REACTOR DEVELOPMENT
Reactor development and fuel
Nuclear Reactor Development
The first ever power nuclear reactors, which were virtually still experimental, are known as Generation I, or Gen I reactors.
The reactors which started delivering electricity around the world from the 1970s to the 1990s are termed; Gen II. Fukushima was an early Gen II reactor.
A much more advanced class of reactors, called Gen III, came into being in the 1990s, with the first one becoming operational in Japan in 1996.
In the 21st Century rapid advances in nuclear design have led to further significant additional improvements, and those reactors are called Gen III+.
In parallel, further advances into high temperature reactor systems, and designs using advanced Passive Cooling systems arrived on the drawing boards, and they are now known as Gen IV.
The HTMR-100 is a gas-cooled Gen IV reactor.
One must bear in mind that the technological difference between an early Gen II and a modern Gen IV reactor is vast.
Consider the difference between the pioneering 1970s Boeing 707 jetliners and a modern Airbus or Boeing. The differences are huge, not only in functional aeronautical design, but also in all the modern electronics, satellite navigation systems and so on.
Many people do not seem to realize the dramatic extent of the major advances which have taken place in nuclear power development during the last half century.
One really is talking of chalk and cheese.
Koeberg, near Cape Town, consists of two later-model Gen II reactors.
The ocean is required for cooling purposes.
This power station provides about half of the electricity of the Western Cape Province.
The Barakah Nuclear Power Station in the UAE.
There are 160 South Africans working on this plant.
This plant consists of four Gen III+ reactors. It produces 5 600MW
Water or Gas – What does this mean?
Early reactors were all water-cooled, requiring vast quantities of water to extract the heat. So typically, earlier reactors were all built on the coast so as to use the ocean for cooling.
However the HTMR-100 is cooled using Helium gas, which means that the reactor can be built anywhere the customer wishes. It is not constrained to having to be built near the ocean or near a large lake.
Most of the SMR’s under development around the world today are still water-cooled. Many are Gen III technology designs.
International SMR developers have frequently chosen a water-cooling route because they had existing conventional reactor designs on hand, but also because their countries have easy access to an ocean or to large water sources.
South African designers, very intentionally, chose a gas-cooled design route because of the vast sizes of African countries, most of which have little to zero access to oceans or large water sources.
Fuel Supply
Coal-fired or gas-fired power stations need a continuous supply of fuel. The coal or gas fuel has to run on conveyor belts or railway lines, or through pipelines, to ensure a supply on a continuous basis. Only a minimal fuel stockpile is kept at fossil-fuel power stations because it is complex and expensive to store large quantities of fuel. Without the fuel moving, such a power station plain and simply stops operating.
In contrast, a nuclear power station’s fuel only needs to be delivered from time to time because it uses such an extremely small quantity. A truck-load every so often is quite adequate.
Consequently, a nuclear power station manager does not have the headache of worrying about a potential interruption in fuel supply, for example; if there is a flash flood or some breakdown in the supply lines.
A conventional nuclear power station, such as Koeberg, uses large metallic fuel elements and is only refueled approximately every 18 months.
A Koeberg fuel element fabricated in South Africa.
A Koeberg fuel element fabricated in South Africa. This metallic fuel element contains many small pellets of Uranium Dioxide
The HTMR-100 has been designed such that it never has to shut down for refueling.
HTMR-100 fuel is in the shape of a ball, as large as a cricket ball, with each ball containing very small grains of uranium embedded in a graphite matrix. In the Gen IV jargon such fuel is referred to as ‘Pebble Fuel’.
Pebble Fuel is continuously added to the top of the reactor, and it then takes about two years to work its way down to the bottom, at which point each ball is taken out and moved to a spent fuel storage facility on site.
It is possible to store 40 years’ worth of spent fuel on site. This will depend on the decisions of local legislation, and on operating practice.
TRISO Fuel.
The version of Pebble Fuel developed and produced in Pretoria is called TRISO fuel.
This fuel consists of grains of Uranium each coated with a number of different coatings to accommodate all mechanical and chemical effects. These tiny particles are then all embedded in a graphic matrix about the size of a cricket ball.
The fuel looks exactly the same when it comes out of the reactor as when it went in, nothing escapes during the two years that a fuel ball is inside the reactor.
These balls are very robust and can be thrown on a concrete floor and will bounce to a small degree. Even if one were to split in half, it makes no difference. Nothing radioactive, or anything else, will escape from it.
The robust nature of these fuel balls makes it relatively easy to transport them by road over long distances and over rough roads. In other words; an HTMR-100 can be built near a mining community or some other remote place and it presents no problem in the transportation of fuel to the reactor.
Half a dozen TRISO fuel balls will supply enough electricity for a family of four for a decade.
