The power control based subcriticality monitoring (PCSM) method fro ADS reactors

Basing on the extension of the HGPT (Heuristical Generalized Perturbation Theory) methodology to subcritical systems, a procedure is proposed for the online monitoring of the subcriticality level of ADS reactors with minimal interaction with the plant normal operation. The proposed method, which shall be named with the acronym PCSM (for Power Control based Subcriticality Monitoring), consists in compensating slow, small movements of a control rod with as well slow, small alterations of the external source strength, so that the overall power is maintained constant. The estimation of the subcriticality level requires the knowledge of a bias factor. This implies the standard precalculation of a control, rod and the precalculation of the importance function associated with the reactor power control (in this case, the external neutron source strength). To this purpose a calculation procedure will be implemented into the ERANOS code so to extend its present GPT calculation modality. An experimental verification of the proposed method on the TRIGA reactor at the ENEA Casaccia Center is been considered. The reactor would be operated at different subcriticality levels corresponding to different positions of a control rod and would be driven by a suitable neutron source.