Gas Entrainment

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Analysis Division


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Gas Entrainment


Background

In January of 2008 the NRC issued Generic Letter 2008-01 due to longstanding issues related to accumulation of non-condensable gases in ECCS systems. As outlined in the generic letter, there were concerns regarding the potential adverse impact on the ECCS due to gas ingestion by the system pumps or due to pressure surge in system transients. The generic letter required all licensees to evaluate their ECCS, Decay Heat Removal (DHR) system, and containment spray system licensing basis, design, testing, and corrective actions to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems.

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The Analysis Division has developed GOTHIC™ ECCS piping models that can be used to evaluate system locations which have the potential for gas accumulation to determine the behavior of these gases during design basis events. The comprehensive model includes a lumped model for the overall ECCS and individual detailed models representing the suction and discharge piping in the RHR, SI, CS, CCP, and CVC systems. The GOTHIC computer code is used to model the propagation and attenuation of voids in the ECCS piping. The GOTHIC model results allow for the assessment of potential adverse impacts on pump performance from hypothetical void sizes in selected piping locations as well as the evaluation of specific gas volumes in as-found locations.

GOTHIC is the ideal computer software to use for the requested analyses as the code has been sufficiently verified and validated with respect to gas transport in combination with liquid, water hammer and degassing. GOTHIC offers considerable flexibility in modeling three-dimensional flow of gases and liquids and has been qualified against several gas and water flow experiments, including the Westinghouse Purdue tests performed specifically for Generic Letter 2008-01 and a Millstone Unit 3 test performed in response to GL 2008-01.

Analysis Division Experience with Gas Entrainment

RWST Suction Piping Model Gothic Noding
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The Analysis Division has performed numerous gas entrainment analyses for nuclear power plants. Gas accumulation downstream of pumps can lead to water hammer which is discussed here. We also maintain a strong experience base in nuclear plant operations and safety analysis requirements. We are exceptionally and uniquely qualified to complete gas entrainment analyses given our experience, as follows:

Analysis Support

For more information on our ability to analyze gas entrainment and how this can be applied to your plant, please contact Anita Gates or Steve Winter. The Analysis Division contact list is here, including phone numbers.