United States Nuclear Regulatory Commission - Protecting People and the Environment

An Assessment of TRACE V5 RC1 Code Against UPTF Counter Current Flow Tests (NUREG/IA-0230)

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Publication Information

Date Published: August 2010

Prepared by:
S. Hillberg

VTT – Technical Research Centre of Finland
Nuclear Power Plant Modeling
P.O.B. 1000
02044 VTT
Finland

A. Calvo, NRC Project Manager

Published by:
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 International Code Assessment and Maintenance Program (CAMP)

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Abstract

In a loss of coolant situation ECC lines from cold and hot leg sides try to discharge cooling water into reactor core. Simultaneously core generates great amounts of steam which in return is directed towards the break. On the cold leg side cooling water and steam meet in the downcomer where steam flows up and cooling water is heading into lower plenum. If the steam flow is high enough the result is that a portion, if not all, of the ECC water ends up in the break with the steam flow. Similar situation is present at the upper tie plate where ECC water should break through upper tie plate into the core but steam flow may prevent this from happening.

TRACE V5 RC1 was used in this report to build a partial UPTF model and simulations were run comparing them to the data from 2 counter current flow tests. The simulations for downcomer test were run without counter current flow limitation (CCFL) and with Bankoff restriction using Kutateladze scaling. The upper tie plate simulations were run with also using Wallis scaling.

The one dimensional TRACE UPTF model produced reasonable results in roughly half of the downcomer counter current flow simulations. In upper tie plate CCF simulations ECC water countered too much drag in the upper tie plate and core area for the ECC water to reach lower plenum. It is possible that the built nodalization for upper tie plate was not detailed enough to simulate the inconsistent void fraction distribution.

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