PSAM 16 - Paper Overview

PSAM 16 Conference Paper Overview

Welcome to the PSAM 16 Conference paper and speaker overview page.

Lead Author: James Lin

Thermal-Hydraulic Analyses in Spent Fuel Pool PSA
To support the human reliability analysis (HRA) and the development of event sequence models in the Spent Fuel Pool (SFP) Probabilistic Safety Assessment (PSA), thermal-hydraulic analyses of selected, representative event scenarios must be performed. To evaluate such model parameters as the break flow rate of a SFP loss of inventory initiating event, the time available for specific operator actions or the number of equipment trains required to perform a safety-related function, these analyses can be performed based only on first principle energy and mass balance considerations, which are adequate to determine the broad event characteristics required to perform the HRA and develop the event sequence models with the needed accuracy. The results are considered reasonable approximations intended to reveal overall SFP response behavior and insights. This paper will describe in detail the plant and SFP design input information used in the analyses, the derivation of the SFP heat load and the various heat load cases considered, the estimate of the break flow rate of the loss of SFP inventory initiating event, the analysis of the thermal-hydraulic time windows for the loss of SFP cooling events, and the analysis of the thermal-hydraulic time windows for the loss of SFP inventory events. For the analysis of the thermal-hydraulic time windows for the loss of SFP cooling events, there are two time periods of event progression; i.e., SFP temperature increase to boiling and subsequent SFP level decrease after boiling. Following a complete loss of the SFP cooling event, the decay heat generated from the spent fuel assemblies stored in the SFP will initially cause the SFP water temperature to increase. Once the SFP temperature has reached the boiling temperature, the SFP water level will start decreasing due to boiloff. A number of time windows are determined in the analysis to support the HRA and the development and understanding of the event sequence models. They may include time to SFP high temperature alarm, time to SFP boiling temperature, time to SFP low level alarm, time to SFP cooling system suction strainer level, time to minimum SFP level, time to 3’ above top of active spent fuel, time to top of active spent fuel level, etc. Rupture of a pipe section in the SFP cooling system with no anti-siphoning device could potentially lead to a large SFP coolant loss scenario due to the siphoning effect. If the piping component friction losses are conservatively neglected, the maximum, initial break flow rate that could possibly attain due to the siphoning effect could be substantially greater than the realistic coolant loss flow rate with the consideration of the piping component friction losses. Following a loss of SFP inventory event, the SFP water level will continue to decrease. When the SFP water level drops to below the SFP cooling system suction strainer, the SFP heat removal function will be lost, at which point the SFP water temperature will start increasing. Depending on the size of the SFP leak, the order of the timing for the subsequent events, including boiling, reaching top of active spent fuel, and termination of leak, may be different. For a small leak, the rate of SFP level decrease is smaller and as such there is more time for water temperature increase before the water level dropping to the top of active spent fuel and termination of the leak when the SFP level drops to below the opening of the SFP cooling return line distribution header. For a large leak, the SFP water level could drop rapidly to the top of active spent fuel or leak termination level before the SFP water boils.

Thermal-Hydraulic Analyses in Spent Fuel Pool PSA

To support the human reliability analysis (HRA) and the development of event sequence models in the Spent Fuel Pool (SFP) Probabilistic Safety Assessment (PSA), thermal-hydraulic analyses of selected, representative event scenarios must be performed. To evaluate such model parameters as the break flow rate of a SFP loss of inventory initiating event, the time available for specific operator actions or the number of equipment trains required to perform a safety-related function, these analyses can be performed based only on first principle energy and mass balance considerations, which are adequate to determine the broad event characteristics required to perform the HRA and develop the event sequence models with the needed accuracy. The results are considered reasonable approximations intended to reveal overall SFP response behavior and insights. This paper will describe in detail the plant and SFP design input information used in the analyses, the derivation of the SFP heat load and the various heat load cases considered, the estimate of the break flow rate of the loss of SFP inventory initiating event, the analysis of the thermal-hydraulic time windows for the loss of SFP cooling events, and the analysis of the thermal-hydraulic time windows for the loss of SFP inventory events. For the analysis of the thermal-hydraulic time windows for the loss of SFP cooling events, there are two time periods of event progression; i.e., SFP temperature increase to boiling and subsequent SFP level decrease after boiling. Following a complete loss of the SFP cooling event, the decay heat generated from the spent fuel assemblies stored in the SFP will initially cause the SFP water temperature to increase. Once the SFP temperature has reached the boiling temperature, the SFP water level will start decreasing due to boiloff. A number of time windows are determined in the analysis to support the HRA and the development and understanding of the event sequence models. They may include time to SFP high temperature alarm, time to SFP boiling temperature, time to SFP low level alarm, time to SFP cooling system suction strainer level, time to minimum SFP level, time to 3’ above top of active spent fuel, time to top of active spent fuel level, etc. Rupture of a pipe section in the SFP cooling system with no anti-siphoning device could potentially lead to a large SFP coolant loss scenario due to the siphoning effect. If the piping component friction losses are conservatively neglected, the maximum, initial break flow rate that could possibly attain due to the siphoning effect could be substantially greater than the realistic coolant loss flow rate with the consideration of the piping component friction losses. Following a loss of SFP inventory event, the SFP water level will continue to decrease. When the SFP water level drops to below the SFP cooling system suction strainer, the SFP heat removal function will be lost, at which point the SFP water temperature will start increasing. Depending on the size of the SFP leak, the order of the timing for the subsequent events, including boiling, reaching top of active spent fuel, and termination of leak, may be different. For a small leak, the rate of SFP level decrease is smaller and as such there is more time for water temperature increase before the water level dropping to the top of active spent fuel and termination of the leak when the SFP level drops to below the opening of the SFP cooling return line distribution header. For a large leak, the SFP water level could drop rapidly to the top of active spent fuel or leak termination level before the SFP water boils.

Paper JL66 Preview

Author and Presentation Info

Lead Author Name: James Lin (jlin@absconsulting.com)

Bio: Mr. Lin is a senior consultant in the Irvine, California office of ABSG Consulting Inc. He has worked in the area of quantitative risk assessment and risk management for 42 years. Mr. Lin received his master degree in Nuclear Science and Engineering from University of California in Los Angeles. He has authored or co-authored more than 200 technical papers and reports.

Country: United States of America
Company: ABSG Consulting Inc.
Job Title: Director

PSAM 16 Conference Paper Overview

Welcome to the PSAM 16 Conference paper and speaker overview page.

Paper JL66 Preview

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