INVESTIGATION OF FLUID MIXING WITH DIRECT VESSEL INJECTION

The object of this work is to investigate fluid mixing phenomena as th ey related to pressurized thermal shock (PTS) in a pressurized water r eactor vessel downcomer during transient cooldown with direct vessel i njection (DVI), using test models. The test model designs were based o n ABB Combustion Engineering (CE) System 80+ reactor geometry. A cold- leg, small-break loss-of-coolant accident (LOCA) and a main steam line break were selected as the potential PTS events for the ABB-CE System 80+. This work consists of two parts. The first part provides the vis ualization tests of the fluid mixing between DVI fluids and existing c oolant in the downcomer region, and the second part presents the resul ts of thermal mixing tests with DVI in the other test model. Flow visu alization tests with DVI have clarified the physical interaction betwe en DVI fluid and primary coolant during transient cooldown. A signific ant temperature drop was observed in the downcomer during the tests of a small-break LOCA. The measured transient temperature profiles compa re well with the predictions from the REMIX code for a small-break LOC A, and with the calculations from the COMMIX-1B code for a stream line break event.