Assessment of Critical Subcooled Flow Through Cracks in Large and Small Pipes Using TRACE and RELAP5

Abstract of the journal article published in:
NUREG/IA series, U.S. Nuclear Regulatory Commission
February 2017

Author(s):
A. Oussoren, J. Riznic
Canadian Nuclear Safety Commission
S. T. Revankar
Purdue University, School of Nuclear Engineering, W. Lafayette, IN, U.S.

Abstract:

The thermal hydraulics system code TRACE has been used to predict subcooled critical flow in crack geometries. Three different experimental data sets were modelled in this study. The first experiment, performed at Purdue University, measured critical flow in slits with small section thicknesses similar to steam generator tubing. These results are also compared to model predictions using the RELAP5 code. The second experiment, conducted by Ontario Hydro (OH), measured critical flow rates in simulated circumferential cracks in thick-walled piping. The third experiment, from Atomic Energy of Canada Ltd. (AECL), measured critical flow through pressure cycling-induced fatigue cracks in thick-walled vessels.

For the Purdue tests, TRACE predictions were similar to those obtained with RELAP5. For the thin-walled samples in these tests a junction nodalization was found to be more suitable than explicitly modelling the section thickness of the samples. TRACE predictions for both the Purdue and OH tests were in reasonable agreement with measured leak rates, with calculated discharge coefficients of between 0.5 and 1.0 for most cases. However, the model of the OH tests showed a trend towards under-prediction as pressure dropped below 8 MPa. There was no clear trend demonstrated with respect to subcooling. For the AECL experiments, the flow rate was significantly over-predicted, with discharge coefficients as low as 0.1. This result is consistent with the modelling performed by the original experimenters and is likely due to the complexity of the flow pathway in the fatigue cracks used in this test, as compared to the machined geometries of the other samples.

In general, TRACE appears to be a suitable tool for prediction of critical flow rates in crack geometries. Comparison against additional experimental data is recommended.

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