Analysis with TRACE Code of Rosa Test 1.2: Small LOCA in the Hot-Leg with HPI and Accumulator Actuation (NUREG/IA-0420)

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Publication Information

Manuscript Completed: December 2012
Date Published: April 2013

Prepared by:
J.L. Munoz-Cobo, A. Romero, S. Chiva

Instituto de Ingeniería Energética
Universitat Politècnica de Valencia
Camí de Vera s/n
46022 Valencia, Spain

A. Calvo, NRC Project Manager

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

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

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The goal of this report is to explain the main results obtained in the simulations performed with the consolidated code TRACE for the OCDE stratification test ROSA 1.2. The transient was produced by a small break in the hot leg of the loop B of the LSTF facility in Japan. In the experiment, the small break was simulated by a small diameter fissure located at the bottom of the hot-leg. The goal of this report is to analyze the capabilities of the TRACE code to cope with cases where thermal stratifications in the cold and hot legs take place. For this transient is very important the ability of TRACE to predict correctly the fluid regime in the hot leg. At the beginning of the transient the fluid discharged through the bottom of the hot leg is at liquid state and the mass flow rate discharged through the break is very high, and as a consequence the pressure drop very fast during the first seconds of the transient until the beginning of the HPI injection. This behaviour is predicted very well by TRACE code. Later, the flow at the hot leg becomes two-phase with low void fraction, and the mass flow rate discharged through the break is still high because the TRACE off-take model considers the fact that at the bottom of the hot leg we have liquid. Finally, the flow in the hot leg becomes biphasic with high void fraction and we discharge mainly steam through the break. In this test, the contraction of the fluid vein during the steam discharge has an important influence on the depressurization rate during the steam regime. The injection of the HPI in the cold leg produces a significant thermal stratification in the cold leg that attains the value of 100 ºC, but the TRACE code predicts well the average temperature in the cold leg.

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