Encapsulation: what is it and how do we do it?

Ian is a shift team leader at the Magnox Encapsulation Plant (MEP) and Waste Encapsulation Plant (WEP). A Sellafield employee since the 1980s and a veteran of nuclear waste management, Ian was involved in storing some of our very first products when these plants began operation.

Our encapsulation facilities safely store and condition Intermediate Level Waste (ILW). Originally, this was for ILW created when we reprocessed used nuclear fuel. Today, these buildings, and the people who work in them, continue to play a crucial role in our nuclear waste management activities at Sellafield. They now look after the ILW that is being taken out of our legacy ponds and silos.

But what exactly is nuclear encapsulation? And how has it changed over the years?

Ian explains all of that and more as he talks to us about his vital role in our encapsulation plants over the years.?

What is encapsulation?

Encapsulation is a process that conditions waste, making it suitable for geological disposal. This waste includes fuel cladding, radioactive sludges, liquids, and other debris that has been in close contact with nuclear fuel.

We place the waste into 500-litre stainless steel drums, and then fill the gaps with a grout mixture made from ordinary portland cement (available at any builders' merchant) and blast furnace slag, a by-product of iron manufacturing. This process immobilises the waste, creating a solid mass inside the drum. Once the mixture has cured, the drums are monitored and stored in one of our three Encapsulated Product Stores (EPS) until they can be transferred to a Geological Disposal Facility (GDF) in the future.

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How has ILW storage changed over the years?

Our storage methods have advanced significantly. For the site's first 40 years, waste was simply tipped into storage compartments in our initial ILW silos, such as the Pile Fuel Cladding Silo and the Magnox Swarf Storage Silo (MSSS). At the time, we were focused on supporting the country's defence and energy production needs, so these silos were built without plans for future waste removal.

In the 1990s, we introduced encapsulation technology. MEP was launched to condition waste from the UK's fleet of Magnox reactors, operated by British Nuclear Fuels Limited (BNFL). This was part of a larger reprocessing operation that continued until 2021.

WEP was originally built to, and continues to, support Thorp’s operations, receiving, and encapsulating by-products from reprocessing, along with legacy sludge and debris from the Pile Fuel Storage Pond (PFSP)

Today, we're continually improving how we manage Intermediate Level Waste (ILW). WEP, MEP and EPS1 are being repurposed to support current and future UK and site missions in support of creating a clean and safe environment for future generations. At the moment, the waste retrieved from our legacy silos, isn't placed into drums but into 3m3 boxes. These will eventually go to the Box Encapsulation Plant (BEP) when it becomes operational in a few years. In the meantime, with reduced throughput in the encapsulation plants due to the end of reprocessing, we have adapted our original encapsulation facilities to accept 3m3 boxes from MSSS until BEP is ready.

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Do we encapsulate all ILW?

In short, no. Some wastes, like the stainless steel and graphite from the Advanced Gas-cooled Reactors across the UK, are placed into drums, lidded, bolted, and stored without conditioning. These wastes cannot be sent to the GDF right now as they haven't been conditioned, but we are working on that.

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What was Sellafield like when encapsulation started in 1985?

It was very much a family affair. My dad was the building manager for flask maintenance in separation, and my uncles and brother also had various roles across the site. Now, my son works in control systems.

Back then, we were generating power at Calder Hall and reprocessing fuel from the UK's Magnox reactors. It was busy—but even though we no longer reprocess or generate power, I would say we're even busier now.

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What's your favourite memory at work?

I have two really proud moments at work. The first, was being promoted to Duly Authorised Person (DAP) 27 years ago. The second, was when we celebrated processing our 10,000th drum in 1996. We had a dinner at Summergrove to mark the occasion—we thought 10,000 was a huge achievement at the time. It's incredible to think we've nearly processed an additional 40,000 drums since then.