The Finnish nuclear regulator has said that it is satisfied with the modifications proposed for the design of the control and safety systems of the Areva EPR under construction at Olkiluoto, but clearer documentation on the independence of the systems must still be provided.
Reactor designers need to maintain independence between routine control systems and the systems that maintain safety in unusual conditions. This is because some of the safety systems protect against the failure of instrumentation and control (I&C) systems and for that reason it should be impossible for them to fail together.
|The state of the construction at Olkiluoto 3 at the end of May(Image: TVO)
In November 2009, a joint statement from UK, Finnish and French nuclear safety regulators urged Areva to revise control systems for its EPR design. The statement said: "The EPR design, as originally proposed by the licensees and the manufacturer, Areva, doesn't comply with the independence principle, as there is a high degree of complex interconnectivity between the control and safety systems."
This meant Areva had to do a certain amount of revision on the systems to establish sufficient independence while still meeting the varying requirements of the three countries. This is made more difficult for the EPRs in advanced stages of construction in Finland and France, while the UK and US regulatory systems require all studies be complete before construction begins.
The Finnish radiation and safety authority, Stuk, which first raised queries about the EPR's systems in December 2008, has now reviewed technical plans submitted by Teollisuuden Voima Oyj (TVO) concerning the control and safety systems of Olkiluoto 3. It concluded that "no notable change" would foreseeably be needed for the planned design.
However, whilst noting that considerable progress has been made in the design of the systems, Stuk said that it "has requested TVO to update the reviewed documentation in such a manner that it provides the necessary initial information of detailed system design in an unambiguous format."
In particular, Stuk requested that "the principles of securing the mutual independence of systems backing up each other are defined clearly enough."
The EPR under construction at Olkiluoto is expected to be changed to include a separate analogue back-up system in addition to the current digital I&C set-up. This could be an option for the specific model under construction at Flamanville in France and planned for the UK, and British regulators have previously suggested this to Areva. In Britain, the issue could lead to the exclusion of the instrumentation and control system from EPR's Generic Design Acceptance, meaning that a separate licensing process would have to take place for a new control and safety solution.
Construction on two EPRs at Taishan, China is in the early stages with Chinese authorities likely to follow the French regulators. American regulators have not made any public statements on the issue and continue to study the design for future deployment.
Researched and written
by World Nuclear News