Reactor pressure vessel
Russian Soviet era RBMK reactors have each fuel assembly enclosed in an individual 8 cm diameter pipe rather than having a pressure vessel.
In particular, the larger pressure vessel of the boiling water reactor is better shielded from the neutron flux, so although more expensive to manufacture in the first place because of this extra size, it has an advantage in not needing annealing to extend its life.
Both materials have main alloying elements of nickel, manganese, molybdenum, and silicon, but the latter also includes 0.25-0.45 wt% chromium.
Due to harsh conditions, the RPV cylinder shell material is often the lifetime-limiting component for a nuclear reactor.
In 2018 Rosatom announced it had developed a thermal annealing technique for RPVs which ameliorates radiation damage and extends service life by between 15 and 30 years.
[4] Due to the nature of nuclear energy generation, the materials used in the RPV are constantly bombarded by high-energy particles.
As previously mentioned, the chain reaction caused by a PKA often leaves a trail of vacancies and clusters of defects at the edge.
Examples of sinks, or thermodynamically favorable places for defects to migrate to, are grain boundaries, voids, incoherent precipitates, and dislocations.
The physical effect that can occur is that certain elements will be enriched or depleted in these areas, which often leads to embrittlement of grain boundaries or other detrimental property changes.
[6][8] It has been recognized that copper is the dominant detrimental element in steels used for RPVs, especially if the impurity level is greater than 0.1 wt%.
This is especially prevalent when a material is exposed to high stresses at elevated temperatures, because diffusion and dislocation motion occur more rapidly.
In the decohesion mechanism, it is thought that the accumulation of hydrogen ions reduces the metal-to-metal bond strength, which makes it easier to cleave atoms apart.
[6] The pressure theory is the idea that hydrogen can precipitate as a gas at internal defects and create bubbles within the material.
This can be done by adding grain boundaries, oversized solutes, or small oxide dispersants to minimize defect movement.
[5][6] By doing this, there would be less radiation-induced segregation of elements, which would in turn lead to more ductile grain boundaries and less intergranular stress corrosion cracking.
Attempts have been reported of instituting yttrium oxides to block dislocation motion, but it was found that technological implementation posed a greater challenge than expected.
[5] Further research is required to continue improving the radiation damage resistance of structural materials used in nuclear power plants.
Because of the extreme requirements needed to build large state-of-the-art reactor pressure vessels and the limited market, as of January 2020[update] there are only a handful of manufacturers in the world including:[9]
