DERREP: A Computer Code for the Calculation of Decay Heat in CANDU Reactor Nuclear Fuel

Abstract

The ability to determine the decay heat generation rate, days or weeks after a reactor shutdown is important for developing safe and efficient operating strategies under these conditions. An accurate assessment of decay energy production is important for determining parameters such as Emergency Coolant Injection System recall times, loads to heat sinks, and the effectiveness of ice-plug isolation. To aid in these analyses, a FORTRAN computer code, DERREP (Decay Energy Release Rate Estimation Program) has been written incorporating the latest ANSWANS 5.1 methodology. The program uses the ANS standard with data from the POWDERPUFS-V CANDU lattice physics code and calculates individual energy contributions attributable to the major nuclides, including correction to account for neutron capture in fission products. Maximum user flexibility has been built into the code, though for many applications users can take advantage of the default input data provided for all operating Ontario Hydro CANDU reactors. The paper provides an overview of: the methodology employed in the code, the application on a bundle, channel, and core-averaged basis, and identifies the code limitations. Sensitivity studies performed with the code are presented. The studies allow a characterization of the important factors influencing decay energy release rates--including fuel burnup and effective operating time. Comparisons with the ORIGEN code and CANDU measurements are made.