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U.S. NRC slams Westinghouse AP1000's flawed design

Nuclear Monitor Issue: 
#697
5987
06/11/2009
NIRS Southeast
Article

Two new reactor designs were forecast (at least in Europe and North-America) make the nuclear renaissance happen: the Westinghouse AP1000 and Areva’s EPR. The EPR-design, is as we all know, under heavy fire, and now also from the French nuclear regulator (see next article). But in the U.S., the AP1000-design is also running into all kind of problems with the Nuclear Regulatory Commission.

In a highly unusual move, on 15 October 2009, the U.S. nuclear regulator sent a key component of the Westinghouse AP1000 (not-yet-licensed) “standardized design” back to the drawing board. The NRC staff is quoted in a press release stating that the AP1000 “Safety Shield Building,” the outer structure surrounding the AP1000 containment, does not meet “fundamental engineering standards” with respect to design basis loads, as well as several other concerns not disclosed to the public.

The press release indicates, and a review of NRC documents confirms, that NRC had been raising issues with Westinghouse for more than a year. This move impacts 14 out of 26 currently proposed new reactor licenses in the US and throws the review schedule for reactor into the air.

The NRC October 15, press release states that NRC have been talking to Westinghouse regularly about the shield building since October 2008, and "we’ve consistently laid out our questions to the company,” according to Michael Johnson, director of the NRC’s Office of New Reactors. “This is a situation where fundamental engineering standards will have to be met before we can begin determining whether the shield building meets the agency’s requirements.”

The “Safety Shield Building” which surrounds the containment has several functions, among these to hold a large tank of water over containment so that in the event of an accident the water is dribbled over the surface of the steel containment dome (the so-called gravity-fed cooling). The AP1000 containment is a separate, inner structure made of 1 inch (2.54 cm) thick steel. This “passive” convection cooling of the containment surface is projected to lower pressure inside containment, in the event of a major core disaster. Given the weight of water, in two storage tanks of 70 cubic meters each, design basis loading is a serious concern.

The Safety Shield Building is three feet (91.4 cm) thick reinforced concrete, and is intended to protect the reactor from severe weather including tornado- hurled projectiles, hurricanes, earthquakes and air crashes. A somewhat more eerie function is to add shielding in the event of a severe accident; the new 1 inch steel containment does not provide sufficient mass to absorb gamma ray emissions after a major accident. In effect, the Safety Shield Building is a pre-installed “sarcophagus” (like at Chernobyl) which would provide some protection for emergency workers called to the site in the event of a meltdown. The structure, far from containment, also functions as a cooling tower for the melting core, sporting an air-circulation hole at the top.

Given how the US NRC embraced its mandate from industry and Congress to streamline the new reactor licensing process, rejection of a major component of a reactor that was previously certified as “standard” is a substantial departure from this regime. In an apparent attempt at cost-cutting, the new AP1000 version features modular construction – bringing prefab components to the site, rather than construction of the Safety Shield Building on-site from the ground-up. The difference in integrity between pouring concrete on the site and erecting “building blocks” is apparently substantial.

The NRC notified Westinghouse on 15 October in a letter, linked in the NRC news release, that ‘either a confirmation test or a validated (or benchmarked) analysis method” must be used to demonstrate that the “shield building” can survive design basis events. The letters state that the “NRC considers its review of the shield building, as proposed, to be complete” but affirms that a review of other parts of review, now in Revision 17, will continue and that a new review schedule for the “design certification amendment” had yet to be established.

Westinghouse, which is owned by Toshiba, has four AP1000s planned for China. Two nuclear utilities in the U.S. which are pursuing AP1000s are on the U.S. Department of Energy’s short list to receive federal loan guarantees to back private loans for construction. Given the news from the NRC about the design flaws in the AP1000 design, a number of U.S. public interest groups wrote to the DOE on 19 October, calling on a halt to the imminent issuance of “conditional” loan guarantees for the projects. They stated: "Given that the action by the NRC is so serious in nature, it is imperative that the Department of Energy immediately halt the issuance of any conditional loan guarantees to any utilities which are basing their plans on the AP1000 reactor design. Issuance of DOE loan guarantees at this time to companies which are considering a reactor which may well have serious design problems would not only heighten public concern about DOE’s regard of oversight of nuclear reactor safety but would also further call into question the methodology applied by the DOE’s Loan Guarantee Program (LPG) as it considers which reactor applications garner a loan guarantee subsidy.

That the LGP has been considering issuing loan guarantees to reactors that do not have final certification and also do not have construction and operating licenses is now clearly revealed to be an extremely risky approach. As we now see that it is far from certain if reactors or combined licenses will win regulatory approval, any move to now issue conditional loan guarantees is premature and opens DOE to justified criticism."

Given the serious issued now raised by the reactor regulatory agency itself, the public interest groups call on DOE to "immediately halt issuance of conditional loan guarantees and take action to publicly assure the public that this is the case."

Source: Tom Clements (FOE U.S.A.) and Mary Olson (NIRS Southeast)
Contact: Mary Olson, Nuclear Information and Resource Service (NIRS), Southeast Office. PO Box 7586, Asheville, North Carolina 28802, USA.
Tel: +1 828-252-8409
Email: [email protected]
Web: www.nirs.org

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