Validating the Serpent-Ants Calculation Chain Using BEAVRS Fresh Core HZP Data

The Serpent Monte Carlo code and the Serpent-Ants two step calculation chain are used to model the hot zero power physics tests described in the BEAVRS benchmark. The predicted critical boron concentrations, control rod group worths and isothermal temperature coefficients are compared between Serpent and Serpent-Ants as well as against the experimental measurements. Furthermore, radial power distributions in the unrodded core are compared between Serpent and Serpent-Ants. In addition to providing results using a “best estimate” calculation chain, the effects of several simplifications or omissions in the group constant generation process on the results are estimated. The “best estimate” predictions by Serpent-Ants are reasonably close to the experimental values with RMS differences from measurements of 29.7 ppm, 62.2 pcm and 0.37 pcm/°F for boron, control rod worths and temperature coefficients respectively. The match in the radial power distribution between Serpent and Serpent-Ants was very good with the RMS and maximum for pin power errors being 1.31 % and 5.01 % respectively. While the tested sub-optimal variations in the two-step calculation chain led to a clear worsening of the radial power distribution, the effects in the global parameters were more mixed with some sub-optimal approaches actually providing better results for critical boron and control rod worths than the “best estimate” approach.