Episode: 4583
Title: Nuclear Reactor Technology - Ep 7 Small Modular Reactors
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr4583/hpr4583.mp3
Transcribed: 2026-07-31 16:14:29 (official HPR transcript)

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This is Hacker Public Radio Episode 4583, for 2026-02-25
Today's show is entitled, "Nuclear Reactor Technology - Ep 7 Small Modular Reactors"
The host is Whiskeyjack and the duration is 00:13:42
The flag is Clean, and the license is CC-BY-SA
The summary is "This episode covers Small Modular Reactors, or SMRs."
This episode is the 7th and 8th part series on nuclear reactor technology.
In this episode, we will describe a topic which has been in the news in recent years,
which is small modular reactors or SMRs for short.
What is an SMR?
Basic definition.
A small modular reactor is a nuclear reactor that is designed to be largely built
in a factory and subject to as little on-site assembly as possible.
The main goal is to lower costs by reducing construction times and allowing a more
rapid start of return on investment.
Size-based definition.
Some people put a numerical size limit on SMRs, saying there must be no larger than 300
megawatts to qualify as an SMR.
However, this limit is not universally accepted and not all SMR designs fall within this
arbitrary limit.
I will ignore this numerical limit and just consider anything to be an SMR if it meets
the criteria of being largely built in a factory with minimal on-site assembly.
The actual goal of the SMR idea.
The actual goal of the SMR idea is to build reactors rapidly and efficiently on more
less than a assembly line basis, rather than can crafting each one.
One engineer in the nuclear industry has compared building reactors to building ships.
Traditional shipbuilding techniques involve assembling each ship from the keel up on the slipways
from individual components.
Newer shipbuilding techniques assemble ships as separate blocks inside factory-like
buildings and then join completed blocks together in a final assembly stage.
This requires careful planning and tight-quality control, but results in building ships
much more rapidly and economically.
This engineer said that SMRs are attempting to build this doorway of doing things to the
nuclear reactor industry as well.
SMR categories, small versus micro.
One very important distinction that needs to be made but seldom is happens to be the
difference between size ranges.
These different size ranges are often meant to meet different use cases which in turn
has further influence on their designs.
Small SMRs SMRs in the several hundred megawatt range are meant for normal grid-scale
utility usage.
These designs are often based on well-proven design, scale down and simplified and use
normal commercial fuel.
These small SMRs typically come from companies with long experience in the nuclear
industry.
Small SMRs and small grids.
In addition to normal utility use, these small SMRs are particularly attractive to small grids
where absorbing a large power plant into the grid is difficult.
Adding a large amount of capacity all at once that may be a significant fraction of their
entire total is difficult from an operational and economic standpoint.
Some of these utilities may have built nuclear power plants decades ago when reactors
were much smaller and are finding that newer ones are much larger.
The attraction of SMRs to them is the smaller size.
Checker wet SMRs from micro loads.
Designs in the tens of megawatts are often meant for special use cases, although some vendors
do promote them as alternatives to normal full-scale utility plants.
These use cases can include such things as powering communities in remote areas which are
far from normal utility grids.
These places are usually powered by diesel generators which are very expensive to operate due
to the cost of shipping and fuel.
As well as the higher cost of diesel compared to normal utility power, these communities
often have no normal roads connecting them to the outside world and after bringing the
diesel once per year by ship, winter ice roads or in the worst case by air.
This is exorbitantly expensive but numerous attempts to replace diesel by other means haven't
held now rarely been successful.
Yet another use case is a related one of providing electric power to mines in remote areas.
These face the same problems as remote communities.
Micro SMRs for large industry.
In some cases however, the intent is to provide a process heat for large industrial applications
such as a production of chemicals.
In these cases, the micro SMRs would be replacing natural gas or coal.
The SMRs in these cases are often designed to produce heat at higher temperatures than
typical utility reactors.
As can result in very different designs such as high temperature gas-cooled reactors.
SMRs to power data centers.
Some parts of the AI industry are talking about using SMRs to power their data centers.
However, I suspect that this will be forgotten once the AI bubble pops which could happen
in the near future, possibly even before this podcast airs.
As such, I will ignore this use case.
Let's just nonsense about micro small modular reactors, you say.
Unfortunately, the terminology used today originates from period when ideas were not well-defined.
Furthermore, ideas that were around before the SMI term earthquake have been rebranded
as SMRs for marketing reasons.
The result today is that some very different things are being called SMRs and different
people are using different terms to just try to distinguish between them.
Some people are using the term micro SMRs, while others are calling them MMRs or micro
modular reactors.
I will simply call the very small ones micro SMRs for simplicity.
Small reactors as modular reactors that are not SMRs.
Not every small commercial power reactor is an SMR.
The larger SMRs are more or less in the same size range as reactors built in the 1960s.
However, these were not designed with the sort of modular construction techniques that
are one of the defining features of an SMR.
India was still completing 200 megawatt reactors in the early 2010s before switching to larger
sizes.
These were well within the SMR size range but not considered to be SMRs.
Conversely, one builder of large tube type heavy water reactors which inherently have modular
features has taken experience from building reactors in Asia and applied it to their
newest 1000 megawatt design.
