Computational and Experimental Studies of Reflooding Processes in a Large-Scale Model of a VVER Fuel Assembly

The paper presents a brief review of experimental and computational studies of the reflooding processes occurring during large break LOCAs in the primary circuits with subsequent supply of the coolant in pressurized water-moderated water-cooled power reactors (VVER). The results of the PREMIUM project, carried out by OECD (CSNI), on the assessment of the prediction of reflooding parameters using the most well-known computer codes (RELAP5, CATHARE, ATHLET, APROS, MARS) are analyzed. The calculations were performed using data from one of the experimental regimes simulated at the FEBA test facility (Germany) for reflooding simulation. It is stated that the uncertainty of the estimate of the maximum temperature of fuel rods obtained by known system computer codes can attain 100°С as follows from the results of validation calculations. Based on a statistically significant set of experiments conducted on a unique reflooding test facility at OKB Gidropress with several cooling water supply options, the domestic KORSAR computer code was validated, including the gravity reflooding when water is supplied to the upper part of the reactor pressure plenum model. It has been demonstrated that the KORSAR code is not worse than the best international codes in terms of the accuracy of the predicted maximum temperature of fuel-rod simulators and flooding time for the test fuel assembly.