TRACE Assessment for Effect of Spacer Grid in RBHT Reflood Heat Transfer Experiments (NUREG/IA-0480)

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Publication Information

Manuscript Completed: February 2018
Date Published: February 2018

Prepared by:
Byung-Gil HUH, Ae-Ju CHEONG, Kyung Won LEE

Korea Institute of Nuclear Safety
Daejeon, Korea

K. 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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The effects of the spacer grid model in the TRACE V5.0 patch4 were evaluated for Rod Bundle Heat Transfer (RBHT) reflood heat transfer experiments. The RBHT test section was modeled in the VESSEL and HTSTR components of TRACE. Two PIPE components were modeled as the lower plenum and upper plenum and the injected flow was provided by the FILL component that was connected to the bottom of the lower plenum. The BREAK component was used to set the pressure boundary at the top of the test section. The main parameters of the spacer grid were defined by the experimental data and seven mixing vane grids were modeled in the test section of TRACE. The calculations for six tests of RBHT confirmed that when the spacer grid model was used, the rod temperatures decreased and the rods were quenched at an earlier time. This was because the spacer grid enhanced the convective heat transfer due to the flow acceleration and turbulence increase. In Test 1096 at a low power, a low reflood rate, a low pressure and a low subcooling degree, the peak rod temperature and the quenching time were most significantly affected by the spacer grid. Sensitivity studies were also performed to identify 1) the effect of the number of nodes, 2) the effect of the spacer grid parameters and 3) the effect of the mixing vane. The effect of the spacer grid model in TRACE is largely shown to simulate the RBHT reflood heat transfer experiments. However, since the droplet breakup and the grid rewetting models were not yet fully implemented, there are some limitations to quantitatively predicting their effects and the TRACE code needs to be improved for these models in the future.

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