The Thorp nuclear reprocessing plant at Sellafield in Cumbria, UK, has been issued with two improvement notices by the Nuclear Installations Inspectorate (NII) following a leak of spent nuclear fuel.

The notices were served part way through an investigation at the plant, which began after 83,000 litres of uranium and plutonium dissolved in nitric acid was found to have leaked from a ruptured pipe into a sealed cell.

While the leak was discovered in April, an internal investigation determined that it may have remained undetected for up to nine months.

The notices do not preclude further action following the investigation but are aimed at achieving prompt action to prevent similar events recurring and include orders for Thorp operators BNG to improve leak detection and ensure any leak detection equipment is fully maintained and tested.

BNG has until 8 October to comply, although it can appeal.

Although no radioactive material left the site and no-one was injured in the incident, the aftermath of the leak could see the plant remain closed for as much a six months, a situation that would present the Nuclear Decommissioning Authority (NDA) with up to £300 million ($546 million) in lost revenue.