Self-shielding factor calculations of heterogeneous samples in activation measurements for neutron spectrum unfolding

Highlights: • Activation measurements for samples irradiated in CEA EOLE reactor central channel. • Monte Carlo (2 codes) calculated spectra and self-shielding factors in samples. • The C/M agreement is mostly within the uncertainty of up to 10%. • Construction of the spectrum covariance matrix from analytical function parameters. • Adjustment of the calculated spectrum by taking into account the measurements. - Abstract: Activation measurements can be used for neutron spectrum determination in irradiation facilities. It is very important that self-shielding is taken correctly into account. Activation measurements of monitor materials were performed at the CEA EOLE facility. Self-shielding factors for the monitor materials were calculated at the Commissariat a l'Energie Atomique with the TRIPOLI 4.6 code using a detailed whole-core model, and at the Jožef Stefan Institute with the MCNP code using a simplified model. The results were compared to assess the relative merits and the achievable accuracy of the calculations. In the end, the results were used to determine the neutron spectrum of the studied location in the EOLE irradiation facility.