Unanticipated Large-Diameter Pipe Rupture Accidents in the RBMK-1000 Circulation Loop with Reactor Emergency Cooling System Failure

Abstract

The results of calculations of large-diameter pipe rupture accidents in the RBMK circulation loop (pressure header of the main circulation pump, down pipe of the steam drum, and distribution group header) with failure of the reactor emergency cooling system are presented. The main computational problem is to evaluate the onset time of fuel-element cladding depressurization in the damaged half of the core and the integrity of the channel tubes. It is shown that for rupture of the pressure header fuel-element cladding depressurization starts at the 10th minute after the initial event and depressurization of the down-pipe near the steam drum and distribution group header start at the 17th and 40th minutes, respectively. The possible rupture of the channel tubes can have the form of only individual small flaws, for which the structural integrity of the reactor space is preserved. The calculations were performed with the RELAP5/mod3.2 computer code adapted for RBMK.