Aircraft impact modelling for nuclear structures, UK

The 9/11 attacks in 2001 highlighted the potential for aircraft to be used deliberately to harm buildings and infrastructure. And with an ever-rising number of flights, the risk of accidental impacts was rising.

We carried out an aircraft impact analysis using detailed finite element approach that was a first in the UK nuclear industry. It provided our client CGN with data to produce a more efficient and cost-effective structural design, improving constructability as well as enhancing safety.

Opportunity

The Office for Nuclear Regulation and the Environment Agency use a generic design assessment process to scrutinise the safety, security, and environmental protection aspects of new nuclear power plant designs in the UK.

Aircraft impact hazards (accidental and malicious) often dictate the civil design of new nuclear facilities, particularly the reactor shells and safety critical facilities. An overly conservative definition of aircraft impact threat could result in significantly increased construction costs, while under-estimation could have safety implications.

Solution

We provided design assessment of a new nuclear structure, considering its performance when subjected to impact by different types of aircraft including military and commercial planes. We moved away from generating load time functions using conventional semi-empirical approach to adopting missile-target interaction analyses, which required detailed finite element models of the aircrafts as well as the nuclear structure.

Finite element modelling has always been a challenge, especially for structures with complex geometry. We developed a series of automated tools which not only allowed us to quickly re-analysing various impact scenarios effectively but also ensuring that the work undertaken can be verified efficiently with clear auditable trails.

Our work assessed the response of the structure as well as the plant and equipment housed within it. We looked at the forces generated by the impact, for the first time recognising and modelling the energy dissipation resulting from deformation of the aircraft as well as of the structure.

Outcome

The level of detail of our analysis was unprecedented in the UK nuclear industry. The outcome of our approach allowed the design to be optimised, which reduced the overall costs of the project at the construction stage and also improved constructability and hence safety during construction.

The approach has since been accepted and commended by the Office for Nuclear Regulation, the UK's independent regulator for the nuclear industry with legal authority for nuclear safety and security, as well as conventional health and safety at all licensed sites.