PSAM 16 - Paper Overview

PSAM 16 Conference Paper Overview

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

Lead Author: Jan Grobbelaar Co-author(s): Zander Mausolff, amausolff@terrapower.com Brian Johnson, bjohnson@terrapower.com Brandon Chisholm, BMCHISHO@SOUTHERNCO.COM

Probabilistic Risk Assessment of the Molten Chloride Reactor Experiment Conceptual Design
A probabilistic risk assessment (PRA) is being developed for the Molten Chloride Reactor Experiment (MCRE). The MCRE is a low power, fast reactor which will provide key reactor physics data to support the design and licensing of the commercial Molten Chloride Fast Reactor (MCFR). The reactor uses sodium chloride and highly enriched uranium trichloride (NaCl-UCl3) eutectic as its fuel. The United States Department of Energy (DOE) awarded a contract to Southern Company-led team including TerraPower (TP) in 2020 to support the design and development of the MCRE. It is proposed to site MCRE within a testbed at the Idaho National Laboratory (INL). The final operating location at INL will be determined following the NEPA review. DOE review and approval of the MCRE safety basis will be required. The approach chosen for developing the analyses to support the MCRE safety basis is based on the Licensing Modernization Project’s (LMP) risk-informed performance-based (RIPB) approach documented in NEI 18-04. The longer-term goal in applying the LMP RIPB process on MCRE is to build experience for the future licensing of the MCFR. To support the RIPB approach, a PRA is being developed in conjunction with plant design. The scope of the PRA is all-modes all-hazards. The internal events PRA for the MCRE Conceptual Design was completed in 2021. Initiating events have been identified from hazards analysis of the Aircraft Reactor Test, the Oak Ridge National Laboratory Molten Salt Reactor Experiment, recent industry-publications, and a master logic diagram developed at TP. With little operational and component reliability data available for molten salt reactors, available liquid sodium component reliability data have been used for salt-wetted components. The safe stable end states modeled in the PRA are with the fuel subcritical in the fuel salt drain tank (cold shutdown) or maintained subcritical in the reactor vessel and heated to prevent freezing (hot shutdown). In the current model, core freezing in the reactor vessel has conservatively been assumed to be an undesired end state due to neutronic and mechanical challenges. However, this assumption will be refined as the maturity of the design information and safety analyses increases. Deterministic thermal-hydraulic analyses are in progress to confirm the transient evolutions. To this end, a new version of GOTHIC has been developed to better model a liquid core where the delayed neutron fraction is a function of flow rate, for example. Event trees and fault trees have been developed on a safety functional basis for reactivity control, decay heat removal control, fuel pump trip, core offload, and prevention of fuel freezing. In contrast to typical LWR PRAs, the MCRE PRA is much smaller as the event sequences are not complicated and there are far fewer systems to be modelled. For example, active decay heat removal is not needed as decay heat is removed passively via system losses. Standby safety injection systems are also not included in the design. A self-assessment was performed against the requirements of the ASME/ANS PRA Standard for Advanced Non-LWR Nuclear Power Plants (ASME/ANS RA-S-1.4-2021). The PRA has been applied to select the safety basis events (SBEs) and the preliminary results were plotted against frequency-consequence targets based upon relevant DOE regulatory limits. Although the safety classification of the MCRE SSCs will be informed by a comparison between the SBE results and the regulatory limits, additional details and analysis is required for elements such as uncertainties and defense-in-depth before the final SSC classifications can be made. The other PRA hazard groups are scheduled for analysis in 2022. Acknowledgment: "This material is based upon work supported by the Department of Energy under Award Number DE-NE0009045.” Disclaimer: "This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof."

