Small Modular Nuclear Reactors
Climate change is real and happening fast and the culprit is human generated green
house gases. Energy production plays a key role in this process about 30% of all
greenhouse gas generation is done by electricity production. That’s the reason the
world has started to move to clean energy sources at and astounding rate. The main
sources of clean energy are solar, wind and hydro but what about nuclear, many people
don’t even know nuclear is a clean energy source. So why has nuclear energy received
a bad reputation.
High risk associated with nuclear plants and nuclear material.
High construction cost
Long construction time
Large areas needed for construction
Problem of safely storing nuclear waste
Also, three nuclear plant accidents Chernobyl, three-mile island accident and
Fukushima disasters played a key role in the bad attitudes from the public toward
nuclear energy. So why exactly do we need nuclear when we have solar, wind or hydro
the main reason is reason is reliability we can only produce energy with solar for less
than 24 hours, for wind turbines there should be good constant stream of wind and in
dry seasons electricity production from hydro plants become constrained we can clearly
see this happening in Sri Lanka in some seasons. The best example of this challenge
was seen recently when a giant snow storm hit Texas and crippled the states energy
supply this left people in freezing temperatures without electricity for days. With nuclear
reactors you can generate electricity 24 hours any time of years in any climate condition
So how do we use this great energy source in a safer, cost effective reliable way enter
SMRs or small Modular nuclear reactors. The future of clean energy.
SMRs are a type of nuclear reactor
designed to be smaller in size than a
traditional reactor they are based on the
same physics behind larger reactors
splitting a heavy unstable atom into to two
or more atoms releasing energy this heat
energy is used to boil water which in
exchange rotate a turbine to produce
electricity. The US NRC classifies SMRs
as reactors that produce less than 300MW
of energy compared to 1,600MW of energy
produce by larger reactors.
Now lets understand in depth how SMRs
work in detail. The process begins at the
reactor core where atoms are split apart
almost every nuclear reactor uses
Uranium-235, this in exchange produces
smaller atoms, heat energy and neutrons
which go and hit other Uranium atoms
causing a chain reaction to control this
unstable process a series on neutron
absorbing control rods are inserted to the
core of the reactor this is the main method
in which power of the reactor is controlled including shutting down the reactor. The heat
from the above process is used to heat the primary coolant of the reactor shown in red
color in the above diagram, using convection and natural buoyancy water goes up
through the riser then heat is transferred from primary coolant through the walls of the
tubes in the steam generator heating the water in the secondary coolant (shown in white
color) inside them it turns to steam which is removed through steam lines the cooled
water “falls” back to the reactor pressure vessel this cycle continues. This is only a basic
idea practically this is a much complex process.
Now that we have understanding how nuclear reactors work lets look why SMRs are
better than conventional reactors.
Figure 1 Basic cross section of a SMR reactor
1. Production & Cost
The biggest problem with conventional nuclear power plants is the huge upfront cost
they take to build. It takes approximately about $10 billion a 1,100MW plant in $5,500
per kW to $8,100/kW range even this is an optimistic case with final cost going past
planned original estimate. In 2017, the US state South Carolina abandoned two
unfinished Westinghouse AP1000 reactors due cost overruns leaving just two other
AP1000 reactors under construction even these have exceeded the original cost
estimate of $14 billion has risen to $23 billion, The main reason for this huge cost is due
to building custom machinery, tools and reactors but with SMRs modular design this is
not the case we can build a standard design and mass scale manufacture them using
factory methods. A US company called NuScale estimates it will only take under
$3 billion to build their first reactor with $5000 per kW.
Figure 2 A reservoir compartment with a space for six SMRs
2.Saftey
SMRs enhance safety through lower power of the
reactor core and use passive safety systems
meaning they have less reliance on active safety
systems like additional pumps, grid power and
generators or batteries with models like NuScales
SMRs they employ natural water circulation to
passively cool its reactors down. The thermal
safety system uses an onsite water reservoir
located at the sides of the outer vessel which
removes heat and avoid complete melt down.
In an emergency valves open automatically which
allows steam to be released from the reactor
vessel into the containment vessel. The steam
then condenses and water flows back from the
core into the core through a second set of valves
at the bottom of the reactor, all this happens
without any external interference no AC or DC
power, no operator and no additional water.
3.Infastructure and Time
Because of the standard design and modularity of SMRs they can be integrated in to
existing platforms reducing the need for new infrastructure to be built, since these are
smaller reactors the area needed for operations and safety for public is a very smaller.
Even though we have been using SMRs for many decades now in Navy submarines
commercially they are in a very young stage many countries including US, Russia and
China have started development in SMRs but only few have received nuclear regulatory
approvals. If successful SMRs will be a good highly efficient green option for Sri Lanka
to adopt to combat our ever-increasing energy needs.
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