Small Sample Reactivity Worth Calculation: Comparison of Serpent2 and TRIPOLI4 Perturbation Techniques

In support of lead cooled SMR technologies, oscillation experiments are under design at the VENUS-F fast zero-power reactor at the Belgian Nuclear Research Center SCK CEN. In this paper, the performance of two Monte Carlo codes to model small reactivity worth of an oscillating sample is compared. The capability of the first order perturbation theory implemented in Serpent2-XGPT is assessed by comparing it to the exact perturbation theory implemented in TRIPOLI4-IFP. A of merit is proposed to discriminate cases where approximated formulation is sufficient to those figure where the more accurate exact perturbation theory is needed. The analysis is performed in fast and thermal systems showing significant limitations of the first order perturbation in the latter. For calculating small sample reactivity worth in VENUS-F, Serpent2 first order perturbation method provided reliable results, although there are limitations on reactivity component due to scattering reactions.