Análisis Integrado de Seguridad de un accidente de SGTR en un reactor nuclear tipo PWR

El accidente de rotura de tubos de un generador de vapor (Steam Generator Tube Rupture, SGTR) en los reactores de agua a presión es uno de los transitorios más exigentes desde el punto de vista de operación. Los transitorios de SGTR son especiales, ya que podría dar lugar a emisiones radiológicas al exterior sin necesidad de daño en el núcleo previo o sin que falle la contención, ya que los SG pueden constituir una vía directa desde el reactor al medio ambiente en este transitorio. En los análisis de seguridad, el SGTR se analiza desde un punto determinista y probabilista, con distintos enfoques con respecto a las acciones del operador y las consecuencias analizadas. Cuando comenzaron los Análisis Deterministas de Seguridad (DSA), la forma de analizar el SGTR fue sin dar crédito a la acción del operador durante los primeros 30 min del transitorio, lo que suponía que el grupo de operación era capaz de detener la fuga por el tubo roto dentro de ese tiempo. Sin embargo, los diferentes casos reales de accidentes de SGTR sucedidos en los EE.UU. y alrededor del mundo demostraron que los operadores pueden emplear más de 30 minutos para detener la fuga en la vida real. Algunas metodologías fueron desarrolladas en los EEUU y en Europa para abordar esa cuestión. En el Análisis Probabilista de Seguridad (PSA), las acciones del operador se tienen en cuenta para diseñar los cabeceros en el árbol de sucesos. Los tiempos disponibles se utilizan para establecer los criterios de éxito para dichos cabeceros. Sin embargo, en una secuencia dinámica como el SGTR, las acciones de un operador son muy dependientes del tiempo disponible por las acciones humanas anteriores. Además, algunas de las secuencias de SGTR puede conducir a la liberación de actividad radiológica al exterior sin daño previo en el núcleo y que no se tienen en cuenta en el APS, ya que desde el punto de vista de la integridad de núcleo son de éxito. Para ello, para analizar todos estos factores, la forma adecuada de analizar este tipo de secuencias pueden ser a través de una metodología que contemple Árboles de Sucesos Dinámicos (Dynamic Event Trees, DET). En esta Tesis Doctoral se compara el impacto en la evolución temporal y la dosis al exterior de la hipótesis más relevantes encontradas en los Análisis Deterministas a nivel mundial. La comparación se realiza con un modelo PWR Westinghouse de tres lazos (CN Almaraz) con el código termohidráulico TRACE, con hipótesis de estimación óptima, pero con hipótesis deterministas como criterio de fallo único o pérdida de energía eléctrica exterior. Las dosis al exterior se calculan con RADTRAD, ya que es uno de los códigos utilizados normalmente para los cálculos de dosis del SGTR. El comportamiento del reactor y las dosis al exterior son muy diversas, según las diferentes hipótesis en cada metodología. Por otra parte, los resultados están bastante lejos de los límites de regulación, pese a los conservadurismos introducidos. En el siguiente paso de la Tesis Doctoral, se ha realizado un análisis de seguridad integrado del SGTR según la metodología ISA, desarrollada por el Consejo de Seguridad Nuclear español (CSN). Para ello, se ha realizado un análisis termo-hidráulico con un modelo de PWR Westinghouse de 3 lazos con el código MAAP. La metodología ISA permite la obtención del árbol de eventos dinámico del SGTR, teniendo en cuenta las incertidumbres en los tiempos de actuación del operador. Las simulaciones se realizaron con SCAIS (sistema de simulación de códigos para la evaluación de la seguridad integrada), que incluye un acoplamiento dinámico con MAAP. Las dosis al exterior se calcularon también con RADTRAD. En los resultados, se han tenido en cuenta, por primera vez en la literatura, las consecuencias de las secuencias en términos no sólo de daños en el núcleo sino de dosis al exterior. Esta tesis doctoral