Austenitic stainless steels are used extensively as the main material of con­struction for process vessels and pipework. Much effort has been expended in defining the operating limits of these steels. After many thousands of hours of laboratory testing and decades of plant experience, it has been possible to define realistic and predictable corrosion rates before and after welding, cold working and hot working. The main advantages of austenitic stainless steels are their inherently high resistance to corrosion in oxidizing media such as nitric acid and the relative ease with which they can be decon­taminated. They also have excellent impact resistance down to sub-zero temperatures, they are readily available and are easy to fabricate and weld.

There are two main types of austenitic stainless steel used throughout a reprocessing plant (Baldev, 2006). The first is a special grade developed by British Nuclear Fuels Limited and the steel companies which has been given the name NAG (nitric acid grade) 18/10L (Merrill, 1990). NAG 18/10L is basically a 304L type stainless steel with reduced carbon levels and close control on residual elements to give improved corrosion resistance. Careful controls are also placed on the manufacturing and testing processes for this material and it can only be manufactured by a limited number of companies which have to meet stringent technical and quality assurance requirements. It is used on all high integrity nitric acid applications. The 304L grade is used for less arduous duties such as cladding, water jackets and low or non­active pipework and vessels.