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Separação e recuperação de chumbo-208 dos resíduos de tório terras raras gerados na unidade piloto de purificação de nitrato de tórioSENEDA, JOSE A. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:51:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:59Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Distribuição elementar e de radionuclídeos na produção e uso de fertilizantes fosfotados no BrasilSAUEIA, CATIA H.R. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:52:02Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:56Z (GMT). No. of bitstreams: 0 / O fertilizante é considerado um componente essencial para a agricultura, pois sua utilização aumenta e repõe os nutrientes naturais do solo, perdidos por desgaste ou erosão. No processo de obtenção dos fertilizantes fosfatados, o concentrado de rocha reage com ácido sulfúrico concentrado produzindo ácido fosfórico e sulfato de cálcio (fosfogesso), como subproduto. O ácido fosfórico é utilizado para a produção do superfosfato triplo (TSP), superfosfato simples (SSP), monoamônio fosfato (MAP) e diamônio fosfato (DAP). A rocha fosfatada usada como matéria prima apresenta em sua composição radionuclídeos das séries naturais do urânio e tório. Durante o ataque químico do concentrado de rocha, as espécies presentes na reação, estáveis e radioativas, são redistribuídas entre o ácido fosfórico (matéria prima dos fertilizantes), e o fosfogesso, de acordo com sua solubilidade e características químicas. Enquanto os fertilizantes são comercializados, o fosfogesso fica estocado em pilhas podendo impactar o meio ambiente. Com a finalidade de entender a distribuição dos elementos e dos radionuclídeos no processo industrial de produção de fertilizantes fosfatados, foram analisadas amostras de concentrado de rocha, de fertilizantes (SSP, TSP, MAP e DAP) e fosfogesso de três procedências nacionais denominadas indústrias A, B e C. A técnica utilizada para a análise elementar foi a análise por ativação com nêutrons, que permitiu analisar os elementos Ba, Co, Cr, Fe, Hf, Na, Sc, Ta, Th, U, Zn e Zr, e as terras raras, La, Ce, Nd, Sm, Eu, Tb, Yb e Lu. Os resultados obtidos permitiram concluir que em geral, as terras raras se distribuem de forma homogênea em todos os fertilizantes e no fosfogesso, exceto o Lu. Os fertilizantes SSP e TSP apresentaram concentrações de todos os elementos analisados da mesma ordem de grandeza da rocha de origem. O mesmo comportamento foi observado nos fertilizantes MAP e DAP, exceto para os elementos Co, Sc e U. Os elementos pertencentes à série radioativa natural do urânio (238U, 234U, 230Th, 226Ra e 210Pb), do tório (232Th, 228Ra e 228Th) e o K-40, foram determinados por meio da espectrometria gama e alfa. As amostras de fertilizantes MAP e DAP, que são diretamente derivadas do ácido fosfórico, apresentaram baixa concentração para o 226Ra, 228Ra e 210Pb, enquanto que para o U e Th as concentrações encontradas foram da mesma ordem de grandeza da rocha de origem. Os fertilizantes SSP e TSP, que são obtidos pela mistura de ácido fosfórico com concentrado de rocha, apresentaram concentrações mais elevadas para os radionuclídeos das séries naturais. Avaliou-se a exposição devido a sucessivas aplicações de fertilizantes e fosfogesso, calculando-se a dose interna devida à aplicação por 10, 50 e 100 anos. Os valores encontrados estão abaixo do limite de 2,4 mSv a-1, mostrando que esta prática é negligenciável. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Separação e recuperação de chumbo-208 dos resíduos de tório terras raras gerados na unidade piloto de purificação de nitrato de tórioSENEDA, JOSE A. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:51:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:59Z (GMT). No. of bitstreams: 0 / 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 = 14,6 +/- 0,7 mb diferentemente do chumbo natural de s? o = 174,2 +/- 7,0 mb. Estudos preliminares de recuperação do tório e terras raras neste resíduo também foram apresentados. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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L'uranium et ses descendants dans la chaine alimentaireJeambrun, Marion 24 September 2012 (has links) (PDF)
