Windscale Pile 2
Source: gov.uk (2025-10-14)

Windscale Pile 2 is one of the The Windscale Piles. These were  were the UK's first nuclear reactors and are some of the oldest buildings on the Sellafield site.

We’re cleaning-up and decommissioning these iconic reminders of our pioneering nuclear history and transforming the Sellafield skyline in the process.

What is Windscale Pile 2?

Windscale Pile 2 was the second of two air-cooled, graphite-moderated nuclear reactors built as part of Britain’s post-war atomic weapons program.

It became operational in 1951, following the launch of Pile 1 in 1950.

Like its twin, Pile 2 was designed to produce plutonium-239 by irradiating natural uranium fuel.

Windscale Pile 2 when operational on the original Windscale site.

Both Piles remained in operation until they were shut down in 1957 following a fire in the core of Pile 1.

How did it work?

Both reactors shared the same basic design, centred around plutonium production. It consisted of three key structural components: the reactor, the blower houses, and the chimney.

Together, these 3 components formed a vertically integrated cooling and ventilation system.

Reactor

At the heart of the system was the reactor, a graphite-moderated, air-cooled unit where natural uranium fuel underwent nuclear fission to produce plutonium.

Reactor decommissioning progress

By the late 1950s, the reactor had been isolated, with the inlet and outlet air ducts being sealed off from the buildings ventilation system.

Following this, the reactor was defueled as per standard operations.

It has now transitioned into a state of care and maintenance.

Blower houses

Adjacent to the reactor were the blower houses, which housed powerful fans that forced air through the reactor core to remove the intense heat generated during fission.

Blower houses decommissioning progress

The west side blower house was refurbished in the 1960s and renamed the Post Irradiation Examination (PIE) Metallurgy Lab. While operational it handled various fuel types from different reactor types.

PIE Metallurgy Lab shut down at various points between 1987 and 2007 and was later renamed the Redundant Active Handling Facility (RAHF).

RAHF is now in a period of surveillance and maintenance following some post operational clean out (POCO) and asset improvement.

The east side blower house was converted into a series of shielded caves for work on higher dose investigations and is now operated by National Nuclear Laboratory (NNL).

Chimney

The heated air from the blower houses, was expelled through the towering chimney, which featured a filter gallery at its top to trap radioactive emissions before they entered the atmosphere.

The two 125-metre-tall ventilation chimneys were designed identically by Windscale Chief Engineer John Cockcroft, he insisted that the filters were added to the chimneys.

Chimney decommissioning progress

Pile 2’s chimney was in a state of care and maintenance until commencement of decommissioning operations in 1989.

Throughout the 1990s demolition work continued, including the removal of the diffuser and filter sections.

Windscale Pile 2 chimney being taken down.

The final phase was the dismantling of the main shaft down to 30 metres from ground level, approximately one quarter of the chimney’s original height, which was completed in 2001.

Next steps

Pile 2 is a more traditional decommissioning project than pile 1, which explains why work has been completed on a faster time scale.

Windscale reactor 2 today without a chimney.

Over the past 4 years we have been preparing pile 2’s facilities for remediation as we continue to dismantle the buildings to a safe and secure end state.