On the impact of phonon spectrum shifts of the hydrogen binding in ZrH

In the framework of the ECATS (Experiments Coupling Accelerator Target Sub-critical blanket) project within the EC FP6 IP-EUROTRANS a coupling of external sources with a TRIGA core had been considered. In order to simulate dynamical transients in ADS (Accelerator Driven Systems) the reactivity feedback coefficients should be accurately determined. Two reported independent experiments at RC-1 Casaccia and at Sloven MARK II TRIGA reactor Ljubljana have shown an anomaly reactivity feedback coefficient at temperatures between 100 - 150 Celsius degrees. This increased negative reactivity feedback in the mentioned temperature domain is not predicted by the General Atomic (manufacturer of the TRIGA Core) reactivity curve. In this study the influence of the phonon spectrum on the temperature dependant reactivity feedback coefficient is being analyzed in view of the experimental results and existing studies of Malik et al., Slaggie and others. In particular the scattering kernels of hydrogen bound in zirconium, and in general phonon spectrum shapes and changes are studied. It appears that the modified scattering kernel for ZrHx, based on the idea of temperature dependent shift of the phonon spectrum agrees better with the experimental data