SMR – Small Modular Nuclear Reactors in Australia

What are Small Modular Reactors?
Two Categories of SMR's
Two critical components of SMR’s
Basic Types of SMR's an overview
Nuclear Hydrogen Production
Heavy Industry Use
As Base-load Power
Prerequisites for SMRs in Australia
Sources

What are Small Modular Reactors?

A small modular reactor (SMR) is a factory-built nuclear reactor small enough to be transported to site.
Like all nuclear reactors SMR's produce and control the release of energy from splitting the very large unstable atoms of certain elements into smaller more stable atoms.
The smaller atoms require less energy to exist and the excess energy is released in the form of heat.
The released heat is used, most often, to generate electricity but may also be used for industrial processes.

Small Modular Reactors Come in Several Designs
SMR Types

The use of Small Modular Nuclear Reactors (SMR's) is being actively suggested as a means to provide base-load electrical power at sites of former coal-burning power generation stations here in Australia.
Currently, there are no licensed designs, or constructed or operating SMRs in Australia,or in any Organisation for Economic Co-operation and Development (OECD) countries.
There are 14 individual OECD designs that meet the definition of an SMR and are considered by the World Nuclear Association to be in “near term deployment – development well advanced”.

SMR's should have most, if not all, of the following features:

standardised power plant infrastructure with a small physical footprints, small size so they can be transported to site
factory built identical self contained modular units, rather than custom-designed
some designs are capable of a “daisy chain” configuration - running multiple cores in one power plant
small electrical output up to 35-350 Megawatts
from 1 Megawatt 2/3rd is used for non-residental purposes and 1/3rd for residential use
based on above 1 Megawatt from a SMR translates to very roughly about 20,000 homes
safety zone reduced from about 15km to 2km, so can be built nearer urban centres
more efficient fuel usage and less highly radioactive waste
simplified design, fewer components, less piping
inherent reactor passive cooling,in the case of power failure, so many designs lack a containment structure
some designs cannot be refueled, so no refueling safety risk but you end up with a throw away reactor after maybe 30 years

The biggest general difference in these new SMR designs is that most run at considerably higher temperatures and lower pressures than the large water-cooled base-load nuclear power stations currently in use overseas. (see below...)

Large Water Cooled Reactor Type - Currently in use overseas for Base-load electricity
Conventional Large Reactor

Two Categories of SMR's
Basically there are two categories of SMR reactors:

Slow reactors that use a “moderator” to make the nuclear reactions more efficient, need a specific fuel and run at lower temperatures. They produce some very radioactive long-lived waste.
Fast reactors that do not use a “moderator”, are less efficient but can run on a greater range of fuels and run at very high temperatures. The high temperatures can convert some waste into fuel. They produce less very radioactive long-lived waste.

Uranium Oxide Fuel Pellet
Uranium Oxide Pellet

Two critical components of SMR’s

SMR's rely on two critical components: fuel and coolant.

There are numerous, diverse SMR designs employing new fuel types/configurations and innovative coolants.

Innovative Fuels
- most commonly and in most SMR's regular, small "barrel-shaped" pellets of fuel are placed into pipes (called "rods") that can be raised, lowered,re-ordered, removed or replaced as required
- but some SMR's designs require more complex fuel -"layered spheres", "pebbles" or "prismatic blocks"
- some of these fuels are actually "mixed" in the coolant in a sort of fuel/coolant slurry
- TRISO, or tri-structural isotropic particle fuel is one of the most popular options. TRISO particles contain uranium, enclosed in ceramic and carbon-based layers. This keeps the fuel contained, keeping all the products of fission reactions inside and allowing the fuel to resist corrosion and melting.
- Other reactors use HALEU: high-assay low-enriched uranium. Most nuclear fuel used in commercial reactors contains between 3% and 5% uranium-235. HALEU, on the other hand, contains between 5% and 20% uranium-235, allowing reactors to get more power in a smaller volume.

Innovative Coolants

Water

Water-cooled SMR's are the most developed designs and the most likely to be promoted if a short development time is required
SMR's that employ water as a coolant generally suffer from the same safety issues as large nuclear reactors
in double loop designs, one coolant loop is inside the reactor and goes to a heat exchanger where a second physically separated loop is heated to steam and sent to the electricty generator
in single loop designs; a single loop goes both inside and outside the; reactor -there is no physical separation; leak potential of radioactive contamination exiting the reactor enclosure
efficiency can be increased by raising temperatures and pressures through at a considerable increase in materials cost

Gas

large qualtities of helium or carbon dioxide need to be cooled quickly
uses a direct Brayton cycle gas turbine in a gas stream operating at up to 750°C. for high thermal efficiency
high temperature requires heat resistant fuels: composite ceramic fuel, advanced fuel particles, or ceramic-clad actinide compounds.
core reactor configurations involve pin or plate-based fuel assemblies or prismatic blocks.

Molten Salt

liquid fuel - salt and fuel are mixed and circulate like a slurry
uranium tetrafluoride (UF₄) or thorium tetrafluoride (ThF₄),dissolved in molten fluoride salt
self regulating -temperature and reactivity correlate negatively so when the temperature goes up in the reactor, the number of nuclear fissions goes down.
works at low pressure
salt will solidify if not kept very hot all the time
high grade heat can be used to make hydrogen or for industrial processes
special alloys need to overcome corrosion risk
refueling obscured by the opaque coolant
coolant can flow over solid fuel like other reactors or fissile materials can be dissolved directly into the primary coolant so that the fission directly heats the salt

Molten Metal

molten sodium or molten lead or molten lead/bismuth
will solidify if cooled
high operating temperatures facilitate use of greater range of fuels
high temperatures may be used for industrial processes rather than just electricity generation
heat resistant fuel designs required

Heat Resistant TRISO Fuel Sphere
temperature resistant TRISO Fuel Pellet

Basic Types of SMR's an overview

₂₃₅

14 possible reactor designs.

