Probabilistic determination of neutronic trip setpoints at Cernavoda NPP, Romania

This paper describes the methodology used for probabilistic determination of the Regional Overpower tripsetpoints at Cernavoda Nuclear Power Plant Unit 1 (a CANDU project). The shutdown systems use in-core flux detectors to protect against local power increases that can lead to fuel dryout and melting. These flux detectors are spread throughout the reactor core and are assigned to 3 independent trip channels per shutdown systems. The design criteria is that each shutdown system must trip the reactor with a confidence of 98% on a 2 of 2 logic, i.e. assuming the best trip channel unavailable. Parameter considered in the calculation of the trip-setpoints (TSP) are affected by random and systematic error. The probabilistic approach described here was developed by AECL specialists and allows error margins of ∼ 10%, lower than the deterministic margin of 15-20%.(author)