This incorporates modular design and rapid assembly techniques in order to build a reactor
more quickly, but as these are large reactors, they are also not SMRs even if they are
modular.
Standard versus proprietary fuel.
SMRs which are based on scaled down conventional designs normally used standard commercial
fuel.
This is typically uranium oxide fuel enriched between 3 and 5%.
Some SMRs, particularly the micro SMR ones, use a proprietary fuel, often with higher
enrichment levels.
These proprietary fuels are often enriched to just below 20% uranium to 35.
If you recall from a previous episode in this series, uranium which is enriched to 20%
or higher is considered to be military material and cannot be used in civilian applications
aside from a few research reactors.
As a result of this, there are currently no commercial suppliers for this great a fuel
outside of small amounts that are made in Russia and very limited experimental amounts
that are made in the US from diluted surplus weapons stockpiles.
While some of the SMR vendors claim to have fuel suppliers lined up, this fuel is not
in production from reliable sources and so buyers face additional risks in using these reactors.
There is no such risk when it comes to SMRs which you standard commercial fuel.
Wear SMRs are currently being built.
There are many different proposals for SMR designs, but I will just focus on ones that
are actually built under construction or have signed utility customers and will almost
certainly be built.
HDR-PM in China.
This is an SMR that often gets mentioned as it is seen as the first to actually go into
operation.
This reactor was mentioned in a previous episode in this series.
It is a high temperature gas cooled, pebble bed reactor.
The basic design is descended from reactors built in Germany starting in the 1960s.
A Chinese research group bought the design information from Germany and continued to work
on it further.
The fuel is contained together with graphite moderator in billiard ball size spheres which
are in bins.
The fuel is uranium enriched to 8.5% to coolant is helium gas.
Two reactors jointly feed a single 210 megawatts steam turbine generator.
The reactor went into operation delivering power to the grid at the end of 2021.
Repurposed ship reactors in Russia.
Several different models of reactors originally designed for powering ships have been used
to provide power for remote Arctic communities in Russia.
These are pressurized water reactors using uranium enriched to under 20%.
They have been mounted on barges and on land.
They are used to replace diesel or small coal plants.
Some people like to cite these as the first SMRs.
However, as repurposed marine reactors, it is questionable whether these are true SMRs,
but that is a matter of semantics.
They are, however, a good example of how micro SMRs can be used to provide power to remote
towns and mines.
300 megawatt BWR in Canada.
Canada is building a power plant just use of Toronto that has 4 300 megawatt boiling water
SMRs for a total of 1,200 megawatts.
These are scaled down and simplified conventional reactor designs using standard commercial
fuel.
The production started at late 2024 and the first reactor is expected to go into commercial
operation in 2029.
Recent news suggests that the province of Ontario may go back to building larger reactors
after this plant is built.
But several smaller provinces are interested in this SMR, due to its small size, soothing
their small electricity grids.
470 megawatt PWR in the UK.
The UK has announced plans to build a series of 470 megawatt, pressurized water reactors
from a UK company.
These are scaled down and simplified conventional reactor designs using standard commercial
fuel.
The reactors are designed to be transported to this site in modules and assembled there,
but with most of the work being done in the factory.
At 470 megawatt, these are notably larger than the 300 megawatt cutoff used by some people,
but as the ultimate goal is modularity, if they can meet that intent, I think they can
recently be called SMRs.
Construction has not yet started, but as plans are well advanced, they are probably worth
mentioning.
25 megawatt PWR in Argentina.
This is often cited in sub-articles as one of the first commercial SMRs, but is actually
a scaled down prototype for an SMR that is intended to be four times the size.
This is a scaled down pressurized water reactor.
Construction has been on again off again due to financial and economic problems in Argentina,
so it's hard to say when or if this will ever be completed.
I thought it was worth describing here though, because it is mentioned in a number of news
articles on SMRs.
Various experimental SMRs.
There are numerous experimental SMRs on the drawing board or under test.
Some may be built as prototypes.
This, however, will probably never be built or, if built, go beyond the prototype stage.
Modular large reactors, newer large reactors are starting to incorporate modularity into
their designs as well.
These are composed of large modules weighing from 100 to 1000 tons.
The amount of concrete and steel required in construction has also been drastically reduced.
There can be large economies of scale in electric power generation.
As larger reactors incorporate modular construction, and as SMRs get larger, the advantages
of SMRs in grid scale utility applications may fade away except for smaller grids.
Conclusion, SMRs are a new trend in nuclear reactor design.
However, there are really two different things which fill two different needs.
One style is intended to adopt designs which allow for more rapid construction with
more of the work being done in the factory and less on the construction site with the overall
goal of reducing costs.
The other style is to provide very small reactors to power remote communities and minds
or to provide process heat to large industries.
The first SMRs are in operation or under construction.
The most promising grid scale designs that present are simply scaled down and simplified
conventional designs that use standard commercial fuel.
larger reactors will incorporate modular construction techniques, blurring the lines
between them and SMRs.
In the next episode, we will talk about future reactor technologies, particularly what
are referred to as generation 4 reactors.
This concludes the seventh episode of an eight-part series on nuclear reactor technology.
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