demuestra la necesidad de analizar todas las consecuencias que contribuyen al riesgo en un accidente como el SGTR. Para ello se ha hecho uso de una metodología integrada como ISA-CSN. Con este enfoque, la visión del DSA del SGTR (consecuencias radiológicas) se une con la visión del PSA del SGTR (consecuencias de daño al núcleo) para evaluar el riesgo total del accidente. Abstract Steam Generator Tube Rupture accidents in Pressurized Water Reactors are known to be one of the most demanding transients for the operating crew. SGTR are special transient as they could lead to radiological releases without core damage or containment failure, as they can constitute a direct path to the environment. The SGTR is analyzed from a Deterministic and Probabilistic point of view in the Safety Analysis, although the assumptions of the different approaches regarding the operator actions are quite different. In the beginning of Deterministic Safety Analysis, the way of analyzing the SGTR was not crediting the operator action for the first 30 min of the transient, assuming that the operating crew was able to stop the primary to secondary leakage within that time. However, the different real SGTR accident cases happened in the USA and over the world demonstrated that operators can took more than 30 min to stop the leakage in actual sequences. Some methodologies were raised in the USA and in Europe to cover that issue. In the Probabilistic Safety Analysis, the operator actions are taken into account to set the headers in the event tree. The available times are used to establish the success criteria for the headers. However, in such a dynamic sequence as SGTR, the operator actions are very dependent on the time available left by the other human actions. Moreover, some of the SGTR sequences can lead to offsite doses without previous core damage and they are not taken into account in PSA as from the point of view of core integrity are successful. Therefore, to analyze all this factors, the appropriate way of analyzing that kind of sequences could be through a Dynamic Event Tree methodology. This Thesis compares the impact on transient evolution and the offsite dose of the most relevant hypothesis of the different SGTR analysis included in the Deterministic Safety Analysis. The comparison is done with a PWR Westinghouse three loop model in TRACE code (Almaraz NPP), with best estimate assumptions but including deterministic hypothesis such as single failure criteria or loss of offsite power. The offsite doses are calculated with RADTRAD code, as it is one of the codes normally used for SGTR offsite dose calculations. The behaviour of the reactor and the offsite doses are quite diverse depending on the different assumptions made in each methodology. On the other hand, although the high conservatism, such as the single failure criteria, the results are quite far from the regulatory limits. In the next stage of the Thesis, the Integrated Safety Assessment (ISA) methodology, developed by the Spanish Nuclear Safety Council (CSN), has been applied to a thermohydraulical analysis of a Westinghouse 3-loop PWR plant with the MAAP code. The ISA methodology allows obtaining the SGTR Dynamic Event Tree taking into account the uncertainties on the operator actuation times. Simulations are performed with SCAIS (Simulation Code system for Integrated Safety Assessment), which includes a dynamic coupling with MAAP thermal hydraulic code. The offsite doses are calculated also with RADTRAD. The results shows the consequences of the sequences in terms not only of core damage but of offsite doses. This Thesis shows the need of analyzing all the consequences in an accident such as SGTR. For that, an it has been used an integral methodology like ISA-CSN. With this approach, the DSA vision of the SGTR (radiological consequences) is joined with the PSA vision of the SGTR (core damage consequences) to measure the total risk of the accident.

