Validation of Selected Cesar Friction Models of the ASTECV21 Code Based on Moby Dick Experiments

Abstract

In the event of a loss of integrity of the main coolant line, a large mass and energy release from the primary circuit to the containment is to be expected. The temporal evolution of such depressurization is mainly governed by the critical flow, whose correct prediction requires, in first place, a correct description of the different friction terms. Within this work, selected friction models of the CESAR module of the Accident Source Term Evaluation Code (ASTEC) V2.1 integral code are validated against data from the Moby Dick test facility. Simulations are launched using two different numerical schemes: on the one hand, the classical five equation (drift flux) approach, with one momentum conservation equation for an average fluid plus one algebraic equation on the drift between the gas and the liquid; on the other hand, the recently implemented six equation approach, where two differential equations are used to obtain the phase velocities. The main findings are listed hereafter: The use of five equations provides an adequate description of the pressure loss as long as the mass fluxes remain below 1.24 kg/cm2 s and the gas mass fractions below 5.93 × 10 − 4. Beyond those conditions, the hypotheses of the drift flux model are exceeded and the use of an additional momentum equation is required. The use of an additional momentum equation leads to a better agreement with the experimental data for a wider range of mass fluxes and gas mass fractions. However, the qualitative prediction for high gas mass fractions still shows some deviations due to the decrease of the regular friction term at the end of the test section.

Astec V2.2 Code Validation: Illustrative Results and Main Outcomes

“…A summary of the main lessons that have been drawn from the code-to-data assessment in the field of RCS thermal-hydraulics is provided in the Section 4 of this paper. Details about these numerous and various ASTEC V2.2 CESAR simulations, may be found in [26] [27] [28] [29].…”

ASTEC V2.2 code validation: Illustrative results and main outcomes

“…A summary of the main lessons that have been drawn from the code-to-data assessment in the field of RCS thermal-hydraulics is provided in the Section 4 of this paper. Details about these numerous and various ASTEC V2.2 CESAR simulations, may be found in [26] [27] [28] [29].…”

Interfacial heat transfer with non-condensable gas in ASTEC V2.2: Application to severe accidents study during PWR cold shutdown states

“…In the calculations presented in this section, the equation system solved by CESAR is a classical two-fluid 6 equations system. A thorough description of CESAR 6 equation flow modelling can be found in [16], while validation elements are exposed in [17]. For complete plant calculations, CESAR is used along with ASTEC other modules.…”