STORED ENERGY CALCULATION: THE STATE OF THE ART, 1978.

This report is the result of an investigation to determine the current state of the art of fuel temperature, gap conductance, and stored energy calculations. Major emphasis was placed on the propagation of input and model uncertainties. To support this study a comparison was made to the observed variability of experimental data for fuel centerline temperature and gap conductance values. The uncertainty analysis was performed by identifying major thermal models and collecting them into an abstract of a thermal performance code. Uncertainties in the calculations were determined using the method of propagation of uncertainties with a first order Taylor series approximation to the nonlinear functions. Output uncertainty results are presented for the beginning of fuel life, the end of life, and throughout a typical power history. Also presented is an influence and importance analysis for the input parameters. It is concluded that the relative uncertainty in stored energy is approximately plus or minus 20% at beginning of fuel life, and increases to plus or minus 25-40% contact. The foregoing are 3 sigma (99. 9%) confidence intervals. The most important contributors to stored energy uncertainty are linear heat rating and fuel thermal conductivity.