Investigations on the thermal-hydraulic behavior of a generic PWR KONVOI during a 1% cold leg small-break loss of coolant accident using the system code ATHLET

In the presented paper, a simulation of a small-break loss of coolant accident (SBLOCA) with a 1% break in the cold leg 1 in a generic German PWR KONVOI model is carried out and investigated by means of the thermal-hydraulic system code ATHLET 3.1A. The accident analysis is focused first on a thermal-hydraulic characterization of the SBLOCA, and a subsequent qualitative comparison with the test PKL H1.1. With this aim, in the simulation with ATHLET 3.1A, the nominal plant operational parameters of the generic KONVOI reactor are transposed with the boundary conditions of the test PKL H1.1.
The test PKL H1.1 reproduces a SBLOCA superposed by additional system failures, such as unavailability of the high-pressure safety injection and the automatic secondary-side cool-down. The test was conducted in the framework of the OECD/PKL3 project in the large-scale test facility PKL (“Primärkreislauf”), operated by Framatome Germany, as a counterpart test of LSTF/ROSA SB-CL-32.
The second part of the paper is devoted to the study of the boron dilution into the steam generators, and the subsequent transport and fluid mixing phenomena in the reactor pressure vessel. The results in the simulation, show how the implementation of a 200 K/h cool-down through the steam generators, initiated at a peak cladding temperature (PCT) of 500°C, is able to eventually achieve a long-term safe stable condition, due to the injection of cold water, first from the hydro-accumulators at a pressure of 26 bar, and then the actuation of the low pressure safety injection at a pressure of 10 bar.
This outcome is also observed in the test H1.1. Nevertheless, unlike the results obtained in the test, the implementation of the 200 K/h cool-down during the SBLOCA in the simulation cannot avoid core damage, fact strongly influenced by the initial pressure differences between the KONVOI model and the PKL test facility, being the latter limited by design constraints to a maximum pressure of 50 bar.