Blykalla’s SEALER reactors will use alumina forming steels to protect all surfaces exposed to liquid lead:

1. A ferritic alumina forming steel (FeCrAl) with superior corrosion tolerance for protection of components operating at high temperature (550°C)
2. An easily weldable alumina forming austenitic steel (AFA) for protection of components operating at lower temperature (420°C)
3. A harder alumina forming martensitic steel (AFM) for protection of the pump impeller and housing.

Nuclear reactors generate power through fission, which is the process of splitting atoms to release energy. The heat released by fission is typically used to create high-pressure steam that spins a turbine, which powers a generator that generates electricity. The process of splitting atoms is carefully controlled through several safety mechanisms, with the cooling function at its centre. 

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The spent fuel from a SEALER reactor is intended to be reprocessed. Fissile materials and minor actinides will be extracted and recycled into new fuel, adding only depleted uranium. The residual high level waste consists of fission products, which will be vitrified, requiring geological storage for less than 1000 years.

Once SEALER is in serial production, the intent is that it will take one year to build one unit, and another year to install and commission the same.

The fuel of a SEALER reactor can operate for at least 25 full power years without any reload. The limit is set by radiation damage to the fuel cladding tube.

The liquid lead coolant operates between 420°C at the inlet of the core, and 550°C at the outlet.

Thorium is not a nuclear fuel, but can be converted to fissile U-233 in any type of nuclear reactor. SEALER would be capable of operating on such a ”thorium-cycle”, but this option is more expensive than using conventional fuel.

Each SEALER has 800 tons of liquid lead that is melted and poured into the reactor vessel, where the core will be operating at a maximum coolant temperature of approximately 550°C. Because lead has a boiling point of 1740°C, this means that the risk for loss of coolant is practically eliminated. This may be compared to water-cooled reactors, where water has a boiling point of 100°C (up to 300°C in pressurised water-cooled reactors). Such loss of coolant has been a contributing factor to all three major nuclear power accidents.

Some major advantaged associated with using liquid lead as a coolant include:

• The primary circuit operates at ambient pressure, permitting a thin reactor vessel and reducing the driving force for dispersion of radioactive nuclides in case of core damage.

• Lead does not react violently with other materials in the reactor.

• The boiling temperature of lead is very high (1740°C), practically eliminating the potential for loss of coolant accidents.

• Thanks to its high density, natural circulation of lead is capable of removing decay heat in a very compact configuration.

• Lead constitutes an in-situ gamma-shield, reducing the need for concrete structures in the reactor building

• Lead forms non-volatile compounds with volatile fission products, such as iodine and caesium, reducing the radiological consequence of core damage.

The SEALER has a passive safety system, also known as “walk-away-safe”. This means that no external power or action is required to maintain safety. Its self-cooling function relies on the natural convection of lead for removal of decay heat. Due to lead’s high density, and the high difference in density between hot and cold lead, it is possible to achieve natural circulation in a very compact reactor vessel. Since the reactor vessel does not need to be pressurised, it can be much thinner than for water-cooled reactors (3 cm vs 15-20 cm). Also, the intrinsic radiation shielding of lead makes it possible to avoid constructing expensive and thick  concrete walls, as is the case for water-cooled reactors. 

A single SEALER unit would operate at a thermal power of up 150 MW, which can be converted to 55 MW of electricity. Alternatively, the heat can be used directly for production of biochar, bio-oil and syngas by pyrolysis of biomass, and/or to enhance the efficiency of hydrogen production by electrolysis.

A 12% enriched uranium nitride fuel with 40% higher content of uranium and seven times higher thermal conductivity than oxide fuel. The choice of this fuel permits to achieve a breeding ratio larger than one in a very compact configuration, minimizes the need for control rod assemblies and practically eliminates the potential for fuel melting.

Lead-cooled Fast Reactors (LFRs), such as the SEALER, require a higher level of uranium enrichment than traditional nuclear reactors. This is because the neutrons are not slowed down in collision with water molecules, which slims the chances of neutrons interacting with uranium nuclei. Therefore, we need a higher fraction of fissile material (U-235) to reach a self-sustaining fission reaction (i.e. criticality). The other side of that coin is that in fast reactors, the fission of U-235 releases more neutrons than in slow reactors. This in turn, means that neutrons not only sustain criticality, but also are able to produce new fissile material that can be used for further fission reactions. In simpler terms, the reactor creates new fissile material that can be recycled and used again. It enables the reprocessing of the spent fuel, making full use of the world’s uranium. This process makes it a breeder reactor, and means we can finally close the nuclear fuel cycle.

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