontes radioativas, para a contagem alfa, foram separação por cromatografia de troca iônica e eletrodeposição para urânio e tório e deposição espontânea para o polônio. Os resultados obtidos para as concentrações de atividade dos radionuclídeos são semelhantes aos de sedimentos marinhos em regiões não contaminadas...

‣ Potentialities and practical limitations of absolute neutron dosimetry using thin films of uranium and thorium applied to the fission track dating

Bigazzi, G.; Guedes, S.; Hadler, J. C.; Iunes, P. J.; Paulo, SR; Oddone, M.; Osorio, A. M.; Zuniga, A.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 651-656
Português
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Neutron dosimetry using natural uranium and thorium thin films makes possible that mineral dating by the fission-track method can be accomplished, even when poor thermalized neutron facilities are employed. In this case, the contributions of the fissions of (235)U, (238)U and (232)Th induced by thermal, epithermal and fast neutrons to the population of tracks produced during irradiation are quantified through the combined use of natural uranium and thorium films.If the Th/U ratio of the sample is known, only one irradiation (where the sample and the films of uranium and thorium are present) is necessary to perform the dating. However, if that ratio is unknown, it can be determined through another irradiation where the mineral to be dated and both films are placed inside a cadmium box.Problems related with film manufacturing and calibration are discussed. Special attention is given to the utilization of thin films having very low uranium content. The problems faced suggest that it may be better to substitute these films by uranium doped standard glasses calibrated with thicker uranium films (thickness greater than 1.5 x 10(13) mu m).

‣ Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

Iunes, P. J.; Hadler, J. C.; Bigazzi, G.; Tello, C. A.; Guedes, S.; Paulo, SR
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 201-211
Português
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In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

‣ The behavior of dissolved uranium in groundwaters of the Morro do Ferro thorium deposit, Brazil

Marcos Bonotto, Daniel
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 155-168
Português
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Groundwater samples were collected for several months in boreholes drilled at Morro do Ferro, a thorium and rare earth deposit located on the Poços de Caldas Plateau, Minas Gerais State, Brazil. An aquifer system has developed in the weathered mantle due to in situ intense alteration. The weathered zone includes a thick argillaceous laterite greater than 100 m thick. The U content and 324U/238U activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body. Some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays. © 1989.

‣ Potentiometric and conductometric studies on the formation of thorium molybdates as a function of pH

Prasad,Shiva; Gonçalves,Sílvia B.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2000 Português
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The formation of thorium molybdates obtained by interaction of thorium nitrate and sodium molybdate at specific pH levels 7.8, 5.5 and 4.1 have been studied by electrometric techniques involving pH and conductometric titrations. The well-defined inflections and breaks in titration curves provide cogent evidence for the formation of thorium normal-ThO2.2MoO3 and para-3ThO2.14MoO3 molybdates in the vicinity of pH 5.3 and 4.4, respectively. Analytical investigations on the precipitates of thorium molybdates have also been carried out, which support the electrometric results.

‣ Spectrophotometric simultaneous determination of uranium and thorium using partial least squares regression and orthogonal signal correction

Niazi,Ali
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2006 Português
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A simple, novel and sensitive spectrophotometric method was described for simultaneous determination of uranium and thorium. The method is based on the complex formation of uranium and thorium with Arsenazo III at pH 3.0. All factors affecting the sensitivity were optimized and the linear dynamic range for determination of uranium and thorium found. The simultaneous determination of uranium and thorium mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. By multivariate calibration methods such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 600-760 nm range for 25 different mixtures of uranium and thorium. Calibration matrices contained 0.10-21.00 and 0.25-18.50 µg mL-1 of uranium and thorium, respectively. The RMSEP for uranium and thorium with OSC and without OSC were 0.4362...

