Effects of fill gas composition and pellet eccentricity. [BWR]

Data and an analysis are presented showing that when the operating pellet-cladding gap size of contemporary UO/sub 2/ fuel rods is carefully considered, the gap conductances are closely proportional to the thermal conductivities of the fill gases. Pellet-cladding gap eccentricity is shown to raise the gap conductance appreciably in cases of high thermal gradients across the gap. Ignoring the azimuthal heat flow can lead to an underestimation of the thermal time constant of the rod, resulting in a slower calculated thermal response during power transients. The data for this report were obtained during the startup of the NRC-RSR/BPNL test assembly IFA-431 in the Halden Boiling Water Reactor in Norway

GAPCON-THERMAL-1: a computer program for calculating the gap conductance in oxide fuel pins

GAPCON-THERMAL-1, a modification of GAPCON, can be used to calculate the gap conductance and fuel temperatures in oxide fuel pins. The code in its current form was developed for the Regulatorv Staff who use the code as a tool to independently calculate gap conductances for understanding various thermal performance models supplied by fuel venders. The code is capable of calculating fuel temperatures for several coolant, cladding, and fuel material combinations. Changes in the diametral gap width are modeled. The source of these changes include differential thermal expansion of pellet and cladding, elastic and creep deformation of cladding, fission product expansion of the pellet, and fuel expansion induced by cracks and subsequent thermal ratcheting. In addition to the gap changes, the code simulates a variety of fill gas compositions and changes to the gas composition caused by the release of fission gap and volatile impurities. Comparisons of calculations and experimental data indicate iuel temperatures are predicted reasonably well for short term irradiations and small gaps. The disagreement between predictions and experimental data is roughly proportional to the gap width and the calculated values are typically higher than the experimental values. Fuel temperature calculations for extended periods of irradiation become more uneertain because of inadequacies in the code and the dearth of well characterized data. These inadequacies are related principally to the kinetics of gap closure and fission gas release. On-going work is focused on reducing the uncertainty in these two areas of the code and in other areas of somewhat lesser significance. The effects of these uncertainties on the fuel stored energy are offset somewhat by the reduction in rod powers with burnup. (auth

Method for determining the uncertainty of gap conductance deduced from measured fuel centerline temperatures. [BWR]

The paper describes the method which was developed to determine the uncertainties of gap conductances deduced from measured fuel centerline temperatures of NRC-RSR/BPNL fuel rods irradiated in the Halden Boiling Water Reactor. The ..integral..k(t)dt method is used to calculate the fuel surface temperature from the measured fuel centerline temperature and the fuel thermal conductivity. The gap conductance is calculated from the fuel surface temperature, the calculated cladding inside surface temperature, and the measured fuel assembly power. The uncertainties in the input parameters for calculating the gap conductance were established and the uncertainty in the gap conductance was calculated using the method of propagation of uncertainties with a first order Taylor series approximation to the nonlinear functions. An example of the calculational method is given

MODEL OF A PROCESS FOR DRYING Eucalyptus spp AT HIGH TEMPERATURES

A mathematical model of a process for drying of Eucalyptus spp is presented. This model was based on fundamental heat and mass transfer equations and it was numerically solved using a segregated finite volume method. Software in the FORTRAN language was developed to solve the mathematical model. The kinetic parameters of drying for Eucalyptus spp were experimentally obtained by isothermal thermogravimetry (TG). The theoretical results generated using the mathematical model were validated by experimental data