The UK’s nuclear safety and security regulator last week raised a regulatory issue against Westinghouse’s AP1000 nuclear reactor design, saying it was not satisfied that the modular construction methodology could protect the third-generation pressurized water reactor from severe weather or physical impact. The finding comes on the heels of a similar issue raised by the U.S. Nuclear Regulatory Commission (NRC).

As proposed by Westinghouse, the modular construction approach for the reactor design involves a sandwich of steel plates filled with concrete, rather than the more conventional reinforced concrete, which is strengthened with internal steel bars.

But the UK Health and Safety Executive’s Nuclear Directorate (HSE’s ND) said it is “not yet satisfied” that the steel-concrete-steel methodology, which would be used in some key structures, could hold up against severe weather or other external hazards. The ND said it has asked Westinghouse for better evidence to prove that the strength and durability of the structures have been justified.

According to the regulatory body, Westinghouse is now considering a number of possible solutions, such as “further analysis and testing and possible changes to the design.” The company reportedly intends to provide detailed proposals and supporting evidence by the end of October 2010.

The U.S. NRC raised similar concerns in October last year, when it told the Toshiba Corp. company that it had not “demonstrated… certain structural components of the revised AP1000 shield building [could] withstand design basis loads.” The shield building protects the reactor’s primary containment from severe weather and other events, but it also provides a radiation barrier during normal operation and supports an emergency cooling water tank.

Though the NRC would continue reviewing the remainder of the next-generation reactor’s design certification amendment application, it told Westinghouse in a letter that it expected the company to make design modifications and conduct testing to ensure the shield building design could sustain its safety functions. Completion of the AP1000’s certification review is expected by December 2010.

The AP1000 designs being developed for the UK and U.S. vary slightly, but the issues raised concerning the civil structures are similar. The UK’s ND said in a statement that it was working closely with the NRC “to ensure maximum leverage and harmonisation of outcomes.” Westinghouse would have to respond to each of the nuclear regulators to address their respective issues, but as the designs and issues are similar, it is anticipated that the solution will be similar, although not necessarily identical, the ND said.

The UK body stressed that by raising the issue, it does not deem the design unsafe. “ND is still assessing designs on paper, so any safety detriment is still in the design stage. The Generic Design Assessment (GDA) process ND is using is specifically designed to help it identify potential problems at the design stage, when a solution can be identified and implemented more effectively and efficiently. The fact that ND is identifying these issues so early in the development of these designs demonstrates that GDA is working.”

The HSE is reviewing AREVA’s design for its EPR alongside Westinghouse’s AP1000 design. Both assessments are expected to be completed by the end of 2011. AREVA received a similar warning last year about possible problems with its reactor over concerns that its operational systems had not been adequately separated from its safety systems.

French utility Electricité de France is looking to build the UK’s first new nuclear plant in years—an EPR, by 2017. AREVA has already suffered costly delays building the world’s first EPR in Finland, at Teollisuuden Voima Oyj’s Olkiluoto site. The Finnish utility now expects that project to be completed in 2012.

Sources: POWERnews, POWER, HSE, AREVA, Westinghouse, TVO