Nuclear plant design needs blue sky approach

Designers of nuclear plants should have more responsibility over plant design throughout the operating lifetimes of all their reactors, according to a new study by a working group of the World Nuclear Association (WNA).

The WNA's working group on Cooperation in Reactor Design Evaluation and Licensing (CORDEL) promotes standardization of nuclear reactor designs on the merit of improved economics and safety. It suggests that stronger involvement of the original designers would bring widespread safety and economic benefits to the nuclear industry.

The new study – entitled Aviation Licensing and Lifetime Management: What Can Nuclear Learn? – was written by CORDEL's Design Change Management (DCM) Task Force. It compares the civil aviation industry's approach to managing changes to aircraft design with the nuclear industry's system of design change management. In the aviation industry, the original designer of a particular type of aircraft is always involved in the response to events and safety-relevant findings. In contrast, nuclear vendors do not have ongoing design responsibility for their reactors. This situation leads to differences between nuclear reactors of the same model.

In order to prevent marked differences in design occurring within a fleet of reactors, the DCM Task Force recommends that the benefits of standardization must be given full consideration in all design change decisions. "The vendor/designer should at least have an advisory role to ensure that important design improvements are implemented in all reactors of the same design around the globe," the report states.

A 2012 report by the DCM Task Force – Design Change Management in Regulation of Nuclear Fleets - noted that improvements to the emergency venting system in boiling water reactors with Mark I containment systems – the type of reactor that was involved in the March 2011 accident at Japan's Fukushima Daiichi plant – had been implemented according to the preferences of the individual operators.

Although the Fukushima accident was triggered by extreme events that were not considered in the design basis and subsequent modifications of the plant, the Task Force claims that this accident highlights the differences in the implementation of design changes such as upgrading the venting system. The Task Force acknowledges that every operator must have a sound knowledge and understanding of its plant; however, it claims the expectation that each utility should be the "design authority" for its plant could be both impractical and expensive.

Although some elements of voluntary coordination in the nuclear industry have been introduced by owners groups (which unite the vendor with the operators of nuclear units of the same design), the study points out that there is nevertheless no formal international system of design change management.

The DCM Task Force calls on the industry to move towards "stronger international cooperation of all stakeholders in a system of balanced and clearly attributed responsibilities." The civil aviation industry's system of international cooperation could serve as a model in this area, it suggests.

Researched and written
by World Nuclear News