Experimental Investigations on the Reflooding and Deformation Behavior of an Advanced Pressurized Water Reactor Tight-Lattice Fuel Rod Bundle in a Loss-of-Coolant Accident

The work performed in the FLORESTAN program at the Karlsruhe Nuclear Research Center on the reflooding and deformation behavior of a tight-lattice fuel rod bundle in a loss-of-coolant accident of an advanced pressurized water reactor (APWR) is described. The present forced-feed reflooding tests in an extremely tight bundle with a pitch-to-diameter ratio p/d = 1.06 show a very different thermal-hydraulic behavior compared to a standard pressurized water reactor. Blind code predictions have shown that most thermal-hydraulic computer codes do not adequately predict the reflooding behavior of this type of bundle. Deformation tests on stainless steel cladding tubes have shown that those with integral helical fins limit the burst strains and have high potential for APWR fuel rod cladding.