Preliminary validation of ASTEC V2.2.b with the QUENCH-20 BWR bundle experiment

Abstract

ASTEC is an integral severe accident code which aims to simulate entire severe accident transients of the nuclear reactors. New BWR-related models are implemented in the new versions of European ASTEC integral code by IRSN for BWR-typical core structures such as absorber blades, canister, etc. during the In-vessel core degradation after a severe accident in a BWR. The goal is to improve the simulation of the whole severe accident sequence in a BWR, such as the Fukushima accidents. An important step is the validation of the new models (oxidation, molten material formation and melt relocation, etc.) before the code is used to simulate severe accident scenarios in BWRs. The QUENCH-20 BWR test was specifically performed to investigate the oxidation, hydrogen generation, melt formation and oxidation during the reflooding of the test section representing a quarter of a SVEA-96 Optima-2 fuel assembly. The data measured during the QUENCH-20 BWR test e.g. temperature of the fuel rod simulators, of the blade and of the canister as well as the hydrogen production, quench front movement is used for the validation of the code’s prediction capability. In this work, the code ASTEC V.2.2.b is used to simulate the behavior of the QUENCH-20 test section. For this purpose, a detailed model of the QUENCH facility and test section was developed. This model was used to analyze the severe accident phenomena taking into account the same boundary conditions i.e. electrical power, mass flow rates, pressure, etc. as in the test. It was found out that the evolution of the temperature distribution in the bundle is reasonably evaluated by ASTEC for the entire duration of the transient. Besides, oxidation processes are also well reproduced. ASTEC predicts a total hydrogen generation of about 53 g while the measured value is around 57 g. In addition, ASTEC rather well predicted that about 15% of this hydrogen amount comes from the B4C-oxidation. Such good overall agreement between ASTEC and experimental measurements leads to further validation possibilities on BWR plant applications.