Experimental investigation of the effect of control rod guide tubes on the breakup of a molten metal jet in the lower plenum of a boiling water reactor under isothermal conditions

摘要

It is important to clarify the molten material jet breakup process to estimate corium behavior in the lower plenum of a boiling water reactor (BWR). To identify the effect of control rod guide tubes (CRGTs) on the jet breakup behavior, a molten material (U-alloy) breakup experiment considering CRGTs in a BWR lower plenum was conducted under isothermal conditions. The experiment results show that jet breakup fraction for the case with CRGTs (pitch/diameter ratio of 1.37) was only approximately 20 % of that for the case without CRGTs. A coarser pitch/diameter ratio of 2.47 was also tested, but this configuration only slightly reduced the amount of jet breakup. The experiments also indicate that the CRGTs had no significant effect on the fragmentation of droplet diameter. Furthennore, the velocity distribution was measured around the jet with particle image velocimetry. The velocities of the water surrounding the jet for the cases with CRGTs were relatively larger than those in the case without CRGTs.