Operation at steady full power, i.e. baseload operation, of nuclear power plants (NPPs) is
usually considered to be the most efficient use of capital investment. Therefore, design and
operation of most existing nuclear power plants (NPPs) are optimised to operate in baseload mode.
Recently, there is an increasing need to operate NPPs in non-baseload mode, specifically
performing frequency control and load following. These needs are typically due to a large nuclear
generating capacity, increasing share of renewable generation, deregulation or evolution of the
electricity supply systems and markets. Re-optimization of NPP design and operation for nonbaseload
(flexible) mode of operation necessitates operational, economic and financial
rearrangements to maintain the capital investment, in addition the adaptation of technical and
regulatory changes. This paper discusses the aspects of design or operation of NPPs in flexible
mode based on the existing knowledge and experience and it is primarily based on the recent study
that was prepared by the International Atomic Energy Agency (IAEA)