‣ Adsorption of thorium(IV) on chemically modified Amazon clays

Guerra,Denis L.; Viana,Rúbia R.; Airoldi,Claudio
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2009 Português
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Kaolinite and smectite clay samples from the Amazon region, Brazil, were modified with 2-mercaptobenzimidazole (MBI) using homogeneous and heterogeneous routes. The modified clay samples (K HOM, S HOM, K HET and S HET) were characterized by textural analysis, SEM and 13C NMR spectroscopy. The chemically modified clay samples showed modifications of their physical-chemical properties including: specific area 48.0 (S) to 869.8 m² g-1 (S HET). The ability of these materials to remove thorium(IV) from aqueous solution was followed by a series of adsorption isotherms adjusted to a Sips equation at room temperature, and pH 2.0. The maximum number of moles adsorbed was determined to be 8.29, 8.86, 9.57 and 9.89 10-1 mmol g-1 for K HOM, K HET, S HOM and S HET, respectively. The energetic effects (ΔintH, ΔintG and ΔintS) caused by thorium(IV) cation adsorption were determined through calorimetry.

‣ The Growth of Monoraphidium sp. and Scenedesmus sp. Cells in the Presence of Thorium

de Queiroz, Juliana Cristina; Ferreira, Ana Cristina de Melo; da Costa, Antonio Carlos Augusto
Fonte: The Scientific World Journal Publicador: The Scientific World Journal
Tipo: Artigo de Revista Científica
Publicado em 29/04/2012 Português
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Toxicity of thorium by Monoraphidium sp. and Scenedesmus sp. was studied. Microalgal cultures were inoculated in ASM-1 medium in presence and absence of thorium. Its effect was monitored by direct counting on Fuchs-Rosenthal chamber and with software. The toxicity of thorium over the species was observed for concentrations over 50.0 mg/L. After 30 days, Monoraphidium cells decreased their concentration from 4.23 × 106 to 4.27 × 105 and 8.57 × 105 cells/mL, in the presence of 50.0 and 100.0 mg/L of thorium, respectively. Scenedesmus sp. cells were more resistant to thorium: for an initial cell concentration of 7.65 × 104 cells/mL it was observed a change to 5.25 × 105 and 5.12 × 105 cells/mL, in the presence of thorium at 50.0 and 100.0 mg/L, respectively. This is an indication that low concentrations of the radionuclide favored the growth, and that Scenedesmus cells are more resistant to thorium than Monoraphidium cells. The software used for comparison with direct count method proved to be useful for the improvement of accuracy of the results obtained, a decrease in the uncertainty and allowed recording of the data. The presence of thorium suggests that low concentrations have a positive effect on the growth, due to the presence of the nitrate...

‣ Inelastic collisions of atomic thorium and molecular thorium monoxide with cold helium-3

Au, Yat Shan
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
Português
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We measure inelastic cross sections for atomic thorium (Th) and molecular thorium monoxide (ThO) in collisions with $^3$He at temperatures near 1 K. We determine the Zeeman relaxation cross section for Th ($^3$F$_2$) to be $sim 2 imes 10^{-17}$~cm$^{-2}$ at 800~mK. We study electronic inelastic processes in Th ($^3$P$_0$) and find no quenching even after $10^6$ collisions at 800~mK. We measure the vibrational quenching cross section for ThO~(X,~$ u=1$) to be $(7.9 pm 2.7) imes 10^{-19}$~cm$^{-2}$ at 800~mK. Finally, we observe indirect evidence for ThO (X, $ u=0$)--$^3$He van der Waals complex formation, and measure the 3-body recombination rate constant to be $Gamma_3 = (8 pm 2) imes 10^{-33}$~cm$^6$s$^{-1}$ at 2.4~K. The stability of the ground Th ($^3$F$_2$) state, metastable Th ($^3$P$_0$) state, and vibrational excited ThO (X, $ u=1$) state provides data on anisotropic interactions in new systems and opens up the possibility for further studies and experiments, including trapping.; Physics

‣ The Spectrum of Thorium from 250 nm to 5500 nm: Ritz Wavelengths and Optimized Energy Levels

