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 PROJECTSRESEARCH FOCUS I:

TRITIUM TRANSPORTRESEARCH 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 Websitehttp://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 1600oC.

• Graphite pebble fuel elements host the

micro-particles, and provide accident

scenario temperatures < 1000oC.

• 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/m3) of

the core and low pressures allows the

core to be smaller and cheaper.

• Flibe (2LiF-BeF2) 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 MWth

100 MWe base-load

242 MWe 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 9th 2015