Regulators are a step closer to approving the design planned for five nuclear reactors proposed in Florida.

In the past few years, the Nuclear Regulatory Commission flagged several problems with the design by Westinghouse that both FPL and Progress Energy want to use for their proposed reactors. The commission questioned whether the design could withstand hurricane-force winds or a plane crashing into it.

Westinghouse worked to fix the problems with its AP 1000 design and the Advisory Committee on Reactor Safeguards approved the design last week, saying the problems have been addressed. The 5-member NRC panel is expected to weigh the design in the coming months, with a decision expected by the end of the year.

"The agency has spent more than four years carefully reviewing the amended design, including taking significant time to ensure the amended shield building design meets appropriate requirements, as well as taking time to properly process thousands of comments on the proposed rule," said NRC Spokesman Scott Burnell.

Still, opponents of nuclear plant expansions aren't backing down on their concerns about the design and other aspects of the projects. They're holding a rally in Fort Lauderdale Saturday as part of a series of protests being organized in Florida and nationally. The rally is at 10 a.m. in Stranahan Park and will feature performances by poets and drummers and speeches by university professors and groups such as the Citizens Allied for Safe Energy and the Clean Energy Coalition. CASE will be collecting signatures to present at an Oct. 24 Public Service Commission hearing where regulators will decide whether to allow FPL and Progress to charge customers millions more for nuclear design and planning costs before the plants are approved.

Criticism of the AP1000 design is still fierce leading up to the NRC's decision on it. The sun’s heat in places like Florida could result in the structure buckling if there’s external pressure beyond what the Westinghouse building is designed to handle from an unexpected disaster such as an earthquake, according to a complaint filed by several groups opposed to new nuclear projects.

The AP1000 Oversight Group, the North Carolina Waste Awareness and Reduction Network, and Friends of the Earth noted the design includes a 7-million-pound water tank atop the building and overheating led concrete to buckle at several airports and bridges this summer and water pipes to burst open.

The groups said regulators are allowing Westinghouse to keep confidential its new calculations on pressure in the containment structures and they have not released a full report by one if their structural engineers, John Ma, who disagreed about the strength of the AP1000 design.

But the NRC's advisory group said Westinghouse tested a worst-case temperature of 117 degrees Fahrenheit and it also tested 129 degrees Fahrenheit to address concerns raised by the nuclear opponents.

The advisory panel said the results are acceptable: "Their stress analysis using this surface temperature showed that the solar gain has no significant effect on the load combination...and there is no significant reduction in the overall design margin,: it wrote. "This result is consistent with our expectation that any change would be relatively small...We therefore conclude that this issue can be considered resolved."

Westinghouse Spokesman Scott Shaw said the design is "highly robust and safe."

"The AP1000 is very likely the most closely scrutinized nuclear energy plant in history, now having undergone several years of exhaustive system and component testing, public debates, design reviews and multi-national regulatory oversight," Shaw wrote in an email. "Any concerns that Dr. Sterrett has currently raised or possibly raised in the past about the AP1000 were thoroughly examined by Westinghouse and others, and deemed not to be issues."

FPL Spokesman Mike Waldron said the design meets regulatory requirements after going through computer modeling and laboratory tests replicating "severe conditions associated with extreme events."