Probabilistic Risk Assessment of the Molten Chloride Reactor Experiment Conceptual Design

A probabilistic risk assessment (PRA) is being developed for the Molten Chloride Reactor Experiment (MCRE). The MCRE is a low power, fast reactor which will provide key reactor physics data to support the design and licensing of the commercial Molten Chloride Fast Reactor (MCFR). The reactor uses sodium chloride and highly enriched uranium trichloride (NaCl-UCl3) eutectic as its fuel. The United States Department of Energy (DOE) awarded a contract to Southern Company-led team including TerraPower (TP) in 2020 to support the design and development of the MCRE. It is proposed to site MCRE within a testbed at the Idaho National Laboratory (INL). The final operating location at INL will be determined following the NEPA review. DOE review and approval of the MCRE safety basis will be required. The approach chosen for developing the analyses to support the MCRE safety basis is based on the Licensing Modernization Project’s (LMP) risk-informed performance-based (RIPB) approach documented in NEI 18-04. The longer-term goal in applying the LMP RIPB process on MCRE is to build experience for the future licensing of the MCFR. To support the RIPB approach, a PRA is being developed in conjunction with plant design. The scope of the PRA is all-modes all-hazards. The internal events PRA for the MCRE Conceptual Design was completed in 2021. Initiating events have been identified from hazards analysis of the Aircraft Reactor Test, the Oak Ridge National Laboratory Molten Salt Reactor Experiment, recent industry-publications, and a master logic diagram developed at TP. With little operational and component reliability data available for molten salt reactors, available liquid sodium component reliability data have been used for salt-wetted components. The safe stable end states modeled in the PRA are with the fuel subcritical in the fuel salt drain tank (cold shutdown) or maintained subcritical in the reactor vessel and heated to prevent freezing (hot shutdown). In the current model, core freezing in the reactor vessel has conservatively been assumed to be an undesired end state due to neutronic and mechanical challenges. However, this assumption will be refined as the maturity of the design information and safety analyses increases. Deterministic thermal-hydraulic analyses are in progress to confirm the transient evolutions. To this end, a new version of GOTHIC has been developed to better model a liquid core where the delayed neutron fraction is a function of flow rate, for example. Event trees and fault trees have been developed on a safety functional basis for reactivity control, decay heat removal control, fuel pump trip, core offload, and prevention of fuel freezing. In contrast to typical LWR PRAs, the MCRE PRA is much smaller as the event sequences are not complicated and there are far fewer systems to be modelled. For example, active decay heat removal is not needed as decay heat is removed passively via system losses. Standby safety injection systems are also not included in the design. A self-assessment was performed against the requirements of the ASME/ANS PRA Standard for Advanced Non-LWR Nuclear Power Plants (ASME/ANS RA-S-1.4-2021). The PRA has been applied to select the safety basis events (SBEs) and the preliminary results were plotted against frequency-consequence targets based upon relevant DOE regulatory limits. Although the safety classification of the MCRE SSCs will be informed by a comparison between the SBE results and the regulatory limits, additional details and analysis is required for elements such as uncertainties and defense-in-depth before the final SSC classifications can be made. The other PRA hazard groups are scheduled for analysis in 2022. Acknowledgment: "This material is based upon work supported by the Department of Energy under Award Number DE-NE0009045.” Disclaimer: "This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof."

Paper JG277 Preview

Author and Presentation Info

Lead Author Name: Jan Grobbelaar (jgrobbelaar@terrapower.com)

Bio: Mr. Jan Grobbelaar has been with Terrapower since March 2021. He is the lead in developing the PRA for the Molten Chloride Reactor Experiment to support the request for DOE approval of the MCRE safety basis. Prior to joining Terrapower, he started his career at a PWR utility as a principal developer of their PRA for about 10 years, followed by working as a PRA consultant in the light water reactor industry for about 20 years. During this time he had participated as a peer reviewer in ASME/ANS PRA Standard peer reviews both in the USA and abroad. He holds a B.Sc. degree in nuclear engineering.

Country: United States of America
Company: Terrapower, Inc.
Job Title: Principal PRA Engineer

PSAM 16 Conference Paper Overview

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

Paper JG277 Preview

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