Control Rod Worth Uncertainty Propagation from Nuclear Data for NUR Research Reactor

Control rod worth is one of the most critical parameters in operating and controlling any nuclear reactor. Accurate calculation is more and more required; any uncertainties should be identified and estimated. In this work, we focalize on the control rod worth uncertainties due to the nuclear data uncertainties. The sensitivity and uncertainty (S/U) analysis of the control rod worth has been performed for the NUR research reactor using the first-order perturbation theory as implemented in the SCALE package. The IV.N configuration -with fresh fuel elements and five control rods- has been simulated in a 3D model using the KENO V.a of the SCALE package. Only one control rod worth has been considered in the analysis to simplify the problem. Uncertainty propagation of nuclear data has been evaluated by calculating sensitivity coefficients of eigenvalue-difference worth coefficients after computing sensitivity coefficients for the k-eigenvalues at every two states of the NUR reactor configuration and combining them to obtain sensitivity coefficients for the difference. Each state has been defined by an incrementing of control rod insertion. The k-eigenvalue sensitivities have been calculated using the TSUNAMI-3D sequences in SCALE. The reactivity sensitivity coefficients have been combined with covariance data to determine the uncertainty in the reactivity response using the TSAR code of the SCALE package. The main contributors (nuclide and reaction) in the control rod worth uncertainties have been identified for each step of control rod insertion. The contribution amount of each element and reaction has been evaluated.