When the first- and second-generation nuclear power plants were built, they mostly came from integrated suppliers such as Westinghouse in each country, who required little from external suppliers.  Today most of a new plant comes from a range of international suppliers, and vendor companies such as Westinghouse are focused on design, engineering and project management.  There is demand from customers for maximum local supply, which often means a high level of technology transfer.  Westinghouse’s readiness to transfer the technology for its AP1000 to China was a major factor in its selection.

For very large generation 3+ reactors, production of the pressure vessel requires, or is best undertaken by, forging presses of about 14-15,000 tonnes capacity which accept hot steel ingots of 500-600 tonnes.  These are not common, and individual large presses do not have high throughput – about four pressure vessels per year appears to be common at present, fitted in with other work, though the potential is greater than this.  Westinghouse was constrained as of 2009 in that the AP1000 pressure vessel closure head and three complex steam generator parts can only be made by JSW.  Areva has a little more choice.

Reactor vendors prefer large forgings to be integral, as single products, but it is possible to use split forgings which are welded together.  These welds then need checking through the life of the plant.  Also, whereas Generation II reactors might require some 2000 tonnes of forgings, EPR and AP1000 units require about twice the amount.

Westinghouse says that the minimum requirement for making the largest AP1000 components is a 15,000 tonne press taking 350 tonne ingots.

The very heavy forging capacity in operation today is in Japan (Japan Steel Works), China (China First Heavy Industries and China Erzhong) and Russia (OMZ Izhora).

New capacity is being built by JSW and JCFC in Japan, Shanghai Electric Group (SEC) and subsidiaries in China, and in South Korea (Doosan), France (Le Creusot), Czech Rep (Pilsen) and Russia (OMZ Izhora  and ZiO-Podolsk).

New capacity is planned in UK (Sheffield Forgemasters) and India (Larsen & Toubro, Bharat Heavy Electricals, Bharat Forge Ltd).  In China the Harbin Boiler Co. and SEC subsidiary SENPE are increasing capacity.

Nothing in North America currently approaches these enterprises.* The changed position of the USA is remarkable. In the 1940s it manufactured over 2700 Liberty ships, each 10,800 tonne DWT – possibly pioneering modular construction at that scale (average construction time was 42 days in the shipyard). In the 1970s it had a substantial heavy infrastructure, but today China, Japan, South Korea, India, Europe and Russia are all well ahead of it. Steelmaker ArcelorMittal, based in Luxembourg, now owns the US company which built most US reactor pressure vessels in the 1970s-1980s.

* In the 1970s, requirements were more modest: both US Steel and Bethlehem Steel had 8000 tonne presses and could handle 300 tonne ingots.  US forging capacity has not been significantly upgraded since, partly due to lack of integration with steel mills and melt shops to supply the hot steel as 600-tonne ingots.

However, another development is Westinghouse going upstream and setting up factories in USA and China to produce modules for AP1000 reactors.  In the USA Global Modular Solutions, a joint venture with Shaw Group, has built a large factory in Louisiana.  In China a similar factory was opened in July 2008 by Shandong Nuclear Power Construction Group, apparently with 64% held by SNPTC and 29% by CNEC.

Suppliers of nuclear equipment must be qualified and quality controlled.  The American Society of Mechanical Engineers (ASME) nuclear accreditation known as N-stamp is internationally recognized.  N-stamp means that the authorized vendor has produced the commercial nuclear-grade components in accordance with the ASME Boiler and Pressure Vessel Nuclear Codes and Standards.  It applies to both design and fabrication of components.  RCC-M is another international standard developed in France and used outside the USA for nuclear mechanical and pressure components. For China, NNSA registration is linked to US NRC standards, though both ASME and RCC codes are used.  ISO-9001 is increasingly important.

A further issue emerging with manufacturing is metallurgy. Generation III+ plants can use existing metal alloys, but Gen IV plants operating at higher temperatures will require new materials, which will need a long (eg 15-year) lead time to develop. At 700ºC degradation problems are much more severe than at today’s operating temperatures.

Large nuclear power plants 1,000MWe+ usually have low-speed (1500 rpm) turbines, such as Siemens Arabelle, which are more reliable and efficient.  The generators however are heavier than those with the 3000 rpm turbine, and the price is also higher.

from: http://www.world-nuclear.org/info/inf122_heavy_manufacturing_of_power_plants.html