United States Nuclear Regulatory Commission - Protecting People and the Environment

TRAC-PF1 MOD1 Post Test Calculations of the OECD LOFT Experiment LP-SB-1 (NUREG/IA-0011)

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Publication Information

Date Published: April 1990

Prepared by:
E.J. Allen

United Kingdom Atomic Energy Authority
Winfrith, Dorchester
Dorset, England

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
under the International Thermal-Hydraulic Code Assessment
and Application Program (ICAP)

Published by:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555

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Analysis of the small, hot leg break, OECD LOFT Experiment LP-SB-I using the "best-estimate" computer code TRAC-PFlI/MOD1 is presented.

Descriptions of the LOFT facility and the LP-SB-1 experiment are given and development of the TRAC-PF1/MOD1 input model is detailed. The calculations performed in achieving the steady state conditions, from which the experiment was initiated, and the specification of experimental boundary conditions are outlined.

Results of a "Base Case" transient calculation are found to be generally consistent with those reported by other members of the OECD LOFT Program Review Group. The experimental trends with respect to pressure histories and minimumsystem mass inventory are reasonably well reproduced by the TRAC-PFl/MODl calculation. However, the inability of TRAC-PF1/MODI to account for main-pipe stratification in determining fluid conditions in a side branch leads to significant discrepancies between the measured and predicted break line and hot leg densities and is identified as the main reason for the poorly predicted break mass flow rate.

Implementation, via the TRAC-PFI/MODI control system, of correlations for determining side branch quality as a function of main-pipe stratified liquid level are shown to be effective in improving the predicted hot leg and break line densities and break mass flow rate. The remaining differences between measured and predicted data are considered to be due to deficiencies in the TRAC-PFl/MOD1 critical flow model and the sensitivity of the break flow to the hot leg liquid level behaviour.

It is recommended that some means of accounting for the effect of main-pipe stratified liquid level, in determining fluid conditions in a side branch, be implemented in the TRAC-PFl/MODl code.

It is also suggested that a closer examination of the factors influencing the draining of the steam generator tubes is required to resolve the observed discrepancies in hot leg liquid level behaviour.

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