In nuclear safety analysis, it is very important to be able to simulate the different transients that can occur in a nuclear power plant with a very high accuracy. Although the best estimate codes can simulate the transients and provide realistic system responses, the use of nonexact models, together with assumptions and estimations, is a source of uncertainties which must be properly evaluated. This paper describes a Rod Ejection Accident (REA) simulated using the coupled code RELAP5/PARCSv2.7 with a perturbation on the cross-sectional sets in order to determine the uncertainties in the macroscopic neutronic information. The procedure to perform the uncertainty and sensitivity (U&S) analysis is a sampling-based method which is easy to implement and allows different procedures for the sensitivity analyses despite its high computational time. DAKOTA-Jaguar software package is the selected toolkit for the U&S analysis presented in this paper. The size of the sampling is determined by applying the Wilks’ formula for double tolerance limits with a 95% of uncertainty and with 95% of statistical confidence for the output variables. Each sample has a corresponding set of perturbations that will modify the cross-sectional sets used by PARCS. Finally, the intervals of tolerance of the output variables will be obtained by the use of nonparametric statistical methods.

No abstract

No abstract

No abstract

One of the challenges of study the neutronics of reactor is to generate reliable parameterized libraries, which contains information to simulate the core in all possible operational and transient conditions. These libraries must include tables of cross-sections and other neutronics and kinetics parameters and are obtained by simulating all the assemblies in a transport code. At lattice level, one can use branch calculations to change "instantaneously" the feedback parameters as a function of burnup. When using random sampling for the lattice calculations, one can obtain statistical information of the output parameters and use it in a core simulation to characterize the accuracy of the data estimating uncertainties when simulating a heterogeneous system at different scales of detail. This work presents the methodology to generate NEMTAB libraries from data obtained in SCALE code system to be used in PARCS simulations. The code TXT2NTAB is used to reorder the cross-sections tables in NEMTAB format and generate another NEMTAB of standard deviation. With these libraries, the authors perform a steady state calculation for an LWR to propagate several uncertainties at the core level. The methodology allows to obtain statistical information of the most important output parameters: multiplication factor (keff), axial power peak (Pz) and axial peak node (Nz).