The nuclear industry is aiming to replicate the blueprints and approach to constructing nuclear power stations in the UK and other parts of the world to cut costs and boost timescales. Yet, no matter what the location of a new reactor, nuclear ready concrete has clear and exacting requirements, says Will Pearson, nuclear commercial director at Tarmac.
Concrete is part of the critical path to delivering a new generation of UK nuclear reactors which are essential to meeting both current and future energy needs, ensuring energy security, and supporting the transition to net zero.
The selection and specification of the material will also ultimately play a key role in the long-erm safety, security and performance of the plant.
Nuclear concrete structures are required to undertake a radiation shielding and secondary containment role in addition to their structural performance. Much of this concrete will become inaccessible once the plant becomes operational. The material must therefore be able to perform for the whole lifecycle of the station (up to 60 years) and the quality of the concrete must be assured.
Failure to deliver a consistent, high-performance supply of concrete, in large volumes and to precise specifications, can have significant implications for the cost and timings of new build programmes. There is no margin for error.
To reduce the risks of defects in concrete, there are some key requirements for nuclear ready supply. Product and constituent material traceability at every stage of the lifecycle and long-term quality records for the material and production process are essential.
This is not just a technical requirement, but a cultural one too. In line with all aspects of nuclear operations, organisations involved in the supply of material must embrace the principles of nuclear safety within their businesses. Everyone involved must understand the critical nature of the work they are delivering.
From a materials perspective, this is about being able to trace each stage of the extraction and manufacturing process – from reviewing the geological data at the quarry through to blasting, crushing, screening and washing of the aggregates and then transporting the material to site. It requires tight auditing and stringent controls over selected raw materials and a management system that delivers ongoing inspection and validation.
During construction, concrete will need to possess the required workability and fluidity to be pumped over long distances and for long periods of time whilst retaining the cohesion properties. For example, the construction of the raft for the nuclear reactor foundation is likely to require a concrete ‘peak pour’ on a nuclear project which could require a continuous supply of concrete for 70 hours or more.
The reactor building will demand a high-strength and dense concrete that can deliver the structural resilience required to contain and protect the reactor. This concrete mix and process is carefully designed to ensure the thermal behaviours of the concrete can be controlled keeping the overall temperature of the material low.
As well as delivering continuous volumes at these exacting specifications, there is, of course, a real need to deliver the lowest carbon concrete possible. Identifying an optimised mix that balances sustainability, and performance requires early engagement with client and supply chain, this effects not just the mix process but also the fundamental sourcing strategy for the constituent materials.
Sourcing material as close as possible to the development site, and utilising train and shipping routes will help to drive out carbon from the overall construction process, as well as minimising the impact on local communities. This is also one of the parts of nuclear construction which will always change due to the location of the reactor, requiring a flexible approach to the sourcing of required constituent materials and potential investment in infrastructure to allow for alternative delivery strategies.
In terms of the material mix, being able to source materials that reduce cement content such as Ground Granulated Blast Furnace Slag (GGBS), a key constituent which is becoming harder to obtain following the closure of blast furnaces in the steel industry, from sources with the shortest distances to travel is essential.
Delivering surety of supply in high volumes of constituent materials is therefore a major consideration, requiring long-term logistical planning across a provider’s estates, technical and logistics teams. It calls for early engagement to plan industrial assets.
This planning process needs to feed into development programmes which are a very different to other non-nuclear heavy civils programmes. The testing and development work to challenge and assess the ‘what-ifs’ scenario to ensure that the long-term performance and of nuclear ready concrete commences several years prior to any site pours.
As new reactors are delivered using established designs, the requirements for nuclear-ready concrete will remain exacting, and the need for supply chain partners that understand the nuclear environment will be just as critical. What will evolve is the opportunity to deliver lower carbon solutions by considering logistics and sourcing strategies.
