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Session Overview
4.03: MSR and Advanced Reactors - III
Wednesday, 18/Mar/2020:
2:00pm - 3:30pm

Session Chair: Ayodeji Babatunde Alajo, Missouri University of Science & Technology, United States of America
Location: L-2012

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Opportunities and challenges for the Safety of Molten Salt Reactor

Joel Guidez1, Paul Gauthé1, Guillaume Campioni1, Stephane Bourg1, Elsa Merle2, Daniel Heuer2, Delphine Gerardin2, Axel Laureau3, Bernard Carluec4

1CEA; 2LPSC-IN2P3-CNRS; 3Laboratory for Reactor Physics and Systems behaviour (LRS); 4Framatome

The Chernobyl and Fukushima accidents, with population displacement, have contributed significantly to a societal mistrust of nuclear energy. These accidents have also contributed to changing the safety rules for new reactors. In this area, MSRs have some potential intrinsic safety advantages that could help to better public acceptance.

First of all, in the event of a criticality accident, there is no fusion of the fuel and interaction with the cooling fluid. As the core is already melted, there is only expansion / expulsion of the fuel without significant release of mechanical energy and with instantaneous and very negative feedback coefficients. Calculations are presented showing the reactions to brutal introductions of reactivity

Then these reactors work with salts at high temperature and therefore without pressure. If leaks are still possible, they don’t correspond to sudden breaks in the tank or pipes. If molten salt leaks out of the first barrier, good retention capabilities of the main fission products, including cesium, in the salt, are expected. Fission gases on MSR are treated in line and there is therefore no significant relaxation of gas during an accident at the reactor level, as in the case of the melting of a solid core where fission gases are accumulated in the cladding.

A safety pre-analysis has been carried out, within the pre-conceptual framework of the French concept MSFR, to take into account all these elements and it is presented in this paper. In particular, a list of initiating events has been established, as well as a preliminary assessment of their consequences. Proposals for the notions of barriers and severe accidents are also discussed.

Besides these opportunities, some challenges related to the safety assessment of MSR will also be highlighted in the paper.

Development of Neutron Measurements for In-Situ Interface Corrosion Kinetics and Salt Properties

Emily Gao, Kemal Ramic, Jinghua Feng, Li Emily Liu

Rensselaer Polytechnic Institute-RPI

The main goal of the study is to understand the corrosion and chemical properties of molten salts and then to provide fundamental data for material selection of Molten Salt Reactors. In the past two years, we collaborate with National Institute of Standards and Technology (NIST), and Spallation Neutron Source (SNS) of Oak Ridge National Laboratory (ORNL) to develop in-situ neutron scattering setup targeting molten chloride salt property and corrosion kinetics with metal containment. Two innovative and unique in-situ approaches have been designed and implemented for molten salt studies: Molten-Salt Cell (MSC) for Neutron Reflectometry (NR) in NIST and VISION-to-Modeling (VM) methodology for Vibrational Spectroscopy (VISION) in SNS.

The presentation will focus on the currently designed and implemented in-situ neutron techniques for fundamental understanding of the mechanisms of molten salt corrosion, and the micro-structural response of containment alloys thereto, to measure the surface corrosion kinetics. We are working on realization and initial application of in-situ techniques for measuring molten salt fundamental properties including molten salt structure, dynamics, and salt density, etc. and the micro-structural and -chemical response of containment alloys to corrosive molten salt environments. The two neutron techniques involved, VISION and NR, both have unique characteristics for complex liquids at high temperatures. After designing and manufacturing sample environments for harsh environments (high temperature and corrosive), we provide first-of-the-kind experimental data for molten salt systems. Experimental and associated modeling results for ternary chloride salts MgCl2/NaCl/KCl will be shown. In-depth temperature, from solid to molten liquid state, and corrosion effects will be discussed.

A Numerical Study on Sodium Natural Circulation with an Ex-Vessel Cooling System Using TRACE

Ji-Hwan Hwang, Dong-Wook Jerng

Chung-Ang University

The Reactor Vault Cooling System (RVCS), which cools the external surface of the containment vessel in pool-type SFRs, can be a means of severe accident mitigation, especially when no decay heat removal system (DHRS) is available. Also, the RVCS is possible to provide extra safety as it stimulates the natural circulation inside sodium by cooing exterior surface of sodium pool when the primary pumps are not available. However, owing to the complex geometry inside sodium pool, the asymmetric flow would be inside sodium pool, and 1-dimensional modeling may not be enough to predict such flow. Therefore, in this study, using the TRACE code, a comparison of 1-dimensional and 3-dimensional approach on the RVCS decay heat removal performance was conducted. For reference design, the PGSFR, a pool-type SFR being developed in the Republic of Korea, was used. For conservative analysis, the decay heat removal systems (DHRS) and the primary pump is assumed to be unavailable. The RVCS is modeled as 1-dimensional, as the airflow is large enough to cover whole faces of the exterior surface of the containment vessel. According to the TRACE calculation result, the RVCS can prevent sodium boiling and vessel creep failure. However, two models predict the trend of temperature and heat transfer differently. The 1-dimensional model conservatively predicts the temperature of sodium and vessel at the early phase, but the temperature decays faster than the 3-dimensional model after reaching peak temperature. Also, two models predict about local heat transfer through the RVCS quite differently. While 1-dimensional model predicts a big difference in axial direction, the 3-dimensional model predicts a smaller difference. This is mainly attributed to the sodium flow at the outmost part of sodium pool. Therefore, the dimension of the sodium pool modeling should be carefully chosen.

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