Estudio en CFX de la distribución de temperatura en el tanque de calandria de la Central Nuclear Embalse

En este trabajo se presentan los cálculos de las distribuciones de temperatura y velocidad del fluido en el recipiente del moderador (calandria de ahora en más) de un reactor tipo CANDU-6, mediante simulaciones en estado estacionario con el software ANSYS CFX 15.0, versión académica. El recipiente de la calandria contiene 380 tubos de calandria que, a su vez, incluyen los tubos de presión y el combustible. Adicionalmente, dentro de la calandria se encuentran los internos del reactor que, para esta etapa de cálculo, no fueron tenidos en cuenta. La geometría se representó a partir de los planos correspondientes al recipiente del moderador y el de sus internos, y como condiciones decontorno se establecieron el caudal de entrada, la presión de salida, y la potencia por moderación y por conducción distribuida radial y axialmente. Finalmente, los resultados obtenidos permitieron demostrar que el modelo en CFX del tanque de calandria posibilitó identificar y representar patrones de flujo determinados experimentalmente y por otros modelos en fluidodinámica computacional (CFD por sus siglas en ingles). Además se determinó que para las condiciones de operación del reactor CANDU-6 el patrón de flujo que domina la distribución de flujo dentro del tanque de calandria es de tipo flujo mixto caracterizado por corrientes de flujo dominadas por fuerzas de momento y por fuerzas boyantes.Publicado en: Mecánica Computacional vol. XXXV no.31Facultad de Ingenierí

Modelo de la Central Nuclear Embalse con RELAP5 : Accidente de pérdida de refrigerante en la tubería de aspiración de una de sus bombas

En el marco de la extensión de vida de la Central Nuclear Embalse, la Autoridad Regulatoria Nuclear con soporte externo del Centro de Investigación de Métodos Computacionales (CIMEC) ha desarrollado un modelo termo-hidráulico de la planta en RELAP5 mod. 3.3 patch4 que incluye la cinética puntual, con el fin de simular accidentes dentro de la base de diseño. Este modelo independiente es utilizado para la revisión del análisis de seguridad de la Central Nuclear Embalse. El presente trabajo tiene por objetivo la simulación de un accidente de pérdida de refrigerante primario (LOCA), debido a la rotura de la cañería de aspiración de una de las bombas principales, con pérdida del suministro eléctrico normal. En el caso de este tipo de reactores, la rotura conduce a una rápida descarga de refrigerante provocando el incremento de la fracción de vacío en el núcleo y una rápida inserción de reactividad que causa un aumento de la potencia que es controlado por los mecanismos de extinción para el apagado del reactor. El aumento de la presión en el edificio de la contención, produce el inicio del sistema de rociado para mitigar ese aumento de presión. Como la presión del circuito primario se reduce considerablemente (debido a la pérdida de inventario) y aumenta la presión en la contención, se dispara la señal de LOCA que habilita al sistema de inyección de refrigeración de emergencia del núcleo (ECCS). El presente análisis consiste en la verificación de la secuencia del accionamiento de los sistemas de seguridad, los tiempos de disparo del correspondiente mapa de cobertura de los sistemas de extinción y la acción del ECCS para reinundar el núcleo con refrigerante líquido. Se verifica el cumplimiento de las funciones de los sistemas de seguridad y que los tiempos de disparo se producen de acuerdo con lo esperado por diseño, demostrándose que el modelo independiente es una herramienta útil con la capacidad para realizar estudios de licenciamiento.Publicado en: Mecánica Computacional vol. XXXV no.31Facultad de Ingenierí

Validación experimental de un modelo que describe la etapa axial de un plasma focus sin electrodo externo

