Validation of the hem and moody critical flow models in polca-T

• The Homogeneous Equilibrium Model (HEM) and Moody critical flow models implemented in POLCA-T are validated against the Marviken experiments, which is necessary for qualification of the code for simulations of the hypothetical loss-of-coolant accident. Seven Marviken cases covering a range of initial conditions are simulated and the POLCA-T results are compared to the experimental data and to other similar codes including GOBLIN, RELAP5 and TRACE. Sensitivity studies are performed with respect to nodalisation and initial conditions. The HEM model predicts the break flow accurately with an uncertainty mostly below 20 %. The largest uncertainties are found for small exhaust pipe diameter and initial conditions far from saturation. The results could be improved by finer nodalisation and an extrapolation of the initial temperature profile inside the exhaust pipe. The Moody model is conservative in the 2-phase region, where it overpredicts the break flow as it should. The overprediction is smaller compared GOBLIN, so the conservatism is reduced.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

Critical-flow

HEM

Marviken

Moody

POLCA-T

Critical flow

Critical flow models

Homogeneous equilibrium models

Initial temperatures

Sensitivity studies

Loss of coolant accidents

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