XADS source transients analyzed by means of RELAP5/PARCS

Following the large interest aroused in the world on Accelerator Driven Systems (ADSs), a team of Italian industrial and research organizations (ANSALDO, CRS4, ENEA and, INFN) participated in the design of an 80 MW lead-bismuth cooled eXperimental Accelerator Driven System (XADS), a key step towards the assessment of the feasibility and operability of an ADS prototype. Among the R&D activities pursued in parallel, special attention has been paid to the development of suitable numerical tools for studying operational transients and accidental sequences of ADS-like systems. In particular, an adapted version of the thermal-hydraulic-neutronic coupled code RELAP5/PARCS allows a suitable simulation of the XADS dynamic response to typical plant transients. This paper concerns a parametric analysis of overpower transients due to the anticipated insertion of the external neutron source when the XADS is at Hot Zero Power (HZP), namely isothermal at 300 C. Beginning of Cycle (BOC) configuration has been considered for the core, while the external neutron source has been varied from nominal full power at BOC to nominal full power at End of Cycle (EOC), namely doubling its intensity. The results presented in this work allow stating that the XADS plant presents a high level of inherent safety also for abrupt power variations as in the case of source transients.