AP1000: making the passive plant a reality in China1 April 2010
AP1000 construction projects in China are demonstrating the benefits of having a very high degree of modularisation.
As well as passive safety, compactness and a reduced number of components, the Toshiba/Westinghouse 1100 MWe AP1000 “Generation III+” pressurised water reactor also boasts a high degree of modularisation and promises fast building times among its attractive features.
The first AP1000 projects, which will employ MHI steam turbines, are now underway in China: Sanmen 1 & 2 (Zhejiang Province) and Haiyang 1 & 2 (Shandong Province). These are providing an opportunity to see how AP1000 construction aspirations match up to reality, and the early indications are encouraging, although the projects have a long way to go yet, of course.
Historically, construction performance has not been one of the nuclear industry’s strong points, notably in the USA and Europe - and the Finnish EPR experience at OL3 is not helping. On the other hand the Asians can point to some very impressive projects, for example 1350 MWe ABWRs in Japan built in about 38 months, from first concrete to fuel loading (with, interestingly, Toshiba very much involved as a BWR licensee of GE).
The fact that there are also EPRs now under construction in China (Taishan 1 and 2) will in addition provide some very illuminating comparisons with the AP1000. The EPR has been described in construction circles as “stick built” compared with the highly modularised AP1000.
China’s constantly expanding nuclear ambitions also create a great opportunity for learning by doing. The Chinese government plans to increase the country’s installed nuclear power capacity almost ten-fold by 2020, to around 80 GWe, superceding the 40 GW announced in 2008, and the 70 GW target of earlier this year.
The Sanmen and Haiyang sites, both coastal, are each able to accommodate at least four more AP1000 units, in addition to the two at each site already under construction, while further AP1000 projects are planned for inland sites – creating the opportunity for a real learning curve, which is already providing benefits.
It is estimated that the AP1000 should eventually achieve a construction time (first permanent concrete to fuel loading) of as little as 36 months. But the schedule for the first four units in China – which are also the first AP1000s to be built anywhere – is understandably somewhat more leisurely than this, 50 months from first concrete to fuel loading, with the first, Sanmen 1, due to enter service in November 2013, followed closely by Haiyang 1, in May 2014 (see diagram above).
Contracts for Sanmen 1 & 2 and Haiyang 1 & 2 were signed between Westinghouse Electric Company and its consortium partner, the Shaw Group, and China’s State Nuclear Power Technology Corporation Ltd, Sanmen Nuclear Power Company Ltd, and Shandong Nuclear Power Company Ltd, in July 2007.
At Sanmen, which is located about 200 miles south of Shanghai, excavation for the nuclear island of unit 1 started as planned in February 2008.
The construction permit was issued on 26 March 2009, following submission of the PSAR (preliminary safety analysis report) and provision of acceptable answers to the more than 2000 questions posed, allowing construction proper to start, “first concrete.”
Placement of the nuclear island basemat concrete was successfully completed on 31 March 2009, exactly as scheduled. This involved a continuous pour of nearly 5000 cubic meters of concrete over a period of about two days. During the excavation and rebar placement period, the China-based module factory (at Haiyang) started construction of the early major modules, as well as the bending and forming of the containment vessel bottom head plates. These 64 plates are welded together to form a hemisphere of about 130 ft in diameter.
The extent of modularisation was demonstrated in June 2009 when the China project team sucessfully set in place a large structural module named CA20, consisting of two sections of the auxiliary building comprising plant and equipment for spent fuel storage and handling, a heat exchanger, and waste collection equipment. The CA20 module is approximately 14 m wide, 20.5 m long, and 21 m high; equivalent in height to a five-story building. This 750 t module was lifted and set in place using an immense Lampson crawler crane (LTL 2600), currently the largest mobile heavy-lift crane in the world.
The fabrication and welding of the containment vessel bottom head for Sanmen unit 1 has also been completed and the bottom head was lifted into place on 21 December 2009, another major milestone achieved.
Other significant modules, including the reactor vessel cavity (CA04), steam generator and refuelling canal module (CA01) and the access tunnel and walls module (CA05) have also been fabricated.