L'uranium, le thorium et leurs descendants se trouvent a l'état de traces dans toutes les roches sur Terre. Sous l'action de l'érosion, des mécanismes de formation des sols et des transferts sol-plante, ces radionucléides sont disséminés dans toutes les composantes de l'environnement et via les chaînes alimentaires, ils sont transmis aux animaux et à l'homme. L'objectif de cette étude consiste à améliorer les connaissances sur les niveaux et la variabilité des activités de ces radionucléides dans différentes denrées et à faire progresser les connaissances sur leurs sources et leurs transferts. Cette étude s'intéresse à la variabilité géologique des sites étudiés (substrat granitique, volcanique et alluvial) sur lesquels sont prélevés différentes denrées (légumes, céréales, viandes, oeufs et produits laitiers). Les sources potentielles de radionucléides (eau d'irrigation et sol pour les végétaux ; eau d'abreuvage, aliments et sol pour les produits animaux) sont prélevées afin d'étudier leur contribution aux activités mesurées dans les denrées. Les résultats obtenus montrent une grande variabilité des activités dans les végétaux, moins prononcée dans les produits animaux. La source principale de radionucléides aux végétaux semble être le sol de culture. La remise en suspension de particules de sol et leur adhésion à la surface des végétaux ainsi que l'eau d'irrigation semblent important dans certains cas. Concernant les activités dans les produits animaux, une contribution significative du sol a l'activité en thorium a été mise en évidence. La contribution de l'eau à l'activité en uranium dans les volailles constitue une piste à approfondir.
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[en] SELECTIVE DETERMINATION OF FLUORQUINOLONES FOR CELLULOSE SURFACE ROOMTEMPERATURE PHOSPHORIMETRY WHITH THORIUM NITRATE / [pt] DETERMINAÇÃO SELETIVA DE FLUOROQUINOLONAS POR FOSFORIMETRIA NA TEMPERATURA AMBIENTE SUPORTADA EM SUBSTRATO DE CELULOSE COM NITRATO DE TÓRIOILFRAN DA SILVA NAVA JUNIOR 16 October 2007 (has links)
[pt] Neste trabalhou desenvolveu-se métodos analíticos baseados
na
fosforimetria em temperatura ambiente em substrato sólido
(FTASS) para
determinação seletiva de fluorquinolonas. Mais
especificamente, avaliou-se a
viabilidade do uso do nitrato de tório como sal de átomo
pesado indutor de
fosforescência visando a determinação seqüencial de
norfloxacino (NOR) e
levofloxacino (LEV), determinação seletiva de NOR em
presença de
ciprofloxacino (CIP), assim como a determinação seletiva
de CIP em presença
de gatifloxacino (GAT) ou moxifloxacino (MOX). Realizou-se
uma cuidadosa
comparação entre o sinal fosforescente obtido com o uso do
nitrato de tório e os
obtidos pelos sais indutores tradicionalmente utilizados
na FTASS. Estudou-se
univariadamente o efeito da quantidade de sal indutor de
átomo pesado
depositado no substrato sólido, a quantidade de um
surfactante modificador de
superfície e a concentração hidrogeniônica da solução
carreadora de analito na
magnitude do sinal fosforescente. Também foram avaliadas
possíveis interações
entre esses fatores experimentais por meio de um
planejamento fatorial 23. Com
a estratégia de análise bem definida, desenvolveram-se
metodologias para a
determinação de NOR, LEV e CIP em formulações
farmacêuticas comerciais e
simuladas e em urina enriquecida sem que se fosse aplicado
procedimentos de
separação do analito de interesse das outras substâncias
concomitantes. Para
tal, a estratégia de varredura sincronizada foi
fundamental. Os parâmetros
analíticos de mérito obtidos com o uso do nitrato de tório
foram comparados com
os obtidos com o do acetato de cádmio (átomo pesado
indutor de fosforescência
de fluorquinolonas já descrito na literatura). Em todos os
casos estudados, a
resposta analítica apresentou comportamento linear em
função da massa
depositada de NOR, LEV e CIP no substrato (R2>0,99), com
boa repetitividade e
sensibilidade (avaliada pelos limites de detecção e
quantificação absolutos na
ordem de ng). Tanto nas formulações farmacêuticas quanto
em urina
enriquecida, os resultados obtidos com o método
desenvolvido com o uso do sal de tório na determinação
seqüencial de NOR/LEV e na determinação seletiva de
NOR/CIP foram mais vantajosos que os obtidos com o uso do
sal de cádmio. Em
ambos os casos, o método desenvolvido com o uso do Th(NO3)
4 mostrou-se
válido desde que a proporção molar das misturas NOR/LEV e
NOR/CIP não
ultrapassem a condição de 1 (analito) para 5
(interferente). Para o método
desenvolvido na determinação seletiva de CIP em misturas
contendo GAT, o
Th(NO3)4 também mostrou-se mais adequado que o acetato de
cádmio,
Cd(OAc)2, sendo obtidos resultados satisfatórios, desde
que a proporção molar
CIP/GAT não ultrapassasse 1 para 2. No entanto,
interferências do tipo nãoespectral
foram observadas na presença de quantidades maiores de GAT
(até
10 vezes mais), as quais podem ser facilmente corrigidas
utilizando o método de
adição do analito. Já nas misturas contendo CIP/MOX, o
método desenvolvido
para a determinação seletiva de CIP com o uso do sal de
tório foi muito favorável
em proporções equimolares e em quantidades contendo duas
vezes mais MOX.
