The UK nuclear regulator said that its concerns with Westinghouse’s AP1000 shield building design are an issue that could prevent the reactor from being licenced in the UK. The design is being reviewed in a pre-construction approval process called the GDA (the generic design assessment).

The regulator, the UK health and safety executive’s nuclear directorate (ND), said:

“Westinghouse is proposing to use a new construction methodology for key structures within the nuclear Island, essentially using a sandwich of steel plates filled with concrete, rather than using more conventional reinforced concrete, which is strengthened with internal steel bars.”

Westinghouse said that it changed the original reinforced concrete shield building in response to the NRC’s enhanced aircraft impact standards. The new shield building consists of reinforced concrete and steel concrete composite, according to a December 2009 presentation.

The UK regulator continued: “This is new and we need to be reassured that key structures would be sufficiently robust to protect the reactor’s safety systems under normal conditions, and also from severe weather and other external hazards, such as physical impacts.  In order to get that reassurance, we need to see appropriate evidence to demonstrate the strength and durability of the structures. In essence, we want to be assured that the structure will hold together.

“The fact that we have issued a regulatory issue does not mean that the design is unsafe – ND is still assessing designs on paper, so any safety detriment is still in the design stage.”

“Westinghouse is considering a number of possible solutions, such as further analysis, testing and possible changes to the design, and intend to provide detailed proposals and supporting evidence by the end of October 2010.”

The construction of the shield building is also being examined by the Nuclear Regulatory Commission in the USA. In October 2009, the NRC issued a letter requesting more tests to prove that the containment structure would work in the event of a design-basis event (DBE), according to a Westinghouse presentation in December 2009. It said it is planning to provide data and revised technical reports to the NRC in February, March and April 2010.

The UK regulator said that as its concerns were similar to those of the USA, it expects that Westinghouse will aim to make the same kinds of modifications as in the USA.

Mike Tynan, Chief Executive of Westinghouse UK, commented: 

“The Regulatory Issue is further evidence of the level of scrutiny which is – quite rightly – being applied by the regulators to the proposed reactor designs. We are pleased that the regulators have confirmed they do not see this – or anything else – as a likely “showstopper” to the AP1000 being licensed in the UK, but we recognise that there is a significant amount of work which needs to be done before we can achieve a positive outcome to the Generic Design Assessment process. 

“The matters highlighted in the Regulatory Issue are not new and we have been working with the regulators for some months towards a plan to provide them with the assurances and information which they need. That plan is reflected in the timescales set out in the Regulatory Issue actions. We remain totally committed to resolving these – and all other – concerns so that a meaningful GDA outcome can be achieved in mid-2011.”

It is the second regulatory issue raised in the UK against the AP1000; the first related to a lack of information about waste strategy, site descriptions, dose assessments and other issues, and was resolved in 2008.

Late in 2009, the UK GDA process moved into its final stage, which involves detailed review of the evidence of safety claims made by the reactor vendors. Only two reactor designs are currently being reviewed in this process: the AP1000 and the Areva/EDF EPR.