A. Escrivá

Non linear analysis of out of phase oscillations in boiling water reactors

Abstract Out of phase oscillations have been observed recently in many boiling water reactors during stability tests and also in start up conditions. Many authors have attempted to explain these regional oscillations, but the explanations given are not complete. In this paper, we develop a non linear phenomenological model that can explain, both in phase and out of phase oscillations. The neutronic loop has been described on the basis of an expansion in terms of A-modes. Furthermore, for a semiquantitative representation of the dynamics, reduced order model have been obtained reducing the number of regions, modes and energy groups considered in the problem. In this line, we propose a model that qualitatively explains the dynamic behavior of these oscillations verifying that in phase oscillations only appear when the azimuthal mode has not enough thermal-hydraulic feedback to overcome the eigenvalue separation and also, that it is possible that self-sustained out of phase oscillations arise due to the different thermal-hydraulic properties of the two reactor core lobes, if the modal reactivities have appropriate feedback gains.

Consistent generation and functionalization of one-dimensional cross sections for TRAC-BF1

A method of calculation of correct functionalized cross sections and diffusion coefficients for TRAC-BF1, based on the one-dimensional kinetic files of the tridimensional simulator SIMULATE-3, is developed. The method allows the user to obtain first the consistent one-dimensional cross sections, diffusion coefficients, and bucklings, which upon being inserted into TRAC-BF1 conserve the three-dimensional eigenvalues, the planar reaction rates, and the fast and thermal radially averaged fluxes at each axial node. This method also compensates for the differences between the thermal-hydraulic models of the three-dimensional simulator and the transient analysis code. The errors obtained with this method are very small.

Use of the Principles of Maximum Entropy and Maximum Relative Entropy for the Determination of Uncertain Parameter Distributions in Engineering Applications

The determination of the probability distribution function (PDF) of uncertain input and model parameters in engineering application codes is an issue of importance for uncertainty quantification methods. One of the approaches that can be used for the PDF determination of input and model parameters is the application of methods based on the maximum entropy principle (MEP) and the maximum relative entropy (MREP). These methods determine the PDF that maximizes the information entropy when only partial information about the parameter distribution is known, such as some moments of the distribution and its support. In addition, this paper shows the application of the MREP to update the PDF when the parameter must fulfill some technical specifications (TS) imposed by the regulations. Three computer programs have been developed: GEDIPA, which provides the parameter PDF using empirical distribution function (EDF) methods; UNTHERCO, which performs the Monte Carlo sampling on the parameter distribution; and DCP, which updates the PDF considering the TS and the MREP. Finally, the paper displays several applications and examples for the determination of the PDF applying the MEP and the MREP, and the influence of several factors on the PDF.

Interaction between natural convection and condensation heat transfer in the passive containment cooling condensers of the ESBWR reactor

Abstract The passive containment cooling condensers (PCCC) are the crucial part of several new reactor designs. In this paper we have developed several models to compute the heat transfer coefficients for the following cases: (i) condensation in presence of noncondensable gases inside the PCCC tubes; (ii) laminar natural convection for vertical cylinders; (iii) turbulent natural convection for vertical cylinders. These models have been implemented in the TRAC-BF1 code, and we have studied the interaction between the conservation regime inside the condenser tubes and the natural convection outside.

Development of Conductivity Sensors for Multi-Phase Flow Local Measurements at the Polytechnic University of Valencia (UPV) and University Jaume I of Castellon (UJI)

This paper describes all the procedures and methods currently used at UPV (Universitat Politécnica de Valencia) and UJI (University Jaume I) for the development and use of sensors for multi-phase flow analysis in vertical pipes. This paper also describes the methods that we use to obtain the values of the two-phase flow magnitudes from the sensor signals and the validation and cross-verification methods developed to check the consistency of the results obtained for these magnitudes with the sensors. First, we provide information about the procedures used to build the multi-sensor conductivity probes and some of the tests performed with different materials to avoid sensor degradation issues. In addition, we provide information about the characteristics of the electric circuits that feed the sensors. Then the data acquisition of the conductivity probe, the signal conditioning and the data processing including the device that have been designed to automatize all the measurement process of moving the sensors inside the channels by means of stepper electric motors controlled by computer are shown in operation. Then, we explain the methods used for bubble identification and categorization. Finally, we describe the methodology used to obtain the two-phase flow information from the sensor signals. This includes the following items: void fraction, gas velocity, Sauter mean diameter and interfacial area concentration. The last part of this paper is devoted to the conductance probes developed for the annular flow analysis, which includes the analysis of the interfacial waves produced in annular flow and that requires a different type of sensor.

EXPERIENCES IN DEVELOPING AND APPLYING A NEW METHODOLOGY IN MASTER’S DEGREE

In the subject Advanced Energy and Thermal Machines of the Master’s Degree in Industrial Engineering a great effort was made to apply a new methodology based on the development of activities directly related to the real or professional applications together with the use of computer codes to solve these real problems. The simulation based learning has been the basis of the application of this new methodology. The goal is that students can achieve a high level of theory knowledge together with a high capacity of autonomy in solving problems. For that, a plan has been stablished to be implemented gradually. According to this plan, the subject is clearly defined in each of the sections: objectives, contents, methodology, activities and assessment looking for the constructive alignment. Besides, new materials have been created. In this paper, the experiences and results obtained in the process of improving the way of teaching this subject are shown and analyzed from the point of view of the teacher and from the point of view of the student.