Em misturas contendo maiores quantidades de MOX, observou-
se interferências
do tipo espectral que não puderam ser contornadas por
sincronização, devido
seus (Lambda)sinc.muito próximos. Porém, utilizando Cd(OAc)
2 nas
misturas contendo
CIP/MOX em razões molares maiores que 1:2 se observou
interferências apenas
do tipo não-espectral, que podem ser corrigidas por
procedimento adequado de
calibração. Esse caso foi o único cujo sal de cádmio
mostrou-se superior ao
método desenvolvido com o uso do sal de tório. / [en] In this work, analytical methods based on solid surface
room-temperature
phosphorimetry were developed aiming the selective
determination of
fluorquinolones. More spectilly, thorium nitrate was
evaluated as
phosphorescence inducer aiming the sequential
determination of norfloxacin
(NOR) and levofloxacin (LEV), selective determination of
NOR in presence of
ciprofloxacin (CIP), as well as the selective
determination of CIP in the presence
gatifloxacin (GAT) or moxifloxacin (MOX). In order to
that, the phosphorescence
induced by thorium nitrate was compared with the ones
achieved using other
traditionally employed heavy atom enhancers in solid
surface room-temperature
phosphorimetry (SSRTP). Univariated studies were made in
order to evaluate the
effect of the amounts of heavy atom salt and surface
modifier present in the
substrate as well as the influence of the pH of the
analyte carrier solution. The
interaction among these factors were also studied through
experimental factorial
desings (23). After the definition of the analytical
strategy to be employed,
analytical methods were developed for the determination of
NOR, LEV and CIP in
simulated mistures and analyte spiked urine without
employing any procedure to
physically separate the analyte from the others components
of the sample. In
order to do that, the use of syncronized scanning was
fundamental. The
analytical figures of merit achieved using thorium nitrate
and cadmium acetate
(heave atom inducer already reported in the literature for
fluorquinolones) were
campared. In both cases, linear analytical responses in
function of the amount of
analyted present in the substrate were achieved (R2>0,99).
Good repetitivity of
results and sensibility (evaluated through the estimation
of the limits of detection
and quantification) were in the ng order. When testing
pharmaceutical
formulations and spiked urine, the use of Th(NO3)4 showed
clear advantage over
Cd(OAc)2, allowing the sequential determination of NOR/LEV
and the selective
determination of NOR in the presence of CIP. The selective
determination of
NOR using Th(NO3)4 could be made for mixtures containing
up to five times more LEV or CIP in molar proportion. For
the developed method aiming the
determination of CIP in mistures containing GAT, Th(NO3)4
was found to be more
adequate heavy atom enhancer than Cd(OAc)2. The method was
free from
interferences for samples containing two times more GAT
than CIP (in molar
proportion). However, interferences observed for mixtures
containing higher
amounts of GAT could be easily corrected by the using of
the standard addition
method for quantification. In mixtures containing CIP and
MOX, the developed
method using Th(NO3)4 was suitable for mixtures containing
equimolar
proportions of these two fluorquinolones. Spectral
interferences were observed
for higher amounts of MOX. Such interference could not be
resolved due to close
(lambda) values characteristic for the two FQs. However,
for the
method using
Cd(OAc)2 in mixtures containing CIP/MOX in molar
proportion more them 1:2
only non spectral interferences were observed, but this
interferences can be
corrected by the use of proper calibration strategy. This
was the only situation
where Cd(OAc)2 demonstrate better results than Th(NO3)4.
