| Popis: |
The Accelerator Driven Systems (ADSs) have great potential as transmuting systems of the long-lived nuclear wastes both from industrial energy production and from nuclear weapon dismantling. In the frame of national and European research programs, a team of Italian industrial and research organizations designed an 80 MWth lead-bismuth cooled experimental Accelerator Driven System (XADS), as a key step towards the assessment of the feasibility and operability of an ADS prototype. In parallel with these basic activities and as an important issue among the R&D needs, the original coupled neutronic thermal-hydraulic code RELAPS/PARCS has been modified and adapted to lead-bismuth cooled subcritical systems. This paper aims to present a preliminary analysis of the flowblockage accidents in the XADS plant, classified as Design Basis Accidents. These accidents are caused by the partial or total blockage of a part of the core. Due to the mixing of the lead-bismuth at the exit of the fuel assemblies, the obstruction of a single channel cannot be detected by a signal of high lead-bismuth temperature at core exit. Thus, fission power continues to be generated because the control system does not stop the accelerator and, consequently, cladding melting and the destruction of the affected fuel element can occur. In order to investigate the effect of thermal feedback on the fission power density, especially for the fuel assembly of the affected channel, this analysis has been performed by means of the neutronic thermal-hydraulic coupled code RELAPS/PARCS. |
