Episode: 4533
Title: Nuclear Reactor Technology - Ep 2 Nuclear Fuel
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr4533/hpr4533.mp3
Transcribed: 2026-07-31 16:13:23 (official HPR transcript)

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This is Hacker Public Radio Episode 4533, for 2025-12-17
Today's show is entitled, "Nuclear Reactor Technology - Ep 2 Nuclear Fuel"
The host is Whiskeyjack and the duration is 00:19:05
The flag is Clean, and the license is CC-BY-SA
The summary is "Types of nuclear fuel, recycling of fuel, uranium and thorium resources, and medical isotopes."
This episode is the second in an eight-part series on nuclear reactor technology.
This episode will cover types of nuclear fuel, recycling of nuclear fuel, uranium and
thorium resources, and medical isotopes.
Types of nuclear fuel, natural uranium.
This is the simplest of nuclear fuels that use purified natural uranium that has not been
enriched.
The enrichment is not necessary if you use an efficient moderator and reactor design.
Natural uranium is the least expensive of nuclear fuels.
It also allows countries to have an independent fuel cycle without having to build a uranium
enrichment industry.
It has been in use in numerous large-scale commercial power reactors around the world
for decades, with more due ones recently announced to be built.
An enriched uranium.
This is the most familiar to many people.
And rich uranium is more expensive than natural uranium, but it allows for more compact
reactors and less efficient but cheaper moderator.
It has a disadvantage that you need access to uranium enrichment facilities, which are
very large and expensive industrial plants.
Most commercial enriched uranium fuel has between 3 and 5% you to 35.
Some reactors have been designed to use fuel enriched to only around 1.2%.
This is commonly referred to as slightly enriched uranium.
Some reactor designs require a fuel and rich to just below 20%.
Mixed oxide fuel or marks.
Mixed oxide fuel is a blend of plutonium and natural depleted or recovered uranium.
Recovered uranium is extracted from used nuclear fuel.
The plutonium is extracted from used nuclear fuel and takes the place of the U235
in a reactors that use enriched uranium.
Plutonium is produced when U238 interacts with neutrons, producing a variety of different plutonium
isotopes.
Using mox fuel allows for spent fuel to be recycled, reducing the amount of fresh uranium
required, and also reducing the amount of stored space required for spent fuel.
8% plutonium content is roughly equivalent to 5% enriched uranium.
France uses mox fuel extensively and mox fuel constitutes about 10% of their fuel usage.
Thorium fuel.
Thorium is not nuclear fuel when used by itself.
It is almost entirely thorium 232 which is not a fizzile isotope.
Instead, thorium can be used in a mixed oxide or mox fuel where it takes place of U238.
This is added either in rich uranium or plutonium with most studies indicating that plutonium
is the most feasible.
While in the reactor, some of the TH232 is converted to U233.
U233 is a fizzile isotope and can take the place of the U235 in reactor fuel.
Some of the U233 will be consumed in the reactor, but the rest will come out in a spent
fuel and can be recycled to make new fuel taking the place of some of the plutonium.
Even with the reuse of the re-covered U233, it general opinions seems to indicate that
he studies supply of plutonium from uranium cycle reactors will still be deated to keep
the cycle going.
No new reactor technology is required to use thorium fuel.
Existing reactors based on natural uranium designs that have been in large-scale commercial
operation for decades can use thorium fuel either as is or with mitermotification.
Natural uranium reactors are suitable for this because they make very efficient use of
neutrons that is they have good neutron economy, something that is important for thorium.
Thorium is not used now because thorium-based mox fuel is more expensive to make than
the natural uranium that the reactors which could use thorium normally run on.
The main advantage of thorium is for countries that have large thorium reserves but much
less uranium.
India in particular has a long-interm interest in thorium fuel due to their abundant reserves
of it and they also use natural uranium reactors whose design can be changed to use thorium
fuel.
Plutonium in uranium cycle reactors, in uranium cycle reactors plutonium is produced as part
of the reaction.
Some of that plutonium is then consumed while still in the reactor.
This actually constitutes a significant share of the total energy output.
In typical light water reactors we'll get to reactor types later.
About a third of the total energy output comes from plutonium that was created and then
consumed while still in the reactor.
For heavy water natural uranium reactors it's actually about 60% of the total energy.
Plutonium is strictly speaking not a type of fuel by itself.
Rather it is what is left over after most of the U-235 has been extracted from fresh
uranium in order to make enriched uranium.
To put it in another way in order to get U-235 to make enriched uranium you must extract
it from other uranium.
What is left over is mainly U-238 with a small amount of left over U-235.
This is called depleted uranium.
But cannot be used directly as nuclear fuel itself.
It can be used to make dew fuel by adding plutonium to make mixed oxide or mox fuel.
There are currently very large stock piles of depleted uranium.
If fast reactors become commercially viable these stock piles of depleted uranium could
be used to make fuel for them.
Oxide or ceramic versus metallic fuel.
Nuclear fuel is usually in the form of a ceramic pellet.