Methods of Tree Appraisal: A Review of Their Features and Application Possibilities

Se revisan los métodas de valoración de arbolado

Application of a dynamic event tree methodolgy to steam generator tube rupture sequences

The Integrated Safety Assessment (ISA) methodology, developed by the Spanish Nuclear Safety Council (CSN), has been applied to a thermo-hydraulical analysis of a Westinghouse 3-loop PWR plant by means of the dynamic event trees (DET) for Steam Generator Tube Rupture (SGTR) sequences. The ISA methodology allows obtaining the SGTR Dynamic Event Tree taking into account the operator actuation times. Simulations are performed with SCAIS (Simulation Code system for Integrated Safety Assessment), which includes a dynamic coupling with MAAP thermal hydraulic code. The results show the capability of the ISA methodology and SCAIS platform to obtain the DET of complex sequences.

Efficient algorithms for dynamic probabilistic safety assessment. An application to convex damage domain.

The design of nuclear power plant has to follow a number of regulations aimed at limiting the risks inherent in this type of installation. The goal is to prevent and to limit the consequences of any possible incident that might threaten the public or the environment. To verify that the safety requirements are met a safety assessment process is followed. Safety analysis is as key component of a safety assessment, which incorporates both probabilistic and deterministic approaches. The deterministic approach attempts to ensure that the various situations, and in particular accidents, that are considered to be plausible, have been taken into account, and that the monitoring systems and engineered safety and safeguard systems will be capable of ensuring the safety goals. On the other hand, probabilistic safety analysis tries to demonstrate that the safety requirements are met for potential accidents both within and beyond the design basis, thus identifying vulnerabilities not necessarily accessible through deterministic safety analysis alone. Probabilistic safety assessment (PSA) methodology is widely used in the nuclear industry and is especially effective in comprehensive assessment of the measures needed to prevent accidents with small probability but severe consequences. Still, the trend towards a risk informed regulation (RIR) demanded a more extended use of risk assessment techniques with a significant need to further extend PSA’s scope and quality. Here is where the theory of stimulated dynamics (TSD) intervenes, as it is the mathematical foundation of the integrated safety assessment (ISA) methodology developed by the CSN(Consejo de Seguridad Nuclear) branch of Modelling and Simulation (MOSI). Such methodology attempts to extend classical PSA including accident dynamic analysis, an assessment of the damage associated to the transients and a computation of the damage frequency. The application of this ISA methodology requires a computational framework called SCAIS (Simulation Code System for Integrated Safety Assessment). SCAIS provides accident dynamic analysis support through simulation of nuclear accident sequences and operating procedures. Furthermore, it includes probabilistic quantification of fault trees and sequences; and integration and statistic treatment of risk metrics. SCAIS comprehensively implies an intensive use of code coupling techniques to join typical thermal hydraulic analysis, severe accident and probability calculation codes. The integration of accident simulation in the risk assessment process and thus requiring the use of complex nuclear plant models is what makes it so powerful, yet at the cost of an enormous increase in complexity. As the complexity of the process is primarily focused on such accident simulation codes, the question of whether it is possible to reduce the number of required simulation arises, which will be the focus of the present work. This document presents the work done on the investigation of more efficient techniques applied to the process of risk assessment inside the mentioned ISA methodology. Therefore such techniques will have the primary goal of decreasing the number of simulation needed for an adequate estimation of the damage probability. As the methodology and tools are relatively recent, there is not much work done inside this line of investigation, making it a quite difficult but necessary task, and because of time limitations the scope of the work had to be reduced. Therefore, some assumptions were made to work in simplified scenarios best suited for an initial approximation to the problem. The following section tries to explain in detail the process followed to design and test the developed techniques. Then, the next section introduces the general concepts and formulae of the TSD theory which are at the core of the risk assessment process. Afterwards a description of the simulation framework requirements and design is given. Followed by an introduction to the developed techniques, giving full detail of its mathematical background and its procedures. Later, the test case used is described and result from the application of the techniques is shown. Finally the conclusions are presented and future lines of work are exposed.

Analysis of the damage domains of sbo sequences with rcp passive thermal shutdown

The integrated Safety Assessment (ISA) methodology, developed by the Spanish Nuclear Safety Council (CSN), has been applied to a thermal-hydraulic analysis of PWR Station Blackout (SBO) sequences in the context of the IDPSA (Integrated Deterministic-Probabilistic Safety Assessment) network objectives. The ISA methodology allows obtaining the damage domain (the region of the uncertain parameters space where the damage limit is exceeded) for each sequence of interest as a function of the operator actuations times. Given a particular safety limit or damage limit, several data of every sequence are necessary in order to obtain the exceedance frequency of that limit. In this application these data are obtained from the results of the simulations performed with MAAP code transients inside each damage domain and the time-density probability distributions of the manual actions. Damage limits that have been taken into account within this analysis are: local cladding damage (PCT>1477 K); local fuel melting (T>2499 K); fuel relocation in lower plenum and vessel failure. Therefore, to every one of these damage variables corresponds a different damage domain. The operation of the new passive thermal shutdown seals developed by several companies since Fukushima accident is considered in the paper. The results show the capability and necessity of the ISA methodology, or similar, in order to obtain accurate results that take into account time uncertainties.

