Applying thermal hydraulics modeling in coupled processes of nuclear power plants: Dissertation

This thesis focuses on the validation of the coupled codes developed in Finland for the safety analyses of the lLight wWater rReactors in design basis accidents. The validation efforts and applications of the thermal hydraulics code SMABRE and the three-dimensional neutron kinetics codes are introduced for both the separate and coupled codes. The code development and coupling of codes for the safety analyses in Finland are discussed, and the present situation and possible future directions are described. The data for the code validation consists of the experimental data from test facilities, numerical benchmarks and data measured in real nuclear power plants. The nuclear core is relevant for the couplings of neutron kinetics and thermal hydraulics codes. Two European Union projects, in which ten transients at real VVER plants have been documented, as well as the other international benchmarks are dealt with as useful forums in the code validation. The simulation of plant measurements and several plant modeling aspects emerging from the validation work are gathered together. The main steam line break in different kinds of plants is dealt as an example of the application of the coupled codes in safety analysis. The coupling of a thermal hydraulic code with a fuel transient performance code is illustrated in the thesis as a new approach to performing the safety analyses. Another new approach is the sensitivity and uncertainty analyses performed for a Loviisa plant turbine trip case. In addition to this summary, the thesis consists of seven publications in appendices: five articles in scientific journals and two conference papers.