Se presenta una modificación al modelo de la barredora de nieve tradicional donde se supone que la lámina se forma sobre el aislante y tiene un espesor , pudiendo luego evolucionar tanto en la dirección radial como en la axial. La evolución se realiza planteando la ecuación de conservación de la cantidad de movimiento en la cual, para tener en cuenta la curvatura de la lámina, se agrega un segundo parámetro (eficiencia de transferencia de impulso, ) en el término que contabiliza la cantidad de movimiento cedida al gas barrido. El modelo incluye la ecuación del circuito eléctrico y el sistema de ecuaciones resultante se resuelve numéricamente. Los parámetros libres se ajustan a partir de mediciones de la cinemática de la lámina obtenidas con una sonda magnética inductiva en un equipo Plasma Focus con un electrodo central de 9,5 mm de diámetro y 90 mm de longitud. El segundo electrodo está formado por un disco plano sobre el que asienta el aislante y el electrodo central. Los gases empleados fueron hidrógeno y nitrógeno, en el rango 0,5 – 10 mbar. Se encuentra que tanto como decrecen al aumentar la presión del gas de llenado.An extension to the standard Snow Plow model is presented which assumes that the current sheath is formed along the insulator with a width , and it is then able to evolve both in the axial and radial directions. This evolution is modelled taking into account the conservation of momentum, but a second parameter is included (momentum transfer efficiency ) in order to consider the curvature of the current sheath. The model also includes an equation for the electric circuit. The resulting set of equations is solved numerically. Both parameters are fitted using measurements of sheath cinematics taken with magnetic probes. A Plasma Focus device with a central electrode of 9.5 mm in diameter, 90 mm long and with no outer electrode was used. The filling gas was either hydrogen or nitrogen and the filling pressure was varied in the range 0.5 – 10 mbar. We found that both and decrease as the filling gas pressure is increased.ISSN 0327-358

Adding 6 months of androgen deprivation therapy to postoperative radiotherapy for prostate cancer: a comparison of short-course versus no androgen deprivation therapy in the RADICALS-HD randomised controlled trial

Background Previous evidence indicates that adjuvant, short-course androgen deprivation therapy (ADT) improves metastasis-free survival when given with primary radiotherapy for intermediate-risk and high-risk localised prostate cancer. However, the value of ADT with postoperative radiotherapy after radical prostatectomy is unclear. Methods RADICALS-HD was an international randomised controlled trial to test the efficacy of ADT used in combination with postoperative radiotherapy for prostate cancer. Key eligibility criteria were indication for radiotherapy after radical prostatectomy for prostate cancer, prostate-specific antigen less than 5 ng/mL, absence of metastatic disease, and written consent. Participants were randomly assigned (1:1) to radiotherapy alone (no ADT) or radiotherapy with 6 months of ADT (short-course ADT), using monthly subcutaneous gonadotropin-releasing hormone analogue injections, daily oral bicalutamide monotherapy 150 mg, or monthly subcutaneous degarelix. Randomisation was done centrally through minimisation with a random element, stratified by Gleason score, positive margins, radiotherapy timing, planned radiotherapy schedule, and planned type of ADT, in a computerised system. The allocated treatment was not masked. The primary outcome measure was metastasis-free survival, defined as distant metastasis arising from prostate cancer or death from any cause. Standard survival analysis methods were used, accounting for randomisation stratification factors. The trial had 80% power with two-sided α of 5% to detect an absolute increase in 10-year metastasis-free survival from 80% to 86% (hazard ratio [HR] 0·67). Analyses followed the intention-to-treat principle. The trial is registered with the ISRCTN registry, ISRCTN40814031, and ClinicalTrials.gov, NCT00541047. Findings Between Nov 22, 2007, and June 29, 2015, 1480 patients (median age 66 years [IQR 61–69]) were randomly assigned to receive no ADT (n=737) or short-course ADT (n=743) in addition to postoperative radiotherapy at 121 centres in Canada, Denmark, Ireland, and the UK. With a median follow-up of 9·0 years (IQR 7·1–10·1), metastasis-free survival events were reported for 268 participants (142 in the no ADT group and 126 in the short-course ADT group; HR 0·886 [95% CI 0·688–1·140], p=0·35). 10-year metastasis-free survival was 79·2% (95% CI 75·4–82·5) in the no ADT group and 80·4% (76·6–83·6) in the short-course ADT group. Toxicity of grade 3 or higher was reported for 121 (17%) of 737 participants in the no ADT group and 100 (14%) of 743 in the short-course ADT group (p=0·15), with no treatment-related deaths. Interpretation Metastatic disease is uncommon following postoperative bed radiotherapy after radical prostatectomy. Adding 6 months of ADT to this radiotherapy did not improve metastasis-free survival compared with no ADT. These findings do not support the use of short-course ADT with postoperative radiotherapy in this patient population

Duration of androgen deprivation therapy with postoperative radiotherapy for prostate cancer: a comparison of long-course versus short-course androgen deprivation therapy in the RADICALS-HD randomised trial