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Influence du retraitement physico-chimique du sel combustible sur le comportement du MSFR et sur le dimensionnement de son unité de retraitementDoligez, Xavier 14 October 2010 (has links) (PDF)
L'industrie électronucléaire, pour faire face aux besoins énergétiques croissant, à besoin de développer une nouvelle génération de réacteur : la quatrième génération. Parmi les six candidats, on trouve les réacteurs à sels fondus, qui, en configuration rapide, semble avoir de très bonnes propriétés : la régénération est facilement accessible tout en gardant des coefficients de contre-réaction négatifs. Le procédé de retraitement du sel combustible n'est toutefois toujours pas établi de manière définitive. Beaucoup d'incertitude sur les paramètres physicochimiques des sels combustibles empêchent de définir de manière précise chaque étape du procédé. Grâce à la simulation numérique nous avons pu étudier le comportement du cœur du réacteur couplé à une unité de retraitement de référence. De cette manière nous avons pu quantifier les flux de chaleurs et les radiations pour identifier les étapes qui nécessiteront une attention particulière lors du dimensionnement. Nous avons aussi pu identifier les éléments pour lesquels une mauvaise extraction mettrait en péril le bon fonctionnement du réacteur. Enfin, toujours grâce à la simulation numérique, ce travail présente une analyse des sensibilités du procédé de retraitement sur un certain nombre de grandeurs physique représentative du cœur du MSFR.
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The radium distribution in some Swedish soils and its effects on radon emanationEdsfeldt, Cecilia January 2001 (has links)
The aim of this study has been to clarify how the radiumdistribution in soils affects the radon emanation. Thedistribution of radium, uranium and thorium has been determinedusing sequential extractions. In the study, soils from twodifferent locations were investigated. In the first part the applicability of the sequentialextraction method for determining Ra distribution in differentsoil types was investigated, using a simple sequentialextraction method. Sampled soils were clay, sand and till fromthe vicinity of the Stockholm Esker. The main part of Rnemanating Ra was associated with Fe oxides in the soil. Themethods applied provided information about the radon risk ofthe soil, but, inorder to gain more information on theprocesses governing Ra distribution and radon emanation insoils, a more detailed sequential extraction procedure would bedesirable. The second part consisted of a detailed study of theradionuclide distribution and the geochemistry in a podzolisedglacial till from Kloten in northern Västmanland. A moredetailed sequential extraction procedure was used, and thespecific surface area of samples was measured. Samples weretaken from E, B, and C horizons; radium and thorium wereenriched in the B horizon, whereas uranium had its maximumconcentration in the C horizon. Extractable radium primarilyoccurred in the exchangeable pool, possibly organicallycomplexed, whereas extractable uranium and thorium were mainlyFe oxide bound. Oxide-bound Ra was important only in the Bhorizon. The radon emanation was not correlated with the amountof exchangeable Ra, but instead with the oxide bound Ra.However, the amount of oxide-bound Ra was too small to accountfor all the emanated Rn, thus, exchangeable Ra was interpretedas the main source of emanated Rn. This exchangeable Ra wasmore emanative in the B horizon than in the C horizon. Theexplanation is the larger surface area of the B horizonsamples; the specific surface area appears to be the maingoverning parameter for Rn emanation in this soil. The surfacearea is largely created by the precipitation of amorphous Feoxides, thus, Fe oxides has a significant effect on Rnemanation. Comparing the two studies, the Stockholm samples had thesame amounts of oxide-bound Fe and surface-bound Ra. Still theradon emanation was much smaller for these samples than in theKloten soil. The amount of organic matter in the B horizon ofthe Kloten soil is however, much larger than the organic mattercontent in the Stockholm samples. It is suggested that thelarge Rn emanation in the B horizon of Kloten is caused by thecombined effect of Fe oxides and organic matter. The variability of226Ra distribution in soils was also investigated.The226Ra distribution was determined for samples from60-70 cm and 80-90 cm depth, from three adjacent soil profilesin a podzolic glacial till. Ra distributions, and estimationsof Rn risk based on the Ra distributions, of a single soilprofile, are likely to be representative for a similar area,provided that the samples are taken from a sufficientdepth. KEYWORDS: distribution, emanation, extraction, glacial till,podzol, Ra, radium, radon, Rn, sequential soil, spodosol, Th,thorium, U, uranium, variability
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Advanced Fuel Cycle Scenarios with AP1000 PWRs and VHTRs and Fission Spectrum UncertaintiesCuvelier, Marie-Hermine 2012 May 1900 (has links)
Minimization of HLW inventories and U consumption are key elements guaranteeing nuclear energy expansion. The integration of complex nuclear systems into a viable cycle yet constitutes a challenging multi-parametric optimization problem. The reactors and fuel cycle performance parameters may be strongly dependent on minor variations in the system's input data. Proven discrepancies in nuclear data evaluations could affect the validity of the system optimization metrics.
