The Nuclear Directorate of the UK Health and Safety Executive regulator has released two detailed interim technical reports of its pre-construction ‘generic design assessment’ of the Westinghouse AP1000 and Areva/EDF EPR reactors.
One query with the AP1000 relates to the containment building design
Both reports were broadly optimistic that both reactors would finish this first, general phase of the UK reactor licencing process by June 2011, although it would not guarantee there would not be further design changes needed.
In the so-called step 3 reports, it flagged up several technical issues with each reactor that will require further work. Kevin Allars, the UK Nuclear Installations Inspectorate’s director of new build, said that at the moment, Westinghouse has more to do than the Areva/EPR team, to pave the way for the next stage, site-specific licencing, in 2011 and beyond.
Two key technical issues in the AP1000 reactor revolved around the containment building and a particular type of emergency valve. The AP1000 design calls for a modular containment building made of a steel-concrete-steel sandwich structure. The ND contends that there is a lack of design code for the design, which therefore requires extensive evaluation and testing.
Another issue concerns a new type of fast-acting valve that is actuated by a gunpowder charge, called a squib, to release primary coolant in case of an overpressurisation. These valves have not been used in the UK, in nuclear, or at the scale required by the reactor, and so require additional analysis.
Allars said that a meeting between Westinghouse, the ND and the NRC in the USA in mid-November suggested that a way forward had been found to start to deal with both problems.
The ND also requires Westinghouse to supply more information about aspects of reactor design paperwork, including revising its external impacts analysis and the role of human factors in risk.
In response to the criticisms, Westinghouse has reorganised its balance of power to supply a greater corporate authority to the UK to facilitate the GDA process locally. That operation is headed up by Mike Tynan.
EPR
Earlier this year, the ND flagged an issue concerning the EPR’s instrumentation and control system; it was concerned that the reactor safety system, which shuts the reactor down in emergencies, was interconnected too tightly with the reactor control system that operates the reactor under normal conditions. The amount of interconnection between the two systems risks the possibility of a higher-than-expected failure rate, ND says.
Since then, EDF and Areva have since suggested a possible solution. The report summarises it: “They have proposed a way forward which includes provision of a non-computer based backup system, safety classified displays and manual controls in the control room, reduction of reliability claims for the computer based SIS and other measures such as one-way communication from high to lower classified safety systems. We anticipate that the proposed modifications will be acceptable, but we await the full details.”
In the interim report, the ND also said that more evidence is needed to prove the proposed use of prestressed tendons in the containment, on construction codes and external and internal hazards.
“I am confident that we can complete a meaningful GDA by June 2011,” Allars said in a press conference, adding, “I am particularly more confident because we now have the necessary resources to take the project forward.” He said that the next stage of the process, which examines the evidence for safety claims laid out in the reactor applications, would have to gain ground lost earlier in the process from inadequate staffing.
Robert Davies, Areva UK new-build director, said in a press conference that the UK licensing process, which deals with many difficult technical issues up front before construction begins, is a big departure from that used in building the UK’s fleet of AGR and Magnox reactors in the 1960s and 1970s. “It is an interesting process. This is the first time it has been done this way, the first time ever. The HSE has a policy of no surprises, which is not very nice at the time, but it is very nice at the end.”
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