Analysis of fission product reduction strategy in SGTR accident using CFVS

Abstract

In order to reduce risks from the Steam Generator Tube Rupture (SGTR) accident and to meet safetytargets, various measures have been analyzed to minimize the amount of fission product (FP) release. Inthis paper, we propose an introduction of a Containment Filtered Venting System (CFVS) connected tothe steam generator secondary side, which can reduce the amount of FP release while minimizingadverse effects identified in the previous studies. In order to compare the effect of new equipment withthe existing strategy, accident simulations using MELCOR were performed. As a result of simulations, it isconfirmed that CFVS operation lowers FP release into the environment, and the release fractions arelower (minimum 0.6% of the initial inventory for Cs) than that of the strategy which intends todepressurize the primary system directly (minimum 15.2% for Cs). The sensitivity analyses identify thatrefill of the CFVS vessel is a dominant contributor reducing the amount of FP released. As the newstrategy has the possibility of hydrogen combustion and detonation in CFVS, the installation of an igniterinside the CFVS vessel may be considered in reducing such hydrogen risk.