UNCERTAINTIES ASSOCIATED TO THE USE OF THE ERANOS CODE SYSTEM WHEN APPLIED TO THE MODERATED ECRIX IRRADIATIONS IN THE FAST REACTOR PHENIX
Résumé
The ECRIX experimental irradiation foreseen in the PHENIX reactor (between 2000 and 2004) aims at studying the feasibility of burning americium in dedicated moderated targets. For this purpose, an americium pin will be placed at the centre of specific sub-assemblies and loaded with different moderating materials: 11 B4C (ECRIX-B) and CaH2 (ECRIX-H). In this paper, calculations and associated uncertainties required for the design of such S/A are presented. The moderated sub-assemblies have been optimised specifically for each experiment, taking into account the moderator, the peaking power in the target pin (by thermalized neutrons) and the increase of power in the fuel pins of the neighbouring sub-assemblies. In order to quantify the performances of the irradiations and the impact of the ECRIX S/As on the core, different calculational methods were used. The approach for the determination of uncertainties is the following: 1) Evaluation of the approximations due to the standard design calculation, by comparison between the design calculation scheme and a reference calculation scheme, using the same code system (ERANOS). 2) Validation of the calculation methods, by comparing results generated with the MONTE-CARLO code TRIPOLI to the ERANOS reference results. 3) Calculation of uncertainties of various neutronic parameters due to nuclear data. Sensitivity of these parameters to nuclear data are obtained by a specific methodology, which is presented in this paper. These sensitivity coefficients are then used with covariance matrices on nuclear data to produce the induced uncertainties. This work has enable the design of the ECRIX irradiation while waiting for the COSMO i experiments, which are currently under way in the critical facility MASURCA.
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