SMR #1 - Boiling Water Reactor (BWR) 300Megawatts

has a reactor core that heats water, which then boils and turns into steam directly within the reactor vessel.
this steam is used to drive a turbine generator to produce electricity.
direct production of steam within the reactor vessel.
a single-loop system where the reactor coolant also serves as the steam source.
use of enriched uranium as uranium oxide pellets as fuel.
any fuel leak can make the water radioactive and that radioactivity can reach the turbine and the rest of the coolant loop
efficiency up 35%

Boiling Water Reactor

SMR #2 - High Temperature Gas-cooled Reactor (HTGR) 80 Megawatts

uses a gas, typically helium, as the coolant.

these reactors operate at high temperatures, which makes them efficient for electricity generation and suitable for industrial process heat applications.
use of graphite as a moderator (to slow down neutrons, allowing the fission chain reaction to continue).

helium is used as a coolant because it does not absorb neutrons and remains chemically inert.

huge volume of gas must be cooled before looping through system again
some designs cannot be re-fueled

very high operating temperatures, which can exceed 850°C.

the heated gas spins a gas turbine which requires a critical and inaccessible magnetic bearing in the heated gas flow
efficiency up to 41%

Gas Cooled Reactor

SMRs #3, 4, 5, 6 - Molten Salt Reactor (MSR) 35-300Megawatts

can have the reactor fuel dissolved in a molten salt (fluoride or chloride) mixture.
these reactors also use molten salt as the primary coolant.
MSRs can operate at high temperatures and low pressures, providing efficient thermal energy conversion.
they are also suitable for process heat applications.
can use molten salts as both fuel and coolant.
refueling if feasible likely requires shutdown and draining of fuel/coolant mix
high operating temperatures allow for efficient electricity generation.
corrosion issues
850°C

Molten Salt Cooled Reactor

SMRs #7, 8, 9, 10, 11. Pressurised Water Reactor (PWR) 60-300 Megawatts

is a type of nuclear reactor that uses pressurised water as both a coolant and a neutron moderator.
the primary loop of high-pressure water transfers heat from the reactor core to a secondary loop, where steam is generated to drive turbines.
use of pressurised water to prevent boiling within the reactor core.
a two-loop system separating the reactor coolant from the steam generator.
higher pressure and temperature result in efficiency up to about 35%
expensive piping due to heat and pressure, higher cost of components
similar safety issues to existing Large Water Cooled Reactors
reactor vessel visible during refueling
uses uranium oxide pellets
similar to Boiling Water Reactor but two water loops (one inside and one outside with a heat exchanger)

SMRs #12, 13, 14 - Sodium or Lead or Lead-Bismuth-cooled Fast Nuclear Reactor (Liquid Metal FNR) 100-345 Megawatts

uses liquid sodium as the coolant.
Sodium FNRs operate at high temperatures and use fast neutrons to sustain the nuclear reaction, which allows for more efficient fuel utilisation and the ability to burn some long-lived actinides.
these reactors can be used for process heat applications.
liquid sodium as the coolant, which has excellent heat transfer properties.
fast neutron spectrum, they do not use a moderator.
high operating temperatures allow for efficient electricity generation. 550-800°C
opaque coolant so no visibility on re-fueling
less long lived radioactive waste
sodium cooled uses metallic UZr with minor actinides; and the lead-cooled SMR uses mononitride-mixed fuel (UN-PuN)
can use "spent fuel" from conventional nuclear reactor waste
sodium reacts violently if it comes in contact with water
operates at low pressures
circulated by natural convection

Nuclear Hydrogen Production

hydrogen

Heavy Industry Use

cement/lime 1370°C
copper 1083°C
lead 327°C
zinc 419°C
iron 1200-1530°C
gold 1063°C
stainless steel 1363°C
aluminium 659°C
ammonia via Haber-Bosch process 400-450°C

As Base-load Power

What are the advantages / disadvantages of creating base-load electricity from multiple locations?
In the critical time gap between now and mature renewables around ***2040 is there even enough time to proto-type, test, manufacture and install SMRs?
Would the move to SMRs make us dependent of foreign imports of alloys, reactors and complex fuels? or Is there time to create a domestic capability from scratch?
for the fast reactor designs would we be importing high level radioactive waste to maximise reactor efficiencies?

Prerequisites for SMRs in Australia"

have transitioned from full-scale prototypes to ongoing commercial SMRs
delivered using well-established domestic manufacturing facilities and robust supply chains.
have on offer a choice of SMR systems from various established and successful vendors.
developed the expertise to refine exotic alloys, test components;
construct, maintain and safely dispose of nuclear waste and components at end of life
ability to make and recycle domestic nuclear fuels
provide transparent and proven capital and operating costs from multiple operating vendors and sites.
demonstrate the operational safety and environmental performance of SMRs in line with Australian society’s expectations.
require a suitably scaled nuclear-power qualified local skills base.