Taking the new fuel into use is a multi-year project requiring regulatory approvals. In order to gain experience of the new fuel, the aim is to license the new fuel type and to take it in use as soon as possible. As a part of the licensing of a new fuel type, deterministic safety analyses needed to be updated accordingly. Thanks to the experienced in-house experts, own analysis software Apros and existing Loviisa NPP analysis model, Fortum was able to update the deterministic safety analyses with a tight schedule and that way greatly expedite the fuel licensing process.
As part of this project, all Loviisa FSAR analyses were reviewed and those in which the new fuel type has a remarkable impact on the analysis results, were chosen to be updated. Those analyses included large break loss-of-coolant-accident (LBLOCA), main steam line break (MSLB), main circulation pump trips, main circulation pump startup and reactivity transients like control rod ejection and uncontrolled withdrawal of control rods. Also, lift force calculations of the reactor inner parts had to be updated.
Loviisa Apros 3D core model was updated (e.g. geometry, pressure losses and fuel material properties) by Fortum experts according to the input data provided by Westinghouse. Wide range 3D cross-sections and other group constants needed for the neutronics calculation of Apros were calculated with CASMO-4E software, equilibrium loading pattern was designed for the new fuel type and fuel burnup distribution was calculated with HEXBU-3D software by reactor physicists of Fortum. New method previously developed to take into account uncertainty in measurement signal values was taken into use in the analysis work. At the moment, Apros analysis work has been finished and Fortum has sent the updated analyses to Finnish regulatory authority STUK by the end of the year 2023.
Thanks to in-house expertise in nuclear fuel, reactor physics and deterministic safety analysis and close collaboration with the fuel supplier, Fortum will be able to license the new fuel type in record speed and gain valuable operating experience from the fuel before new fuel supply tenders are needed for the extended plant lifetime to 2050.
Fortum has a long history of using Apros in the field of safety and engineering analysis. We use Apros to calculate all the deterministic safety analyses for Loviisa nuclear power plant. We have provided analysis and modelling expertise to external customers such as OKG, Forsmark Kraftgrupp, Ringhals AB, KHNP CRI and Japan NRA. The Finnish Radiation and Nuclear Safety Authority (STUK) has accepted deterministic safety analyses carried out with Apros by Fortum since 1990s and The Swedish Radiation Safety Authority (SSM) has approved the Independent Core Cooling analysis done by Forsmark with Apros.
Westinghouse Electric Sweden uses Apros Nuclear in their work. Apros software quality system has been audited by Westinghouse Electric Sweden and Apros software has been accepted to be used for deterministic analysis and engineering use in their projects.
