Application of adjoint based node optimization method to nuclear thermal-hydraulic system analysis code

In nuclear engineering, traditionally, deterministic safety analyses of nuclear power plants have been performed with conservative assumptions. Recently, the Best Estimate plus Uncertainty (BEPU) approach is also being used along with a conservative approach. Results from thermal hydraulic (TH) system analysis codes with BEPU approach are unavoidably uncertain and naturally, an uncertainty analysis has been an important issue with this approach. In general, 1-D thermal hydraulic system analysis code simulates the system by dividing it into arbitrarily determined nodes based on the user experiences. Previously, uncertainties related to spatial discretization in the process of nodalization have been considered to be less dominant than other user effects due to their difficulty in quantification. However, in recent years, there are some results that they are comparable to other uncertainties such as uncertainties due to physical models and could be significant in some simulations. Previous studies have been conducted by evaluating and optimizing the uncertainty related to user effect by performing iterative calculations on many occasions using genetic algorithms or parallel computation techniques. Since these methods consume a large amount of resources for computation, this study suggests a method of consuming less resources. For this purpose, the adjoint method that analyzes the sensitivity for many parameters efficiently is applied to nuclear thermal-hydraulic system analysis code for node optimization in this study.