Redman, Stephen L.; Nave, Gillian; Sansonetti, Craig J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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We have made precise observations of a thorium-argon hollow cathode lamp emission spectrum in the region between 350 nm and 1175 nm using a high-resolution Fourier transform spectrometer. Our measurements are combined with results from seven previously published thorium line lists (Giacchetti et al. 1974; Zalubas & Corliss 1974; Zalubas 1976; Palmer & Engleman 1983; Engleman et al. 2003; Lovis & Pepe 2007; Kerber et al. 2008) to re-optimize the energy levels of neutral, singly-, and doubly-ionized thorium (Th I, Th II, and Th III). Using the optimized level values, we calculate accurate Ritz wavelengths for 19874 thorium lines between 250 nm and 5500 nm (40000 1/cm to 1800 1/cm). We have also found 102 new thorium energy levels. A systematic analysis of previous measurements in light of our new results allows us to identify and propose corrections for systematic errors in Palmer & Engleman (1983) and typographical errors and incorrect classifications in Kerber et al. (2008). We also found a large scatter in the thorium line list of Lovis & Pepe (2007). We anticipate that our Ritz wavelengths will lead to improved measurement accuracy for current and future spectrographs that make use of thorium-argon or thorium-neon lamps as calibration standards.; Comment: 15 pages...

‣ Band structure and decay channels of thorium-229 low-lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

Borisyuk, P. V.; Vasilyev, O. S.; Krasavin, A. V.; Lebedinskii, Yu. Yu.; Troyan, V. I.; Tkalya, E. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/06/2015 Português
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The results are presented on the study of the electronic structure of thorium atoms adsorbed by the liquid atomic layer deposition from aqueous solution of thorium nitrate on the surface of CaF2. The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF2 system on CaF2 substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF2 system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF2. It is concluded that the presence of the observed features in the REELS spectra is associated with the chemical state of thorium atoms and is caused by the presence of uncompensated chemical bonds at the Th/CaF2 interface, and, therefore, by the presence of unbound 6d- and 7s-electrons of thorium atoms. Assuming the equivalence of the electronic configuration of thorium-229 and thorium-232 atoms, an estimate was made on the time decay of the excited state of thorium-229 nuclei through the channel of the electron conversion. It was found that the relaxation time is about 40 {\mu}s for 6d-electrons, and about 1 {\mu}s for 7s-electrons.; Comment: 5 pages, 4 figures

‣ The use of reduced-moderation light water reactors for transuranic isotope burning in thorium fuel

Lindley, Benjamin A.
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
Português
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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...

‣ Sustainability Indicators for Open-Cycle Thorium-Fuelled Nuclear Energy

Ashley, S. F.; Fenner, R. A.; Nuttall, W. J.; Parks, Geoffrey T.
Fonte: Faculty of Economics, University of Cambridge, UK Publicador: Faculty of Economics, University of Cambridge, UK
Tipo: Trabalho em Andamento
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The potential for countries which currently have a nominal nuclear energy infrastructure to adopt thorium-uranium-fuelled nuclear energy systems, using a once-through ?open? nuclear fuel cycle, has been presented by the International Atomic Energy Agency. This paper highlights Generation III and III+ nuclear energy technologies that could potentially adopt an open thorium-uranium fuel cycle and qualitatively highlights the main differences between the open thorium-uranium and open uranium fuel cycles. Furthermore, 28 indicators (and corresponding metrics) have been identified that could elucidate the advantages and disadvantages of nuclear energy systems which utilise thorium-uranium fuels in an open cycle. Such systems will be compared to an AREVA EPR operating with a once-through uranium fuel cycle. The indicators determined in this work have been drawn by grouping 270 indicators from eight previous studies of indicators associated with holistic and specific appraisals of the various life-cycle stages associated with the nuclear fuel cycle. The 28 indicators cover technoeconomic, environmental, waste, social, and proliferation-resistance themes and can be determined quantitatively, either by explicit determination or from an appropriate sensitivity analysis.

