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8.2. Plutonio-238

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8.2. Plutonio-238 Estudio y dimensionado de una RTG para satélites de exploración de objetos transneptunianos Pág. 1 Resumen Este proyecto es un State of the Art de la exploración espacial a través de la tecnología nuclear. Esto se realiza mediante el estudio de la historia de la exploración espacial y su tecnología, realizando un paso por sus inicios, las primeras misiones, las últimas misiones e incluso un planteamiento inicial de misión espacial interesante. Una vez conocidos los orígenes de la misma, se continuará explicando la influencia que ha poseído la tecnología nuclear, destacando y comentando los diseños tecnológicos basados en el uso de fuentes de radioisótopos. Se ofrecerán datos generales sobre estos, destacando aquellos aspectos más interesantes de cada diseño. Después de adquirir un conocimiento general sobre esta tecnología, la tecnología nuclear basada en fuentes radioisotópicas, se pretende explicar el por qué un isotopo determinado (el Pu-238) es el más utilizado como fuente energía. Esto se realizará mediante el aporte de conocimientos sobre el mismo (características principales y nucleares, producción, etc.) Se considera necesario, un estudio en profundidad sobre la tecnología radioistopica más exitosa a día de hoy, el GPHS-RTG. Ofreciendo detalladas explicaciones y especificaciones sobre este diseño en concreto. Tras tener conciencia y conocimientos sobre la forma de alimentar las misiones de exploración espacial, se procede al diseño de una misión basada en casos de exploración anteriores (principalmente la New Horizons) así como el estudio de los componentes que forman parte de una nave de exploración que deba satisfacer unas condiciones como las deseadas. Por ello en forma de pre-diseño de misión se continúan ofreciendo conocimientos prácticos. El estudio de la seguridad en una misión que incluya medios nucleares es muy importante. De esta manera se continúa, mediante el análisis de las diferentes etapas y condiciones de seguridad en el proceso de calificación de una fuente GPHS-RTG para exploración espacial. Pasando desde las pruebas al combustible, hasta el transporte de una GPHS-RTG completamente montada. Y para finalizar todo el proceso desde los orígenes de la exploración espacial, hasta el diseño de una misión. Se muestran los apartados y pasos principales de la evaluación de impacto ambiental de una misión como las lanzadas desde Cabo Cañaveral (Florida, Estados Unidos) por la NASA (National Aeronautics and Space Administration). Pág. 2 Estudio y dimensionado de una RTG para satélites de exploración de objetos transneptunianos Estudio y dimensionado de una RTG para satélites de exploración de objetos transneptunianos Pág. 3 Sumario RESUMEN ___________________________________________________ 1 SUMARIO ____________________________________________________ 3 1. GLOSARIO _______________________________________________ 7 2. PREFACIO ______________________________________________ 11 2.1. Origen del proyecto ........................................................................................ 11 2.2. Motivación ...................................................................................................... 12 3. INTRODUCCIÓN _________________________________________ 15 3.1. Objetivos del proyecto .................................................................................... 15 3.2. Alcance del proyecto ...................................................................................... 16 4. HISTORIA DE LA ENERGÍA ATÓMICA EN EL ESPACIO _________ 17 4.1. Inicios históricos de la exploración espacial. ................................................. 17 4.2. Átomos para la paz (1953) ............................................................................. 18 4.3. Programa Espacial Americano y las RTGs ................................................... 20 5. USOS DE LA ENERGÍA NUCLEAR EN EL ESPACIO. ____________ 23 6. DISPOSITIVOS RADIOISOTOPICOS DE ENERGÍA. _____________ 28 6.1. Generadores Termoeléctricos (TEGs) .......................................................... 28 6.1.1. Los TEG y los radionucléidos ............................................................................. 30 6.2. CONVERTIDORES TERMOIÓNICOS. ......................................................... 35 6.2.1. Eficiencia de un generador termoiónico. ............................................................. 36 6.2.2. Radionucléidos en Generadores Termoiónicos. ................................................ 37 6.2.3. Baterías de Generadores Termoiónicos. ............................................................ 38 6.3. CONVERTIDORES AMTEC .......................................................................... 