UK regulators query AP1000 ventilation system

28 June 2010

Nuclear regulators in the United Kingdom have questioned the design of the ventilation system of the Westinghouse AP1000 reactor design, which is currently undergoing a pre-certification design review called generic design assessment (GDA).

AP1000 diagram
AP1000 diagram

The query concerns one of two plant ventilation systems during normal operations. They do not relate to the containment ventilation system, but to the radiologically controlled area ventilation system (VAS), which serves other areas of the site. As this area is not generally expected to be contaminated with radioactivity, it is discharged untreated into the main plant vent. If radiation monitors in the VAS stream are triggered, the ventilation is diverted into the containment ventilation system treatment stream, according to a UK Environment Agency consultation document published in late June.

The issue may become a stumbling block for government's approval of the design. In the document, the Environment Agency listed this as one of three potential barriers to approval of the design. "We will apply a potential GDA issue to the radiologically controlled area ventilation system and any other ventilations systems [sic] where there is the potential for the release of radioactive wastes to the atmosphere which do not have passive HEPA filtration as part of the design".

The other two main issues it raised were how the reactor would be decommissioned, and how the spent fuel would be disposed. These same two issues were raised by the Environment Agency for the EPR, the EDF/Areva reactor also undergoing design review. Provided these points, and others (see factfiles below) were addressed, the Environment Agency would issue a so-called statement of design acceptability. (The Environment Agency consultation is open until 18 October; interested parties can respond to it by emailing

However, the UK's nuclear installations inspectorate, which is managing the pre-certification design review, had not flagged ventilation as a regulatory issue by late June, so that point may be relatively simple to resolve.

In its quarter one progress report, which was published late following the UK parliamentary elections, the NII said that some progress had been made on both of the two outstanding regulatory issues remain: EPR control and instrumentation computer software and AP1000 shield building design. Of the former, the potential interaction between the control system and safety system, it said: "EDF and AREVA have proposed modifications and we anticipate that these will confirm that an acceptable position can be reached for GDA." (NEI understands that EDF/Areva is planning to install a hardwired backup). Of the latter, it said that Westinghouse was planning to supply supporting evidence that its novel steel-concrete-steel design will be sufficiently robust in stages up to October 2010.

The NII reported that the process continued to proceed relatively smoothly on its goal to a final assessment by June 2011. It said that the biggest obstacle is receiving timely answers to its questions. It said: "In a significant number of technical areas, the detailed evidence we would require to resolve all our technical issues does not yet exist and this may result in issues that will not be fully closed-out by June 2011. However, as we have always said, for GDA to be successful our assessment must be meaningful, which means that the design companies must provide sufficient information for us to carry out a thorough and detailed assessment in all of the key technical topic areas."

It also said that it is currently working on a plan to enable construction of what will likely be the first new nuclear reactor, an EPR at Hinkley Point, to start construction in late 2012.

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