Coupled neutronic/thermal-hydraulic calculations in support to the power uprate of the Ringhals-3 PWR

Paper in proceeding, 2007

Many power utilities worldwide are applying for power uprates, i.e. for increasing the power output of their reactors. The Swedish Nuclear Power Inspectorate (SKI) received an application related to the Ringhals-3 Pressurized Water Reactor (PWR) in March 2004. The increase of the thermal power in Ringhals-3 is a relatively large one: from 2778 MWth (original power level - 100%) to 3160MWth (113.5%). It is essential to identify the main consequences of the increased power level of the reactor, and their impact on the safety of the plant. For that purpose, coupled neutronic/thermal-hydraulic calculations have to be performed. This paper presents the on-going efforts to develop a state-of-the-art coupled Ringhals-3 model based on the use of the PARCS and RELAP5 codes, for modelling the neutron flux and the flow velocity/temperature fields, respectively. On the neutronic side, a unique cross-section interface, allowing feeding PARCS with realistic data, was developed. On the thermal-hydraulic side, each of the 157 fuel assemblies is modelled. Validation of the coupled model against measured plant data at steady-state conditions is then reported. Comparisons between calculated/measured parameters demonstrate that the coupled model is able to correctly represent the steady-state conditions of the plant. The validation of the coupled model against measured transient plant data is then described. The transient chosen for this validation task was a house-load (load rejection) transient, which occurred on January 8, 2005. It is demonstrated that the coupled model is able to catch the main features of the transient with a sufficient level of accuracy.