40 6.4. CONVERTIDORES STIRLING ...................................................................... 43 6.5. CONVERSIÓN DIRECTA DE RADIACIÓN NUCLEAR ................................ 45 6.5.1. Baterías Betavoltaicas. ........................................................................................ 47 7. SELECCIÓN DE RADIONUCLEIDOS PARA SU USO COMO FUENTES DE POTENCIA TÉRMICA. _________________________ 49 8. EL PLUTONIO (PU-238) ____________________________________ 51 8.1. Propiedades Nucleares del Plutonio .............................................................. 51 8.2. Plutonio-238 ................................................................................................... 52 Pág. 4 Estudio y dimensionado de una RTG para satélites de exploración de objetos transneptunianos 8.2.1. Por qué Plutonio-238 .......................................................................................... 53 8.3. Suministro de Pu-238 .................................................................................... 53 8.3.1. La situación actual del Plutonio-238. .................................................................. 53 8.3.2. Producción detallada del Pu-238 ........................................................................ 56 8.3.3. Producción futura del Plutonio-238 (y su problemática actual). ........................ 63 8.3.4. Opciones actuales para la producción de 238Pu en los Estados Unidos. ......... 65 9. ESTUDIO DETALLADO DE UNA RTG ________________________ 68 9.1. Descripción del GPHS-RTG .......................................................................... 70 9.2. Módulos generadores de radioisótopos (GPHS)........................................... 72 9.2.1. Especificaciones técnicas de las pastillas de combustible (Pu-238) ............... 75 9.2.2. Revestimiento de las pastillas de combustible (FC) .......................................... 76 9.2.3. Escudo de grafito del combustible, contra impactos (GIS) ................................ 78 9.2.4. Aerocubierta ........................................................................................................ 79 9.2.5. Materiales y Pesos del GPHS. ............................................................................ 80 9.3. El convertidor de la GPHS-RTG: Ensamblaje de la termopila y Escudo Externo. .......................................................................................................... 81 9.4. Configuración inicial como generador termoeléctrico calentado eléctricamente (ETG). .................................................................................... 84 9.5. Masa Global. .................................................................................................. 86 9.6. SOPORTES DE LA FUENTE DE CALOR .................................................... 90 9.6.1. Ensamblaje del Soporte Interior de la Fuente de Calor (IBSA, Inboard Heat Source Support Assembly) ................................................................................. 90 9.6.2. Ensamblaje del Soporte Exterior de la Fuente de Calor (OBSA, Outboard Heat Source Support Assembly) ................................................................................. 91 9.6.3. Ensamblaje del Soporte Intermedio (MSA, Midspan Support Assembly) ......... 92 10. ESPECIFICACIONES DE LA TERMOPILA _____________________ 94 10.1. Termopar de Silicio-Germanio ....................................................................... 94 10.2. Sistema de Aislamiento. ................................................................................ 95 10.3. Ensamblaje de la Termopila. ......................................................................... 98 10.3.1. Circuito eléctrico. ................................................................................................. 98 10.3.2. Interconexión eléctrica. ..................................................................................... 100 11. ESPECIFICACIONES DEL ESCUDO EXTERNO _______________ 101 11.1. Características de Diseño ............................................................................ 101 11.2. Aletas de radiación ....................................................................................... 102 12. ÚLTIMAS MEJORAS DE DISEÑO ADOPTADAS EN LOS GPHS-RTG.104 Estudio y dimensionado de una RTG para satélites de exploración de objetos transneptunianos Pág. 5 12.1. Dispositivo de alivio de presión (PRD) ......................................................... 104 12.1.1. Características del nuevo diseño del PRD ....................................................... 104 12.1.2. Pruebas de fiabilidad del PRD .......................................................................... 106 12.2. Dispositivos dmedidores de temperatura (RTD) ......................................... 106 13. LA MISIÓN DE EXPLORACIÓN, KAYAK. _____________________
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