A Near-Term-Deployable Salt-Cooled Advanced Nuclear Reactor Huali Wu, Francesco Carotti, Michael Young, Mohamed Abou Dbai, Raluca O. Scarlat Department of Engineering Physics, Nuclear Engineering http:// heatandmass.ep.wisc.edu / ABSTRACT KEY SYSTEM COMPONENTS THE INTEGRATED RESEARCH PROJECTS RESEARCH FOCUS I: TRITIUM TRANSPORT RESEARCH FOCUS II: FREEZING TRANSIENTS EXTERNAL LINKS PREVIOUS EXPERIENCES The Fluoride-Salt-Cooled High-Temperature Reactor (FHR) is an advanced nuclear reactor concept that combines high temperature fluoride salt coolants with solid fuel elements containing ceramic fuel micro particles and a Nuclear Air-Brayton Combined Cycle (NACC). NACC allows for base-load, power peaking with natural gas, and heat processing applications. Tritium control is important in FHR design because Tritium is created from neutron irradiation of molten salt and it will permeate through metal at FHR operation temperature. Another focus of our research regards the freezing and overcooling transients of fluoride salt, in which the coolant solidifies or becomes highly viscous as it approaches freezing around 459ºC. Adapted from (UCBTH-12-003, 2013) LARGE TRITIUM PRODUCTION Tritium is produced by neutron irradiation with Li and Be in FHR coolant, and it produces 1,000 to 10,000 times more tritium than a PWR. TO WHAT EXTENT CAN GRAPHITE FUEL BE AN EFFECTIVE AND REMOVABLE TRITIUM SINK IN THE FHR? SYSTEM TRANSPORT Tritium is produced in the core, absorbed on graphite, and may leak to air through metallic heat exchangers (Atsumi, 2011) DIFFUSION MECHANISM IN GRAPHITE Tritium diffuses through open pores and could be trapped on crystalline surfaces. INCREASED RETENTION WITH IRRADIATION Neutron irradiation will increase tritium retention in graphite. (Atsumi, 2009) Heat and Mass Transport Group – UW-Madison HEATandMASS.ep.wisc.edu UC-Berkeley FHR Website FHR.nuc.berkeley.edu Energy from Thorium energyfromthorium.com Oak Ridge National Laboratory FHR Website http://www.ornl.gov/science-discovery/nuclear-science/research- areas/reactor-technology/advanced-reactor-concepts/fluoride-salt- cooled-high-temperature-reactors International Thorium Energy Organization www.itheo.org In 2011, Department of Energy (DOE) initiated a 3 year Integrated Research Project (IRP I) involving universities (University of Wisconsin-Madison, University of California-Berkeley and MIT) and National lab (ORNL) to develop the technical basis to design, develop, and license a commercially attractive FHR. The new project (IRP II), supported by DOE starting in 2015, involving more universities and resources, shows the intention to pursue the development of FHR as a safe future source of energy . NON-EQUILIBRIUM FREEZING SUPER- COOLING PHENOMENON Cooling rate, nucleation sites and purity of the salt also affects freezing phenomena HOW DOES THE FREEZING AFFECT THE FLOW IN A PIPE AND IN THE NATURAL CIRCULATION SYSTEM? FREEZING POINT Freezes at 459ºC and FHRs operate in the temperature range of 600ºC to 700ºC, and the ultimate heat sink is ambient air or water (Kelleher, 2014) EQUILIBRIUM FREEZING PHASE DIAGRAM Freezing temperature and phenomenology depends on composition (Romberger, 1972) 2 - A COMPACT HIGH- TEMPERATURE, LOW-PRESSURE CORE 3 - UNIQUE PROPERTIES OF FLUORIDE MOLTEN SALT AS A HEAT TRANSFER FLUID 4 – PASSIVE SAFETY SYSTEMS RELY ON NATURAL CIRCUALTION COOLING 5- COMMERICIALLY AVAILABLE TECHNOLOGIES AND EASY TO COUPLE WITH OTHER ENERGY SOURCES • Micro-particles encapsulate fuel with low failure rates up to 1600 o C. • Graphite pebble fuel elements host the micro-particles, and provide accident scenario temperatures < 1000 o C. • This fuel technology has been developed for gas-cooled reactors since 1960s. • Heterogeneous mixed pebble-bed in an annular core design • High thermal density (23 MW/m 3 ) of the core and low pressures allows the core to be smaller and cheaper. • Flibe (2LiF-BeF 2 ) as a coolant of the reactor. • Unique heat transfer properties. • Limited corrosion and low vapor pressure. • Good neutron physics behavior inside the reactor. • Successfully used during Molten Salt Rector Experiment (1960s-1970s) • Challenges connected to its toxicity, tritium generation, and its high freezing point (459ºC). • Coolant properties enable inherent safety features of the FHR design. • High operating temperatures, 600- 700ºC, allowing high thermal efficiency (42% at baseload and 65% peaking; compared to 34% conventional nuclear). • Natural gas co-firing enables power peaking, opening a new part of the electricity market for nuclear plants. • Natural circulation cooling systems (“DRACS”) rely on buoyancy as the driving force. • A fluidic diode is used to restrict parasitic flow during normal operation of the reactor and to passively activate natural circulation upon pump failure. • DRACS were demonstrated for liquid-metal cooled reactors (since 1960s), and they are more compact for salts due to more effective coolant properties. 1 - A ROBUST FUEL DESIGN 3.5 m vessel diameter (rail transportable) The Pebble Bed Fluoride-Salt Cooled, High-Temperature Reactor (PB-FHR) 236 MW th 100 MW e base-load 242 MW e peaking Molten Salt Reactor Experiment (MSRE) ORNL (1960s) - Power reactor using molten salt technology successfully operated for 5 years. Aircraft Reactor Experiment (1946-1961) – High power density reactor designed to be placed inside an aircraft to power the turbines. Very High Temperature Reactors (VHTR) introduced the concept of pebble-bed core design. (ORNL/TM-2009/181,2010) (Stacy, Susan M, INL) (Stefan Kühn, Deutschland) (Kelleher, 2013) (UCBTH-14-002, 2014) (UCBTH-14-002, 2014) (UCBTH-14-002, 2014) (UCBTH-14-002, 2014) (UCBTH-14-002, 2014) April 9 th 2015