Japan Steel Works
The number of companies that manufacture certain parts for nuclear reactors is limited, particularly the large forgings used for reactor vessels and steam systems. In 2010, only four companies (Japan Steel Works, China First Heavy Industries, Russia's OMZ Izhora and Korea's Doosan Heavy Industries) manufacture pressure vessels for reactors of 1100 MWe or larger. Some have suggested that this poses a bottleneck that could hamper expansion of nuclear power internationally, however, some Western reactor designs require no steel pressure vessel such as CANDU derived reactors which rely on individual pressurized fuel channels. The large forgings for steam generators — although still very heavy — can be produced by a far larger number of suppliers.