A nuclear power plant is a very complex dynamic system with a lot of built in regulators and security systems that make it almost impossible to know by reasoning,exactly how the system dynamics is going to react due to e.g. plant modifications,transients or operator behaviors. A common way to find out is to build a computer model and simulate the system.
This study is about building a dynamic model of the steam system in the boiling water reactor Ringhals 1. The model has been developed in the modeling-/simulating software Dymola and the components are written in the programming language Modelica. The model contains the most critical components in the steam system from reactor tank to condenser and also the most important parts of the control systems.
The final model has been compared to real power plant data from Ringhals 1 for full power operation, reduced power and a turbine trip. During steady state conditions the model has good compliance with the available data in most positions of the steam system.
Due to absence of good data the results of the dynamic verification for the drop of load and turbine trip is incomplete. Instead the plausibility of the system behavior has been done. The results are good but the magnitudes of the transients are impossible to evaluate.
Two major weaknesses have been found during the verification of the model. They are the turbine behavior during off-design load and various transients, and the control of the flow through the tube side of the reheater. The lack of mass flow data is also making it hard to fully trust the model.
The final conclusion is that the steam system model is not ready to take on real problems, but it is a good basis for further development and utilization. The above mentioned problems have to be looked further into and depending on the intended usage of the model; it may be necessary to modify it to more exactly describe certain parts of the steam system.
Source: Uppsala University
Author: Norberg, Thomas
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