Articles
There’s been talk for years of new nuclear power stations being built in Britain, but as yet no turf has been dug and no metal has been cut. That’s not to say that progress isn’t being made. It’s just that, with safety and security always the main priority, technical assessment of the two nuclear reactor designs under consideration takes immense time and effort.
That work is being carried out by the Health and Safety Executive (HSE) and the Environment Agency which together are charged with compiling the generic design assessment (GDA) of the safety cases for Areva’s UK European Pressurised Reactor (EPR) and Westinghouse’s AP1000. That work, which has been ongoing for the past couple of years, is expected to come to an end on 30 June, as long as some outstanding technical concerns can be overcome. Only then will what’s known as an Interim Design Acceptance Confirmation and Interim Statement of Design Acceptability be issued for both designs.
At this stage, the HSE says that it doesn’t expect there to be any “showstoppers” that might prevent the conclusion of the GDA process by the end of June. But the latest quarterly progress report shows that there are still specific technical questions to be answered on both the UK EPR and the AP1000. And it says that in some instances the quality of key information has not been of the standard it expects and there have been some instances of late delivery. These shortfalls of information have made it difficult for the GDA team to manage assessment of the designs within the decreasing time available, says the HSE.
On the Areva EPR design, there are outstanding issues in areas such as internal hazards, probabilistic safety analysis, control and instrumentation and electrical engineering. Civil engineering remains an area of intense activity and where there are significant outstanding issues. Remaining GDA issues include verification and validation of software packages used in the analysis and design of the nuclear island structures; computer modelling of the nuclear island structures; the layout, sensitivity and operation of containment instrumentation; and the design analysis of the containment.
The assessment of seismic analysis of the nuclear island structures is nearing completion. Progress on aircraft impact remains reasonable, says the HSE, and it has received the bulk of documents related to aircraft crashes, the original programme for which had slipped.
However there has been a concern over the ability to exchange information on security door design due to international security issues. There had been a hold-up in security classified information on aircraft crash and door design, which had made assessment difficult.
Meanwhile, the Westinghouse AP1000 design has its set of technical challenges that need to be overcome in areas such as reactor chemistry, radiation protection and structural integrity. In the complex area of fault studies, transient analysis and severe accidents, HSE says consideration was being given to the level of diversity required to protect against some faults and the consequences of single failures, and whether some additional control and instrumentation functions such as additional reactor flux trip protection, or some additional cooling systems functions, might be required.
In terms of mechanical engineering, the HSE says that Westinghouse had responded well to GDA issues across a number of areas. But issues remained: on the novel fast-acting squib valves featured within its design, more work was required on issues of maintenance and surveillance. There was also a requirement for the provision of adequate isolation and drainage arrangements.
Finally, there are mechanical engineering aspects to the topic of metrication that remained under discussion. The HSE says that further work was required in the area of pipe flanges, valves and bolting, where Westinghouse is currently proposing the widespread use of imperial fasteners.
The HSE says that the remaining volume of work to be completed is challenging and will require timely and in-depth responses from Areva and Westinghouse.
But it says: “Although there are a number of significant technical issues that remain to be addressed for both reactor designs, we remain of the opinion that both are capable of being shown to be acceptable in the UK.”