This study first analyzes various advanced AP1000-VHTR fuel cycle scenarios by assessing their TRU destruction and their U consumption minimization capabilities, and by computing reactor performance parameters such as the time evolution of the effective multiplication factor keff, the reactors' energy spectrum or the isotopic composition/activity at EOL. The performance metrics dependence to prompt neutron fission spectrum discrepancies is then quantified to assess the viability of one strategy. Fission spectrum evaluations are indeed intensively used in reactors' calculations. Discrepancies higher than 10% have been computed among nuclear data libraries for energies above 8MeV for 235U.
TRU arising from a 3wt% 235U-enriched UO2-fueled AP1000 were incinerated in a VHTR. Fuels consisting of 20%, 40% and 100% of TRU completed by UO2 were examined. MCNPX results indicate that up to 88.9% of the TRU initially present in a VHTR fueled with 20% of TRU and 80% of ThO2 were transmuted. Additionally, the use of WgPu instead of RgPu should reduce the daily consumption of 235U by 1.3 and augment core lifetime.
To estimate the system metrics dependence to fission spectrum discrepancies and validate optimization studies outputs, the VTHR 235U fission spectrum distribution was altered successively in three manners. keff is at worst lowered by 1.7% of the reference value and the energy spectrum by 5% between 50meV and 2MeV when a significantly distorted fission spectrum tail is used. 233U, 236Pu and 237Pu inventories and activities are multiplied by 263, 523 and 34 but are still negligible compared to 239Pu mass or the total activity.
The AP1000-VHTR system is in conclusion not dependent on the selected fission spectrum variations. TRU elimination optimization studies in AP1000-VHTR systems will be facilitated by freeing performance metrics dependency from 1 input parameter.
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The radium distribution in some Swedish soils and its effects on radon emanationEdsfeldt, Cecilia January 2001 (has links)
<p>The aim of this study has been to clarify how the radiumdistribution in soils affects the radon emanation. Thedistribution of radium, uranium and thorium has been determinedusing sequential extractions. In the study, soils from twodifferent locations were investigated.</p><p>In the first part the applicability of the sequentialextraction method for determining Ra distribution in differentsoil types was investigated, using a simple sequentialextraction method. Sampled soils were clay, sand and till fromthe vicinity of the Stockholm Esker. The main part of Rnemanating Ra was associated with Fe oxides in the soil. Themethods applied provided information about the radon risk ofthe soil, but, inorder to gain more information on theprocesses governing Ra distribution and radon emanation insoils, a more detailed sequential extraction procedure would bedesirable.</p><p>The second part consisted of a detailed study of theradionuclide distribution and the geochemistry in a podzolisedglacial till from Kloten in northern Västmanland. A moredetailed sequential extraction procedure was used, and thespecific surface area of samples was measured. Samples weretaken from E, B, and C horizons; radium and thorium wereenriched in the B horizon, whereas uranium had its maximumconcentration in the C horizon. Extractable radium primarilyoccurred in the exchangeable pool, possibly organicallycomplexed, whereas extractable uranium and thorium were mainlyFe oxide bound. Oxide-bound Ra was important only in the Bhorizon. The radon emanation was not correlated with the amountof exchangeable Ra, but instead with the oxide bound Ra.However, the amount of oxide-bound Ra was too small to accountfor all the emanated Rn, thus, exchangeable Ra was interpretedas the main source of emanated Rn. This exchangeable Ra wasmore emanative in the B horizon than in the C horizon. Theexplanation is the larger surface area of the B horizonsamples; the specific surface area appears to be the maingoverning parameter for Rn emanation in this soil. The surfacearea is largely created by the precipitation of amorphous Feoxides, thus, Fe oxides has a significant effect on Rnemanation.