Autonomous Acquisition of Natural Language

An important part of human intelligence is the ability to use language. Humans learn how to use language in a society of language users, which is probably the most effective way to learn a language from the ground up. Principles that might allow an artificial agents to learn language this way are not known at present. Here we present a framework which begins to address this challenge. Our auto-catalytic, endogenous, reflective architecture (AERA) supports the creation of agents that can learn natural language by observation. We present results from two experiments where our S1 agent learns human communication by observing two humans interacting in a realtime mock television interview, using gesture and situated language. Results show that S1 can learn multimodal complex language and multimodal communicative acts, using a vocabulary of 100 words with numerous sentence formats, by observing unscripted interaction between the humans, with no grammar being provided to it a priori, and only high-level information about the format of the human interaction in the form of high-level goals of the interviewer and interviewee and a small ontology. The agent learns both the pragmatics, semantics, and syntax of complex sentences spoken by the human subjects on the topic of recycling of objects such as aluminum cans, glass bottles, plastic, and wood, as well as use of manual deictic reference and anaphora.

[Colección de fotografías de Cullera, II]. [Material gráfico].]

[59-62]. En la playa del Dosel Isabel Orrico Vidal bañándose, paseando con su hijo Paquito, Paquito Roglá Orrico con sombrero blanco de pie y sentado en la arena de la playa, 1920 (6 pares estereoscópicos) (4 fot.) [63-64]. Jardín de Villa Rosalía, mujer trabajando en el campo de la Villa (2 pares estereoscópicos) (2 fot.) [65-66]. La matanza del cerdo, 1920 (3 pares estereoscópicos) (2 fot.) [67]. Luís Roglá Orrico, nacido el 10 de octubre de 1920, en brazos de su niñera (1 par estereoscópico) (1 fot.) [68]. Francisco y Luís Roglá Orrico con las niñeras, 1920 (1 par estereoscópico) (1 fot.) [69]. Jardín de Villa Rosalía: Manolo Orrico Guzmán con sus nietos Paquito, Luisito (al brazo) y Merceditas hija de Manolo Orrico Vidal que está montada en un triciclo, 1921 (1 par estereoscópico) (1 fot.) [70]. Jardín de Villa Rosalía: Manolo Orrico Vidal con su hija Merceditas sobre un carrito de niño y su sobrino Paquito Roglá Orrico, 1921 (1 par estereoscópico) (1 fot.) [71]. Merceditas Orrico Gay montada en un triciclo con una escopeta y casco de juguete, 1921 (1 par estereoscópico) (1 fot.) [72-76]. Paquito y Luisito Roglá Orrico con su madre Isabel Orrico Vidal, con las niñeras, con su madre y las niñeras jugando con caballitos de cartón, Luisito con Pilar la niñera junto a un rosal, 1921 (5 pares estereoscópicos) (5 fot.) [77-79]. Paquito Roglá Orrico sentado en un sillón pequeño de mimbre, junto a dos caballitos de cartón, y montado en su caballito al fondo ropa tendida, 1921 (3 pares estereoscópicos) (3 fot.) [80]. Pilar con Luisito bajo la sombrilla al fondo Paquito juega con la arena y un pozal (1 par estereoscópico) (1 fot.) [81-83]. Isabel Orrico Vidal, sentada en un banco en el jardín, de pié junto a un árbol, sentada en el banco junto con Luisito y Paquito, 1921 (3 