Currently, there are two advanced nuclear reactors being developed in New Brunswick,
Canada, that can burn nuclear waste to generate electricity.
How is that possible?
Well, that’s what I’m here to explain.
But before we dive into these advanced, nuclear waste burning reactor designs, let’s take
a step back and quickly review our nuclear physics.
The basic idea behind any nuclear reactor is to fire neutrons at fissile material, usually
uranium-235, splitting their atoms open to release energy and more neutrons.
Those extra neutrons maintain the chain reaction in the nuclear power plant.
In a traditional reactor, something called a moderator is used to slow down the released
neutrons, because this makes them more effective at splitting the uranium-235.
But the reactors being developed in New Brunswick don’t use a moderator, which makes them
fast neutron spectrum reactors, or fast reactors.
It’s the fact that the neutrons are “fast” that allows these new reactor designs to burn
nuclear waste.
In traditional reactors, those “slow” or “thermal” neutrons might be really
good at splitting uranium-235, but they’re not so good at doing anything to the heavier
uranium-238 isotope, which makes up the vast majority of natural uranium.
So when a traditional reactor has spent its fuel, it’s only used a small portion of
the uranium and a lot of waste is left over.
In contrast, the “fast” neutrons aren’t quite as good at splitting uranium-235, but
unlike their “slow” counterparts, they are better able to convert uranium-238 into
plutonium-239.
The plutonium is fissionable like the uranium-235 – hence the reactor can “breed” its
own fuel.
Since the fast reactor is able to make better use of the uranium-238, it uses fuel much
more efficiently.
Nuclear waste from traditional reactors can also be reprocessed into fuel usable in these
fast reactors.
That’s the basics of how a fast reactor works, but they also have a lot of other features
that set them apart from traditional reactors.
Let’s take a closer look at the first of the two reactors being developed in New Brunswick,
the ARC-100.
The first thing to know about this reactor is that it’s a Small Modular Reactor that
would only produce 100 MW of electricity – that’s much smaller than any nuclear power plant
operating in Canada today.
It would also have a 20-year refuelling cycle, meaning it would only have to refuel once
every 20 years.
The ARC-100 would also use liquid sodium as a coolant instead of the traditional water.
Because water normally boils at 100 degrees Celsius, in traditional reactors pressure
vessels or tubes have to be used to keep the water under high pressure so it doesn’t
boil away.
If the pressure vessels fail, then the pressurized 300 degree Celsius water will flash into steam
and disperse radioactive materials.
Liquid sodium, however, has a boiling point of 900 degrees Celsius, which eliminates the
need for these pressure vessels, making the reactor safer and cheaper.
Sodium is also 100 times better at transferring heat than water – this means that in an
emergency where the plant’s electricity is shut off, the liquid sodium can passively
cool down the reactor and prevent a meltdown without any operator intervention.
But using sodium as a coolant does have its downsides – since sodium is highly reactive
with both air and water, the coolant can’t be allowed to come into contact with either,
which does add some additional complexity to the reactor.
While sodium’s reactivity might sound concerning, the concept of a liquid sodium fast reactor
has already been proven safe and effective.
The EBR-II was a sodium cooled fast reactor that operated in Idaho between 1964 and 1994.
The EBR-II was even smaller than the ARC-100, generating 20 MW of electricity.
Importantly though, the EBR-II demonstrated that sodium cooled fast reactors can passively
shut themselves down in the event of an emergency.
But if you think that the ARC-100 reactor sounds cool, just wait until you hear about
the second reactor being developed, the Moltex SSR-W, which stands for Stable Salt Reactor
– Wasteburner.
The Moltex design is also a small modular reactor which would produce 300 MW of electricity
– while that’s more than the ARC-100, it’s still quite a bit smaller than current
reactors.
The stable salt reactor gets its name from the fact that both the coolant and nuclear
fuel are molten salts.
The fuel is contained in tubes, similar to those used in a conventional reactor, and
a separate molten salt acts as a coolant.
Like the sodium reactor, since the molten salt has a much higher boiling point than
water, there’s no need for pressure vessels in the Moltex design.
Another feature of this design is its passive safety response – as the temperature of
the reactor increases, the reaction automatically slows down, making the system self-controlling
– no operator intervention is needed to slow down the reaction.
A WAste To Stable Salt, or WATSS, facility would be located on site to recycle nuclear
waste into fuel for the reactor.
The site would also have a Grid Reserve power system, which would store some hot molten
salt.
When the grid needs extra power, the Grid Reserve’s stored heat would be used to operate
steam turbines, allowing the reactor to temporarily increase its power output to up to 900 MW
of electricity.
This means the Moltex design would work well with intermittent renewables like wind and
solar, since the reactor could temporarily increase its output during cloudy or windless
days, and recharge the Grid Reserve system when wind and solar are generating more power.
At this point you might be thinking – both these designs sound great, when will they
be built?
Well, if all goes according to plan, the ARC-100 will be complete by 2030 and the Moltex SSR-W
will be complete sometime in the early 2030s.
But the construction of both of these reactors will require continued support from politicians.
The New Brunswick Green Party has raised concerns about these reactors, mainly about the cost.
While small modular reactors promise to be cheaper than their traditional counterparts,
nuclear power plants do have a history of going over-budget during construction.
The cost of building the world’s only functioning SMR in Russia was four times its initial budget.
Others have raised concerns over the fact that both reactors are “paper designs”
– nothing has been built and tested yet.
Despite these concerns, the projects have received strong support from both the Liberal
and Progressive Conservative parties in New Brunswick, and the federal government supports
the projects as well, so for the time being it seems that both projects will go ahead.
But there’s actually no need to wait until the 2030s for a reactor that can burn nuclear
waste in Canada – Canada’s current CANDU reactors technically have the ability to use
nuclear waste as fuel too.
Since Canadian CANDU reactors run on natural uranium instead of enriched uranium, nuclear
waste from light water reactors can be reprocessed into Natural Uranium Equivalent Fuel and used
in CANDU reactors.
But if you want to learn more about CANDU reactors, as well as other Canadian small
modular reactor plans, than you need to watch this video next!