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Regulators raise questions on EPR design

Nuclear Monitor Issue: 
Rianne Teule, Greenpeace International Nuclear Campaigner

Both the Finnish and UK regulators have raised serious questions about the safety of the EPR reactor design. The regulator concerns come on top of already soaring problems in the EPR’s currently under construction in Finland and France. Rejection of design approval of the EPR in the UK would be a devastating blow to the French industry plans for nuclear expansion in Britain.

On 2 July, the Finnish regulator STUK (Radiation and Nuclear Safety Authority) has asked the Finnish operator TVO (Teollisuuden Voima Oyj) for further clarification of the overall design of automation systems (Instrumentation & Control systems, I&C) for the Olkiluoto-3 reactor. The I&C system, sometimes described as the ‘cerebral cortex’ of a nuclear reactor, governs computers and systems that monitor and control the reactor’s performance.

Already in summer last year, STUK demanded that TVO would revise the architecture of the plant’s automation systems, because of safety concerns. Their main point of concern was the mutual independence of automation system components that back each other up. TVO has submitted a revised plan, but so far did not answer STUK’s worries. For Jukka Laaksonen, director general of STUK, getting the instrumentation and control right is absolutely critical to the safety of the plant.

In the beginning of July, the UK Nuclear Installations Inspectorate (NII) published a letter from April 2009, sent to Areva and EDF, the French companies that jointly applied for a ‘generic design acceptance’ (GDA) for the construction of  EPR’s in the UK. The NII has concerns similar to STUK’s, about the instrumentation and control system of the EPR.

According to the regulators, two independent computer-based systems would have a ‘high degree of interconnectivity’. Several automation system components, that are supposed to back each other up, are mutually dependent. This compromises the overall safety of the systems. The NII letter to Areva and EDF also highlighted concerns about the absence of safety display systems or manual controls that would allow the reactor to be shut down, either in the station’s control room or at an emergency remote shutdown station.

STUK has required a hardwired backup system for the I&C, but until now has not been satisfied with the hardwired system Areva has proposed. It requires a more complete hardwired safety system, including more functions, more signals and more measurements. But even that hardwired backup will still rely on software whose reliability may be difficult to demonstrate.

The French nuclear safety authority ASN is currently reviewing the EPR I&C design and expects to publish an opinion in September or October of this year. Flamanville-3 does provide for a hardwired reactor shutdown option, but this is less developed than the system STUK is demanding. ASN apparently doubts the need for a more complex hardwired system. According to ASN, I&C systems built for different operators could differ, to comply with the various regulator’s views. However, if there are differences, “we have to understand why”, according to ASN Chairman Lacoste.

The UK Health and Safety Executive, which oversees the NII, warned that the EPR design could be rejected for use in Britain if the concerns regarding the automation system could not be satisfactorily addressed. It is likely that the regulatory concerns will cause the design assessment phase to be seriously delayed. The UK design approval is critical to EDF, who wants to build four EPR reactors in Britain. Last year it spent more than BP 12 billion (14 billion Euro or US$ 20 billion) acquiring British Energy, the UK nuclear generator, to secure access to suitable sites.

In a reaction, Areva stated that the company is committed to ensuring the safety of the EPR’s and is confident to find a solution that will satisfy UK’s specific requirements. The French company blames the Finnish regulator for being slow in approving design documents, and hence being partly responsible for the currently 3-year delay in the Olkiluoto-3 project.

Meanwhile, STUK is still awaiting a report from Areva on the causes of cracking in two of three primary coolant piping hot legs, the most important pipes in the reactor from a safety point of view, that were recently welded in France. STUK wants to know the safety implications of a potentially undiscovered crack. Unlike previous French reactor designs, for the EPR the safety of high-pressure main steam lines relies on so-called break preclusion, meaning the piping needs to be so robust that a break in the main steam line can be excluded as a design-basis accident.

Sources: “UK regulator raises French nuclear concerns”, The Times, 1 July 2009 / “Nuclear dawn delayed in Finland”, BBC News, 8 July 2009 / “Finnish, UK regulators seek changes in EPR I&C design”, Nucleonics Week, 9 July 2009 / “STUK official ‘cautiously optimistic’ on Olkiluoto-3 I&C design approval”, Nucleonics Week, 21 May 2009
Contact: Rianne Teule, Greenpeace International, Ottho Heldringstraat 5, 1066 AZ Amsterdam, The Netherlands.

Tel: +31 20 718 2229