fot.) [84]. Luisito Roglá Orrico de pié junto a un árbol, 1921 (1 fot.) [85]. Paquito Roglá Orrico con babero y sombrero blanco sentado en el banco del jardín, 1921 (1 fot.) [86]. Pilar con Ignacio Roglá Orrico en brazos (nacido el 5 de junio de 1922) en la playa de San Antonio de Cullera con Paquito junto a una barca, 1922 (1 par estereoscópico) (1 fot.) [87]. En la playa de San Antonio de Cullera Isabel Orrico Vidal con sombrilla y su hijo Ignacio Roglá Orrico al brazo, Luís Roglá Orrico llorando y el niño que está sentado en la arena en primer plano es Francisco Roglá Orrico, sentada detrás Mercedes Gay y su hija Merceditas, 1922 (1 par estereoscópico) (1 fot.) [88, 90]. Paquito Roglá Orrico y Merceditas Orrico Gay sentados en una barca en la playa de San Antonio de Cullera, 1922 (2 pares estereoscópicos) (2 fot.) [91]. Paquito en la playa, una niña y un niño más pequeño detrás de él (1 par estereoscópico) (1 fot.) [92-93]. Isabel Orrico Vidal con Paquito Roglá Orrico y Merceditas Orrico Gay a la derecha la niñera con el bebé Ignacio Roglá Orrico, 1922 (2 pares estereoscópicos) (1 fot.) [94]. Francisco, Ignacio y Luís Roglá Orrico jugando en un carrito de bebé, 1923 (1 par estereoscópico) (1 fot.) [95]. Ignacio Roglá Orrico al brazo de Pilar, 1923 (1 par estereoscópico) (1 fot.) [96]. Comiendo paella en Villa Rosalía, Isabel Orrico Vidal, Matilde Vidal, Ignacio Roglá Orrico acariciado por su abuelo Manolo Orrico, Mercedes Gay, Manolo Orrico Vidal con Merceditas, Luís Roglá Orrico, 1923 (1 par estereoscópico) (1 fot.) [97]. Los niños Luís y Paco Roglá Orrico sentados en una pinada con la niñera, los dos niños llevan sombrero blanco, 1923 (1 fot.) [98]. Ignacio Roglá Orrico de pié al fondo la puerta de la casa, 1923 (1 par estereoscópico) (1 fot.) [99]. Francisco, Ignacio y Luís Roglá Orrico con su madre Isabel Orrico Vidal sentados junto a una bomba de agua con manivela de hierro fundido, 1923 (1 par estereoscópico) (1 fot.) [100]. Playa de San Antonio (Cullera) Isabel Orrico Vidal con sus tres hijos y su madre Matilde Vidal Gasco que coge de la manita a su nieto Ignacio, los niños están subidos a una barca, 1923 (1 par estereoscópico) (1 fot.) [101]. Isabel Orrico Vidal con su hijo Paquito, una amiga y la perrita Isa sentados en la arena de la playa, al fondo dos barcas y unas casas, 1924 (1 par estereoscópico) (1 fot.) [102]. Francisco, Ignacio y Luís Roglá Orrico y una niña en una barca, muchas cuerdas alrededor, 1924 (1 par estereoscópico) (1 fot.) [103-104]. Playa de Cullera una barca al fondo con tres personas, embarcadero (puerto) en lo que hoy es la playa de Cap Blanc, 1924 (2 pares estereoscópicos) (2 fot.) [105-107]. Playa de San Antonio en Cullera Isabel Orrico Vidal con Ignacio, Luis, Paco y las niñeras tomando el baño, verano 1924 (3 pares estereoscópicos) (3 fot.) [108-109]. Paquito Roglá Orrico regando una planta, y con sus hermanos en el jardín, 1924 (3 pares estereoscópicos) (2 fot.) [110]. Las niñeras en el lavadero de Villa Rosalía, 1925 (1 par estereoscópico) (1 fot.) [111]. Sirvienta junto a unas macetas (1 fot.) [112]. Francisco Roglá López en Villa Rosalía, 1925 (1 par estereoscópico) (1 fot.) [113-114]. El abogado Ribera y secretario en Villa Rosalía, junto a la fachada, y en el pozo vertiendo el agua del pozal, 1925 (2 pares estereoscópicos) (2 fot.)