Thorp Reprocessing

The Thermal Oxide Reprocessing Plant (Thorp) at Sellafield combines all of the facilities needed to reprocess spent oxide fuel under one roof. It reprocesses both UK and foreign spent fuel. 

Thorp Reprocessing
Thorp Reprocessing


The Thorp reprocessing plant at Sellafield combines all the facilities necessary for reprocessing spent oxide fuel under one roof.

The construction of Thorp was one of the world’s most complex civil engineering projects employing up to 5,000 contractors on site and supporting a further 10,000 with suppliers and subcontractors. Construction began on the Thorp Head End and Chemical Separation plants in 1985 and the first fuel was sheared in 1994.

Thorp’s operations are divided into three main areas:

  • Fuel Receipt and Storage
  • Head End plant operations where spent fuel is chopped up and dissolved in nitric acid
  • Chemical Separation where uranium, plutonium and waste products are separated out

After 3 to 4 years in a reactor nuclear fuel becomes less efficient so is removed. 97% of the spent fuel can be recycled to produce new fuel (96% uranium, 1% plutonium). The rest is nuclear waste.

Transport flasks containing spent fuel from the power stations are delivered by rail to the Sellafield site. 

On arrival at Sellafield the fuel is removed from the transport flasks underwater and stored in storage ponds to allow the fuel to cool further before reprocessing.

The empty flasks are sent for cleaning and quality checks before being returned to the power station for another consignment.

Once the fuel has cooled sufficiently it is monitored and transferred from the storage pond to the Head End Plant shear cave where the fuel is chopped into sections. The fuel drops into a basket in a dissolver vessel where the fuel is dissolved in nitric acid. The fuel cladding remains in the basket.

The dissolved fuel liquor is forwarded to the chemical separation plant within Thorp, where solvent extraction takes place to separate the 3% wastes from the 96% uranium and 1% plutonium. 

The wastes from this process are sent to the High Level Waste plants for concentration, storage and eventual conversion to glass. The uranium and plutonium are converted to oxide powders and stored. Both the uranium and the plutonium can be recycled and manufactured into new uranium oxide or Mixed Oxide (MOX) fuels.

Thorp has dispatched over 1,200 tonnes of uranium for customers to recycle back into new fuel, this will save more than 14 million tonnes of CO2 from fossil fuel generation.