AP1000 (Westinghouse), EPR (AREVA), and APWR (Mitsubishi) use pretty much the same technology as Gen 3 plants, and in fact the reference fuel designs are those in current operation (17x17 with 9.5mm cladding OD). Fuel cladding, spacer grid and guide tubes are still Zr alloys, nozzles are still SS304 or derivative, and springs are still Inconel (usually 718). The core operating conditions are much the same as current PWRs, but AP1000 is rated with the highest duty PWRs, currently Braidwood, Byron and Vogtle. The EPR and APWR have lower core average LGHRs.
All three PWRs use 14-ft fuel, althought EPR and APWR are designed with a 13.8 ft (4.2 m) active fuel length. The AP1000 is designed 157 assemblies while EPR has 241 (like Palo Verde) and APWR has 257 assemblies. Larger (wider) cores may be more susceptible to flow-induced vibration, which may increase the potential for grid-to-rod fretting.
AP1000 has a thermal rating of approximately 3400 MWt and that is the nominal output of a standard W 4-loop NSSS with 193 assemblies and 12 ft (3.66 m) active fuel length.
The ABWR (GEH and Toshiba) is an extension of current BWR/6 technology, and the major innovation is the location of the recirculation pumps inside the pressure vessel as opposed to the jet pumps. ABB and Siemens introduced internal recirc pumps in their most modern designs which are currently operating.
The ESBWR is an innovative design that extends the height of the PV and exploits the difference in density of the coolant water in the annulus and the core to produce natural convection, although the feedwater system does still use forced (pumped) flow.
The Gen IV systems, which use water coolant, are considerably different. For example, the SWR (Superheated Water Reactor) necessarily uses higher pressure because of the superheat.
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Here's an abstract of an upcoming paper that would be worth getting.
Contributions from Service Experience with Failure Investigations and Age Related Degradation Mechanisms in the Materials and Manufacturing Selection for the New AP1000 Nuclear Power Plant Design
Gutti Rao, Cynthia M. Pezze, Westinghouse Electric Co.
The evolution of the Westinghouse AP1000 Nuclear Power Plant design is based on careful evaluation of failure investigations and assessment of mitigating approaches to potential material degradation issues based on nearly 40 years of operating plant experience. The purpose of the current paper is to review key component material degradation issues based on metallurgical investigations, and discuss the remedial actions and improvements implemented to mitigate the issues. Westinghouse has reviewed specific aging degradation mechanisms and operating experiences to assure lessons learned are effectively factored into the AP1000 design. On this basis, it was determined that most agingrelated degradation has been accounted for in the AP1000 design and selection of materials and processes. Ongoing successful usage of these materials in existing plants supports confidence in their similar application in the AP1000 design.
This paper provides a summary of key considerations and AP1000 attributes. Mechanisms of degradation considered will include environmentally induced, fabrication process induced, mechanically induced, and radiation induced conditions. The features of the AP1000 design, material selections, manufacturing process, and fabrication that mitigate degradation will be summarized.
Design enhancements discussed will include elimination of susceptible materials by replacing with proven and superior materials; innovative approaches in fabrication technology to prevent sources of degradation; and improvements in diagnostic techniques.
To be presented at the Charles R. Morin Memorial Symposium on Failure Analysis & Prevention
ASM International, MS&T '09, Pittsburgh, Oct 25-29, 2009
