TRANSURANUS Code Research Articles

Extension of the TRANSURANUS burnup model to heavy water reactor conditions

The extension of the light water reactor burnup equations of the TRANSURANUS code to heavy water reactor conditions is described. Existing models for the fission of 235 U and the buildup of plutonium in a heavy water reactor are evaluated. In order to overcome the limitations of the frequently used RADAR model at high burnup, a new model is presented. After verification against data for the radial distributions of Xe, Cs, Nd and Pu from electron probe microanalysis, the model is used to analyse the formation of the high burnup structure in a heavy water reactor. The new model allows the analysis of light water reactor fuel rod designs at high burnup in the OECD Halden Heavy Water Reactor.

Mechanical behaviour modelling of fractured nuclear fuel pellets

The mechanical behaviour of fractured nuclear fuel pellets is far from simple. In order to take correctly into account this behaviour and model it in the frame of a computer code, a lot of phenomena must be examined. Most of them can hardly be assessed physically and so only empirical models are available. This paper deals with some mechanical and physical phenomena which participate in the total radial deformation of a fuel rod during its in-reactor lifetime and which are mainly relevant to pellet fracturing and pellet-cladding mechanical interaction (PCMI) in normal (steady state) and off-normal (transient) operating situations. Based on qualitative considerations and comparison with experimental results, empirical models for pellet fracturing and PCMI have been established, introduced into the transuranus code and calibrated against various experimental results, so that the evolution of fuel radial deformation can be correctly simulated.

TRANSURANUS: a fuel rod analysis code ready for use

TRANSURANUS is a computer program for the thermal and mechanical analysis of fuel rods in nuclear reactors and was developed at the European Institute for Transuranium Elements (TUI). The TRANSURANUS code consists of a clearly defined mechanical-mathematical framework into which physical models can easily be incorporated. Besides its flexibility for different fuel rod designs the TRANSURANUS code can deal with very different situations, as given for instance in an experiment, under normal, off-normal and accident conditions. The time scale of the problems to be treated may range from milliseconds to years. The code has a comprehensive material data bank for oxide, mixed oxide, carbide and nitride fuels, Zircaloy and steel claddings and different coolants. During its development great effort was spent on obtaining an extremely flexible tool which is easy to handle, exhibiting very fast running times. The total development effort is approximately 40 man-years. In recent years the interest to use this code grew and the code is in use in several organisations, both research and private industry. The code is now available to all interested parties. The paper outlines the main features and capabilities of the TRANSURANUS code, its validation and treats also some practical aspects.

Modelling of fuel rod behaviour and recent advances of the transuranus code

Modern fuel rod performance codes form a clearly defined mechanical/mathematical framework into which the detailed models describing the physical behaviour can easily be incorporated. Emphasis in this paper is directed more towards these concepts rather than to the review of the various existing physical submodels. The basic equations of the thermal and the mechanical analysis are outlined; simplifying assumptions are discussed as well as numerical solution techniques, the inherent uncertainties of these analyses and the problems related with the coupling of both. Examples of results of the TRANSURANUS code are used to illustrate accuracies achievable by state-of-the-art fuel rod modelling.

A fast and simple iteration scheme for the temperature calculation in a fuel rod

A new and simple iteration scheme for solving the nonlinear heat conduction in a fuel rod is developed. The method is based on a Newton-Raphson iteration scheme and takes two distinctive characteristics of the problem into account. The result is a scalar Regula Falsi technique which is superior to a relaxation technique. The new iteration scheme has been applied successfully over 2 years in the TRANSURANUS code, analysing several hundred complicated data cases under normal, off-normal and accident conditions. Convergence problems never occurred and the computational costs were significantly reduced.