Investigation of heat transfer mechanisms under shutdown plant conditions with TRACEv4.160

This paper presents the results of simulations of the PKL experiment F1.2 with the TRACE code (version v4.160). The PKL experiment F1.2 was performed in a closed primary system, stepwise reducing the primary coolant mass inventory at a constant pressure in order to evaluate the heat transfer mechanisms and transport of borated water from the steam generator inlet to outlet sides as a function of the primary coolant mass inventory. A complete TRACE input model of the primary system and the four secondary loops of the PKL facility was developed for this purpose. The aim of the TRACEv4.160 calculations presented in this paper was to assess the code predictions of the heat transfer mechanisms occurring during the different phases of the experiment: single-phase natural circulation, two-phase natural circulation and reflux-condensation in the steam generator U-tubes. In addition, TRACEv4.160 calculated de-boration rates during the reflux-condensation phase in various parts of the primary system were compared with the results of the experiment in order to assess the capabilities of the code to predict the formation of low-boron concentration coolant slugs in the primary system during plant transients under similar conditions.