‣ Life-Cycle Impacts From Novel Thorium?Uranium-Fuelled Nuclear Energy Systems

Ashley, S. F.; Fenner, R. A.; Nuttall, W. J.; Parks, Geoffrey T.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
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This is the final published version of the article. It was originally published in Energy Conversion and Management (Ashley SF, Fenner RA, Nuttall WJ, Parks GT, Energy Conversion and Management, 2015, 101, 136?150, doi:10.1016/j.enconman.2015.04.041). The final version is available at http://dx.doi.org/10.1016/j.enconman.2015.04.041; Electricity generated from nuclear power plants is generally associated with low emis- sions per kWh generated, an aspect that feeds into the wider debate surrounding nuclear power. This paper seeks to investigate how life-cycle emissions would be affected by includ- ing thorium in the nuclear fuel cycle, and in particular its inclusion in technologies that could prospectively operate open Th?U-based nuclear fuel cycles. Three potential Th?U- based systems operating with open nuclear fuel cycles are considered: AREVA?s European Pressurised Reactor; India?s Advanced Heavy Water Reactor; and General Atomics? Gas- Turbine Modular Helium Reactor. These technologies are compared to a reference U-fuelled European Pressurised Reactor. A life-cycle analysis is performed that considers the con- struction, operation, and decommissioning of each of the reactor technologies and all of the other associated facilities in the open nuclear fuel cycle. This includes the development of life-cycle analysis models to describe the extraction of thorium from monazitic beach sands and for the production of heavy water. The results of the life-cycle impact analysis highlight that the reference U-fuelled system has the lowest overall emissions per kWh generated...

‣ The Effectiveness of Full Actinide Recycle as a Nuclear Waste Management Strategy when Implemented over a Limited Timeframe ? Part II: Thorium Fuel Cycle

Lindley, Benjamin A.; Fiorina, Carlo; Gregg, Robert; Franceschini, Fausto; Parks, Geoffrey T.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
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This is the accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0149197014003114#.; Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ?500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ?final? core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors...

‣ Proposal for improved nuclear fuel utilisation and economic performance by utilising thorium

du Toit,Marina; Chirayath,Sunil
Fonte: Journal of Energy in Southern Africa Publicador: Journal of Energy in Southern Africa
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2015 Português
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A systematic and strategic nuclear power reactor deployment roadmap has been developed for South Africa within the national strategic plan, utilizing thorium-based fuel. The roadmap was developed through analysis of economical, strategic and historical aspects. The accumulated advantages of thorium-based fuels are summarized, which could form the initiative to implement thorium-based nuclear fuels in South Africa. A timeline (which forms the basis of the roadmap) was constructed and consists of three different phases. Phase 1 starts in 2015 and extends to 2030. Phase 2 starts in 2031 and ends in 2044 whilst Phase 3 is from 2045 to 2060. Each phase is discussed with regard to construction, implementation and research activities. This roadmap starts at current pressurized water reactors (PWRs) and advances to future reactor technologies, using an evolutionary approach. In addition to the results reported in this paper, the economic advantages to introducing thorium as a fertile component in PWR fuels as compared to once-through conventional uranium-only cycles is explored (Du Toit & Cilliers, 2014). The economic evaluation compares uranium fuel to thorium-uranium fuel in terms of the fuel cycle costs, reactor downtime costs due to refuelling and income derived from electricity sales.

‣ Thorium in high-titania slag

Nell,J.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 Português
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Radioactive elements associated with heavy mineral deposits may be removed from the ilmenite concentrate before smelting or, alternatively, from the high-titanium slag after smelting. Either way, the radioactivity removal process will involve leaching and/or flux-roasting. However, the volume of slag is approximately 50 per cent less than the volume of ilmenite concentrate and it may therefore be more efficient to remove radioactive elements from the slag. Several slags with different compositions (in terms of iron to titanium ratio, silica content and radio activity) were studied. All the slags contain iron-titanium oxide phases with M3O5 (M = Fe2+, Ti3+, Ti4+, Mg2+, Al2+, Cr3+) stoichiometry, silicate phases and a small amount of entrained metal droplets. The silicate phases have variable compositions; in all the samples it was found that droplets of a silica-rich phase (containing about 60% SiO2) unmixes from a low-silica phase (containing about 40% SiO2). Both the highand low-silica phases are considered to be glass, representing quenched, immiscible silicate melt phases. The silicate and oxide phases were analysed by electron microprobe to determine the distribution of thorium in the slag (the concentrations of the radioactive daughter products of the thorium decay series are too low to be detected with the microbeam analytical facilities that were available during the investigation). The results are unequivocal: the concentration of thorium in M3O5 oxide phases is below the detection limit of the technique (500 ppm) while the concentration in the silicate phases is at the one per cent level. Furthermore...