02.07.2009 Lauri Myllyvirta

Finnish and UK regulators have criticized the design of the control and instrumentation systems of the French EPR reactor, the first prototype of which has been under construction in Olkiluoto, Finland for four years. The Finnish regulator STUK said the present design does not fulfil "basic standards of nuclear safety". Both regulators stated that unless significant corrections are made, defects in the design will prevent the deployment of the reactor.

The electronic control systems are among the most vulnerable and crucial components of a nuclear reactor. They control everything in the reactor from pressure valves and pumps to control rods and emergency systems.

The main concern with the nerve center of the EPR is that the subsystems are interconnected in a very complex way and lower level subsystems are allowed to override higher level systems. Nuclear risk minimization stipulates that different subsystems need to be separated and failure of one subsystem should not render the whole system dysfunctional.

The fact that Areva and EdF, the companies building and marketing the EPR reactor, are again failing to meet basic nuclear safety requirements reflects three key problems with the reactor.

First, the design is extraordinarily complex and hard to implement, which makes it even more vulnerable to quality flaws and construction problems than earlier reactors. Second, the design is not finished and Areva is working under increasing pressure to fill in the missing pieces, which leads to substandard design.

Third, the fact that the Finnish regulator has only raised these concerns four years into construction, shows again that the reactor project has been allowed to proceed regardless of outstanding safety concerns. Scrutiny of key design features should take place before the construction permit is granted, in order to prevent commitment to choices that are not compatible with the eventual, approved design. The UK regulator has also raised the possibility of allowing construction of an EPR to start without resolving problems with the control system.

The French regulator, responsible for the oversight of the second iteration of the EPR, has been alarmingly silent. This raises stark questions about the level of scrutiny in the project.

Press communique from Finnish nuclear regulator STUK on the issue

Latest report of UK nuclear regulators on progress in licensing the EPR in the UK