On-line reactivity calculation using Lagrange method.

Highlights: [•] Lagrange method is proposed for on-line reactivity calculation in nuclear reactors. [•] The need for nuclear power history or the Laplace transform is vanished. [•] The three- and five-point formulas are presented and examined in different benchmark cases. [•] Computational time-steps of up to 1s lead to highly reliable reactivity calculations. [•] The main advantage of the proposed approach is its stability and convergence in large time-step calculations. [Copyright &y& Elsevier]