Matthew Klinczar, Eric Savage
Computer simulation of nuclear reactors is an important field of study that is necessary for designing and regulating reactors. The behavior of reactors can include physical phenomena that must be accurately and reliably simulated to design, license, and operate reactors. Boiling Water Reactor (BWR) stability is the behavior studied in this thesis. BWRs can experience power level oscillations increasing in magnitude that can force a SCRAM of the reactor. This has led to constant study of BWR stability simulation to improve models and understand the stability behavior.
Oskarshamn-2 is a BWR unit in Sweden, which experienced an instability even on February 25th, 1999. This particular event was caused by a decrease in feedwater temperature due to the loss of feedwater heaters. This increased the core power, which led to pump rundowns in order to decrease the flow through the core and the core power. Also, a partial SCRAM was performed to reduce the power to 65 %, but because the core inlet temperature continued to decrease, the power continued to increase. At this point, the power experienced oscillations of increasing amplitude, reaching a peak of 132 % power, at which point a full SCRAM was performed to shut down the reactor.
Computer simulation models have been developed to study and better understand these types of phenomena. One such model that is the focus of this thesis uses the TRACE/PARCS code system. TRACE is a thermal-hydraulics system code developed and used by the United States Nuclear Regulatory Commission (US NRC). PARCS is a reactor neutronics code developed at Purdue University, which is coupled with TRACE to create a model for BWR stability events. This model has been used in the past to simulate the Oskarshamn-2 event as well as stability tests that occurred previous to and following the event.
The purpose of this research is to modify the TRACE/PARCS model to use NEMTAB crosssection libraries rather than the Purdue Macroscopic cross-section file (PMAXS). Doing so allows the NEMTAB file format to be verified against the results obtained using the PMAXS cross section format in the Oskarshamn-2 model. These NEMTAB libraries are important because they can be used in more models with different codes as part of the benchmark analysis, and also for potential future work that requires cross-section generation.