Assessment of Critical Subcooled Flow Through Cracks in Large and Small Pipes Using TRACE and RELAP5 (NUREG/IA-0457)

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Publication Information

Manuscript Completed: November 2015
Date Published: August 2017

Prepared by:
Andrew Oussoren; J. Riznic; S.T. Revankar*

Canadian Nuclear Safety Commission
280 Slater Street
P.O. Box 1046 Station B
Ottawa, ON, Canada

*School of Nuclear Engineering, Purdue University
W. Lafayette, IN, USA

Kirk Tien, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
The Agreement on Research Participation and Technical Exchange Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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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.