</p><p>Comparing the two studies, the Stockholm samples had thesame amounts of oxide-bound Fe and surface-bound Ra. Still theradon emanation was much smaller for these samples than in theKloten soil. The amount of organic matter in the B horizon ofthe Kloten soil is however, much larger than the organic mattercontent in the Stockholm samples. It is suggested that thelarge Rn emanation in the B horizon of Kloten is caused by thecombined effect of Fe oxides and organic matter.</p><p>The variability of<sup>226</sup>Ra distribution in soils was also investigated.The<sup>226</sup>Ra distribution was determined for samples from60-70 cm and 80-90 cm depth, from three adjacent soil profilesin a podzolic glacial till. Ra distributions, and estimationsof Rn risk based on the Ra distributions, of a single soilprofile, are likely to be representative for a similar area,provided that the samples are taken from a sufficientdepth.</p><p>KEYWORDS: distribution, emanation, extraction, glacial till,podzol, Ra, radium, radon, Rn, sequential soil, spodosol, Th,thorium, U, uranium, variability</p>
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Contribution à l'étude de la production d'U-233 en combustible MOX-ThPu en réacteur à eau sous pression. Scénarios de transition vers des concepts isogénérateurs Th/U-233 en spectre thermique. Développement du code MURE d'évolution du combustible.Michel-Sendis, Franco 21 December 2006 (has links) (PDF)
Dans le contexte d'un déploiement massif du nucléaire civil au niveau mondial, le problème de l'approvisionnement en U-235 se posera à des échéances humaines. L'industrie nucléaire d'aujourd'hui, sous-génératrice, serait, dans un tel cas de figure, inapte à satisfaire les besoins énergétiques du monde de façon durable. La transition vers des filières iso ou surgénératrices, qui optimisent l'utilisation de la matière fissile, est alors pertinente. Parmi les technologies qui permettent une telle optimisation, le cycle du thorium, Th/U-233 utilisé en spectre de neutrons thermique, est doublement intéressant; il permettrait, dans des concepts de type réacteur à sels fondus thermique, l'isogénération de la matière fissile tout en nécessitant de faibles inventaires initiaux en U-233. La production de cette quantité d'U-233, nécessaire au démarrage de la filière, peut être produite en amont, dans des réacteurs d'aujourd'hui (à eau sous pression), utilisant un combustible de type mixte oxyde thorium-plutonium. <br /><br />Ce travail concerne d'une part le développement d'outils de calcul nécessaires à l'étude neutronique, par simulation Monte Carlo (M.C), des réacteurs nucléaires et de leur combustible. Qu'ils soient de génération future ou de technologie actuelle utilisant un combustible innovant, la simulation des réacteurs par les méthodes M.C. est particulièrement bien adaptée car elle ne repose que sur la connaissance des données nucléaires, et peut traiter des géométries complexes et exactes en effectuant le transport des neutrons à énergie continue. <br /><br /><br />Le code MURE, qui encapsule le code de transport validé et reconnu MCNP, a été écrit pour simuler l'évolution du combustible sous irradiation. C'est un code modulaire, écrit en C++, qui permet, entre autres, de simuler des évolutions à puissance et à réactivité constantes. <br /><br /><br />Dans un deuxième temps, nous avons entrepris l'étude du combustible MOX ThPu en REP en vue de détérminer des teneurs en plutonium satisfaisant les critères de sûreté et avons quantifié la production d'uranium-233 en fin de combustion. Ceci nous permet de considèrer et de valider différents scénarios de transition du parc français vers un parc de réacteurs isogénérateurs utilisant le cycle du thorium, où l'U-233, aura été produit dans des réacteurs à eau sous pression utilisant du MOX thorié.
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