Characterization of nuclear material by neutron resonance transmission analysis

Schillebeeckx, P.*; Alaerts, G.*; Becker, B.*; Paradela, C.*; Heyse, J.*; Kopecky, S.*; Vendelbo, D.*; Wynants, R.*; Harada, Hideo   ; Kitatani, Fumito  ; Koizumi, Mitsuo ; Tsuchiya, Harufumi 

The appearance of resonance structures in neutron induced reaction cross sections are fingerprints to study properties of materials and objects. Resonance structures are the basis of an analytical technique, i.e. Neutron Resonance Transmission Analysis (NRTA), which is being developed at the time-of-flight facility GELINA of the JRC-IRMM to characterize special nuclear materials. NRTA is based on the analysis of dips in a transmission spectrum that is obtained from a measurement of the attenuation of the neutron beam by a sample. To apply NRTA for the analysis of particle like debris samples of melted fuel produced in a severe nuclear accident is not evident. From this work one concludes that the accuracy of the results is strongly affected by the characteristics of the samples, in particular by the presence of neutron absorbing impurities, e.g. B, and the variety in shape and size of the particle like debris samples. To account for these effects, improved data analysis procedures and interpretation models have been developed. These procedures and models will be presented and validated by results of measurements carried out at GELINA. It will be demonstrated that the relative amount of fissile material can be derived absolutely with an accuracy better than 2% without the need of calibration samples, even in the presence of strong neutron absorbing materials.