Modeling of Pressurizer Using APROS and TRACE Thermal Hydraulic Codes

The objective of the study is detailed thermal hydraulic modeling of the PWR pressurizer using both APROS simulation software package and TRACE code. The constructed models have been assessed against data from insurge, outsurge and spray experiments conducted at test facilities suitable for separate effect pressurizer tests in order to find an optimal modeling approach for simulating pressurizer transients. A main goal of the research was validating the pressurizer model of APROS against the background provided by experiments from three different test facilities, namely PACTEL, MIT pressurizer and Neptunus facility. In addition, a model of the Loviisa NPP pressurizer has been generated and the pressurizer behavior during a turbine trip transient was simulated for the purpose of investigating the scaling effect on the performance of the APROS pressurizer calculation. The separate tests have been simulated using different nodalization schemes and modeling options, and extensive comparisons between the results given by APROS and TRACE have been made. The TRACE simulations are also a part of the international CAMP code validation program of the United States Nuclear Regulatory Commission. Based on the simulation results, an evaluation of the capabilities of the heat transfer models to predict pressure behavior in the two codes has been provided. A significant drawback in the APROS pressurizer calculation was discovered and an improvement to the calculation was achieved by incorporating a new wall condensation correlation into the code.