Modeling of the steam system in a BWR : A Model of Ringhals 1

Abstract: A nuclear power plant is a very complex dynamic system with a lot of built inregulators 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 computermodel and simulate the system. This master thesis is about building a dynamic modelof the steam system in the boiling water reactor Ringhals 1. The model has beendeveloped in the modeling-/simulating software Dymola and the components arewritten in the programming language Modelica. The model contains the most criticalcomponents in the steam system from reactor tank to condenser and also the mostimportant parts of the control systems. The final model has been compared to real power plant data from Ringhals 1 for fullpower operation, reduced power and a turbine trip. During steady state conditionsthe model has good compliance with the available data in most positions of the steamsystem. Due to absence of good data the results of the dynamic verification for thedrop of load and turbine trip is incomplete. Instead the plausibility of the systembehavior has been done. The results are good but the magnitudes of the transientsare impossible to evaluate. Two major weaknesses have been found during the verification of the model. Theyare the turbine behavior during off-design load and various transients, and the controlof the flow through the tube side of the reheater. The lack of mass flow data is alsomaking it hard to fully trust the model. The final conclusion is that the steam system model is not ready to take on realproblems, but it is a good basis for further development and utilization. The abovementioned problems have to be looked further into and depending on the intendedusage of the model; it may be necessary to modify it to more exactly describe certainparts of the steam system.