Background Previous evidence supports androgen deprivation therapy (ADT) with primary radiotherapy as initial treatment for intermediate-risk and high-risk localised prostate cancer. However, the use and optimal duration of ADT with postoperative radiotherapy after radical prostatectomy remains uncertain. Methods RADICALS-HD was a randomised controlled trial of ADT duration within the RADICALS protocol. Here, we report on the comparison of short-course versus long-course ADT. Key eligibility criteria were indication for radiotherapy after previous radical prostatectomy for prostate cancer, prostate-specific antigen less than 5 ng/mL, absence of metastatic disease, and written consent. Participants were randomly assigned (1:1) to add 6 months of ADT (short-course ADT) or 24 months of ADT (long-course ADT) to radiotherapy, using subcutaneous gonadotrophin-releasing hormone analogue (monthly in the short-course ADT group and 3-monthly in the long-course ADT group), daily oral bicalutamide monotherapy 150 mg, or monthly subcutaneous degarelix. Randomisation was done centrally through minimisation with a random element, stratified by Gleason score, positive margins, radiotherapy timing, planned radiotherapy schedule, and planned type of ADT, in a computerised system. The allocated treatment was not masked. The primary outcome measure was metastasis-free survival, defined as metastasis arising from prostate cancer or death from any cause. The comparison had more than 80% power with two-sided α of 5% to detect an absolute increase in 10-year metastasis-free survival from 75% to 81% (hazard ratio [HR] 0·72). Standard time-to-event analyses were used. Analyses followed intention-to-treat principle. The trial is registered with the ISRCTN registry, ISRCTN40814031, and ClinicalTrials.gov , NCT00541047 . Findings Between Jan 30, 2008, and July 7, 2015, 1523 patients (median age 65 years, IQR 60–69) were randomly assigned to receive short-course ADT (n=761) or long-course ADT (n=762) in addition to postoperative radiotherapy at 138 centres in Canada, Denmark, Ireland, and the UK. With a median follow-up of 8·9 years (7·0–10·0), 313 metastasis-free survival events were reported overall (174 in the short-course ADT group and 139 in the long-course ADT group; HR 0·773 [95% CI 0·612–0·975]; p=0·029). 10-year metastasis-free survival was 71·9% (95% CI 67·6–75·7) in the short-course ADT group and 78·1% (74·2–81·5) in the long-course ADT group. Toxicity of grade 3 or higher was reported for 105 (14%) of 753 participants in the short-course ADT group and 142 (19%) of 757 participants in the long-course ADT group (p=0·025), with no treatment-related deaths. Interpretation Compared with adding 6 months of ADT, adding 24 months of ADT improved metastasis-free survival in people receiving postoperative radiotherapy. For individuals who can accept the additional duration of adverse effects, long-course ADT should be offered with postoperative radiotherapy. Funding Cancer Research UK, UK Research and Innovation (formerly Medical Research Council), and Canadian Cancer Society

Experimental Validation of RELAP5 and TRACE5 for Licensing Studies of the Boron Injection System of Atucha II

This paper presents an experimental validation of RELAP5 and TRACE5 for licensing studies of the Atucha II-PHWR nuclear power plant. A scaled experimental facility, representing the boron injection system of Atucha II, was built. The system has a fundamental importance for loss of coolant accidents (LOCA) and anticipated transients without scram (ATWS). The experiment consists of the discharge of a tank that represents the boron tank filled with air or a mixture of air-water onto a discharge tank that represents the moderator tank. Both tanks are connected by a pipe which includes a valve and an orifice plate to model the pressure losses due to the fittings in the real system. The pressure and water level measured in the tanks are compared with the RELAP5 and TRACE5 predictions. The codes predict the pressure in the tanks accurately. However, both codes overpredict the heat transfer in the boron tank air-water interface which produces a greater expansion of the air which leads to a small discrepancy in the boron tank level prediction

High-temperature creep deformation evaluation in CANDU pressure tubes under a station black-out

In this work the deformation of pressure tubes in CANDU6 nuclear reactor under a Station BlackOut event is analyzed. Firstly, the thermal–hydraulic simulation of the whole reactor is carried out using RELAP5Mod3 in order to get the spatial and temporal temperature profiles along the axial coordinate for five representative coolant channels in the core. Then, these temperature fields are mapped into a mechanical model for the PT to estimate the creep deformation by ballooning. Without consider the CT, the pressure tube to Calandria tube contact was estimated with relative accurate added to the contact location and area of contact in time. To address the mechanical model a novel 3D code based on correlations of Shewefelt effective strain for Zr–2:5%Nb alloy is developed in OpenFoam-5.0. This pressure tube to Calandria tube contact causes a large heat transfer from the coolant to the moderator giving an additional heat sink, which should be carefully considered during the progression of the Station BlackOut event.Fil: Corzo, Santiago Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina. Invap S. E.; ArgentinaFil: Lazarte, Alejandro I.. Invap S. E.; ArgentinaFil: Ramajo, Damian Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; Argentina. Invap S. E.; Argentin