Abstract:
Materials play a crucial role in the economic competitiveness of electricity produced from fast reactors.
It is necessary to increase the fuel burn-up and design life in order to realize this objective. The burnup
is largely limited by the void swelling and creep resistance of the fuel cladding and wrapping materials.
India’s 500 MWe Prototype Fast Breeder Reactor (PFBR) is in advanced stage of construction. The major
structural materials chosen for PFBR with MOX fuel are D9 austenitic stainless steel as fuel clad and wrapper
material, 316LN austenitic stainless steel for reactor components and piping and modified 9Cr-1Mo
steel for steam generator. In order to improve the burnup, titanium, phosphorous and silicon contents
in alloy D9 have been optimized for decreased void swelling and increased creep strength and this has
led to the development of a modified version of alloy D9 as IFAC-1. Ferritic steels are inherently resistant
to void swelling. The disadvantage is their poor creep strength. Creep resistance of 9Cr-ferritic steel has
been improved with the dispersion of nano-size yttria to develop oxide dispersion strengthened (ODS)
steel clad tube with long-term creep strength, comparable to alloy D9 so as to achieve higher fuel burnup.
Improved versions of 316LN stainless steel with nitrogen content of about 0.14 wt% having higher creep
strength to increase the life of fast reactors and modified 9Cr-1Mo steel with reduced nitrogen content
and controlled addition of boron to improve type IV cracking resistance for steam generator application
are other developments being perused towards improving the economic competitiveness of fast reactor
technology.