That is it is a uranium oxide powder pressed into a small cylindrical pellet and then
heated to a high temperature to form a ceramic.
This is known as sintering.
In ceramic form it is very durable and with a high melting point.
Some reactors use uranium in metallic form but these are quite rare.
Metal has a higher heat conductivity than ceramic but is less durable and more prone to corrosion
or other chemical influences.
In oxide form the fuel pellets are normally inserted into hollow metal tubes which hold
the fuel in place.
Multiple tubes may then be assembled into bundles for handling purposes.
The size and length of these bundles will vary depending on the reactor type.
Some unusual reactor designs use completely different fuel designs.
I will cover these in episodes where I talk about the reactors themselves.
Recycling spent fuel.
Once fuel has been used up it is considered to be spent.
However there are ways of recycling or reusing spent fuel.
Once through fuel cycles both commercial reactors run in a once-through fuel cycle.
They load fresh fuel in the form of enriched natural uranium in the reactors.
Use it until it is spent and then put it in the storage or disposal.
Many countries consider this to be the cheapest option as fresh uranium is relatively inexpensive
and no reprocessing facilities required to be built or operated.
Reprocessing spent uranium fuel into mixed oxide or mocks fuel.
However some countries with France being the best known example reprocessors spent fuel so they
can use it again.
Spent nuclear fuel contains elements and isotopes that were created in the nuclear
act reaction that interfere with the reaction by absorbing neutrons without contributing
to further fission.
Processing fuel is basically a chemical process to extract uranium and plutotium from
the spent fuel and leaves the undesired elements behind.
These undesired elements become waste.
The recovered uranium still contains a fair bit of fizzile U235.
In the case of reactors that use enriched uranium the amount of leftover U235 is typically
higher than is found in natural uranium.
This recovered uranium can then be put back through the enrichment process to be turned
into a regular enriched fuel.
The plutonium however contains the greatest amount of unused energy.
This plutonium is mixed in with natural uranium recovered uranium or depleted uranium and made
it to mix oxide or mocks fuel.
This mocks fuel can then be used in the reactor.
Apparently in France mocks fuel amounts to 30% of the fuel they use.
The spent mocks fuel cannot be used again because too much of the fizzile isotope of plutonium
have been used up, leaving the non-fizzile isotopes and it is not practical to separate
the two.
Fast reactors do not face this limitation but that is a subject for later episode.
Reprocessing and thorium fuel.
With thorium fuel reprocessing is inherent to an indifuel cycle that I am aware of.
Actually the process is similar to reprocessing uranium fuel except that U233 takes
a place of plutonium and thorium takes place of U238.
Direct reuse of spent light water fuel and heavy water moderated reactors.
We haven't covered heavy water moderated reactors yet that will come in a later episode.
However at this point just accept that there are reactors that use fuel more efficiently
than the common light water reactors.
These reactors can use natural uranium without any enrichment at all.
As a result of this what is used up fuel from a light water reactor is equivalent to high
grade fuel for these more efficient reactors.
This means you can use a fuel twice once in a light water moderated reactor and again
in a heavy water moderated reactor.
Work has been done on two processes which take advantage of this.
To pick direct use of used PWR fuel and can do.
This is a process for reusing spent fuel from common light water moderated pressurized
water reactors or PWR and using them in a type of heavy water reactor don't as can
do.
I will cover both types of reactors in more detail in a later episode.
At this point you just need to know that these are two of the three most commonly used
commercial nuclear reactors.
The third common type may be compatible with this as well but I don't know if it has
been tested.
The fuel rods in a PWR are longer than those in a can do fuel bundle.
The PWR rods are therefore cut to the correct length.
The ends are sealed and they are assembled into a can do compatible bundle.
This fuel bundle is now ready to use as fuel in a can do style reactor.
The do pick process destroys a lot of the actinized plutonium in the spent PWR fuel.
It extracts up to 25% more energy from the fuel compared to other PWR use fuel recycling
technologies.
It reduces a deed for PWR fuel disposal by up to 70%.
It reduces fresh uranium requirements by 30%.
This was jointly developed by South Korea and Canada.
So far as I'm aware, South Korea, who have both PWR and can do reactors, have not put
this into commercial operation.
The major problem is that these re-manufactured fuel bundles are as radioactive as spent
fuel and so are more difficult to handle and load into a reactor than fresh fuel.
Repue reprocess uranium fuel and can do.
This is similar to the do pick process except instead of simply cutting the fuel rods
at the correct length, they are opened up and the fuel pellets are crushed and blended
with fresh uranium additive necessary and then re-centered.
This gives a more consistent product than do pick process but they at the expense of additional
manufacturing steps.
However, this is still less involved than making traditional mocks fuel which includes
chemical processes to separate different elements.
This process has been demonstrated in China who also use PWR and can do reactors.
Uranium and Thorium resources start with uranium.
The top six producers of uranium are in order, Australia, Kazakhstan, Canada, Namibia,
Russia and Niger.
