Development and validation of sensitivity and uncertainty calculations using the 3-D neutron transport code CRONOS2 at an industrial scale

Evaluating uncertainties on reactivity is a major issue for conception of nuclear reactors. These uncertainties mainly come from the lack of knowledge on nuclear and technological data. The common method for the propagation of the nuclear data uncertainties consists in using the Standard Perturbation Theory to calculate reactivity sensitivity to the desire nuclear data. In such a method, sensitivities are combined with a priori nuclear data covariance matrices, such as the COMAC set developed by Cea. In this study, COMAC nuclear data uncertainties have been propagated on the BEAVRS benchmark using a classical two-step APOLLO2/CRONOS2 scheme. A procedure implementing Standard Perturbation Theory has been created using the 3-D neutron transport code CRONOS2 in order to allow a full-core uncertainty propagation with 4 groups industrial scheme. CRONOS2 sensitivities are compared to sensitivities calculated by the IFP method in Monte Carlo codes. For the purpose of the tests, dedicated covariance matrices have been created by condensation from 49 to 4 groups of the COMAC matrix. In conclusion, CRONOS2 sensitivities are agreed with the sensitivities calculated by the IFP method, which validates the calculation procedure. In addition, reactivity uncertainty calculated by this method is close to values found for this type of reactor. Finally, the calculation method allows computing sensitivities quickly with a good accurate. (author)