Analysis with TRACE Code of ROSA Test 1.1: ECCS Water Injection Under Natural Circulation Condition (NUREG/IA-0419)

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Publication Information

Manuscript Completed: July 2012
Date Published: October 2012

Prepared by:
A. Julbe, J.L. Muñoz-Cobo, A. Escrivá, A. Romero

Instituto de Ingenierίa Energética
Polytechnic University of Valencia
Camino de Vera s/n. 46022 Valencia

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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Abstract

The goal of this report is to explain the main results obtained in the simulation performed with the consolidated thermal-hydraulic code TRACE of the OECD/NEA natural circulation test ROSA 1.1, conducted at the Large Scale Test Facility (LSTF) in Japan. To attain the initial conditions the power was reduced from 7.11 MW to 1.44 MW, followed by a shutdown of the primary coolant pump with the 100% of water inventory in the primary. After some time the test initial conditions are attained and steady-state natural circulation conditions are established in the primary loop. The test can be divided in three different stages, each one characterized by attaining natural circulation conditions under different two-phase states in the primary coolant circuit, achieved reducing the primary inventory to 80, 70 & 50% of its original value, discharging the primary coolant water via auto bleed line located near the bottom of the RPV. The main goal of this report is to analyze the ability of TRACE code to precisely simulate the stratification and natural circulation conditions of both single and two-phase flows inside the primary circuit. During the experiment, the secondary side conditions were obtained by manually controlling the steam and feed-water flow rates in order to maintain the secondary pressure at 6.7 MPa, while in the simulation the secondary conditions were automatically controlled. At the beginning of the conditioning phase the severe power reduction and the shutdown of the coolant pump produces a mass flow rate reduction which is almost perfectly matched by the simulation with the TRACE code, with only a slightly higher mass flow rate than in the experiment. Meanwhile, the pressure remains practically constant in the experiment while it drops during the simulation with TRACE to recover after some time. After the first extraction (20% of main inventory) two-phase flow natural circulation conditions are attained in the primary loop. It is worth to note that TRACE properly models the pressure and temperature evolution with time in the primary system when the secondary pressure is kept constant at 6 MPa. The predictions of the natural circulation mass flow rates are good after the first extraction but after the second extraction are below the experimental values.