The primary purpose of both plants was to produce weapons-grade plutonium for the UK's nuclear weapons programme, but they also generated electrical power for the National Grid.

The site is partially demolished and is expected that only the reactor cores and associated radiation shielding will remain by 2027, when it will enter a period of extended care and maintenance using the "safestore" principle, before final demolition.

The Calder Hall and Chapelcross design was codenamed PIPPA (Pressurised Pile Producing Power and Plutonium) by the UKAEA to denote the plant's dual commercial and military role.

[13] It was initially owned and operated by the Production Group of the United Kingdom Atomic Energy Authority (UKAEA) until the creation of British Nuclear Fuels Limited (BNFL) in 1971.

The site is expected to be in safe storage by 2027 or later, using the "safestore" principle, which utilises an extended period of care and maintenance to reduce overall decommissioning costs.

[20][21] There had been proposals in 2007 for transforming the station into a museum, involving renovating Calder Hall and preserving the cooling towers, but the costs were found to be too high.

[22] Ownership of all of the site's assets and liabilities was transferred to the Nuclear Decommissioning Authority (NDA), a regulatory body created by the Energy Act 2004.