CA04, the reactor vessel cavity module, was set in place on 26 January 2010, along with other smaller modules, while the CA05 module was set in place on 28 February 2010.
The containment vessel first ring was set in place in March 2010, while placing of the CA01 module was expected at the end of March 2010.
The remaining 2010 milestones for Sanmen unit 1 include setting the remaining containment vessel rings, 2, and 3, and transitioning from civil and structural work to bulk installation.
In fact, by the end of 2010, approximately 50% of the bulk materials will be installed within the first Sanmen containment building.
This rate of progress is necessary to enable installation of major equipment such as the pressuriser and steam generators in 2011.
Concurrently, excavation and preparations for Sanmen unit 2 were completed.
Pouring of the Sanmen 2 nucler island basemat was completed on 17 December 2009, another major milestone achieved on time. Some 5156 m3 of concrete were placed within 42 hours, 7 hours less than the originally planned duration. Placement of the basemat will allow the setting of the containment vessel bottom head, modules CA20, CA01, and CA04, and the containment vessel first ring; all in 2010.
At Haiyang, on the Shandong peninsula about 100 miles northeast of the Chinese coastal city of Qingdao, the nuclear island basemat was successfully laid via one monolithic concrete pour over two days, 24-26 September 2010, repeating the success achieved at Sanmen. This was immediately after issuance of the construction permit, on 23 September, which followed the PSAR.
Containment vessel bottom head plate forming and bending is underway for Haiyang 1 and the CA20 auxiliary building module was set in place in January 2010.
Milestones in the first half of 2010 for Haiyang unit 1 include the placement of the containment vessel bottom head and the other major modules mentioned previously, as well as the setting of the containment vessel first ring.
Lessons learned and early ordering
A formal programme is in place for capturing lessons learned and ensuring they are implemented. This makes sure that Haiyang construction and manufacture benefit from the Sanmen unit 1 experiences. The China project team also employs a formal risk management process, complete with an action tracking risk mitigation process.
Among the benefits already derived from the lessons learned programme are the following:
• Nuclear island basemat at Haiyang 1 and Sanmen 2 laid in less time than Sanmen 1.
• Ultra-large steam generator and reactor vessel forging lead times reduced for the third and fourth units.
• CA20 (auxiliary building) module fabrication for Haiyang 1 took far less time than that for Sanmen 1.
• Containment vessel bottom head fabrication for Haiyang 1 took far less time than that for Sanmen 1, with the welding carried out in a fully enclosed building.
Early ordering of long lead materials and items of equipment started immediately after the agreement on a framework contract in February 2007. Early ordering is particularly important in the case of large forgings, such as those associated with steam generators and reactor vessels, where a limited capacity of supply can influence the achievement of an overall schedule due to critical path equipment delivery dates.
Currently, nearly all Westinghouse major purchase orders are complete, with the exception of instrumentation and control equipment, and spares. Orders placed include those to Doosan for reactor vessels, steam generators, and integrated reactor vessel head packages, and to Curtiss-Wright EMD for canned motor reactor coolant pumps. Other orders placed include: RCP variable frequency drives; control rod drive mechanisms; polar cranes; containment vessels; passive residual heat removal heat exchangers; reflective metal insulation; and valves.
Fabrication of the primary components for China’s first four AP1000 nuclear power plants is a global undertaking, covering North America, Asia, and Europe.
Major items such as the steam generators, reactor vessels, fuel handling equipment, and heat exchangers are at an advanced stage of manufacture.
The control rod drive mechanisms have passed their lifetime tests, and equipment qualification is underway for all safety valves.
Testing time for pumps
The canned motor reactor coolant pumps are undergoing development testing and “design refinements” have been introduced, requiring additional testing (see panel, left). But the additional testing is not expected to have any impact on the overall timetable for the Chinese units, as there is excess time built into the schedule, Westinghouse says.
The canned motor pumps, which are integral to the steam generator channel heads, have not been previously used in a civil nuclear application, but have been employed, at smaller scale, in other applications.
Interestingly, there is a possible alternative to the Curtiss-Wright design, a pump employing a “wet winding” motor developed by KSB of Germany. Westinghouse has been working with KSB on this since about 2004 in the interests of diversifying the supply chain.