Between them they produce roughly two-thirds of total world output.
However, uranium production is driven by market forces and other supplies can be brought
online at its higher cost.
Since the cost of uranium is a very small proportion of the cost of the electricity produced
by a nuclear reactor, prices can increase substantially without increasing the cost of
electricity significantly.
Uranium and sea water.
Uranium is soluble in sea water and there is estimated to be 1,000 times as much uranium
in the sea as this found in commercial deposits on land.
Successful experiments have been done on extracting uranium from sea water.
If uranium were to be extracted from sea water, it would be replenished by natural erosion
of minerals from rocks at a faster pace than humans could extract it from the sea so it
can't be used up.
With current technology extracting uranium from sea water is about 3 to 20 times the cost
of mining it on land.
Thorium is not currently used as nuclear fuel in a significant amount, so it's not
meaningful to talk about production.
The top 3 countries though in terms of thorium deposits are India, Brazil, and Australia.
However, if thorium were to be a valuable nuclear fuel, exploration would undoubtedly turn
up far more in places where nobody has bothered to look.
Medical isotopes, medical isotopes are an important part of modern medicine.
Most of you will be familiar with their use in the treatment cancer and in medical diagnostics.
However, they are also used to sterilize single-use medical instruments such as syringes.
Most of you listening to this have therefore probably benefited from medical isotopes even
if you didn't encounter them directly.
Examples of comemetical isotopes, some examples of comemetical isotopes are, molabdenum 99,
or chemical symbol M099.
This decays into Technitium 99, TC99, and is extensively used in medical diagnostics.
The TTM177, which is LU177, this is used for prostate cancer therapy.
Yetrium 90, which is a chemical symbol Y90, this is used to treat several types of cancer.
A colbalt 60, which is CO60, this is extensively used to sterilize single-use medical
instruments.
It is also used for some types of cancer treatments such as gamma-niphrate radiotherapy.
I-dine 131, this is used to treat thyroid cancer.
How medical isotopes are made?
The typical way that the above isotopes are made is to bombard a source material with
neutrons in a reactor and transmuted into the desired isotopes.
A material known as a target is made from a specific isotope or element.
It is in place in a reactor and bombarded with neutrons, sometimes for years.
At the appropriate time it is removed from the reactor and process further into medical
grade material.
For isotopes with short half-lives, what follows then is a very tightly coordinated logistics
operation to get the isotopes into the customer quickly and reliably to ensure they
are still useful when they arrive.
Using isotopes and research reactors, the traditional way of manufacturing medical isotopes
is to make them a what are called research reactors.
I won't be speaking much about this type of reactor because I will focus on power generation.
Research reactors do not normally generate electric power.
Instead they are used as a source of neutrons.
They usually fairly small if you megawatts in thermal output.
As they don't require high temperatures, they are usually not required to be pressurized
and so operate at or near atmospheric pressure.
They are usually what are called pool-type reactors.
These are basically very large pots filled with lighter heavy water with a lid that can
be removed to access the interior.
Material, whether fuel, test samples or isotope targets are added and removed through
the top or inserted in a removed through dedicated tubes which penetrate your reactor walls
for this purpose.
Using isotopes and power reactors, in recent years medical isotopes have begun to be made
in large commercial power reactors as a byproduct alongside of generating electricity.
Since the medical isotopes are a byproduct of electricity production, overall costs are much
lower than operating a dedicated research reactor for this purpose.
Many power reactor types, however, are not suited to this role as they do not allow
material to be readily added or removed from the reactor except by shutting it down and
opening it up.
However, pressurized heavy water reactors such as can do have a large, un-pressurized
Kalandria holding the moderator and it is a relatively simple matter to add or remove
target material from locations where the target will receive appropriate neutron radiation.
Cool-Balt 60 is mainly made in can-do reactors in Canada, Argentina, China, and South
Korea.
It is also made using RBMK reactors in Russia.
Other isotopes such as the Malebton 99, Dutitium 177, and Itrium 90 are also made in
can-do reactors in Canada.
Romania are building additional can-do power generation reactors and they intend to equip
them with isotope production gear for medical isotopes.
The ability to produce medical isotopes at a large scale, low cost, and routine availability
has sparked more interest in developing still more types of medical isotopes for
additional treatments.
The basis of nuclear fission is nuclear fuel.
There are three main types of nuclear fuel and commercial use today.
These are natural uranium and rich uranium and mixed oxide or mox uranium plutonium mixtures.
It is possible to use thorium in a sort of thorium plutonium or thorium uranium mox fuel,
but this is not currently economically viable at this time when uranium is so cheap and abundant.
Fuel can be recycled in use in a reactor again.
Medical isotopes are an important byproduct of the nuclear industry and a large share of
the world's population has benefited from this at one time or another.
Conclusion.
In the next episode, I will describe the basic features and characteristics of reactors
together with descriptions of the most widely used commercial reactor types.
This concludes the second episode of an eight-part series on nuclear reactor technology.
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