A series of passive neutron measurements performed on TIHANGE I spent fuel assemblies were analyzed for comparison with calculated burn-up values and neutron emission rates. The burn-up range of these assemblies was between 10 and 45 MWd/kg and the cooling time varied from 1 to 8 years approximately.

The measurements, performed with ²³⁵U fission chambers, were correlated with neutron emission and burn-up by means of the ORIGEN-2 point model depletion code, taking into account the irradiation history. A fairly good correlation was found between the ²⁴⁴Cm contributions, as deduced from the measurements corrected with ORIGEN-2, and the burn-up values as calculated with fuel management codes. It was noticed that the ratio of the calculated (ORIGEN-2) neutron emission and the measured neutron detection varied with the burn-up.