Transient Thermal-hydraulic Simulation of a Small modular Reactor in RELAP 5

This thesis analyzes and evaluates relevant thermal-hydraulic features of the integral pressurized water reactor for a new design of nuclear power plant. The chosen design is the NuScale small modular reactor. This reactor has a thermal power of 160 MW and operates usually with more reactors of its kind in a common power plant. The NuScale design is currently in the licensing process from the Nuclear Regulatory Commission. The first part of this thesis deals with basic knowledge about nuclear fission, SMR technology, and the power plant steam cycle. The second part is about the simulation software RELAP 5, which uses a one-dimensional model to simulate nuclear power systems. It describes how to program the different components, which are needed to simulate the NuScale system. In addition, the two fluid model is introduced which is the basis for the RELAP 5 thermal hydraulic simulations. The final part is about the simulation and the evaluation of the SMR. The NuScale design criteria were looked up in the final safety analysis report, which is used for licensing at the NRC. The results show that the steady state values of the simulation matches with the data from the FSAR of the NuScale design. Therefore it can be said that a reactor, which only runs via natural circulation, works and all the heat which is produced by the core is transferred to the secondary cycle of the SMR. The findings of this thesis confirm the benefits of the NuScale SMR design and suggest further theoretical and later experimental investigations