Analysis and sensitivity studies with CORETRAN and RETRAN-3D of the NEACRP PWR rod ejection benchmark

The OECD/NEA PWR rod ejection benchmark has been analysed using the 3-D nodal spatial-kinetic codes CORETRAN and RETRAN-3D. The following results were obtained. A) The agreement in 3-D solution between CORETRAN and RETRAN-3D was found to be very good both during steady-state and transient conditions. In particular at HZP (hot zero power), an excellent agreement in the initial steady-state 3-D power distribution and with regard to the core power excursion during the super-prompt critical phase of the transient (i.e. when the negative reactivity feedback is still very weak) was found. This illustrates the consistency in the neutronic solution between both codes. B) At both HZP and FP (full power) conditions, the CORETRAN and RETRAN-3D results lie well within the range of the previous benchmark solutions. In particular at HZP, both codes predict a power excursion and an increase in maximum pellet temperature that are among the closest results to those obtained with the benchmark reference solution. It must here be emphasised that these analyses are by no means a validation of the codes. However, the good agreement of both CORETRAN and RETRAN-3D with other 3-D solutions provides confidence in the ability of these codes to analyse LWR (light water reactor) core transients. In addition, it was found appropriate to perform, for this well-defined international benchmark problem, some sensitivity studies in order to assess the impact of modelling options on the CORETRAN and RETRAN-3D results. (authors)