A liquid metal fast breeder reactor (LMFBR) is a nuclear reactor capable of producing more fissile product than it takes in. Breeders exhibit remarkable fuel economy compared to light water reactors.
Liquid metal use in fast breeder reactors has long been considered for the improvement of efficiency in their heat transfer systems. Work has been performed around the world on corrosion of sodium- and potassium-cooled fast breeder reactors.
The concept of LMFBRs has led to large-scale research and development programs. The result is a highly reliable knowledge related to liquid metal fast breeder reactors' corrosive behavior.
Liquid metal corrosion can be divided into several categories:
- Dissolution from a surface by direct dissolution
- Intergranular attack
- Impurity and interstitial reactions
- Compound reduction
- Surface reaction involving solid metal atoms and an impurity elements present in the liquid metal
Different compositions of metal and metal alloys lead to varied corrosive behavior. Rapid corrosion is seen during the primary period of exposure and reaches a steady condition as equilibrium is achieved on activity differences in the system depending on the combination of containment material and liquid metal or liquid alloy.
With a pure metal, surface attrition may proceed in an orderly, planar fashion, controlled by either dissolution or a surface reaction. For a multi-component alloy, selective loss of certain elements may lead to a phase transformation.
Three factors that should be evaluated collectively in a liquid metal system are:
- Surface attrition
- Depth of depleted zone for alloys
- Presence of intergranular attack
One important but overlooked aspect of liquid metal corrosion is deposition. By itself corrosion is not a major concern, because yearly maximum surface recession rates are in microns.
Formation of compounds in the circulating liquid metal and the accumulation of deposits in localized regions are serious problems. Hence, it is important to understand the relationship between liquid metal corrosion and fast breeder reactors.