The UK regulator’s latest quarterly statement of its pre-licencing evaluation of the Westinghouse AP1000 and EDF/Areva EPR reactor has laid out how it plans to deal with unresolved issues that spill over beyond its stated deadline of June 2011.
The UK Nuclear Installations Inspectorate has stated that its target is a ‘meaningful’ generic design assessment of the two reactor designs by June 2011, at which point it would issue a so-called design acceptance confirmation (DAC). And the report again states that “we have not identified any showstoppers at this point.”
However it now seems to expect that the work will not in fact be finished by then. The quarter three 2010 report said: “Progress continues on the assessment, however, it is expected that some limited GDA work will be required by the RPs [Westinghouse and EDF/Areva] beyond June 2011 to address some of the issues arising, therefore it is looking more likely that we could issue an Interim DAC rather than a DAC in June 2011.”
Perhaps the two most significant barriers to finishing the process so far have been design queries flagged up as ‘Regulatory Issues’: the EPR’s control and instrumentation, and the design of the AP1000’s shield building. The report offers an update on both.
The EPR query related to concerns that the fully-digital safety system was not sufficiently separate from the control system, and both might be affected by common failures. The report seemed positive about resolving the issue, and stated [as of mid-October] that it had high hopes for technical meetings planned for late October. Nuclear Engineering International understands that EDF/Areva are planning to install a hardwired (analogue) backup of the control system.
The regulator seems to be more concerned about the Westinghouse regulatory issue, which relates to concerns about the construction method of a steel-concrete-steel sandwich design for the shield building surrounding the containment dome, and other site structures. The construction method is unusual in the UK, and regulators have requested evidence of the structure’s strength. Although the NII says that there is enough time left in the process, it said that delivering the required information ‘to time and quality, and subsequent assessment is becoming a significant challenge and represents a risk to completing a meaningful GDA for AP1000 by June 2011.’
It was not the NII’s only area of concern for the AP1000. Although it has not flagged the AP1000’s ‘complex’ control and instrumentation system as a regulatory issue, it said that a meaningful GDA depends on Westinghouse providing more technical information about the system and its safety case: ‘A failure to provide detailed design information (and hence safety arguments) within Step 4 timescales [the last stage of the GDA process] represent a considerable risk to the provision of an Interim DAC in June 2011,’ it said.
Furthermore, the regulator reports that it and Westinghouse have still not agreed on a design reference for the design, or how design changes are to be dealt with in the process. It called resolution of this issue ‘vital’ to meeting the June 2011 deadline.
During the July-September period, NII encountered delays in appointing technical support contractors to help with the work, and to provide expert input. These delays slowed progress, although it added that the problem was resolved, and delays should not prevent it from finishing on time.
In the report’s appendixes, the NII lists tens of areas that are at risk of becoming outstanding issues post June-2011. In the case of the EPR, examples include the assessment of the impact of internal hazards such as loads dropped from the polar crane, and structural integrity of primary circuit components, where the NII’s independent calculations of fracture analysis differ from EDF/Areva’s calculations. In the case of the AP1000, issues include internal hazards such as dealing with internal flooding, the criticality safety case for storage of fuel in the spent fuel pool, the gunpowder-equipped squib valves for safety valve actuation, and metrication—many of the AP1000 submissions have been in Imperial, rather than metric, units.
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