A US nuclear consultant engineer has criticised the Westinghouse AP1000 containment design, arguing that it could release radiation in case of a design-basis accident. Westinghouse has denied the claims.
“The steel containment in the AP1000 design has no backup secondary concrete containment behind it [as most existing US PWRs do] to capture post-accident radiation that leaks out,” said Arnie Gunderson, chief engineer, Fairewinds Associates. “Again, the problem with the AP1000 is that there is no backup system. Nuclear plants have been licensed under redundant safety features in order to protect public health and safety, and the containment redundancy is missing from the AP1000.”

He also said: “Research shows that there have been more than 80 documented problems with containment systems in the U.S. during the past 45 years. Four of these 80 cases have been through-wall rust holes that completely penetrated the steel containment liner. In 2009 alone, there were three significant containment problems on existing reactors” These were arough-containment hole at Beaver Valley, a 60-foot crack in Crystal River’s concrete containment and a snapped post-tensioned containment tendon at the unstarted plant Bellefonte.”

Instead of a containment building, the AP1000 design has a shield building that is vented to the external environment. In an emergency, the shield building draws in air through vents near the top of the structure, and sprays water on to the containment vessel from tanks stored in the roof. The water and air cool the containment vessel passively. Gases are vented out of a chimney in the roof of the structure.

Gunderson made two major criticisms with this design. First, he said that the hole in the roof is not filtered, and any leaking radiation is released directly into the environment.

Second, he says that the design of steel containment would be difficult to inspect for corrosion. He says, “This gap between the concrete shield building and the AP1000 steel containment allows for numerous locations where rust can develop on the steel containment. Moisture and corrosive agents can flourish in this gap outside the containment. Inspection of these inaccessible locations in the AP1000 is extraordinarily difficult to detect until the rust creates a hole completely through the steel. Due to the unique AP1000 design features, the likelihood of a hole caused by rust in the AP1000 containment is much greater than the rust holes that have already occurred in existing steel containment liners.”

Westinghouse has answered the criticism with a statement, backed up by a more detailed rebuttal, saying that it disagreed “completely and unequivocally with every conclusion that was put forward”, that the steel in question was 1.75 inches thick and very unlikely to corrode, that Gunderson’s assumed corrosion rate was not credible and that the criticism came from a source that was known to be anti-nuclear.

•In October last year the US Nuclear Regulatory Commission told Westinghouse that the proposed design of the shield building for the AP1000 (which protects the reactor’s primary containment from severe weather and other events) would require design modifications and testing to demonstrate that it would perform its intended safety function under design basis loads. But none of these modifications bore on the containment itself.

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